fix(bench): resolve pre-existing clippy warnings in report.rs and mmap_reader.rs

lines_read was incorrectly set to max_lines.min(total) (the loop upper bound)
instead of the actual number of successfully read lines. Now tracks lines_read
via get_line(i).is_some() counter and uses max_lines.min(total) as the correct
loop upper bound to handle empty file edge case.

Fixes #43

crates/bench/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "log-viewer-bench"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+name = "log_viewer_bench"
+path = "src/lib.rs"
+
+[[bin]]
+name = "log-viewer-bench"
+path = "src/main.rs"
+
+[dependencies]
+memmap2 = "0.9"
+nix = { version = "0.30", features = ["signal", "resource", "mman", "fs"] }
+libc = "0.2"
+memchr = "2"
+serde_json = "1"
+clap = { version = "4", features = ["derive"] }
+crossbeam-channel = "0.5"
+tempfile = "3"

crates/bench/src/data_gen.rs

@@ -0,0 +1,223 @@
+use std::fs;
+use std::io::{BufRead, BufReader, BufWriter, Write};
+use std::path::{Path, PathBuf};
+
+pub struct TestFileInfo {
+    pub path: PathBuf,
+    pub size_bytes: u64,
+    pub line_count: u64,
+    pub avg_line_length: f64,
+}
+
+/// Check if test file exists and return its info, or generate it
+pub fn ensure_test_file(path: &Path) -> std::io::Result<TestFileInfo> {
+    if path.exists() {
+        return get_file_info(path);
+    }
+    generate_test_file(path)
+}
+
+/// Get info about an existing test file
+fn get_file_info(path: &Path) -> std::io::Result<TestFileInfo> {
+    let metadata = fs::metadata(path)?;
+    let size_bytes = metadata.len();
+    let line_count = count_existing_lines(path)?;
+
+    let avg_line_length = if line_count > 0 {
+        size_bytes as f64 / line_count as f64
+    } else {
+        0.0
+    };
+
+    Ok(TestFileInfo {
+        path: path.to_path_buf(),
+        size_bytes,
+        line_count,
+        avg_line_length,
+    })
+}
+
+/// Generate a large test file (~5GB / ~74M lines) if it doesn't exist
+fn generate_test_file(path: &Path) -> std::io::Result<TestFileInfo> {
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent)?;
+    }
+
+    let mut file = BufWriter::with_capacity(64 * 1024, fs::File::create(path)?);
+    let target_lines: u64 = 74_000_000;
+    for i in 0..target_lines {
+        writeln!(
+            file,
+            "2024-01-15 10:30:{:02} INFO [thread-{}] Application processing request id={} user_id={}",
+            i % 60,
+            i % 16,
+            i,
+            i * 7
+        )?;
+    }
+    file.flush()?;
+    drop(file);
+
+    get_file_info(path)
+}
+
+/// Generate a smaller file (~10MB / ~150K lines) for growth/rotation tests
+pub fn generate_growable_file(dir: &Path) -> std::io::Result<PathBuf> {
+    fs::create_dir_all(dir)?;
+    let path = dir.join("growable.log");
+
+    let mut file = BufWriter::with_capacity(64 * 1024, fs::File::create(&path)?);
+    for i in 0..150_000u64 {
+        writeln!(
+            file,
+            "2024-01-15 10:30:{:02} INFO [thread-{}] Appending test line {}",
+            i % 60,
+            i % 16,
+            i
+        )?;
+    }
+    file.flush()?;
+
+    Ok(path)
+}
+
+/// Append `count` lines to the file
+pub fn append_lines(path: &Path, count: usize) -> std::io::Result<()> {
+    let existing_lines = count_existing_lines(path)?;
+    let mut file = BufWriter::with_capacity(
+        64 * 1024,
+        fs::OpenOptions::new().append(true).open(path)?,
+    );
+    for i in 0..count {
+        writeln!(
+            file,
+            "2024-01-15 10:30:00 INFO Appended line {}",
+            existing_lines + i as u64
+        )?;
+    }
+    file.flush()?;
+    Ok(())
+}
+
+/// Truncate file to specified size
+pub fn truncate_file(path: &Path, size: u64) -> std::io::Result<()> {
+    let file = fs::OpenOptions::new().write(true).open(path)?;
+    file.set_len(size)
+}
+
+/// Rotate file: rename existing file, create new empty file
+pub fn rotate_file(path: &Path) -> std::io::Result<PathBuf> {
+    let rotated = path.with_extension("log.1");
+    fs::rename(path, &rotated)?;
+    fs::File::create(path)?;
+    Ok(rotated)
+}
+
+/// Count lines in a file (helper)
+fn count_existing_lines(path: &Path) -> std::io::Result<u64> {
+    let file = fs::File::open(path)?;
+    let reader = BufReader::new(file);
+    let mut count = 0u64;
+    for line in reader.lines() {
+        line?;
+        count += 1;
+    }
+    Ok(count)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_generate_growable_file_creates_approximately_correct_size() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = generate_growable_file(dir.path()).unwrap();
+
+        assert!(path.exists());
+        let metadata = fs::metadata(&path).unwrap();
+        let size_mb = metadata.len() as f64 / (1024.0 * 1024.0);
+        // ~150K lines × ~67 bytes ≈ ~10MB; allow 5MB–15MB range
+        assert!(
+            (5.0..=15.0).contains(&size_mb),
+            "Expected ~10MB, got {size_mb:.1}MB"
+        );
+    }
+
+    #[test]
+    fn test_append_lines_increases_line_count() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = {
+            let mut f = fs::File::create(dir.path().join("test.log")).unwrap();
+            for i in 0..10u64 {
+                writeln!(f, "line {i}").unwrap();
+            }
+            dir.path().join("test.log")
+        };
+
+        let before = count_existing_lines(&path).unwrap();
+        append_lines(&path, 5).unwrap();
+        let after = count_existing_lines(&path).unwrap();
+        assert_eq!(after, before + 5);
+    }
+
+    #[test]
+    fn test_truncate_file_reduces_size() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("trunc.log");
+        {
+            let mut f = fs::File::create(&path).unwrap();
+            write!(f, "{}", "A".repeat(1024)).unwrap();
+        }
+
+        let before = fs::metadata(&path).unwrap().len();
+        assert_eq!(before, 1024);
+
+        truncate_file(&path, 512).unwrap();
+        let after = fs::metadata(&path).unwrap().len();
+        assert_eq!(after, 512);
+    }
+
+    #[test]
+    fn test_rotate_file_renames_and_creates_empty() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("rotate.log");
+        {
+            let mut f = fs::File::create(&path).unwrap();
+            write!(f, "original content").unwrap();
+        }
+
+        let rotated = rotate_file(&path).unwrap();
+
+        // Rotated file has the old content
+        assert!(rotated.exists());
+        assert_eq!(fs::read_to_string(&rotated).unwrap(), "original content");
+
+        // New file is empty
+        assert!(path.exists());
+        assert_eq!(fs::metadata(&path).unwrap().len(), 0);
+    }
+
+    #[test]
+    fn test_ensure_test_file_generates_when_missing() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("fresh.log");
+        assert!(!path.exists());
+
+        // Override the generator to use a small file for test speed:
+        // We'll test ensure_test_file indirectly by checking it calls generate_test_file.
+        // Since generate_test_file creates 74M lines (too slow for tests), test the logic
+        // by directly creating a small file and checking get_file_info works.
+        {
+            let mut f = fs::File::create(&path).unwrap();
+            for i in 0..100u64 {
+                writeln!(f, "2024-01-15 10:30:00 INFO line {i}").unwrap();
+            }
+        }
+
+        let info = ensure_test_file(&path).unwrap();
+        assert_eq!(info.line_count, 100);
+        assert!(info.size_bytes > 0);
+        assert!(info.avg_line_length > 0.0);
+    }
+}

crates/bench/src/lib.rs

@@ -0,0 +1,24 @@
+pub mod data_gen;
+pub mod line_index;
+pub mod metrics;
+pub mod mmap_reader;
+pub mod pread_reader;
+pub mod report;
+pub mod runner;
+pub mod suites;
+pub mod types;
+
+use std::path::Path;
+
+/// A single reader backend (mmap or pread)
+pub trait FileReaderBackend {
+    fn name(&self) -> &str;
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized;
+    fn file_size(&self) -> u64;
+    fn total_lines(&self) -> usize;
+    fn get_line(&self, idx: usize) -> Option<String>;
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>>;
+    fn close(self);
+}

crates/bench/src/line_index.rs

@@ -0,0 +1,110 @@
+// ─── line_index.rs ───────────────────────────────────────────────────────────
+// Vendored from crates/core/src/io/line_index.rs
+// Sparse line index: sample every 256 lines to reduce memory usage.
+// ──────────────────────────────────────────────────────────────────────────────
+
+const BLOCK_SIZE: usize = 256;
+
+pub struct LineIndex {
+    pub(crate) sampled_offsets: Vec<u64>,
+    pub(crate) total_lines: u64,
+    #[allow(dead_code)]
+    pub(crate) has_trailing_newline: bool,
+}
+
+impl LineIndex {
+    /// Build sparse line index from a streaming reader.
+    /// Uses fill_buf()/consume() to avoid loading the entire file into memory.
+    /// RSS stays at ~64KB (BufReader buffer size), independent of file size.
+    pub fn from_reader(reader: &mut impl std::io::BufRead) -> std::io::Result<Self> {
+        let mut sampled_offsets: Vec<u64> = vec![0]; // line 0 starts at offset 0
+        let mut next_line_idx: usize = 1;
+        let mut newline_count: usize = 0;
+        let mut chunk_offset: u64 = 0;
+        let mut last_byte: Option<u8> = None;
+
+        loop {
+            let buf = reader.fill_buf()?;
+            if buf.is_empty() {
+                break;
+            }
+
+            if let Some(&b) = buf.last() {
+                last_byte = Some(b);
+            }
+
+            for pos in memchr::memchr_iter(b'\n', buf) {
+                newline_count += 1;
+                if next_line_idx.is_multiple_of(BLOCK_SIZE) {
+                    sampled_offsets.push(chunk_offset + pos as u64 + 1);
+                }
+                next_line_idx += 1;
+            }
+
+            let consumed = buf.len();
+            chunk_offset += consumed as u64;
+            reader.consume(consumed);
+        }
+
+        // Empty file: no data at all
+        if chunk_offset == 0 {
+            return Ok(LineIndex {
+                sampled_offsets: vec![],
+                total_lines: 0,
+                has_trailing_newline: false,
+            });
+        }
+
+        let has_trailing_newline = last_byte == Some(b'\n') && newline_count > 0;
+
+        let total_lines: u64 = if has_trailing_newline && newline_count > 0 {
+            newline_count as u64
+        } else {
+            (1 + newline_count) as u64
+        };
+
+        // Trailing \n pop logic
+        if has_trailing_newline && newline_count > 0 {
+            let trailing_line_idx = newline_count;
+            if trailing_line_idx.is_multiple_of(BLOCK_SIZE) {
+                sampled_offsets.pop();
+            }
+        }
+
+        Ok(LineIndex {
+            sampled_offsets,
+            total_lines,
+            has_trailing_newline,
+        })
+    }
+
+    /// Return total line count.
+    pub fn line_count(&self) -> usize {
+        self.total_lines as usize
+    }
+
+    /// Retrieve the content of line `idx` from the given data slice.
+    /// Uses sparse index to locate the block start, then scans forward
+    /// a small number of newlines to find the target line.
+    pub fn get_line<'a>(&self, data: &'a [u8], idx: usize) -> Option<&'a str> {
+        if idx >= self.total_lines as usize || data.is_empty() {
+            return None;
+        }
+        let block = idx / BLOCK_SIZE;
+        let offset_in_block = idx % BLOCK_SIZE;
+        let mut pos = self.sampled_offsets[block] as usize;
+        for _ in 0..offset_in_block {
+            match memchr::memchr(b'\n', &data[pos..]) {
+                Some(rel) => pos = pos + rel + 1,
+                None => return None,
+            }
+        }
+        let end = memchr::memchr(b'\n', &data[pos..])
+            .map(|rel| pos + rel)
+            .unwrap_or(data.len());
+        let line_bytes = &data[pos..end];
+        std::str::from_utf8(line_bytes)
+            .map(|s| s.trim_end_matches(['\r', '\n']))
+            .ok()
+    }
+}

crates/bench/src/main.rs

@@ -0,0 +1,81 @@
+use clap::Parser;
+use std::path::PathBuf;
+
+/// Benchmark: mmap vs pread for large file reading
+#[derive(Parser, Debug)]
+#[command(name = "log-viewer-bench", version, about = "Benchmark mmap vs pread")]
+struct Args {
+    /// Path to the test file (default: /tmp/test-logviewer/extreme.log)
+    #[arg(default_value = "/tmp/test-logviewer/extreme.log")]
+    test_file: PathBuf,
+
+    /// Quick mode: use smaller iterations and skip cold cache tests
+    #[arg(long)]
+    quick: bool,
+
+    /// Output report path (default: benchmark-report.md)
+    #[arg(long, default_value = "benchmark-report.md")]
+    output: PathBuf,
+
+    /// Only run specified suites (comma-separated: startup,render,jump,memory,growth,rotation,concurrent)
+    #[arg(long, value_delimiter = ',')]
+    suites: Option<Vec<String>>,
+}
+
+fn main() {
+    let args = Args::parse();
+
+    let suites = match args.suites {
+        Some(names) => {
+            let parsed: Result<Vec<_>, _> =
+                names.iter().map(|s| s.parse::<log_viewer_bench::runner::Suite>()).collect();
+            match parsed {
+                Ok(s) => Some(s),
+                Err(e) => {
+                    eprintln!("error: {e}");
+                    std::process::exit(1);
+                }
+            }
+        }
+        None => None,
+    };
+
+    println!("=== Benchmark: mmap vs pread ===");
+    println!("Test file: {}", args.test_file.display());
+    println!("Quick mode: {}", args.quick);
+    println!();
+
+    let config = log_viewer_bench::runner::BenchConfig {
+        test_file: args.test_file.clone(),
+        quick_mode: args.quick,
+        suites,
+    };
+
+    if !config.test_file.exists() {
+        eprintln!("ERROR: Test file not found: {}", config.test_file.display());
+        eprintln!(
+            "Generate one with: dd if=/dev/urandom of=/tmp/test-logviewer/extreme.log bs=1M count=5000"
+        );
+        std::process::exit(1);
+    }
+
+    log_viewer_bench::runner::warn_reset_hwm();
+
+    println!("Running benchmarks...");
+    let results = log_viewer_bench::runner::run_all(&config);
+    println!("Completed {} benchmarks.\n", results.len());
+
+    let report = log_viewer_bench::report::format_report(&results);
+
+    println!("{}", report);
+
+    if let Err(e) = std::fs::write(&args.output, &report) {
+        eprintln!(
+            "WARNING: Failed to save report to {}: {}",
+            args.output.display(),
+            e
+        );
+    } else {
+        eprintln!("Report saved to {}", args.output.display());
+    }
+}

crates/bench/src/metrics.rs

@@ -0,0 +1,275 @@
+use std::fs::{self, File};
+use std::os::unix::fs::MetadataExt;
+use std::os::unix::io::AsRawFd;
+use std::path::Path;
+
+pub struct RssMetrics {
+    pub vm_rss_kb: u64,
+    pub vm_hwm_kb: u64,
+}
+
+pub struct PageFaultMetrics {
+    pub minor_faults: u64,
+    pub major_faults: u64,
+}
+
+pub struct MetricsCollector;
+
+impl MetricsCollector {
+    /// Read VmRSS and VmHWM from /proc/self/status
+    pub fn read_rss() -> RssMetrics {
+        let status = fs::read_to_string("/proc/self/status").unwrap_or_default();
+        let mut vm_rss_kb: u64 = 0;
+        let mut vm_hwm_kb: u64 = 0;
+        for line in status.lines() {
+            if line.starts_with("VmRSS:") {
+                vm_rss_kb = parse_kb_value(line);
+            } else if line.starts_with("VmHWM:") {
+                vm_hwm_kb = parse_kb_value(line);
+            }
+        }
+        RssMetrics {
+            vm_rss_kb,
+            vm_hwm_kb,
+        }
+    }
+
+    /// Read page fault counts from getrusage
+    pub fn read_page_faults() -> PageFaultMetrics {
+        let usage =
+            nix::sys::resource::getrusage(nix::sys::resource::UsageWho::RUSAGE_SELF).unwrap();
+        PageFaultMetrics {
+            // getrusage() returns c_long (i64 on 64-bit Linux) — explicit as u64 conversion
+            minor_faults: usage.minor_page_faults() as u64,
+            major_faults: usage.major_page_faults() as u64,
+        }
+    }
+
+    /// Clear page cache (requires root: sync + drop_caches)
+    /// Falls back to doing nothing if no permission
+    pub fn clear_page_cache() -> std::io::Result<()> {
+        let _ = std::process::Command::new("sync").status();
+        fs::write("/proc/sys/vm/drop_caches", "1")
+    }
+
+    /// Clear file cache using posix_fadvise(DONTNEED) — no root required
+    pub fn clear_file_cache(path: &Path) -> std::io::Result<()> {
+        let file = File::open(path)?;
+        let len = file.metadata()?.len();
+        let ret = unsafe {
+            libc::posix_fadvise(file.as_raw_fd(), 0, len as i64, libc::POSIX_FADV_DONTNEED)
+        };
+        // posix_fadvise returns error code directly (not errno), 0 = success
+        if ret != 0 {
+            return Err(std::io::Error::from_raw_os_error(ret));
+        }
+        Ok(())
+    }
+
+    /// Reset VmHWM by writing to /proc/self/clear_refs (requires root)
+    pub fn reset_vm_hwm() -> std::io::Result<()> {
+        fs::write("/proc/self/clear_refs", "5").map_err(|e| {
+            if e.kind() == std::io::ErrorKind::PermissionDenied {
+                std::io::Error::new(
+                    std::io::ErrorKind::PermissionDenied,
+                    "VmHWM reset requires root (can't write /proc/self/clear_refs)",
+                )
+            } else {
+                e
+            }
+        })
+    }
+
+    /// Get file inode number
+    pub fn get_inode(path: &Path) -> std::io::Result<u64> {
+        let meta = fs::metadata(path)?;
+        Ok(meta.ino())
+    }
+
+    /// Check if file was rotated (inode changed)
+    pub fn detect_rotation(original_inode: u64, path: &Path) -> bool {
+        Self::get_inode(path)
+            .map(|ino| ino != original_inode)
+            .unwrap_or(true)
+    }
+}
+
+fn parse_kb_value(line: &str) -> u64 {
+    // Format: "VmRSS:    12345 kB"
+    line.split_whitespace()
+        .nth(1)
+        .and_then(|v| v.parse::<u64>().ok())
+        .unwrap_or(0)
+}
+
+pub fn mean(data: &[u64]) -> f64 {
+    if data.is_empty() {
+        return 0.0;
+    }
+    data.iter().sum::<u64>() as f64 / data.len() as f64
+}
+
+/// Percentile of data at given fraction (0.0–1.0). Returns from a sorted copy.
+pub fn percentile(data: &[u64], p: f64) -> u64 {
+    if data.is_empty() {
+        return 0;
+    }
+    let mut sorted: Vec<u64> = data.to_vec();
+    sorted.sort_unstable();
+    let idx = ((p * (sorted.len() - 1) as f64).round()) as usize;
+    sorted[idx.min(sorted.len() - 1)]
+}
+
+pub fn stdev(data: &[u64]) -> f64 {
+    if data.len() < 2 {
+        return 0.0;
+    }
+    let m = mean(data);
+    let variance: f64 = data
+        .iter()
+        .map(|&v| {
+            let d = v as f64 - m;
+            d * d
+        })
+        .sum::<f64>()
+        / (data.len() - 1) as f64;
+    variance.sqrt()
+}
+
+pub fn p50(data: &[u64]) -> u64 {
+    percentile(data, 0.50)
+}
+
+pub fn p95(data: &[u64]) -> u64 {
+    percentile(data, 0.95)
+}
+
+pub fn p99(data: &[u64]) -> u64 {
+    percentile(data, 0.99)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_rss_returns_values() {
+        let rss = MetricsCollector::read_rss();
+        assert!(
+            rss.vm_rss_kb > 0,
+            "VmRSS should be non-zero for a running process"
+        );
+        assert!(
+            rss.vm_hwm_kb > 0,
+            "VmHWM should be non-zero for a running process"
+        );
+    }
+
+    #[test]
+    fn test_page_faults_returns_values() {
+        let faults = MetricsCollector::read_page_faults();
+        assert!(
+            faults.minor_faults > 0,
+            "Should have some minor page faults"
+        );
+    }
+
+    #[test]
+    fn test_mean() {
+        let data = vec![100, 200, 300, 400, 500];
+        let result = mean(&data);
+        assert!(
+            (result - 300.0).abs() < f64::EPSILON,
+            "mean should be 300.0, got {result}"
+        );
+    }
+
+    #[test]
+    fn test_mean_empty() {
+        assert_eq!(mean(&[]), 0.0);
+    }
+
+    #[test]
+    fn test_percentile_p50() {
+        let data = vec![100, 200, 300, 400, 500];
+        assert_eq!(percentile(&data, 0.50), 300);
+    }
+
+    #[test]
+    fn test_percentile_p99() {
+        let data = vec![10, 20, 30, 40, 50, 60, 70, 80, 90, 100];
+        let p99_result = percentile(&data, 0.99);
+        assert!(p99_result >= 90, "P99 should be near max, got {p99_result}");
+    }
+
+    #[test]
+    fn test_percentile_empty() {
+        assert_eq!(percentile(&[], 0.5), 0);
+    }
+
+    #[test]
+    fn test_stdev() {
+        let data = vec![100, 200, 300, 400, 500];
+        let s = stdev(&data);
+        assert!(s > 100.0, "stdev should be significant, got {s}");
+        assert!(s < 200.0, "stdev should be < 200, got {s}");
+    }
+
+    #[test]
+    fn test_stdev_single() {
+        assert_eq!(stdev(&[42]), 0.0);
+        assert_eq!(stdev(&[]), 0.0);
+    }
+
+    #[test]
+    fn test_parse_kb_value() {
+        assert_eq!(parse_kb_value("VmRSS:    12345 kB"), 12345);
+        assert_eq!(parse_kb_value("VmHWM:\t2048 kB"), 2048);
+        assert_eq!(parse_kb_value("VmRSS: 0 kB"), 0);
+    }
+
+    #[test]
+    fn test_parse_kb_value_malformed() {
+        assert_eq!(parse_kb_value("VmRSS: NaN kB"), 0);
+        assert_eq!(parse_kb_value("garbage"), 0);
+    }
+
+    #[test]
+    fn test_convenience_percentiles() {
+        let data = vec![10, 20, 30, 40, 50];
+        assert_eq!(p50(&data), 30);
+        assert_eq!(p95(&data), 50);
+        assert_eq!(p99(&data), 50);
+    }
+
+    #[test]
+    fn test_inode_for_existing_file() {
+        let tmp = tempfile::NamedTempFile::new().unwrap();
+        let inode = MetricsCollector::get_inode(tmp.path()).unwrap();
+        assert!(inode > 0, "inode should be non-zero");
+    }
+
+    #[test]
+    fn test_detect_rotation_no_rotation() {
+        let tmp = tempfile::NamedTempFile::new().unwrap();
+        let inode = MetricsCollector::get_inode(tmp.path()).unwrap();
+        assert!(!MetricsCollector::detect_rotation(inode, tmp.path()));
+    }
+
+    #[test]
+    fn test_detect_rotation_file_removed() {
+        let inode: u64 = 99999;
+        let result = MetricsCollector::detect_rotation(inode, Path::new("/no/such/file"));
+        assert!(result, "missing file should indicate rotation");
+    }
+
+    #[test]
+    fn test_clear_file_cache() {
+        let tmp = tempfile::NamedTempFile::new().unwrap();
+        let result = MetricsCollector::clear_file_cache(tmp.path());
+        assert!(
+            result.is_ok(),
+            "clear_file_cache should succeed on temp file: {result:?}"
+        );
+    }
+}

crates/bench/src/mmap_reader.rs

@@ -0,0 +1,752 @@
+// ─── mmap_reader.rs ──────────────────────────────────────────────────────────
+// mmap-based FileReaderBackend implementations with 5 variants for benchmarking.
+// Includes SIGBUS handler for file-truncation resilience and remap support
+// for growing-file scenarios.
+// ──────────────────────────────────────────────────────────────────────────────
+
+use std::fs::File;
+use std::io::BufReader;
+use std::path::Path;
+use std::sync::atomic::{AtomicBool, AtomicPtr, AtomicU8, Ordering};
+use std::sync::Once;
+
+use memmap2::{Advice, Mmap, MmapOptions, RemapOptions};
+use nix::sys::signal::{sigaction, SaFlags, SigAction, SigHandler, SigSet, Signal};
+
+use crate::line_index::LineIndex;
+use crate::FileReaderBackend;
+
+// ─── SIGBUS Handler ──────────────────────────────────────────────────────────
+//
+// Signal-safety architecture:
+// - Old handler state is stored in raw atomics (AtomicU8 + AtomicPtr) that are
+//   async-signal-safe to read — no OnceLock, Mutex, or other non-trivial abstractions
+//   in the signal handler path.
+// - Installation uses `Once` for idempotency and follows a strict publish-then-install
+//   sequence to close the "handler-active-but-state-unpublished" race window.
+
+/// Global flag set by the SIGBUS handler when a bus error is intercepted.
+/// Process-global: concurrent benchmarks that reset/check this flag may interfere.
+/// Currently acceptable because only `rotation` suite (sequential) uses it.
+static SIGBUS_OCCURRED: AtomicBool = AtomicBool::new(false);
+
+/// Discriminant values for old SIGBUS handler type.
+const HANDLER_NONE: u8 = 0;
+const HANDLER_DEFAULT: u8 = 1;
+const HANDLER_IGNORE: u8 = 2;
+const HANDLER_PLAIN: u8 = 3; // extern "C" fn(c_int)
+#[allow(clippy::unseparated_literal_suffix, reason = "clarity: this is the SA_SIGACTION variant")]
+const HANDLER_SIGACTION: u8 = 4; // extern "C" fn(c_int, *mut siginfo_t, *mut c_void)
+
+/// Old SIGBUS handler type — raw atomic, async-signal-safe to read.
+static OLD_HANDLER_KIND: AtomicU8 = AtomicU8::new(HANDLER_NONE);
+
+/// Old SIGBUS handler function pointer — raw atomic, async-signal-safe to read.
+static OLD_HANDLER_PTR: AtomicPtr<std::ffi::c_void> = AtomicPtr::new(std::ptr::null_mut());
+
+/// Ensures `install_sigbus_handler` runs exactly once across all threads.
+static INSTALL_ONCE: Once = Once::new();
+
+/// Returns `true` if a SIGBUS was intercepted since the last reset.
+pub fn sigbus_flag() -> bool {
+    SIGBUS_OCCURRED.load(Ordering::SeqCst)
+}
+
+/// Resets the SIGBUS flag. Call before operations where you want to detect
+/// a fresh SIGBUS.
+pub fn reset_sigbus_flag() {
+    SIGBUS_OCCURRED.store(false, Ordering::SeqCst)
+}
+
+/// SIGBUS signal handler.
+///
+/// # Safety Constraints (signal handler context)
+/// - NO TLS access
+/// - NO memory allocation
+/// - NO lock acquisition
+/// - Only: AtomicBool store → mmap → raw atomic loads → chain
+extern "C" fn sigbus_handler(
+    sig: libc::c_int,
+    info: *mut libc::siginfo_t,
+    ctx: *mut std::ffi::c_void,
+) {
+    SIGBUS_OCCURRED.store(true, Ordering::SeqCst);
+
+    // Align fault address down to page boundary.
+    // si_addr is NOT guaranteed to be page-aligned; without this, mmap(MAP_FIXED)
+    // could replace the wrong page.
+    let addr = unsafe { (*info).si_addr() };
+    let aligned = (addr as usize & !0xFFF) as *mut libc::c_void;
+
+    // Map anonymous zero page at fault address to prevent crash on file truncation.
+    let result = unsafe {
+        libc::mmap(
+            aligned,
+            4096,
+            libc::PROT_READ,
+            libc::MAP_PRIVATE | libc::MAP_ANONYMOUS | libc::MAP_FIXED,
+            -1,
+            0,
+        )
+    };
+    if result == libc::MAP_FAILED {
+        // Chain to old handler via raw atomics (async-signal-safe).
+        let kind = OLD_HANDLER_KIND.load(Ordering::Acquire);
+        match kind {
+            HANDLER_PLAIN => {
+                let ptr = OLD_HANDLER_PTR.load(Ordering::Acquire);
+                if !ptr.is_null() {
+                    // SAFETY: ptr was derived from a valid function pointer
+                    // published by install_sigbus_handler before this handler was installed.
+                    let f: extern "C" fn(libc::c_int) = unsafe { std::mem::transmute(ptr) };
+                    f(sig);
+                } else {
+                    unsafe { libc::_exit(128 + sig) };
+                }
+            }
+            HANDLER_SIGACTION => {
+                let ptr = OLD_HANDLER_PTR.load(Ordering::Acquire);
+                if !ptr.is_null() {
+                    let f: extern "C" fn(
+                        libc::c_int,
+                        *mut libc::siginfo_t,
+                        *mut std::ffi::c_void,
+                    ) = unsafe { std::mem::transmute(ptr) };
+                    f(sig, info, ctx);
+                } else {
+                    unsafe { libc::_exit(128 + sig) };
+                }
+            }
+            _ => {
+                // HANDLER_NONE / HANDLER_DEFAULT / HANDLER_IGNORE — no safe chaining.
+                unsafe { libc::_exit(128 + sig) };
+            }
+        }
+    }
+}
+
+/// Install the SIGBUS handler via sigaction(). Chains to any previous handler.
+/// Uses `Once` to guarantee exactly-once installation — safe to call from
+/// multiple threads concurrently.
+///
+/// The install sequence closes the "install-then-publish" race by:
+/// 1. Querying the current handler via raw `libc::sigaction` (no modification).
+/// 2. Publishing old handler state to raw atomics (`Release` stores).
+/// 3. Installing our handler via `nix::sigaction`.
+///
+/// This ensures the atomics are readable *before* our handler can fire.
+fn install_sigbus_handler() {
+    INSTALL_ONCE.call_once(|| {
+        // Step 1: Query current SIGBUS disposition without changing it.
+        let mut old_act: libc::sigaction = unsafe { std::mem::zeroed() };
+        let ret = unsafe { libc::sigaction(libc::SIGBUS, std::ptr::null(), &mut old_act) };
+        if ret != 0 {
+            // Failed to query — skip installation entirely.
+            return;
+        }
+
+        // Step 2: Publish old handler to atomics BEFORE installing ours.
+        let is_siginfo = (old_act.sa_flags & libc::SA_SIGINFO) != 0;
+
+        let raw_usize = old_act.sa_sigaction as usize;
+
+        if raw_usize == 0 {
+            // SIG_DFL (null function pointer → default disposition)
+            OLD_HANDLER_KIND.store(HANDLER_DEFAULT, Ordering::Release);
+        } else if raw_usize == 1 {
+            // SIG_IGN (sentinel value 1 → ignore disposition)
+            OLD_HANDLER_KIND.store(HANDLER_IGNORE, Ordering::Release);
+        } else {
+            // Real handler function pointer
+            OLD_HANDLER_PTR.store(raw_usize as *mut std::ffi::c_void, Ordering::Release);
+            if is_siginfo {
+                OLD_HANDLER_KIND.store(HANDLER_SIGACTION, Ordering::Release);
+            } else {
+                OLD_HANDLER_KIND.store(HANDLER_PLAIN, Ordering::Release);
+            }
+        }
+
+        // Step 3: Install our handler. Atomics are already published,
+        // so the handler can safely read them from the moment it's installed.
+        let new_action = SigAction::new(
+            SigHandler::SigAction(sigbus_handler),
+            SaFlags::SA_SIGINFO,
+            SigSet::empty(),
+        );
+        let _ = unsafe { sigaction(Signal::SIGBUS, &new_action) };
+    });
+}
+
+// ─── Core MmapReader ─────────────────────────────────────────────────────────
+
+/// Core mmap-based reader. Holds the memory mapping, file handle, and
+/// line index. Used as the engine inside each variant wrapper.
+pub struct MmapReader {
+    mmap: Mmap,
+    #[allow(dead_code)]
+    file: File,
+    line_index: LineIndex,
+    file_size: u64,
+}
+
+impl MmapReader {
+    /// Open a file and create an mmap. Does NOT apply madvise.
+    /// The caller is responsible for applying the desired advice.
+    fn open_raw(path: &Path) -> std::io::Result<Self> {
+        let file = File::open(path)?;
+        let file_size = file.metadata()?.len();
+
+        let mmap = unsafe { Mmap::map(&file)? };
+
+        let line_index = {
+            let mut reader = BufReader::new(&file);
+            LineIndex::from_reader(&mut reader)?
+        };
+
+        Ok(Self {
+            mmap,
+            file,
+            line_index,
+            file_size,
+        })
+    }
+
+    /// Open with MmapOptions (for populate, etc.).
+    fn open_with_options(path: &Path, opts: &MmapOptions) -> std::io::Result<Self> {
+        let file = File::open(path)?;
+        let file_size = file.metadata()?.len();
+
+        let mmap = if file_size == 0 {
+            unsafe { Mmap::map(&file)? }
+        } else {
+            unsafe { opts.map(&file)? }
+        };
+
+        let line_index = {
+            let mut reader = BufReader::new(&file);
+            LineIndex::from_reader(&mut reader)?
+        };
+
+        Ok(Self {
+            mmap,
+            file,
+            line_index,
+            file_size,
+        })
+    }
+
+    /// Apply madvise to the entire mapping.
+    fn advise(&self, advice: Advice) {
+        let _ = self.mmap.advise(advice);
+    }
+
+    /// Grow the mmap to `new_size` bytes.
+    ///
+    /// # Safety
+    /// Caller must ensure no `&[u8]` references to the old mmap data exist.
+    /// After remap, any pointers derived from the old mapping may be invalid
+    /// (if the kernel moved the mapping).
+    pub unsafe fn remap(&mut self, new_size: usize) -> std::io::Result<()> {
+        unsafe {
+            self.mmap
+                .remap(new_size, RemapOptions::new().may_move(true))?;
+        }
+        self.file_size = new_size as u64;
+        Ok(())
+    }
+
+    #[inline]
+    pub fn file_size(&self) -> u64 {
+        self.file_size
+    }
+
+    #[inline]
+    pub fn total_lines(&self) -> usize {
+        self.line_index.line_count()
+    }
+
+    #[inline]
+    pub fn get_line(&self, idx: usize) -> Option<String> {
+        self.line_index
+            .get_line(&self.mmap, idx)
+            .map(|s| s.to_owned())
+    }
+
+    #[inline]
+    pub fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        let start = offset as usize;
+        let end = start.checked_add(len)?;
+        if end > self.mmap.len() {
+            return None;
+        }
+        Some(self.mmap[start..end].to_vec())
+    }
+}
+
+// ─── 5 Variants ──────────────────────────────────────────────────────────────
+
+/// Variant 1: Plain mmap, no madvise.
+pub struct MmapReaderPlain {
+    inner: MmapReader,
+}
+
+impl MmapReaderPlain {
+    pub fn remap(&mut self, new_size: usize) -> std::io::Result<()> {
+        unsafe { self.inner.remap(new_size) }
+    }
+}
+
+impl FileReaderBackend for MmapReaderPlain {
+    fn name(&self) -> &str {
+        "mmap_plain"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        install_sigbus_handler();
+        let inner = MmapReader::open_raw(path)?;
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 2: mmap with MADV_SEQUENTIAL — optimal for sequential scan (index build).
+pub struct MmapReaderSequential {
+    inner: MmapReader,
+}
+
+impl FileReaderBackend for MmapReaderSequential {
+    fn name(&self) -> &str {
+        "mmap_sequential"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        install_sigbus_handler();
+        let inner = MmapReader::open_raw(path)?;
+        inner.advise(Advice::Sequential);
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 3: mmap with MADV_RANDOM — optimal for random line access after index is built.
+pub struct MmapReaderRandom {
+    inner: MmapReader,
+}
+
+impl FileReaderBackend for MmapReaderRandom {
+    fn name(&self) -> &str {
+        "mmap_random"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        install_sigbus_handler();
+        let inner = MmapReader::open_raw(path)?;
+        inner.advise(Advice::Random);
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 4: mmap with MAP_POPULATE — pre-fault all pages at mmap time.
+/// Trades higher upfront cost for smoother subsequent access.
+pub struct MmapReaderPopulate {
+    inner: MmapReader,
+}
+
+impl FileReaderBackend for MmapReaderPopulate {
+    fn name(&self) -> &str {
+        "mmap_populate"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        install_sigbus_handler();
+        let mut opts = MmapOptions::new();
+        opts.populate();
+        let inner = MmapReader::open_with_options(path, &opts)?;
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 5: Phase-aware — MADV_SEQUENTIAL during index build, then MADV_RANDOM
+/// for line access. Best of both worlds for the read-index-then-query pattern.
+pub struct MmapReaderPhaseAware {
+    inner: MmapReader,
+}
+
+impl FileReaderBackend for MmapReaderPhaseAware {
+    fn name(&self) -> &str {
+        "mmap_phase_aware"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        install_sigbus_handler();
+        let inner = MmapReader::open_raw(path)?;
+        // Index build used sequential streaming via BufReader. Now switch to random.
+        inner.advise(Advice::Random);
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+// ─── Tests ───────────────────────────────────────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write as _;
+    use tempfile::NamedTempFile;
+
+    fn create_temp_file(content: &[u8]) -> NamedTempFile {
+        let mut f = NamedTempFile::new().unwrap();
+        f.write_all(content).unwrap();
+        f.flush().unwrap();
+        f
+    }
+
+    #[test]
+    fn test_plain_open_and_read_lines() {
+        let f = create_temp_file(b"hello\nworld\nfoo\n");
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "mmap_plain");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(0), Some("hello".to_owned()));
+        assert_eq!(reader.get_line(1), Some("world".to_owned()));
+        assert_eq!(reader.get_line(2), Some("foo".to_owned()));
+        assert_eq!(reader.get_line(3), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_out_of_bounds_returns_none() {
+        let f = create_temp_file(b"line1\nline2\n");
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 2);
+        assert_eq!(reader.get_line(100), None);
+        assert_eq!(reader.get_line(usize::MAX), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_read_range() {
+        let content = b"hello world\nfoo bar\n";
+        let f = create_temp_file(content);
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        let range = reader.read_range(0, 5).unwrap();
+        assert_eq!(&range, b"hello");
+        let range = reader.read_range(6, 5).unwrap();
+        assert_eq!(&range, b"world");
+        assert_eq!(reader.read_range(0, 1000), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_empty_file() {
+        let f = create_temp_file(b"");
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 0);
+        assert_eq!(reader.file_size(), 0);
+        assert_eq!(reader.get_line(0), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_sequential_variant() {
+        let f = create_temp_file(b"alpha\nbeta\ngamma\n");
+        let reader = MmapReaderSequential::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "mmap_sequential");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(1), Some("beta".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_random_variant() {
+        let f = create_temp_file(b"one\ntwo\nthree\n");
+        let reader = MmapReaderRandom::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "mmap_random");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(2), Some("three".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_populate_variant() {
+        let f = create_temp_file(b"x\ny\nz\n");
+        let reader = MmapReaderPopulate::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "mmap_populate");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(0), Some("x".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_phase_aware_variant() {
+        let f = create_temp_file(b"a\nb\nc\n");
+        let reader = MmapReaderPhaseAware::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "mmap_phase_aware");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(1), Some("b".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_file_size() {
+        let content = b"hello world";
+        let f = create_temp_file(content);
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.file_size(), content.len() as u64);
+        reader.close();
+    }
+
+    #[test]
+    fn test_sigbus_flag_api() {
+        reset_sigbus_flag();
+        assert!(!sigbus_flag());
+    }
+
+    #[test]
+    fn test_concurrent_open_installs_handler_once() {
+        let f = create_temp_file(b"line1\nline2\nline3\n");
+        let path = f.path().to_owned();
+        let num_threads = 8;
+
+        let handles: Vec<_> = (0..num_threads)
+            .map(|thread_id| {
+                let path = path.clone();
+                std::thread::spawn(move || {
+                    let reader = match thread_id % 5 {
+                        0 => {
+                            let r = MmapReaderPlain::open(&path).unwrap();
+                            assert_eq!(r.total_lines(), 3);
+                            r.close();
+                            "plain"
+                        }
+                        1 => {
+                            let r = MmapReaderSequential::open(&path).unwrap();
+                            assert_eq!(r.total_lines(), 3);
+                            r.close();
+                            "sequential"
+                        }
+                        2 => {
+                            let r = MmapReaderRandom::open(&path).unwrap();
+                            assert_eq!(r.total_lines(), 3);
+                            r.close();
+                            "random"
+                        }
+                        3 => {
+                            let r = MmapReaderPopulate::open(&path).unwrap();
+                            assert_eq!(r.total_lines(), 3);
+                            r.close();
+                            "populate"
+                        }
+                        _ => {
+                            let r = MmapReaderPhaseAware::open(&path).unwrap();
+                            assert_eq!(r.total_lines(), 3);
+                            r.close();
+                            "phase_aware"
+                        }
+                    };
+                    reader.to_owned()
+                })
+            })
+            .collect();
+
+        let results: Vec<String> = handles
+            .into_iter()
+            .map(|h| h.join().expect("thread panicked"))
+            .collect();
+        assert_eq!(results.len(), num_threads);
+    }
+
+    #[test]
+    fn test_no_trailing_newline() {
+        let f = create_temp_file(b"line1\nline2");
+        let reader = MmapReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 2);
+        assert_eq!(reader.get_line(0), Some("line1".to_owned()));
+        assert_eq!(reader.get_line(1), Some("line2".to_owned()));
+        reader.close();
+    }
+
+    /// Diagnostic test: measure how long each stage of `open_raw()` takes
+    /// on a large file (e.g. the 5GB extreme.log).
+    /// Run with: cargo test -p log-viewer-bench --release -- --nocapture diag_open_stages
+    #[test]
+    fn diag_open_stages() {
+        let path = std::path::Path::new("/tmp/test-logviewer/extreme.log");
+        if !path.exists() {
+            eprintln!("SKIP: test file not found");
+            return;
+        }
+
+        // Stage 1: File::open + metadata
+        let t0 = std::time::Instant::now();
+        let file = File::open(path).unwrap();
+        let file_size = file.metadata().unwrap().len();
+        let stage1 = t0.elapsed();
+        eprintln!(
+            "Stage 1 - File::open + metadata: {:.2}ms ({:.1}GB)",
+            stage1.as_secs_f64() * 1000.0,
+            file_size as f64 / 1073741824.0
+        );
+
+        // Stage 2: mmap::map
+        let t1 = std::time::Instant::now();
+        let _mmap = unsafe { Mmap::map(&file) }.unwrap();
+        let stage2 = t1.elapsed();
+        eprintln!(
+            "Stage 2 - mmap::map:                {:.2}ms",
+            stage2.as_secs_f64() * 1000.0
+        );
+        drop(_mmap);
+
+        // Stage 3: LineIndex::from_reader via BufReader (default 8KB buffer)
+        let t2 = std::time::Instant::now();
+        let mut reader = BufReader::new(&file);
+        let line_index = crate::line_index::LineIndex::from_reader(&mut reader).unwrap();
+        let stage3 = t2.elapsed();
+        eprintln!(
+            "Stage 3 - LineIndex::from_reader:   {:.2}ms ({} lines, {} sampled_offsets)",
+            stage3.as_secs_f64() * 1000.0,
+            line_index.line_count(),
+            line_index.sampled_offsets.len()
+        );
+
+        // Stage 3b: Try with 1MB buffer
+        let file2 = File::open(path).unwrap();
+        let t2b = std::time::Instant::now();
+        let mut reader2 = BufReader::with_capacity(1024 * 1024, &file2);
+        let line_index2 = crate::line_index::LineIndex::from_reader(&mut reader2).unwrap();
+        let stage3b = t2b.elapsed();
+        eprintln!(
+            "Stage 3b - LineIndex (1MB buffer):   {:.2}ms",
+            stage3b.as_secs_f64() * 1000.0
+        );
+
+        eprintln!("\n=== 瓶颈分析 ===");
+        let total_ms = stage1.as_secs_f64() * 1000.0
+            + stage2.as_secs_f64() * 1000.0
+            + stage3.as_secs_f64() * 1000.0;
+        let total_dur = stage1 + stage2 + stage3;
+        eprintln!("Total ~{:.0}ms", total_ms);
+        eprintln!(
+            "  File::open:  {:.1}% ({:.0}ms)",
+            stage1.as_secs_f64() * 1000.0 / total_dur.as_secs_f64() / 1000.0 * 100.0,
+            stage1.as_secs_f64() * 1000.0
+        );
+        eprintln!(
+            "  mmap::map:   {:.1}% ({:.0}ms)",
+            stage2.as_secs_f64() * 1000.0 / total_dur.as_secs_f64() / 1000.0 * 100.0,
+            stage2.as_secs_f64() * 1000.0
+        );
+        eprintln!(
+            "  from_reader: {:.1}% ({:.0}ms)",
+            stage3.as_secs_f64() * 1000.0 / total_dur.as_secs_f64() / 1000.0 * 100.0,
+            stage3.as_secs_f64() * 1000.0
+        );
+
+        // Suppress unused warnings
+        let _ = line_index2;
+    }
+}

crates/bench/src/pread_reader.rs

@@ -0,0 +1,526 @@
+// ─── pread_reader.rs ──────────────────────────────────────────────────────────
+// pread-based FileReaderBackend implementations with 3 variants for benchmarking.
+// Uses ReadCache for 4KB block caching to reduce syscalls, and posix_fadvise
+// for kernel readahead control.
+//
+// CRITICAL: get_line() is custom — it does NOT use LineIndex::get_line() which
+// requires a full &[u8] data slice. Instead it uses sampled_offsets directly
+// and reads on-demand via pread.
+// ──────────────────────────────────────────────────────────────────────────────
+
+use std::cell::RefCell;
+use std::fs::File;
+use std::io::{BufReader, Seek as _, SeekFrom};
+use std::os::unix::fs::FileExt;
+use std::os::unix::io::AsRawFd;
+use std::path::Path;
+
+use crate::line_index::LineIndex;
+use crate::FileReaderBackend;
+
+const BLOCK_SIZE: usize = 256;
+const CACHE_CHUNK: usize = 4096;
+
+// ─── ReadCache ────────────────────────────────────────────────────────────────
+
+/// Single-block read cache. Reduces syscalls by caching the last read.
+/// Typical cache hit: sequential get_line() calls within the same 4KB block.
+struct ReadCache {
+    buf: Vec<u8>,
+    buf_offset: u64,
+    buf_len: usize,
+}
+
+impl ReadCache {
+    fn new() -> Self {
+        Self {
+            buf: vec![0u8; CACHE_CHUNK],
+            buf_offset: 0,
+            buf_len: 0,
+        }
+    }
+
+    /// Read `len` bytes starting at `offset`. Returns a slice into the cache.
+    /// On cache hit (range fully within cached block), no syscall needed.
+    /// On miss, performs a `read_exact_at` syscall.
+    fn invalidate(&mut self) {
+        self.buf_len = 0;
+    }
+
+    fn get(&mut self, file: &File, offset: u64, len: usize) -> std::io::Result<&[u8]> {
+        let end = offset + len as u64;
+        if offset >= self.buf_offset && end <= self.buf_offset + self.buf_len as u64 {
+            let start = (offset - self.buf_offset) as usize;
+            return Ok(&self.buf[start..start + len]);
+        }
+        let alloc_len = CACHE_CHUNK.max(len);
+        self.buf.resize(alloc_len, 0);
+        file.read_exact_at(&mut self.buf[..len], offset)?;
+        self.buf_offset = offset;
+        self.buf_len = len;
+        Ok(&self.buf[..len])
+    }
+}
+
+// ─── PreadReaderCore ──────────────────────────────────────────────────────────
+
+/// Core pread-based reader. Uses ReadCache and sparse LineIndex for on-demand
+/// line retrieval without mmap.
+pub struct PreadReaderCore {
+    file: File,
+    line_index: LineIndex,
+    file_size: u64,
+    cache: RefCell<ReadCache>,
+}
+
+impl PreadReaderCore {
+    /// Open file, build line index via streaming BufReader, prepare pread reader.
+    fn open_raw(path: &Path) -> std::io::Result<Self> {
+        let file = File::open(path)?;
+        let file_size = file.metadata()?.len();
+
+        let line_index = {
+            let mut reader = BufReader::new(&file);
+            LineIndex::from_reader(&mut reader)?
+        };
+
+        Ok(Self {
+            file,
+            line_index,
+            file_size,
+            cache: RefCell::new(ReadCache::new()),
+        })
+    }
+
+    /// Apply posix_fadvise to the entire file.
+    fn advise(&self, advice: libc::c_int) -> std::io::Result<()> {
+        let fd = self.file.as_raw_fd();
+        let ret = unsafe { libc::posix_fadvise(fd, 0, self.file_size as i64, advice) };
+        if ret != 0 {
+            return Err(std::io::Error::from_raw_os_error(ret));
+        }
+        Ok(())
+    }
+
+    /// Custom get_line using sparse index + pread.
+    /// Does NOT use LineIndex::get_line() (which needs full &[u8] slice).
+    ///
+    /// Algorithm:
+    /// 1. Look up sampled_offsets[block] to get approximate byte position
+    /// 2. Scan forward through offset_in_block newlines via memchr
+    /// 3. Collect bytes from that position until next newline (may span 4KB blocks)
+    fn get_line_impl(&self, idx: usize) -> Option<String> {
+        let total = self.line_index.total_lines as usize;
+        if idx >= total || total == 0 {
+            return None;
+        }
+
+        let block = idx / BLOCK_SIZE;
+        let offset_in_block = idx % BLOCK_SIZE;
+
+        let mut cache = self.cache.borrow_mut();
+
+        // Phase 1: Find byte position of the start of line `idx`.
+        // Start at sampled_offsets[block], scan forward through `offset_in_block` newlines.
+        let start_offset = self.line_index.sampled_offsets[block];
+        let mut pos = start_offset;
+        let mut newlines_found = 0;
+
+        while newlines_found < offset_in_block {
+            let remaining = self.file_size.saturating_sub(pos) as usize;
+            if remaining == 0 {
+                return None;
+            }
+            let to_read = CACHE_CHUNK.min(remaining);
+            let data = cache.get(&self.file, pos, to_read).ok()?;
+
+            for byte_pos in memchr::memchr_iter(b'\n', data) {
+                newlines_found += 1;
+                if newlines_found == offset_in_block {
+                    pos = pos + byte_pos as u64 + 1;
+                    break;
+                }
+            }
+
+            if newlines_found < offset_in_block {
+                pos += to_read as u64;
+            }
+        }
+
+        // Phase 2: Collect bytes from `pos` until next newline or EOF.
+        // Line data may span multiple 4KB cache blocks.
+        let mut result = Vec::new();
+
+        while pos < self.file_size {
+            let remaining = (self.file_size - pos) as usize;
+            let to_read = CACHE_CHUNK.min(remaining);
+            let data = cache.get(&self.file, pos, to_read).ok()?;
+
+            match memchr::memchr(b'\n', data) {
+                Some(rel) => {
+                    result.extend_from_slice(&data[..rel]);
+                    break;
+                }
+                None => {
+                    result.extend_from_slice(data);
+                    pos += to_read as u64;
+                }
+            }
+        }
+
+        String::from_utf8(result)
+            .ok()
+            .map(|s| s.trim_end_matches(['\r', '\n']).to_owned())
+    }
+
+    /// Read a raw byte range from the file using pread.
+    fn read_range_impl(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        let end = offset.checked_add(len as u64)?;
+        if end > self.file_size {
+            return None;
+        }
+        let mut buf = vec![0u8; len];
+        self.file.read_exact_at(&mut buf, offset).ok()?;
+        Some(buf)
+    }
+
+    #[inline]
+    pub fn file_size(&self) -> u64 {
+        self.file_size
+    }
+
+    #[inline]
+    pub fn total_lines(&self) -> usize {
+        self.line_index.line_count()
+    }
+
+    pub fn refresh_index(&mut self) -> std::io::Result<()> {
+        let new_size = self.file.metadata()?.len();
+        self.file.seek(SeekFrom::Start(0))?;
+        let new_index = {
+            let mut reader = BufReader::new(&self.file);
+            LineIndex::from_reader(&mut reader)?
+        };
+        self.file_size = new_size;
+        self.line_index = new_index;
+        self.cache.get_mut().invalidate();
+        Ok(())
+    }
+}
+
+// ─── 3 Variants ───────────────────────────────────────────────────────────────
+
+/// Variant 1: Plain pread, no fadvise.
+pub struct PreadReaderPlain {
+    inner: PreadReaderCore,
+}
+
+impl PreadReaderPlain {
+    pub fn refresh_index(&mut self) -> std::io::Result<()> {
+        self.inner.refresh_index()
+    }
+}
+
+impl FileReaderBackend for PreadReaderPlain {
+    fn name(&self) -> &str {
+        "pread_plain"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        let inner = PreadReaderCore::open_raw(path)?;
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line_impl(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range_impl(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 2: pread with POSIX_FADV_RANDOM — disable kernel readahead.
+/// Best for random-access line lookup patterns.
+pub struct PreadReaderRandom {
+    inner: PreadReaderCore,
+}
+
+impl FileReaderBackend for PreadReaderRandom {
+    fn name(&self) -> &str {
+        "pread_random"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        let inner = PreadReaderCore::open_raw(path)?;
+        inner.advise(libc::POSIX_FADV_RANDOM)?;
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line_impl(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range_impl(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+/// Variant 3: pread with POSIX_FADV_SEQUENTIAL — aggressive kernel readahead.
+/// Best for sequential scan patterns.
+pub struct PreadReaderSequential {
+    inner: PreadReaderCore,
+}
+
+impl FileReaderBackend for PreadReaderSequential {
+    fn name(&self) -> &str {
+        "pread_sequential"
+    }
+
+    fn open(path: &Path) -> std::io::Result<Self>
+    where
+        Self: Sized,
+    {
+        let inner = PreadReaderCore::open_raw(path)?;
+        inner.advise(libc::POSIX_FADV_SEQUENTIAL)?;
+        Ok(Self { inner })
+    }
+
+    fn file_size(&self) -> u64 {
+        self.inner.file_size()
+    }
+
+    fn total_lines(&self) -> usize {
+        self.inner.total_lines()
+    }
+
+    fn get_line(&self, idx: usize) -> Option<String> {
+        self.inner.get_line_impl(idx)
+    }
+
+    fn read_range(&self, offset: u64, len: usize) -> Option<Vec<u8>> {
+        self.inner.read_range_impl(offset, len)
+    }
+
+    fn close(self) {}
+}
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write as _;
+    use tempfile::NamedTempFile;
+
+    fn create_temp_file(content: &[u8]) -> NamedTempFile {
+        let mut f = NamedTempFile::new().unwrap();
+        f.write_all(content).unwrap();
+        f.flush().unwrap();
+        f
+    }
+
+    #[test]
+    fn test_plain_open_and_read_lines() {
+        let f = create_temp_file(b"hello\nworld\nfoo\n");
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "pread_plain");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(0), Some("hello".to_owned()));
+        assert_eq!(reader.get_line(1), Some("world".to_owned()));
+        assert_eq!(reader.get_line(2), Some("foo".to_owned()));
+        assert_eq!(reader.get_line(3), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_out_of_bounds_returns_none() {
+        let f = create_temp_file(b"line1\nline2\n");
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 2);
+        assert_eq!(reader.get_line(100), None);
+        assert_eq!(reader.get_line(usize::MAX), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_read_range() {
+        let content = b"hello world\nfoo bar\n";
+        let f = create_temp_file(content);
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        let range = reader.read_range(0, 5).unwrap();
+        assert_eq!(&range, b"hello");
+        let range = reader.read_range(6, 5).unwrap();
+        assert_eq!(&range, b"world");
+        assert_eq!(reader.read_range(0, 1000), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_plain_empty_file() {
+        let f = create_temp_file(b"");
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 0);
+        assert_eq!(reader.file_size(), 0);
+        assert_eq!(reader.get_line(0), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_random_variant() {
+        let f = create_temp_file(b"one\ntwo\nthree\n");
+        let reader = PreadReaderRandom::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "pread_random");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(2), Some("three".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_sequential_variant() {
+        let f = create_temp_file(b"alpha\nbeta\ngamma\n");
+        let reader = PreadReaderSequential::open(f.path()).unwrap();
+        assert_eq!(reader.name(), "pread_sequential");
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(1), Some("beta".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_file_size() {
+        let content = b"hello world";
+        let f = create_temp_file(content);
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.file_size(), content.len() as u64);
+        reader.close();
+    }
+
+    #[test]
+    fn test_no_trailing_newline() {
+        let f = create_temp_file(b"line1\nline2");
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 2);
+        assert_eq!(reader.get_line(0), Some("line1".to_owned()));
+        assert_eq!(reader.get_line(1), Some("line2".to_owned()));
+        reader.close();
+    }
+
+    #[test]
+    fn test_line_spanning_cache_boundary() {
+        // Create a line that spans a 4KB boundary
+        let mut content = vec![b'a'; 4090];
+        content.push(b'\n');
+        content.extend_from_slice(b"target\n");
+        let f = create_temp_file(&content);
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.get_line(0).unwrap().len(), 4090);
+        assert_eq!(reader.get_line(1), Some("target".to_owned()));
+        assert_eq!(reader.get_line(2), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_many_lines_random_access() {
+        // Create 300 lines to test block boundary (256 lines per block)
+        let mut content = String::new();
+        for i in 0..300 {
+            content.push_str(&format!("line_{}\n", i));
+        }
+        let f = create_temp_file(content.as_bytes());
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 300);
+        // Test lines across the 256-line block boundary
+        assert_eq!(reader.get_line(0), Some("line_0".to_owned()));
+        assert_eq!(reader.get_line(255), Some("line_255".to_owned()));
+        assert_eq!(reader.get_line(256), Some("line_256".to_owned()));
+        assert_eq!(reader.get_line(299), Some("line_299".to_owned()));
+        assert_eq!(reader.get_line(300), None);
+        reader.close();
+    }
+
+    #[test]
+    fn test_refresh_index_sees_appended_lines() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("refresh_test.log");
+
+        // Phase 1: write 3 initial lines
+        {
+            let mut f = std::fs::File::create(&path).unwrap();
+            std::io::Write::write_all(&mut f, b"alpha\nbeta\ngamma\n").unwrap();
+        }
+
+        let mut reader = PreadReaderPlain::open(&path).unwrap();
+        assert_eq!(reader.total_lines(), 3);
+        assert_eq!(reader.get_line(0), Some("alpha".to_owned()));
+        assert_eq!(reader.get_line(3), None, "should be out of bounds before append");
+
+        // Phase 2: append 2 more lines
+        {
+            use std::io::Write as _;
+            let mut f = std::fs::OpenOptions::new().append(true).open(&path).unwrap();
+            f.write_all(b"delta\nepsilon\n").unwrap();
+        }
+
+        // Still stale — refresh needed
+        assert_eq!(reader.get_line(3), None, "stale index before refresh");
+
+        reader.refresh_index().unwrap();
+        assert_eq!(reader.total_lines(), 5);
+        assert_eq!(reader.get_line(3), Some("delta".to_owned()));
+        assert_eq!(reader.get_line(4), Some("epsilon".to_owned()));
+        assert_eq!(reader.get_line(5), None);
+
+        reader.close();
+    }
+
+    #[test]
+    fn test_refresh_index_no_change_is_noop() {
+        let f = create_temp_file(b"one\ntwo\n");
+        let mut reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.total_lines(), 2);
+
+        reader.refresh_index().unwrap();
+        assert_eq!(reader.total_lines(), 2);
+        assert_eq!(reader.get_line(0), Some("one".to_owned()));
+        assert_eq!(reader.get_line(1), Some("two".to_owned()));
+
+        reader.close();
+    }
+
+    #[test]
+    fn test_truncation_graceful_error() {
+        // Verify that truncated file access returns None/Err instead of panicking
+        let f = create_temp_file(b"hello\nworld\n");
+        let reader = PreadReaderPlain::open(f.path()).unwrap();
+        assert_eq!(reader.get_line(0), Some("hello".to_owned()));
+        // Truncate behind the reader — pread may return zeros or error
+        let _ = reader.get_line(1); // must not panic
+        reader.close();
+    }
+}

crates/bench/src/report.rs

@@ -0,0 +1,263 @@
+use crate::metrics;
+use crate::types::BenchmarkResult;
+
+fn format_rss_mb(kb: u64) -> String {
+    format!("{:.1}MB", kb as f64 / 1024.0)
+}
+
+fn format_faults(count: u64) -> String {
+    if count < 1000 {
+        count.to_string()
+    } else {
+        let s = count.to_string();
+        let mut result = String::new();
+        for (i, c) in s.chars().rev().enumerate() {
+            if i > 0 && i % 3 == 0 {
+                result.push(',');
+            }
+            result.push(c);
+        }
+        result.chars().rev().collect()
+    }
+}
+
+// Format benchmark results as Markdown, grouped by category.
+pub fn format_report(results: &[BenchmarkResult]) -> String {
+    let mut report = String::new();
+    report.push_str("# Benchmark: mmap vs pread\n\n");
+
+    let mut categories: std::collections::BTreeMap<&str, Vec<&BenchmarkResult>> =
+        std::collections::BTreeMap::new();
+    for r in results {
+        categories.entry(&r.category).or_default().push(r);
+    }
+
+    for (category, category_results) in &categories {
+        report.push_str(&format!("## {}\n\n", capitalize(category)));
+
+        let mut tests: std::collections::BTreeMap<&str, Vec<&BenchmarkResult>> =
+            std::collections::BTreeMap::new();
+        for r in category_results {
+            tests.entry(&r.test_name).or_default().push(r);
+        }
+
+        let mut variants: Vec<(String, String)> = Vec::new();
+        for r in category_results {
+            if !variants
+                .iter()
+                .any(|(b, v)| b == &r.backend && v == &r.variant)
+            {
+                variants.push((r.backend.clone(), r.variant.clone()));
+            }
+        }
+        variants.sort();
+
+        report.push_str("### Latency\n\n");
+        report.push_str("| Test |");
+        for (backend, variant) in &variants {
+            report.push_str(&format!(" {} ({}) |", backend, variant));
+        }
+        report.push_str(" Winner |\n");
+
+        report.push_str("|------|");
+        for _ in &variants {
+            report.push_str("------|");
+        }
+        report.push_str("--------|\n");
+
+        for (test_name, test_results) in &tests {
+            report.push_str(&format!("| {} |", test_name));
+
+            let mut all_means: Vec<f64> = Vec::new();
+            for (backend, variant) in &variants {
+                if let Some(r) = test_results
+                    .iter()
+                    .find(|r| r.backend == *backend && r.variant == *variant)
+                {
+                    let avg = if r.latency_us.is_empty() {
+                        0.0
+                    } else {
+                        metrics::mean(&r.latency_us)
+                    };
+                    all_means.push(avg);
+                }
+            }
+            let use_ms = all_means.iter().any(|&v| v >= 1000.0);
+
+            let mut best_backend = String::new();
+            let mut best_latency = f64::MAX;
+
+            for (backend, variant) in &variants {
+                let matching = test_results
+                    .iter()
+                    .find(|r| r.backend == *backend && r.variant == *variant);
+                if let Some(r) = matching {
+                    let avg = if r.latency_us.is_empty() {
+                        0.0
+                    } else {
+                        metrics::mean(&r.latency_us)
+                    };
+                    let sd = metrics::stdev(&r.latency_us);
+                    let p95_val = metrics::p95(&r.latency_us) as f64;
+
+                    let cell = if use_ms {
+                        format!(
+                            "{:.2}\u{00b1}{:.2}ms (p95:{:.2}ms)",
+                            avg / 1000.0,
+                            sd / 1000.0,
+                            p95_val / 1000.0
+                        )
+                    } else {
+                        format!(
+                            "{:.1}\u{00b1}{:.1}\u{b5}s (p95:{:.1}\u{b5}s)",
+                            avg, sd, p95_val
+                        )
+                    };
+                    report.push_str(&format!(" {} |", cell));
+                    if avg > 0.0 && avg < best_latency {
+                        best_latency = avg;
+                        best_backend = format!("{} ({})", backend, variant);
+                    }
+                } else {
+                    report.push_str(" - |");
+                }
+            }
+            report.push_str(&format!(
+                " {} |\n",
+                if best_backend.is_empty() {
+                    "-"
+                } else {
+                    &best_backend
+                }
+            ));
+        }
+
+        report.push('\n');
+
+        let has_memory = category_results
+            .iter()
+            .any(|r| r.rss_kb > 0 || r.rss_peak_kb > 0);
+
+        if has_memory {
+            report.push_str("### Memory\n\n");
+            report.push_str("| Test | Variant | RSS | Peak RSS | Page Faults |\n");
+            report.push_str("|------|---------|-----|----------|-------------|\n");
+
+            let mut mem_rows: Vec<&BenchmarkResult> = category_results.to_vec();
+            mem_rows.sort_by(|a, b| {
+                (&a.test_name, &a.backend, &a.variant)
+                    .cmp(&(&b.test_name, &b.backend, &b.variant))
+            });
+            for r in mem_rows {
+                let variant_label = format!("{} ({})", r.backend, r.variant);
+                report.push_str(&format!(
+                    "| {} | {} | {} | {} | {} |\n",
+                    r.test_name,
+                    variant_label,
+                    format_rss_mb(r.rss_kb),
+                    format_rss_mb(r.rss_peak_kb),
+                    format_faults(r.page_faults),
+                ));
+            }
+            report.push('\n');
+        }
+
+        type ExtraEntry = (String, f64);
+        type ExtraGroup = (String, String, Vec<ExtraEntry>);
+
+        let mut extras: Vec<ExtraGroup> = category_results
+            .iter()
+            .filter(|r| !r.extra.is_empty())
+            .map(|r| {
+                let mut pairs: Vec<(String, f64)> =
+                    r.extra.iter().map(|(k, &v)| (k.clone(), v)).collect();
+                pairs.sort_by(|a, b| a.0.cmp(&b.0));
+                (
+                    r.test_name.clone(),
+                    format!("{} ({})", r.backend, r.variant),
+                    pairs,
+                )
+            })
+            .collect();
+        extras.sort_by(|a, b| (&a.0, &a.1).cmp(&(&b.0, &b.1)));
+
+        if !extras.is_empty() {
+            report.push_str("### Extra Metrics\n\n");
+            report.push_str("| Test | Variant | Metric | Value |\n");
+            report.push_str("|------|---------|--------|-------|\n");
+
+            for (test_name, variant_label, pairs) in &extras {
+                for (key, val) in pairs {
+                    report.push_str(&format!(
+                        "| {} | {} | {} | {:.3} |\n",
+                        test_name, variant_label, key, val
+                    ));
+                }
+            }
+            report.push('\n');
+        }
+    }
+
+    report.push_str("## Summary\n\n");
+    report.push_str(&format!("- Total benchmarks: {}\n", results.len()));
+    report.push_str("- Categories: ");
+    report.push_str(&categories.keys().cloned().collect::<Vec<_>>().join(", "));
+    report.push('\n');
+
+    report
+}
+
+fn capitalize(s: &str) -> String {
+    let mut c = s.chars();
+    match c.next() {
+        None => String::new(),
+        Some(f) => f.to_uppercase().chain(c).collect(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashMap;
+
+    fn make_result(
+        category: &str,
+        test_name: &str,
+        backend: &str,
+        variant: &str,
+        latency_us: Vec<u64>,
+    ) -> BenchmarkResult {
+        BenchmarkResult {
+            category: category.to_string(),
+            test_name: test_name.to_string(),
+            backend: backend.to_string(),
+            variant: variant.to_string(),
+            latency_us,
+            rss_kb: 0,
+            rss_peak_kb: 0,
+            page_faults: 0,
+            extra: HashMap::new(),
+        }
+    }
+
+    #[test]
+    fn report_ordering_independent_of_input_order() {
+        let set_a = vec![
+            make_result("sequential", "read_1mb", "pread", "default", vec![100, 110, 105]),
+            make_result("sequential", "read_1mb", "mmap", "default", vec![80, 85, 90]),
+            make_result("sequential", "read_4kb", "pread", "default", vec![10, 12, 11]),
+            make_result("sequential", "read_4kb", "mmap", "default", vec![8, 9, 7]),
+        ];
+
+        let set_b = vec![
+            make_result("sequential", "read_4kb", "mmap", "default", vec![8, 9, 7]),
+            make_result("sequential", "read_1mb", "mmap", "default", vec![80, 85, 90]),
+            make_result("sequential", "read_4kb", "pread", "default", vec![10, 12, 11]),
+            make_result("sequential", "read_1mb", "pread", "default", vec![100, 110, 105]),
+        ];
+
+        let report_a = format_report(&set_a);
+        let report_b = format_report(&set_b);
+        assert_eq!(report_a, report_b, "Reports must be identical regardless of input order");
+    }
+}

crates/bench/src/runner.rs

@@ -0,0 +1,221 @@
+use crate::metrics::MetricsCollector;
+use crate::types::BenchmarkResult;
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+/// All recognized benchmark suite identifiers.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Suite {
+    Startup,
+    Render,
+    Jump,
+    Memory,
+    Growth,
+    Rotation,
+    Concurrent,
+}
+
+impl Suite {
+    /// All valid suite identifiers, in execution order.
+    pub const ALL: &[Suite] = &[
+        Suite::Startup,
+        Suite::Render,
+        Suite::Jump,
+        Suite::Memory,
+        Suite::Growth,
+        Suite::Rotation,
+        Suite::Concurrent,
+    ];
+
+    #[must_use]
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Suite::Startup => "startup",
+            Suite::Render => "render",
+            Suite::Jump => "jump",
+            Suite::Memory => "memory",
+            Suite::Growth => "growth",
+            Suite::Rotation => "rotation",
+            Suite::Concurrent => "concurrent",
+        }
+    }
+}
+
+impl std::str::FromStr for Suite {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Suite::ALL
+            .iter()
+            .find(|suite| suite.as_str() == s)
+            .copied()
+            .ok_or_else(|| {
+                let valid = Suite::ALL
+                    .iter()
+                    .map(|s| s.as_str())
+                    .collect::<Vec<_>>()
+                    .join(", ");
+                format!("invalid value '{s}' for '--suites': valid values are {valid}")
+            })
+    }
+}
+
+pub struct BenchConfig {
+    pub test_file: PathBuf,
+    pub quick_mode: bool,
+    pub suites: Option<Vec<Suite>>,
+}
+
+/// Track whether we have already warned about VmHWM reset failure.
+/// Prevents duplicate warnings across multiple suite runs.
+static HWM_WARNED: AtomicBool = AtomicBool::new(false);
+
+pub fn warn_reset_hwm() {
+    if let Err(e) = MetricsCollector::reset_vm_hwm() {
+        if HWM_WARNED.swap(true, Ordering::Relaxed) {
+            return;
+        }
+        if e.kind() == std::io::ErrorKind::PermissionDenied {
+            eprintln!(
+                "WARNING: Failed to reset VmHWM via /proc/self/clear_refs: {e}. \
+                 Memory peak values may be contaminated across benchmark suites. \
+                 Try running as root."
+            );
+        } else {
+            eprintln!(
+                "WARNING: Failed to reset VmHWM via /proc/self/clear_refs: {e}. \
+                 Memory peak values may be contaminated across benchmark suites."
+            );
+        }
+    }
+}
+
+#[cfg(test)]
+fn reset_hwm_warned() {
+    HWM_WARNED.store(false, Ordering::Relaxed);
+}
+
+pub fn run_all(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    let should_run = |suite: Suite| -> bool {
+        match &config.suites {
+            Some(suites) => suites.contains(&suite),
+            None => true,
+        }
+    };
+
+    if should_run(Suite::Startup) {
+        warn_reset_hwm();
+        results.extend(crate::suites::startup::run(config));
+    }
+    if should_run(Suite::Render) {
+        warn_reset_hwm();
+        results.extend(crate::suites::render::run(config));
+    }
+    if should_run(Suite::Jump) {
+        warn_reset_hwm();
+        results.extend(crate::suites::jump::run(config));
+    }
+    if should_run(Suite::Memory) {
+        warn_reset_hwm();
+        results.extend(crate::suites::memory::run(config));
+    }
+    if should_run(Suite::Growth) {
+        warn_reset_hwm();
+        results.extend(crate::suites::growth::run(config));
+    }
+    if should_run(Suite::Rotation) {
+        warn_reset_hwm();
+        results.extend(crate::suites::rotation::run(config));
+    }
+    if should_run(Suite::Concurrent) {
+        warn_reset_hwm();
+        results.extend(crate::suites::concurrent::run(config));
+    }
+
+    results
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Suite;
+    use std::str::FromStr;
+
+    #[test]
+    fn parse_all_valid_suites() {
+        let expected = [
+            ("startup", Suite::Startup),
+            ("render", Suite::Render),
+            ("jump", Suite::Jump),
+            ("memory", Suite::Memory),
+            ("growth", Suite::Growth),
+            ("rotation", Suite::Rotation),
+            ("concurrent", Suite::Concurrent),
+        ];
+        for (s, expected_suite) in expected {
+            assert_eq!(Suite::from_str(s).unwrap(), expected_suite, "failed to parse '{s}'");
+        }
+    }
+
+    #[test]
+    fn misspelled_suite_returns_error() {
+        let err = Suite::from_str("startp").unwrap_err();
+        assert!(
+            err.contains("invalid value 'startp'"),
+            "error should mention the bad value: {err}"
+        );
+    }
+
+    #[test]
+    fn error_message_lists_all_valid_values() {
+        let err = Suite::from_str("bogus").unwrap_err();
+        for name in Suite::ALL.iter().map(|s| s.as_str()) {
+            assert!(
+                err.contains(name),
+                "error should list valid suite '{name}': {err}"
+            );
+        }
+    }
+
+    #[test]
+    fn mixed_valid_invalid_stops_at_first_error() {
+        // "startup" is valid, "zzz" is not — collect hits the first Err
+        let names = ["startup".to_string(), "zzz".to_string()];
+        let result: Result<Vec<Suite>, _> = names.iter().map(|s| s.parse()).collect();
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn hwm_warned_flag_prevents_reentry() {
+        use super::reset_hwm_warned;
+        use std::sync::atomic::Ordering;
+
+        reset_hwm_warned();
+        assert!(
+            !super::HWM_WARNED.load(Ordering::Relaxed),
+            "flag should be false after reset"
+        );
+
+        // Simulate the flag being set (as warn_reset_hwm would do on error)
+        super::HWM_WARNED.store(true, Ordering::Relaxed);
+
+        // swap should now return true (old value), indicating already warned
+        assert!(
+            super::HWM_WARNED.swap(true, Ordering::Relaxed),
+            "swap should return the previous value (true)"
+        );
+    }
+
+    #[test]
+    fn warn_reset_hwm_does_not_panic() {
+        use super::reset_hwm_warned;
+
+        reset_hwm_warned();
+        // Whether reset_vm_hwm succeeds or fails, warn_reset_hwm must not panic.
+        // Multiple calls must also be safe.
+        super::warn_reset_hwm();
+        super::warn_reset_hwm();
+        super::warn_reset_hwm();
+    }
+}

crates/bench/src/suites/concurrent.rs

@@ -0,0 +1,117 @@
+use std::collections::HashMap;
+
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{
+    MmapReaderPhaseAware, MmapReaderPlain, MmapReaderPopulate, MmapReaderRandom,
+    MmapReaderSequential,
+};
+use crate::pread_reader::{PreadReaderPlain, PreadReaderRandom, PreadReaderSequential};
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    results.extend(bench_parallel_reads::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_parallel_reads::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_parallel_reads::<MmapReaderRandom>(
+        "mmap", "random", config,
+    ));
+    results.extend(bench_parallel_reads::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_parallel_reads::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_parallel_reads::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+    results.extend(bench_parallel_reads::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_parallel_reads::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results
+}
+
+fn bench_parallel_reads<B: FileReaderBackend + Send + 'static>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = config.test_file.clone();
+    let iterations = if config.quick_mode { 250 } else { 1000 };
+
+    let total_lines = {
+        let reader = B::open(&path).expect("Failed to open file for line count");
+        let count = reader.total_lines();
+        reader.close();
+        count
+    };
+
+    let overall_start = std::time::Instant::now();
+    let num_threads = 4usize;
+
+    let handles: Vec<_> = (0..num_threads)
+        .map(|thread_id| {
+            let path = path.clone();
+            std::thread::spawn(move || {
+                let reader = B::open(&path).expect("Failed to open file in thread");
+                let mut latencies = Vec::with_capacity(iterations);
+
+                for i in 0..iterations {
+                    let line_idx = (thread_id * iterations + i) % total_lines.max(1);
+                    let t = std::time::Instant::now();
+                    let _ = reader.get_line(line_idx);
+                    latencies.push(t.elapsed().as_micros() as u64);
+                }
+
+                reader.close();
+                latencies
+            })
+        })
+        .collect();
+
+    let thread_latencies: Vec<Vec<u64>> = handles
+        .into_iter()
+        .map(|h| h.join().expect("Thread panicked"))
+        .collect();
+
+    let total_elapsed = overall_start.elapsed();
+
+    let all_latencies: Vec<u64> = thread_latencies.into_iter().flatten().collect();
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("num_threads".into(), num_threads as f64);
+    extra.insert("iterations_per_thread".into(), iterations as f64);
+    extra.insert("total_time_us".into(), total_elapsed.as_micros() as f64);
+    extra.insert("total_lines".into(), total_lines as f64);
+
+    vec![BenchmarkResult {
+        category: "concurrent".into(),
+        test_name: "parallel_reads".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: all_latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}

crates/bench/src/suites/growth.rs

@@ -0,0 +1,295 @@
+use std::collections::HashMap;
+
+use crate::data_gen;
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::MmapReaderPlain;
+use crate::pread_reader::PreadReaderPlain;
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    let dir = tempfile::tempdir().expect("Failed to create temp dir");
+    results.extend(bench_append_visibility_mmap(config, dir.path()));
+    results.extend(bench_append_visibility_pread(config, dir.path()));
+    results.extend(bench_remap_cost(config, dir.path()));
+    results.extend(bench_scroll_during_append(config, dir.path()));
+    results.extend(bench_high_frequency_append(config, dir.path()));
+
+    results
+}
+
+fn bench_append_visibility_mmap(
+    config: &BenchConfig,
+    dir: &std::path::Path,
+) -> Vec<BenchmarkResult> {
+    let path = data_gen::generate_growable_file(dir).expect("Failed to create growable file");
+    let append_count: usize = if config.quick_mode { 100 } else { 1000 };
+
+    let mut reader = MmapReaderPlain::open(&path).expect("Failed to open growable file");
+    let original_lines = reader.total_lines();
+    let original_size = reader.file_size();
+
+    data_gen::append_lines(&path, append_count).expect("Failed to append lines");
+
+    let new_metadata = std::fs::metadata(&path).expect("Failed to read metadata");
+    let new_size = new_metadata.len() as usize;
+
+    let remap_start = std::time::Instant::now();
+    reader.remap(new_size).expect("Failed to remap");
+    let remap_elapsed = remap_start.elapsed();
+
+    let new_line_bytes =
+        reader.read_range(original_size, (new_size - original_size as usize).min(256));
+    let visible = new_line_bytes.is_some();
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("original_lines".into(), original_lines as f64);
+    extra.insert("appended_lines".into(), append_count as f64);
+    extra.insert("new_bytes_visible".into(), visible as u64 as f64);
+    extra.insert("original_size".into(), original_size as f64);
+    extra.insert("new_size".into(), new_size as f64);
+    extra.insert("remap_us".into(), remap_elapsed.as_micros() as f64);
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "growth".into(),
+        test_name: "append_visibility_mmap".into(),
+        backend: "mmap".into(),
+        variant: "plain".into(),
+        latency_us: vec![remap_elapsed.as_micros() as u64],
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_append_visibility_pread(
+    config: &BenchConfig,
+    dir: &std::path::Path,
+) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("pread_growth");
+    let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create growable file");
+    let append_count: usize = if config.quick_mode { 100 } else { 1000 };
+
+    let reader = PreadReaderPlain::open(&path).expect("Failed to open growable file");
+    let original_lines = reader.total_lines();
+    reader.close();
+
+    data_gen::append_lines(&path, append_count).expect("Failed to append lines");
+
+    let reopen_start = std::time::Instant::now();
+    let new_reader = PreadReaderPlain::open(&path).expect("Failed to reopen file");
+    let reopen_elapsed = reopen_start.elapsed();
+
+    let new_lines = new_reader.total_lines();
+    let can_read_new = new_lines > original_lines;
+    if can_read_new {
+        let last_line = new_lines.saturating_sub(1);
+        let _ = new_reader.get_line(last_line);
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("original_lines".into(), original_lines as f64);
+    extra.insert("appended_lines".into(), append_count as f64);
+    extra.insert("new_total_lines".into(), new_lines as f64);
+    extra.insert("reopen_us".into(), reopen_elapsed.as_micros() as f64);
+
+    new_reader.close();
+
+    vec![BenchmarkResult {
+        category: "growth".into(),
+        test_name: "append_visibility_pread".into(),
+        backend: "pread".into(),
+        variant: "plain".into(),
+        latency_us: vec![reopen_elapsed.as_micros() as u64],
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_remap_cost(config: &BenchConfig, dir: &std::path::Path) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("remap_cost");
+    let append_count: usize = if config.quick_mode { 100 } else { 1000 };
+    let iterations: usize = if config.quick_mode { 5 } else { 20 };
+
+    let mut latencies = Vec::with_capacity(iterations);
+
+    for _ in 0..iterations {
+        let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create file");
+        let mut reader = MmapReaderPlain::open(&path).expect("Failed to open file");
+
+        data_gen::append_lines(&path, append_count).expect("Failed to append");
+
+        let new_size = std::fs::metadata(&path).expect("metadata").len() as usize;
+        let t = std::time::Instant::now();
+        reader.remap(new_size).expect("remap failed");
+        latencies.push(t.elapsed().as_micros() as u64);
+
+        reader.close();
+        let _ = std::fs::remove_file(&path);
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("appended_per_iter".into(), append_count as f64);
+    extra.insert("iterations".into(), iterations as f64);
+
+    vec![BenchmarkResult {
+        category: "growth".into(),
+        test_name: "remap_cost".into(),
+        backend: "mmap".into(),
+        variant: "plain".into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_scroll_during_append(config: &BenchConfig, dir: &std::path::Path) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("scroll_append");
+    let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create growable file");
+    let duration_secs: u64 = if config.quick_mode { 2 } else { 10 };
+    let append_rate: usize = if config.quick_mode { 1000 } else { 10000 };
+
+    let bg_path = path.clone();
+    let bg_handle = std::thread::spawn(move || {
+        let batch_size = 100;
+        let batch_interval =
+            std::time::Duration::from_micros(1_000_000 / (append_rate / batch_size).max(1) as u64);
+        let start = std::time::Instant::now();
+        while start.elapsed().as_secs() < duration_secs {
+            data_gen::append_lines(&bg_path, batch_size).ok();
+            std::thread::sleep(batch_interval);
+        }
+    });
+
+    let mut reader = PreadReaderPlain::open(&path).expect("Failed to open file");
+    let initial_lines = reader.total_lines();
+    let mut frame_latencies = Vec::new();
+    let mut current_line = 0usize;
+    let mut refresh_count: u64 = 0;
+    let mut none_count: u64 = 0;
+    let scroll_start = std::time::Instant::now();
+    let mut last_refresh = std::time::Instant::now();
+    let refresh_interval = std::time::Duration::from_millis(250);
+
+    while scroll_start.elapsed().as_secs() < duration_secs {
+        if last_refresh.elapsed() >= refresh_interval {
+            reader.refresh_index().ok();
+            refresh_count += 1;
+            last_refresh = std::time::Instant::now();
+            continue;
+        }
+
+        if let Some(_line) = reader.get_line(current_line) {
+            let t = std::time::Instant::now();
+            frame_latencies.push(t.elapsed().as_micros() as u64);
+            current_line += 1;
+        } else {
+            none_count += 1;
+            std::thread::sleep(std::time::Duration::from_millis(1));
+        }
+    }
+
+    let max_line = current_line;
+    assert!(
+        max_line > initial_lines,
+        "benchmark never read past initial {initial_lines} lines (max={max_line})"
+    );
+
+    reader.close();
+    bg_handle.join().ok();
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("duration_secs".into(), duration_secs as f64);
+    extra.insert("append_rate_per_sec".into(), append_rate as f64);
+    extra.insert("frames_rendered".into(), frame_latencies.len() as f64);
+    extra.insert("refresh_count".into(), refresh_count as f64);
+    extra.insert("none_count".into(), none_count as f64);
+    extra.insert("initial_lines".into(), initial_lines as f64);
+    extra.insert("max_line_seen".into(), max_line as f64);
+
+    vec![BenchmarkResult {
+        category: "growth".into(),
+        test_name: "scroll_during_append".into(),
+        backend: "pread".into(),
+        variant: "plain".into(),
+        latency_us: frame_latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_high_frequency_append(
+    config: &BenchConfig,
+    dir: &std::path::Path,
+) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("high_freq_append");
+    let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create growable file");
+    let duration_secs: u64 = if config.quick_mode { 3 } else { 30 };
+    let append_rate: usize = if config.quick_mode { 1000 } else { 10000 };
+    let batch_size: usize = 100;
+    let batches_per_sec = append_rate / batch_size;
+    let total_batches = (duration_secs as usize * batches_per_sec).max(1);
+
+    let mut detect_latencies = Vec::with_capacity(total_batches);
+
+    for _ in 0..total_batches {
+        data_gen::append_lines(&path, batch_size).expect("Failed to append");
+
+        let t = std::time::Instant::now();
+        if let Ok(reader) = PreadReaderPlain::open(&path) {
+            let total = reader.total_lines();
+            let _ = reader.get_line(total.saturating_sub(1));
+            reader.close();
+        }
+        detect_latencies.push(t.elapsed().as_micros() as u64);
+
+        std::thread::sleep(std::time::Duration::from_micros(
+            1_000_000 / batches_per_sec as u64,
+        ));
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("duration_secs".into(), duration_secs as f64);
+    extra.insert("append_rate_per_sec".into(), append_rate as f64);
+    extra.insert("batch_size".into(), batch_size as f64);
+    extra.insert("total_batches".into(), total_batches as f64);
+
+    vec![BenchmarkResult {
+        category: "growth".into(),
+        test_name: "high_frequency_append".into(),
+        backend: "pread".into(),
+        variant: "plain".into(),
+        latency_us: detect_latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}

crates/bench/src/suites/jump.rs

@@ -0,0 +1,251 @@
+use std::collections::HashMap;
+
+use super::FRAME_LINES;
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{
+    MmapReaderPhaseAware, MmapReaderPlain, MmapReaderPopulate, MmapReaderRandom,
+    MmapReaderSequential,
+};
+use crate::pread_reader::{PreadReaderPlain, PreadReaderRandom, PreadReaderSequential};
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    results.extend(bench_near_jump::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_near_jump::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_near_jump::<MmapReaderRandom>(
+        "mmap", "random", config,
+    ));
+    results.extend(bench_near_jump::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_near_jump::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_near_jump::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+    results.extend(bench_near_jump::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_near_jump::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results.extend(bench_far_jump::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_far_jump::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_far_jump::<MmapReaderRandom>("mmap", "random", config));
+    results.extend(bench_far_jump::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_far_jump::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_far_jump::<PreadReaderPlain>("pread", "plain", config));
+    results.extend(bench_far_jump::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_far_jump::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results.extend(bench_jump_end::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_jump_end::<PreadReaderPlain>("pread", "plain", config));
+
+    results.extend(bench_reverse_scan::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_reverse_scan::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+
+    results
+}
+
+fn bench_near_jump<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+    let iterations: usize = if config.quick_mode { 10 } else { 100 };
+
+    let mut latencies = Vec::with_capacity(iterations);
+    let mut current = 0usize;
+
+    for _ in 0..iterations {
+        let target = (current + 15).min(total.saturating_sub(1));
+        let t = std::time::Instant::now();
+        let _ = reader.get_line(target);
+        latencies.push(t.elapsed().as_micros() as u64);
+        current = target;
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "jump".into(),
+        test_name: "near_jump".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra: HashMap::new(),
+    }]
+}
+
+fn bench_far_jump<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+    let repetitions: usize = if config.quick_mode { 3 } else { 10 };
+
+    let fractions = [0.25, 0.50, 0.75];
+    let mut latencies = Vec::new();
+    let mut extra = HashMap::new();
+
+    for &frac in &fractions {
+        let target = ((total as f64 * frac) as usize).min(total.saturating_sub(1));
+        for _ in 0..repetitions {
+            let t = std::time::Instant::now();
+            let _ = reader.get_line(target);
+            latencies.push(t.elapsed().as_micros() as u64);
+        }
+    }
+
+    extra.insert("jump_positions".into(), 3.0);
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "jump".into(),
+        test_name: "far_jump".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_jump_end<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+    let iterations: usize = if config.quick_mode { 5 } else { 10 };
+
+    let last_line = total.saturating_sub(1);
+    let mut latencies = Vec::with_capacity(iterations);
+
+    for _ in 0..iterations {
+        let t = std::time::Instant::now();
+        let _ = reader.get_line(last_line);
+        latencies.push(t.elapsed().as_micros() as u64);
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("last_line_idx".into(), last_line as f64);
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "jump".into(),
+        test_name: "jump_end".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_reverse_scan<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+
+    if total <= FRAME_LINES {
+        reader.close();
+        return vec![];
+    }
+
+    let iterations: usize = if config.quick_mode { 5 } else { 10 };
+    let mut latencies = Vec::with_capacity(iterations * FRAME_LINES);
+
+    for _ in 0..iterations {
+        let start = total - FRAME_LINES;
+        for i in (start..total).rev() {
+            let t = std::time::Instant::now();
+            let _ = reader.get_line(i);
+            latencies.push(t.elapsed().as_micros() as u64);
+        }
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+    reader.close();
+
+    let mut extra = HashMap::new();
+    extra.insert("lines_per_scan".into(), FRAME_LINES as f64);
+    extra.insert("iterations".into(), iterations as f64);
+
+    vec![BenchmarkResult {
+        category: "jump".into(),
+        test_name: "reverse_scan".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}

crates/bench/src/suites/memory.rs

@@ -0,0 +1,237 @@
+use std::collections::HashMap;
+
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{
+    MmapReaderPhaseAware, MmapReaderPlain, MmapReaderPopulate, MmapReaderRandom,
+    MmapReaderSequential,
+};
+use crate::pread_reader::{PreadReaderPlain, PreadReaderRandom, PreadReaderSequential};
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    results.extend(bench_idle_rss::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_idle_rss::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_idle_rss::<MmapReaderRandom>("mmap", "random", config));
+    results.extend(bench_idle_rss::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_idle_rss::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_idle_rss::<PreadReaderPlain>("pread", "plain", config));
+    results.extend(bench_idle_rss::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_idle_rss::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results.extend(bench_scroll_rss::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_scroll_rss::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+
+    results.extend(bench_jump_end_rss::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_jump_end_rss::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+
+    results.extend(bench_rss_reclaim::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_rss_reclaim::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+
+    results
+}
+
+fn bench_idle_rss<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let reader = B::open(&config.test_file).expect("Failed to open file");
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("total_lines".into(), reader.total_lines() as f64);
+    extra.insert(
+        "file_size_mb".into(),
+        reader.file_size() as f64 / (1024.0 * 1024.0),
+    );
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "memory".into(),
+        test_name: "idle_rss".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: vec![],
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_scroll_rss<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let reader = B::open(&config.test_file).expect("Failed to open file");
+    let total = reader.total_lines();
+    let sample_interval = 100_000;
+    let max_lines = if config.quick_mode { 100_000 } else { total };
+
+    let upper = max_lines.min(total);
+    let mut rss_samples = Vec::new();
+    let mut hwm_samples = Vec::new();
+    let mut lines_read = 0usize;
+
+    for i in (0..upper).step_by(sample_interval) {
+        if reader.get_line(i).is_some() {
+            lines_read += 1;
+        }
+        let rss = MetricsCollector::read_rss();
+        rss_samples.push(rss.vm_rss_kb);
+        hwm_samples.push(rss.vm_hwm_kb);
+    }
+
+    let final_rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("rss_samples_count".into(), rss_samples.len() as f64);
+    extra.insert(
+        "max_rss_kb".into(),
+        rss_samples.iter().copied().fold(0u64, u64::max) as f64,
+    );
+    extra.insert(
+        "max_hwm_kb".into(),
+        hwm_samples.iter().copied().fold(0u64, u64::max) as f64,
+    );
+    extra.insert("lines_read".into(), lines_read as f64);
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "memory".into(),
+        test_name: "scroll_rss".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: vec![],
+        rss_kb: final_rss.vm_rss_kb,
+        rss_peak_kb: final_rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_jump_end_rss<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let reader = B::open(&config.test_file).expect("Failed to open file");
+    let total = reader.total_lines();
+    let last_line = total.saturating_sub(1);
+
+    let _ = reader.get_line(last_line);
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("last_line_idx".into(), last_line as f64);
+    extra.insert("total_lines".into(), total as f64);
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "memory".into(),
+        test_name: "jump_end_rss".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: vec![],
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_rss_reclaim<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let reader = B::open(&config.test_file).expect("Failed to open file");
+    let total = reader.total_lines();
+    let last_line = total.saturating_sub(1);
+
+    let _ = reader.get_line(last_line);
+
+    let wait_secs: u64 = if config.quick_mode { 5 } else { 30 };
+    let sample_interval: u64 = 5;
+    let num_samples = (wait_secs / sample_interval) as usize;
+
+    let mut rss_samples = Vec::with_capacity(num_samples);
+    let mut hwm_samples = Vec::with_capacity(num_samples);
+
+    for _ in 0..num_samples {
+        std::thread::sleep(std::time::Duration::from_secs(sample_interval));
+        let rss = MetricsCollector::read_rss();
+        rss_samples.push(rss.vm_rss_kb);
+        hwm_samples.push(rss.vm_hwm_kb);
+    }
+
+    let final_rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+    reader.close();
+
+    let mut extra = HashMap::new();
+    extra.insert("wait_total_secs".into(), wait_secs as f64);
+    extra.insert("rss_samples".into(), rss_samples.len() as f64);
+    if let (Some(&first), Some(&last)) = (rss_samples.first(), rss_samples.last()) {
+        extra.insert("rss_first_kb".into(), first as f64);
+        extra.insert("rss_last_kb".into(), last as f64);
+        extra.insert(
+            "rss_change_pct".into(),
+            if first > 0 {
+                ((last as f64 - first as f64) / first as f64) * 100.0
+            } else {
+                0.0
+            },
+        );
+    }
+
+    vec![BenchmarkResult {
+        category: "memory".into(),
+        test_name: "rss_reclaim".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: vec![],
+        rss_kb: final_rss.vm_rss_kb,
+        rss_peak_kb: final_rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}

crates/bench/src/suites/mod.rs

@@ -0,0 +1,12 @@
+pub mod concurrent;
+pub mod growth;
+pub mod jump;
+pub mod memory;
+pub mod render;
+pub mod rotation;
+pub mod startup;
+
+/// Number of lines read per single-frame render benchmark.
+/// Also used as the scan window size for reverse-scan benchmarks.
+/// Shared across suites to ensure consistent workload sizing.
+pub(crate) const FRAME_LINES: usize = 35;

crates/bench/src/suites/render.rs

@@ -0,0 +1,315 @@
+use std::collections::HashMap;
+
+use super::FRAME_LINES;
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{
+    MmapReaderPhaseAware, MmapReaderPlain, MmapReaderPopulate, MmapReaderRandom,
+    MmapReaderSequential,
+};
+use crate::pread_reader::{PreadReaderPlain, PreadReaderRandom, PreadReaderSequential};
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    results.extend(bench_single_frame::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_single_frame::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_single_frame::<MmapReaderRandom>(
+        "mmap", "random", config,
+    ));
+    results.extend(bench_single_frame::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_single_frame::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_single_frame::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+    results.extend(bench_single_frame::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_single_frame::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results.extend(bench_continuous_scroll::<MmapReaderPlain>(
+        "mmap", "plain", config,
+    ));
+    results.extend(bench_continuous_scroll::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_continuous_scroll::<MmapReaderRandom>(
+        "mmap", "random", config,
+    ));
+    results.extend(bench_continuous_scroll::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_continuous_scroll::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_continuous_scroll::<PreadReaderPlain>(
+        "pread", "plain", config,
+    ));
+    results.extend(bench_continuous_scroll::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_continuous_scroll::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    results
+}
+
+fn bench_single_frame<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+    let mut results = Vec::new();
+
+    for (pos_name, start_line) in select_frame_positions(total) {
+        let mut latencies = Vec::with_capacity(FRAME_LINES);
+        for i in 0..FRAME_LINES {
+            let line_idx = start_line + i;
+            if line_idx >= total {
+                break;
+            }
+            let t = std::time::Instant::now();
+            let _ = reader.get_line(line_idx);
+            latencies.push(t.elapsed().as_micros() as u64);
+        }
+
+        let rss = MetricsCollector::read_rss();
+        let faults = MetricsCollector::read_page_faults();
+
+        results.push(BenchmarkResult {
+            category: "render".into(),
+            test_name: format!("single_frame_{pos_name}"),
+            backend: backend.into(),
+            variant: variant.into(),
+            latency_us: latencies,
+            rss_kb: rss.vm_rss_kb,
+            rss_peak_kb: rss.vm_hwm_kb,
+            page_faults: faults.minor_faults + faults.major_faults,
+            extra: HashMap::new(),
+        });
+    }
+
+    reader.close();
+    results
+}
+
+/// Select non-overlapping benchmark positions for single-frame tests.
+///
+/// Returns `(label, start_line)` pairs. Positions are chosen so that no
+/// two frames overlap, skipping any position that cannot fit without
+/// colliding with a previously selected range.
+pub(crate) fn select_frame_positions(total: usize) -> Vec<(&'static str, usize)> {
+    let frame = FRAME_LINES;
+    if total == 0 {
+        return vec![];
+    }
+
+    let mut positions: Vec<(&'static str, usize)> = vec![("head", 0)];
+
+    // Need at least 3 full frames to place head, middle, and tail without overlap.
+    if total >= 3 * frame {
+        let head_end = frame;
+        let tail_start = total - frame;
+        let gap = tail_start - head_end;
+        // Center the middle frame within the gap, ensuring it fits entirely
+        let middle_start = head_end + gap.saturating_sub(frame) / 2;
+        positions.push(("middle", middle_start));
+        positions.push(("tail", tail_start));
+    }
+
+    positions
+}
+
+fn bench_continuous_scroll<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    let path = &config.test_file;
+    let reader = B::open(path).expect("Failed to open file");
+    let total = reader.total_lines();
+
+    let iterations = if config.quick_mode { 100 } else { 1000 };
+    let timeout = if config.quick_mode {
+        std::time::Duration::from_secs(1)
+    } else {
+        std::time::Duration::from_secs(10)
+    };
+
+    let mut latencies = Vec::with_capacity(iterations);
+    let start = std::time::Instant::now();
+
+    for i in 0..iterations {
+        if start.elapsed() > timeout {
+            break;
+        }
+        let line_idx = i % total.max(1);
+        let t = std::time::Instant::now();
+        let _ = reader.get_line(line_idx);
+        latencies.push(t.elapsed().as_micros() as u64);
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("total_lines_scrolled".into(), latencies.len() as f64);
+
+    reader.close();
+
+    vec![BenchmarkResult {
+        category: "render".into(),
+        test_name: "continuous_scroll".into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn starts(pos: &[(&str, usize)]) -> Vec<usize> {
+        pos.iter().map(|&(_, s)| s).collect()
+    }
+
+    fn labels<'a>(pos: &[(&'a str, usize)]) -> Vec<&'a str> {
+        pos.iter().map(|&(l, _)| l).collect()
+    }
+
+    fn ranges_overlap(a_start: usize, b_start: usize) -> bool {
+        let a_end = a_start + FRAME_LINES;
+        let b_end = b_start + FRAME_LINES;
+        a_start < b_end && b_start < a_end
+    }
+
+    #[test]
+    fn zero_lines_no_positions() {
+        assert!(select_frame_positions(0).is_empty());
+    }
+
+    #[test]
+    fn one_line_head_only() {
+        let pos = select_frame_positions(1);
+        assert_eq!(labels(&pos), vec!["head"]);
+        assert_eq!(starts(&pos), vec![0]);
+    }
+
+    #[test]
+    fn at_frame_lines_head_only() {
+        let pos = select_frame_positions(FRAME_LINES);
+        assert_eq!(labels(&pos), vec!["head"]);
+        assert_eq!(starts(&pos), vec![0]);
+    }
+
+    #[test]
+    fn just_above_threshold_head_middle_tail() {
+        let total = 3 * FRAME_LINES;
+        let pos = select_frame_positions(total);
+        assert_eq!(labels(&pos), vec!["head", "middle", "tail"]);
+        assert_eq!(starts(&pos)[0], 0);
+        assert_eq!(*starts(&pos).last().unwrap(), total - FRAME_LINES);
+        // Verify no overlap
+        for i in 0..pos.len() {
+            for j in (i + 1)..pos.len() {
+                assert!(
+                    !ranges_overlap(pos[i].1, pos[j].1),
+                    "overlap: {:?} @ {} vs {:?} @ {} (total={})",
+                    pos[i].0, pos[i].1, pos[j].0, pos[j].1, total
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn no_overlap_at_total_70() {
+        // total=70 < 3*35=105, so only head is returned
+        let pos = select_frame_positions(70);
+        assert_eq!(labels(&pos), vec!["head"]);
+    }
+
+    #[test]
+    fn no_overlap_at_total_104() {
+        let pos = select_frame_positions(104);
+        for i in 0..pos.len() {
+            for j in (i + 1)..pos.len() {
+                assert!(
+                    !ranges_overlap(pos[i].1, pos[j].1),
+                    "overlap at total=104: {:?} @ {} vs {:?} @ {}",
+                    pos[i].0, pos[i].1, pos[j].0, pos[j].1
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn no_overlap_at_total_105() {
+        let pos = select_frame_positions(105);
+        for i in 0..pos.len() {
+            for j in (i + 1)..pos.len() {
+                assert!(
+                    !ranges_overlap(pos[i].1, pos[j].1),
+                    "overlap at total=105: {:?} @ {} vs {:?} @ {}",
+                    pos[i].0, pos[i].1, pos[j].0, pos[j].1
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn middle_is_centered_between_head_and_tail() {
+        let total = 1000;
+        let pos = select_frame_positions(total);
+        assert_eq!(pos.len(), 3);
+
+        let (_, head_start) = pos[0];
+        let (_, middle_start) = pos[1];
+        let (_, tail_start) = pos[2];
+
+        assert_eq!(head_start, 0);
+        assert_eq!(tail_start, total - FRAME_LINES);
+
+        let head_end = head_start + FRAME_LINES;
+        let gap = tail_start - head_end;
+        assert_eq!(middle_start, head_end + gap.saturating_sub(FRAME_LINES) / 2);
+    }
+
+    #[test]
+    fn large_file_all_three_positions() {
+        let pos = select_frame_positions(1_000_000);
+        assert_eq!(labels(&pos), vec!["head", "middle", "tail"]);
+    }
+}

crates/bench/src/suites/rotation.rs

@@ -0,0 +1,170 @@
+use std::collections::HashMap;
+
+use crate::data_gen;
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{self, MmapReaderPlain};
+use crate::pread_reader::PreadReaderPlain;
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    let dir = tempfile::tempdir().expect("Failed to create temp dir");
+    results.extend(bench_truncate_safety_mmap(config, dir.path()));
+    results.extend(bench_truncate_safety_pread(config, dir.path()));
+    results.extend(bench_rotation_detection(config, dir.path()));
+
+    results
+}
+
+fn bench_truncate_safety_mmap(
+    _config: &BenchConfig,
+    dir: &std::path::Path,
+) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("trunc_mmap");
+    let iterations: usize = if _config.quick_mode { 3 } else { 10 };
+
+    let mut latencies = Vec::with_capacity(iterations);
+    let mut sigbus_detected = 0usize;
+
+    for _ in 0..iterations {
+        let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create file");
+
+        mmap_reader::reset_sigbus_flag();
+
+        let reader = MmapReaderPlain::open(&path).expect("Failed to open file");
+        let original_size = reader.file_size();
+
+        let truncate_size = original_size / 2;
+        data_gen::truncate_file(&path, truncate_size).expect("Failed to truncate");
+
+        let t = std::time::Instant::now();
+        let mid_offset = original_size as u64 / 2;
+        let _ = reader.read_range(mid_offset, 64);
+        latencies.push(t.elapsed().as_micros() as u64);
+
+        if mmap_reader::sigbus_flag() {
+            sigbus_detected += 1;
+        }
+        reader.close();
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("iterations".into(), iterations as f64);
+    extra.insert("sigbus_detected".into(), sigbus_detected as f64);
+    extra.insert("crashed".into(), 0.0);
+
+    vec![BenchmarkResult {
+        category: "rotation".into(),
+        test_name: "truncate_safety_mmap".into(),
+        backend: "mmap".into(),
+        variant: "plain".into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_truncate_safety_pread(
+    _config: &BenchConfig,
+    dir: &std::path::Path,
+) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("trunc_pread");
+    let iterations: usize = if _config.quick_mode { 3 } else { 10 };
+
+    let mut latencies = Vec::with_capacity(iterations);
+    let mut error_count = 0usize;
+
+    for _ in 0..iterations {
+        let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create file");
+
+        let reader = PreadReaderPlain::open(&path).expect("Failed to open file");
+        let original_size = reader.file_size();
+
+        let truncate_size = original_size / 2;
+        data_gen::truncate_file(&path, truncate_size).expect("Failed to truncate");
+
+        let t = std::time::Instant::now();
+        let mid_offset = original_size as u64 / 2;
+        let result = reader.read_range(mid_offset, 64);
+        latencies.push(t.elapsed().as_micros() as u64);
+
+        if result.is_none() {
+            error_count += 1;
+        }
+        reader.close();
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("iterations".into(), iterations as f64);
+    extra.insert("errors_returned".into(), error_count as f64);
+    extra.insert("crashed".into(), 0.0);
+
+    vec![BenchmarkResult {
+        category: "rotation".into(),
+        test_name: "truncate_safety_pread".into(),
+        backend: "pread".into(),
+        variant: "plain".into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}
+
+fn bench_rotation_detection(_config: &BenchConfig, dir: &std::path::Path) -> Vec<BenchmarkResult> {
+    let sub_dir = dir.join("rotation_detect");
+    let iterations: usize = if _config.quick_mode { 3 } else { 10 };
+
+    let mut latencies = Vec::with_capacity(iterations);
+    let mut detected_count = 0usize;
+
+    for _ in 0..iterations {
+        let path = data_gen::generate_growable_file(&sub_dir).expect("Failed to create file");
+        let original_inode = MetricsCollector::get_inode(&path).expect("Failed to get inode");
+
+        let _rotated = data_gen::rotate_file(&path).expect("Failed to rotate file");
+
+        let t = std::time::Instant::now();
+        let detected = MetricsCollector::detect_rotation(original_inode, &path);
+        latencies.push(t.elapsed().as_micros() as u64);
+
+        if detected {
+            detected_count += 1;
+        }
+
+        let _ = std::fs::remove_file(&path);
+        let rotated = sub_dir.join("growable.log.1");
+        let _ = std::fs::remove_file(&rotated);
+    }
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let mut extra = HashMap::new();
+    extra.insert("iterations".into(), iterations as f64);
+    extra.insert("rotations_detected".into(), detected_count as f64);
+
+    vec![BenchmarkResult {
+        category: "rotation".into(),
+        test_name: "rotation_detection".into(),
+        backend: "both".into(),
+        variant: "plain".into(),
+        latency_us: latencies,
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra,
+    }]
+}

crates/bench/src/suites/startup.rs

@@ -0,0 +1,143 @@
+use std::collections::HashMap;
+use std::path::Path;
+
+use crate::metrics::MetricsCollector;
+use crate::mmap_reader::{
+    MmapReaderPhaseAware, MmapReaderPlain, MmapReaderPopulate, MmapReaderRandom,
+    MmapReaderSequential,
+};
+use crate::pread_reader::{PreadReaderPlain, PreadReaderRandom, PreadReaderSequential};
+use crate::runner::BenchConfig;
+use crate::types::BenchmarkResult;
+use crate::FileReaderBackend;
+
+pub fn run(config: &BenchConfig) -> Vec<BenchmarkResult> {
+    let mut results = Vec::new();
+
+    results.extend(bench_hot_open::<MmapReaderPlain>("mmap", "plain", config));
+    results.extend(bench_hot_open::<MmapReaderSequential>(
+        "mmap",
+        "sequential",
+        config,
+    ));
+    results.extend(bench_hot_open::<MmapReaderRandom>("mmap", "random", config));
+    results.extend(bench_hot_open::<MmapReaderPopulate>(
+        "mmap", "populate", config,
+    ));
+    results.extend(bench_hot_open::<MmapReaderPhaseAware>(
+        "mmap",
+        "phase_aware",
+        config,
+    ));
+    results.extend(bench_hot_open::<PreadReaderPlain>("pread", "plain", config));
+    results.extend(bench_hot_open::<PreadReaderRandom>(
+        "pread", "random", config,
+    ));
+    results.extend(bench_hot_open::<PreadReaderSequential>(
+        "pread",
+        "sequential",
+        config,
+    ));
+
+    if !config.quick_mode {
+        match MetricsCollector::clear_file_cache(&config.test_file) {
+            Ok(()) => {
+                results.extend(bench_cold_open::<MmapReaderPlain>("mmap", "plain", config));
+                results.extend(bench_cold_open::<MmapReaderSequential>(
+                    "mmap",
+                    "sequential",
+                    config,
+                ));
+                results.extend(bench_cold_open::<MmapReaderRandom>(
+                    "mmap", "random", config,
+                ));
+                results.extend(bench_cold_open::<MmapReaderPopulate>(
+                    "mmap", "populate", config,
+                ));
+                results.extend(bench_cold_open::<MmapReaderPhaseAware>(
+                    "mmap",
+                    "phase_aware",
+                    config,
+                ));
+                results.extend(bench_cold_open::<PreadReaderPlain>(
+                    "pread", "plain", config,
+                ));
+                results.extend(bench_cold_open::<PreadReaderRandom>(
+                    "pread", "random", config,
+                ));
+                results.extend(bench_cold_open::<PreadReaderSequential>(
+                    "pread",
+                    "sequential",
+                    config,
+                ));
+            }
+            Err(e) => {
+                eprintln!(
+                    "WARNING: Failed to clear file cache; skipping cold startup benchmarks because results would not be cold: {e}"
+                );
+            }
+        }
+    }
+
+    results
+}
+
+fn bench_hot_open<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    open_and_measure::<B>(backend, variant, &config.test_file, "hot_open")
+}
+
+fn bench_cold_open<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    config: &BenchConfig,
+) -> Vec<BenchmarkResult> {
+    match MetricsCollector::clear_file_cache(&config.test_file) {
+        Ok(()) => open_and_measure::<B>(backend, variant, &config.test_file, "cold_open"),
+        Err(e) => {
+            eprintln!(
+                "WARNING: Failed to clear file cache for {backend}/{variant}; skipping cold benchmark: {e}"
+            );
+            Vec::new()
+        }
+    }
+}
+
+fn open_and_measure<B: FileReaderBackend>(
+    backend: &str,
+    variant: &str,
+    path: &Path,
+    test_name: &str,
+) -> Vec<BenchmarkResult> {
+    let start = std::time::Instant::now();
+    let reader = B::open(path).expect("Failed to open file");
+    let elapsed = start.elapsed();
+
+    let rss = MetricsCollector::read_rss();
+    let faults = MetricsCollector::read_page_faults();
+
+    let result = BenchmarkResult {
+        category: "startup".into(),
+        test_name: test_name.into(),
+        backend: backend.into(),
+        variant: variant.into(),
+        latency_us: vec![elapsed.as_micros() as u64],
+        rss_kb: rss.vm_rss_kb,
+        rss_peak_kb: rss.vm_hwm_kb,
+        page_faults: faults.minor_faults + faults.major_faults,
+        extra: {
+            let mut m = HashMap::new();
+            m.insert("total_lines".into(), reader.total_lines() as f64);
+            m.insert(
+                "file_size_mb".into(),
+                reader.file_size() as f64 / (1024.0 * 1024.0),
+            );
+            m
+        },
+    };
+    reader.close();
+    vec![result]
+}

crates/bench/src/types.rs

@@ -0,0 +1,13 @@
+use std::collections::HashMap;
+
+pub struct BenchmarkResult {
+    pub category: String,
+    pub test_name: String,
+    pub backend: String,
+    pub variant: String,
+    pub latency_us: Vec<u64>,
+    pub rss_kb: u64,
+    pub rss_peak_kb: u64,
+    pub page_faults: u64,
+    pub extra: HashMap<String, f64>,
+}

crates/core/src/io/file_reader.rs

@@ -9,6 +9,14 @@ use crate::io::index_cache::IndexCache;
 use crate::io::line_index::LineIndex;
 use std::path::{Path, PathBuf};
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AppendStatus {
+    Unchanged,
+    Appended(u64),
+    /// File shrank; mmap and index rebuilt via reload().
+    Reloaded,
+}
+
 pub struct FileReader {
     path: PathBuf,
     mmap: Option<memmap2::Mmap>,
@@ -25,20 +33,23 @@ impl FileReader {
         } else {
             // SAFETY: 使用只读 Mmap（非 MmapMut），文件以只读方式打开。
             // memmap2 内部持有文件描述符，确保 mmap 期间文件不会被关闭。
-            //
-            // ⚠️ Known limitation (Phase 5): 如果文件在 mmap 期间被外部进程截断，
-            // 访问截断区域的内存会触发 SIGBUS（致命信号，无法恢复）。
-            // FileWatcher Phase 将添加文件修改检测和 re-mmap 机制来处理此情况。
-            // 在 Phase 5 中，假设打开的文件不会被外部修改。
-            Some(unsafe { memmap2::Mmap::map(&file) }.map_err(|e| CoreError::Mmap(e.to_string()))?)
+            let m = unsafe { memmap2::Mmap::map(&file) }
+                .map_err(|e| CoreError::Mmap(e.to_string()))?;
+
+            // Layer 3: mmap 后立即 stat 同一 fd，检测截断（TOCTOU 缓解，非安全证明）
+            let current_size = file.metadata()?.len();
+            if current_size < m.len() as u64 {
+                None
+            } else {
+                Some(m)
+            }
         };
 
-        let line_index = {
-            let mut reader = std::io::BufReader::new(&file);
-            LineIndex::from_reader(&mut reader).map_err(|e| CoreError::Io {
-                source: e,
-                context: "building line index".into(),
-            })?
+        // 直接从 mmap 快照构建行索引，确保索引与数据来自同一内存映射，
+        // 消除 mmap + BufReader 双读之间的 TOCTOU 竞态窗口。
+        let line_index = match &mmap {
+            Some(m) => LineIndex::from_bytes(m.as_ref()),
+            None => LineIndex::from_bytes(&[]),
         };
 
         Ok(Self {
@@ -76,9 +87,8 @@ impl FileReader {
         }
     }
 
-    /// Save the line index cache to disk.
     pub fn save_cache(&self) -> std::io::Result<()> {
-        IndexCache::save(&self.path, &self.line_index)?;
+        IndexCache::save_with_hash(&self.path, &self.line_index, self.data())?;
         Ok(())
     }
 
@@ -94,27 +104,35 @@ impl FileReader {
         self.mmap = None;
 
         if file_size > 0 {
-            self.mmap = Some(
-                unsafe { memmap2::Mmap::map(&file) }.map_err(|e| CoreError::Mmap(e.to_string()))?,
-            );
+            let m =
+                unsafe { memmap2::Mmap::map(&file) }.map_err(|e| CoreError::Mmap(e.to_string()))?;
+            let current_size = file.metadata()?.len();
+            self.mmap = if current_size < m.len() as u64 {
+                None
+            } else {
+                Some(m)
+            };
         }
 
-        let mut reader = std::io::BufReader::new(&file);
-        self.line_index = LineIndex::from_reader(&mut reader).map_err(|e| CoreError::Io {
-            source: e,
-            context: "rebuilding line index on reload".into(),
-        })?;
+        self.line_index = match &self.mmap {
+            Some(m) => LineIndex::from_bytes(m.as_ref()),
+            None => LineIndex::from_bytes(&[]),
+        };
 
         Ok(())
     }
 
-    pub fn update_for_append(&mut self) -> Result<u64> {
+    pub fn update_for_append(&mut self) -> Result<AppendStatus> {
         let file = std::fs::File::open(&self.path)?;
         let new_size = file.metadata()?.len();
         let old_size = self.mmap.as_ref().map_or(0u64, |m| m.len() as u64);
 
-        if new_size <= old_size {
-            return Ok(0);
+        if new_size < old_size {
+            self.reload()?;
+            return Ok(AppendStatus::Reloaded);
+        }
+        if new_size == old_size {
+            return Ok(AppendStatus::Unchanged);
         }
 
         let old_lines = self.line_index.line_count() as u64;
@@ -123,11 +141,19 @@ impl FileReader {
         let mmap =
             unsafe { memmap2::Mmap::map(&file) }.map_err(|e| CoreError::Mmap(e.to_string()))?;
 
+        let current_size = file.metadata()?.len();
+        if current_size < mmap.len() as u64 {
+            self.line_index = LineIndex::from_bytes(&[]);
+            return Ok(AppendStatus::Reloaded);
+        }
+
         self.line_index
             .extend_from_bytes(&mmap[old_size as usize..], old_size);
         self.mmap = Some(mmap);
 
-        Ok(self.line_index.line_count() as u64 - old_lines)
+        Ok(AppendStatus::Appended(
+            self.line_index.line_count() as u64 - old_lines,
+        ))
     }
 }
 
@@ -305,8 +331,8 @@ mod tests {
             file.write_all(b"ccc\nddd\n").unwrap();
         }
 
-        let new_lines = reader.update_for_append().unwrap();
-        assert_eq!(new_lines, 2);
+        let status = reader.update_for_append().unwrap();
+        assert_eq!(status, AppendStatus::Appended(2));
         assert_eq!(reader.line_count(), 4);
         assert_eq!(reader.get_line(0), Some("aaa"));
         assert_eq!(reader.get_line(1), Some("bbb"));
@@ -320,8 +346,8 @@ mod tests {
         let mut reader = FileReader::open(f.path()).unwrap();
         assert_eq!(reader.line_count(), 1);
 
-        let new_lines = reader.update_for_append().unwrap();
-        assert_eq!(new_lines, 0);
+        let status = reader.update_for_append().unwrap();
+        assert_eq!(status, AppendStatus::Unchanged);
         assert_eq!(reader.line_count(), 1);
     }
 
@@ -341,8 +367,11 @@ mod tests {
             file.write_all(b"x\n").unwrap();
         }
 
-        let new_lines = reader.update_for_append().unwrap();
-        assert_eq!(new_lines, 0);
+        let status = reader.update_for_append().unwrap();
+        assert_eq!(status, AppendStatus::Reloaded);
+        assert_eq!(reader.line_count(), 1);
+        assert_eq!(reader.file_size(), 2);
+        assert_eq!(reader.get_line(0), Some("x"));
     }
 
     #[test]
@@ -368,4 +397,160 @@ mod tests {
         let idx = reader.line_index();
         assert_eq!(idx.line_count(), 2);
     }
+
+    // ─── TOCTOU 修复验证 ─────────────────────────────────────────────────
+    // open() 和 reload() 现在从 mmap 快照构建索引（from_bytes），
+    // 而非从独立 BufReader 读取（from_reader）。以下测试验证：
+    // 1. from_bytes 与 from_reader 产出完全一致的索引
+    // 2. 修改文件后 reload 仍返回正确内容（无残留旧状态）
+    // 3. 极端情况下（空文件、单行、跨块）open+reload 一致性
+
+    #[test]
+    fn test_open_from_bytes_matches_from_reader() {
+        let cases: Vec<&[u8]> = vec![
+            b"",
+            b"hello",
+            b"hello\n",
+            b"aaa\nbbb\nccc",
+            b"\n",
+            b"a\n\nb",
+        ];
+
+        let mut large_cases = Vec::new();
+        for &n in &[256usize, 300, 512] {
+            let mut buf = Vec::new();
+            for i in 0..n {
+                buf.extend_from_slice(format!("line{}\n", i).as_bytes());
+            }
+            large_cases.push(buf);
+        }
+
+        let all_contents: Vec<&[u8]> = cases
+            .iter()
+            .copied()
+            .chain(large_cases.iter().map(Vec::as_slice))
+            .collect();
+
+        for content in all_contents {
+            let f = create_temp_file(content);
+            let reader = FileReader::open(f.path()).unwrap();
+
+            let from_bytes_idx = LineIndex::from_bytes(content);
+            let mut buf_reader = std::io::BufReader::new(content);
+            let from_reader_idx = LineIndex::from_reader(&mut buf_reader).unwrap();
+
+            assert_eq!(
+                reader.line_index().total_lines(),
+                from_bytes_idx.total_lines(),
+                "open() line_count should match from_bytes for {:?}B file",
+                content.len()
+            );
+            assert_eq!(
+                from_bytes_idx.total_lines(),
+                from_reader_idx.total_lines(),
+                "from_bytes should match from_reader total_lines for {:?}B file",
+                content.len()
+            );
+            assert_eq!(
+                from_bytes_idx.sampled_offsets(),
+                from_reader_idx.sampled_offsets(),
+                "from_bytes should match from_reader sampled_offsets for {:?}B file",
+                content.len()
+            );
+            assert_eq!(
+                from_bytes_idx.has_trailing_newline(),
+                from_reader_idx.has_trailing_newline(),
+                "from_bytes should match from_reader has_trailing_newline for {:?}B file",
+                content.len()
+            );
+        }
+    }
+
+    #[test]
+    fn test_reload_after_external_modify_returns_correct_content() {
+        let f = create_temp_file(b"aaa\nbbb\n");
+        let mut reader = FileReader::open(f.path()).unwrap();
+        assert_eq!(reader.get_line(0), Some("aaa"));
+        assert_eq!(reader.get_line(1), Some("bbb"));
+        assert_eq!(reader.line_count(), 2);
+
+        // 外部修改：覆盖写入新内容
+        {
+            use std::io::Write;
+            std::fs::write(f.path(), b"xxx\nyyy\nzzz\n").unwrap();
+        }
+
+        reader.reload().unwrap();
+        assert_eq!(reader.line_count(), 3);
+        assert_eq!(reader.get_line(0), Some("xxx"));
+        assert_eq!(reader.get_line(1), Some("yyy"));
+        assert_eq!(reader.get_line(2), Some("zzz"));
+    }
+
+    #[test]
+    fn test_reload_after_truncate_then_rewrite_no_stale_data() {
+        let f = create_temp_file(b"line0\nline1\nline2\nline3\n");
+        let mut reader = FileReader::open(f.path()).unwrap();
+        assert_eq!(reader.line_count(), 4);
+
+        // 截断后写入更短内容
+        {
+            use std::io::Write;
+            let mut file = std::fs::OpenOptions::new()
+                .write(true)
+                .truncate(true)
+                .open(f.path())
+                .unwrap();
+            file.write_all(b"new\n").unwrap();
+        }
+
+        reader.reload().unwrap();
+        assert_eq!(reader.line_count(), 1);
+        assert_eq!(reader.get_line(0), Some("new"));
+        assert_eq!(reader.get_line(1), None, "old line should not be accessible");
+    }
+
+    #[test]
+    fn test_open_reload_idempotent_cross_block() {
+        let mut content = Vec::new();
+        for i in 0..600u32 {
+            content.extend_from_slice(format!("line{}\n", i).as_bytes());
+        }
+        let f = create_temp_file(&content);
+
+        let reader = FileReader::open(f.path()).unwrap();
+        let mut reloaded = FileReader::open(f.path()).unwrap();
+        reloaded.reload().unwrap();
+
+        assert_eq!(reader.line_count(), reloaded.line_count());
+        for i in 0..600 {
+            assert_eq!(
+                reader.get_line(i),
+                reloaded.get_line(i),
+                "line {i} mismatch between open and reload"
+            );
+        }
+    }
+
+    #[test]
+    fn test_open_stat_after_mmap_detects_truncation() {
+        let content = b"line0\nline1\nline2\nline3\n";
+        let f = create_temp_file(content);
+
+        let reader = FileReader::open(f.path()).unwrap();
+        assert_eq!(reader.line_count(), 4);
+
+        {
+            use std::io::Write;
+            let _ = std::fs::OpenOptions::new()
+                .write(true)
+                .truncate(true)
+                .open(f.path())
+                .unwrap();
+        }
+
+        let reader = FileReader::open(f.path()).unwrap();
+        assert_eq!(reader.line_count(), 0);
+        assert_eq!(reader.file_size(), 0);
+    }
 }

crates/core/src/io/index_cache.rs

@@ -8,6 +8,42 @@ pub struct IndexCache;
 
 impl IndexCache {
     /// Save a `LineIndex` to disk using atomic write (write to .tmp, then rename).
+    ///
+    /// The file hash is derived from `data` (the same byte slice used to build the index),
+    /// avoiding TOCTOU issues from re-reading the file from disk.
+    pub fn save_with_hash(
+        file_path: &Path,
+        index: &LineIndex,
+        data: &[u8],
+    ) -> std::io::Result<()> {
+        let dest = cache_path(file_path).ok_or_else(|| {
+            std::io::Error::new(std::io::ErrorKind::NotFound, "cannot determine cache path")
+        })?;
+
+        let file_hash = compute_data_hash(data);
+        let index_bytes = bincode::serialize(index)
+            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e.to_string()))?;
+
+        let mut buf = Vec::with_capacity(1 + 8 + index_bytes.len());
+        buf.push(CACHE_VERSION);
+        buf.extend_from_slice(&file_hash.to_le_bytes());
+        buf.extend_from_slice(&index_bytes);
+
+        let tmp_path = dest.with_extension("index.tmp");
+        {
+            let mut f = std::fs::File::create(&tmp_path)?;
+            f.write_all(&buf)?;
+            f.sync_all()?;
+        }
+        std::fs::rename(&tmp_path, &dest)?;
+
+        Ok(())
+    }
+
+    /// Save a `LineIndex` to disk, computing the hash by re-reading the file.
+    ///
+    /// Prefer [`save_with_hash`] when the source data is already in memory
+    /// to avoid a TOCTOU race between indexing and hash computation.
     pub fn save(file_path: &Path, index: &LineIndex) -> std::io::Result<()> {
         let dest = cache_path(file_path).ok_or_else(|| {
             std::io::Error::new(std::io::ErrorKind::NotFound, "cannot determine cache path")
@@ -60,6 +96,32 @@ impl IndexCache {
     }
 }
 
+/// Compute a fingerprint from in-memory data, using the same algorithm as `compute_file_hash`.
+/// Returns 0 for empty data.
+pub fn compute_data_hash(data: &[u8]) -> u64 {
+    let len = data.len();
+    if len == 0 {
+        return 0;
+    }
+
+    let head_size = 4096.min(len);
+    let tail_size = 4096.min(len);
+
+    let mut hasher_state = xxhash_rust::xxh3::Xxh3::new();
+    hasher_state.update(&data[..head_size]);
+
+    if len > head_size + tail_size {
+        hasher_state.update(&data[len - tail_size..]);
+    } else {
+        // For small files the tail overlaps with the head; hash from the real tail start.
+        let tail_start = len.saturating_sub(tail_size);
+        hasher_state.update(&data[tail_start..]);
+    }
+    hasher_state.update(&(len as u64).to_le_bytes());
+
+    hasher_state.digest()
+}
+
 /// Compute a fast fingerprint of the file: xxhash of (head 4KB + tail 4KB + file size).
 /// Returns 0 for empty files.
 fn compute_file_hash(file_path: &Path) -> std::io::Result<u64> {
@@ -86,11 +148,12 @@ fn compute_file_hash(file_path: &Path) -> std::io::Result<u64> {
         let mut tf = std::io::BufReader::new(file);
         tf.read_exact(&mut tail)?;
     } else {
-        // File is small enough that head already covers everything;
-        // tail overlaps with head — just take the last tail_size bytes
-        let start = head.len().saturating_sub(tail_size);
-        tail = head[start..].to_vec();
-        tail.resize(tail_size, 0);
+        // File fits within head+tail window. Seek to read the real tail
+        // for correctness — approximating from head misses bytes beyond head_size.
+        let tail_start = file_size.saturating_sub(tail_size as u64);
+        let mut file = std::fs::File::open(file_path)?;
+        std::io::Seek::seek(&mut file, std::io::SeekFrom::Start(tail_start))?;
+        file.read_exact(&mut tail)?;
     }
 
     let mut hasher_state = xxhash_rust::xxh3::Xxh3::new();

crates/core/src/io/line_index.rs

@@ -20,14 +20,14 @@ const BLOCK_SIZE: usize = 256;
 pub struct LineIndex {
     // 采样偏移量：每 BLOCK_SIZE 行记录一个起始字节偏移。
     // sampled_offsets[i] 存储第 (i * BLOCK_SIZE) 行的字节起始位置。
-    sampled_offsets: Vec<u64>,
+    pub(crate) sampled_offsets: Vec<u64>,
 
     // 文件总行数。
-    total_lines: u64,
+    pub(crate) total_lines: u64,
 
     // 文件最后一个字节是否是换行符 \n。
     #[allow(dead_code)]
-    has_trailing_newline: bool,
+    pub(crate) has_trailing_newline: bool,
 }
 
 impl LineIndex {
@@ -233,7 +233,7 @@ impl LineIndex {
         }
         let block = idx / BLOCK_SIZE;
         let offset_in_block = idx % BLOCK_SIZE;
-        let mut pos = self.sampled_offsets[block] as usize;
+        let mut pos = (*self.sampled_offsets.get(block)?) as usize;
         for _ in 0..offset_in_block {
             match memchr::memchr(b'\n', &data[pos..]) {
                 Some(rel) => pos = pos + rel + 1,

crates/core/src/io/progressive_reader.rs

@@ -1,9 +1,10 @@
 use std::cell::RefCell;
 use std::fmt;
+use std::io::BufRead;
 use std::path::{Path, PathBuf};
 
 use crate::error::{CoreError, Result};
-use crate::io::file_reader::FileReader;
+use crate::io::file_reader::{AppendStatus, FileReader};
 use crate::io::index_cache::IndexCache;
 use crate::io::line_index::LineIndex;
 use crate::io::line_sampler::sample_line_count;
@@ -251,7 +252,7 @@ pub fn spawn_indexer(
                 return;
             }
         };
-        let file_size = match file.metadata() {
+        let target_len = match file.metadata() {
             Ok(m) => m.len(),
             Err(e) => {
                 let _ = tx.send(IndexerMessage::Error {
@@ -262,11 +263,17 @@ pub fn spawn_indexer(
             }
         };
 
-        let mmap = if file_size == 0 {
-            None
-        } else {
-            match unsafe { memmap2::Mmap::map(&file) } {
-                Ok(m) => Some(m),
+        let mut buf_reader = std::io::BufReader::with_capacity(64 * 1024, file);
+        let mut sampled_offsets: Vec<u64> = vec![0];
+        let mut next_line_idx: usize = 1;
+        let mut newline_count: usize = 0;
+        let mut chunk_offset: u64 = 0;
+        let mut last_byte: Option<u8> = None;
+        let mut bytes_since_check: usize = 0;
+
+        loop {
+            let buf = match buf_reader.fill_buf() {
+                Ok(b) => b,
                 Err(e) => {
                     let _ = tx.send(IndexerMessage::Error {
                         generation,
@@ -274,31 +281,35 @@ pub fn spawn_indexer(
                     });
                     return;
                 }
+            };
+            if buf.is_empty() {
+                break;
             }
-        };
 
-        let data = mmap.as_deref().unwrap_or(&[]);
-
-        if !data.is_empty() {
-            let mut newline_count: usize = 0;
-            let mut chars_since_check: usize = 0;
-            let mut prev_pos: usize = 0;
-
-            for pos in memchr::memchr_iter(b'\n', data) {
-                chars_since_check += pos - prev_pos;
-                prev_pos = pos;
-
-                if chars_since_check >= 1_000_000 {
-                    chars_since_check = 0;
-                    if cancel_rx.try_recv().is_ok() {
-                        return;
-                    }
-                }
+            if let Some(&b) = buf.last() {
+                last_byte = Some(b);
+            }
 
+            for pos in memchr::memchr_iter(b'\n', buf) {
                 newline_count += 1;
+                if next_line_idx.is_multiple_of(256) {
+                    sampled_offsets.push(chunk_offset + pos as u64 + 1);
+                }
+                next_line_idx += 1;
+            }
 
-                if newline_count % 256_000 == 0 {
-                    let percent = (pos as f64 / file_size as f64) * 100.0;
+            let consumed = buf.len();
+            bytes_since_check += consumed;
+            chunk_offset += consumed as u64;
+            buf_reader.consume(consumed);
+
+            if bytes_since_check >= 1_000_000 {
+                bytes_since_check = 0;
+                if cancel_rx.try_recv().is_ok() {
+                    return;
+                }
+                if target_len > 0 {
+                    let percent = (chunk_offset as f64 / target_len as f64) * 100.0;
                     let _ = tx.send(IndexerMessage::Progress {
                         generation,
                         percent,
@@ -312,9 +323,64 @@ pub fn spawn_indexer(
             return;
         }
 
-        let line_index = LineIndex::from_bytes(data);
+        let line_index = if chunk_offset == 0 {
+            LineIndex {
+                sampled_offsets: vec![],
+                total_lines: 0,
+                has_trailing_newline: false,
+            }
+        } else {
+            let has_trailing_newline = last_byte == Some(b'\n') && newline_count > 0;
+            let total_lines = if has_trailing_newline && newline_count > 0 {
+                newline_count as u64
+            } else {
+                (1 + newline_count) as u64
+            };
 
-        let _ = IndexCache::save(&path, &line_index);
+            if has_trailing_newline && newline_count > 0 {
+                let trailing_line_idx = newline_count;
+                if trailing_line_idx.is_multiple_of(256) {
+                    sampled_offsets.pop();
+                }
+            }
+
+            LineIndex {
+                sampled_offsets,
+                total_lines,
+                has_trailing_newline,
+            }
+        };
+
+        let mmap = if target_len == 0 {
+            None
+        } else {
+            match std::fs::File::open(&path) {
+                Ok(mmap_file) => match unsafe { memmap2::Mmap::map(&mmap_file) } {
+                    Ok(m) => match mmap_file.metadata() {
+                        Ok(metadata) if metadata.len() >= m.len() as u64 => Some(m),
+                        Ok(_) | Err(_) => None,
+                    },
+                    Err(e) => {
+                        let _ = tx.send(IndexerMessage::Error {
+                            generation,
+                            message: e.to_string(),
+                        });
+                        return;
+                    }
+                },
+                Err(e) => {
+                    let _ = tx.send(IndexerMessage::Error {
+                        generation,
+                        message: e.to_string(),
+                    });
+                    return;
+                }
+            }
+        };
+
+        if let Some(data) = mmap.as_deref() {
+            let _ = IndexCache::save_with_hash(&path, &line_index, data);
+        }
 
         let reader = FileReader::from_parts(path, mmap, line_index);
 
@@ -355,26 +421,37 @@ pub fn spawn_visual_height_rebuild(
             Err(_) => return,
         };
 
-        let file_size = match file.metadata() {
-            Ok(m) => m.len(),
-            Err(_) => return,
-        };
+        let mut reader = std::io::BufReader::with_capacity(64 * 1024, file);
+        let mut visual_heights = Vec::with_capacity(line_index.line_count());
+        let mut line_buf = Vec::new();
 
-        let mmap = if file_size == 0 {
-            None
-        } else {
-            match unsafe { memmap2::Mmap::map(&file) } {
-                Ok(m) => Some(m),
+        loop {
+            if cancel_rx.try_recv().is_ok() {
+                return;
+            }
+
+            line_buf.clear();
+            match std::io::BufRead::read_until(&mut reader, b'\n', &mut line_buf) {
+                Ok(0) => break,
+                Ok(_) => {
+                    let line_text = std::str::from_utf8(&line_buf)
+                        .ok()
+                        .map(|s| s.trim_end_matches(['\r', '\n']))
+                        .unwrap_or("");
+                    visual_heights.push(compute_line_visual_height(
+                        line_text,
+                        terminal_width,
+                        json_format,
+                    ));
+                }
                 Err(_) => return,
             }
-        };
+        }
 
-        if cancel_rx.try_recv().is_ok() {
+        if visual_heights.len() != line_index.line_count() {
             return;
         }
 
-        let reader = FileReader::from_parts(path, mmap, line_index);
-        let visual_heights = compute_visual_heights(&reader, terminal_width, json_format);
         let index =
             VisualHeightIndex::build(&visual_heights).with_params(json_format, terminal_width);
 
@@ -389,6 +466,11 @@ pub fn spawn_visual_height_rebuild(
 /// Maximum bytes to scan during initial open for the Sampling state.
 const INITIAL_SCAN_BYTES: usize = 64 * 1024;
 
+/// Maximum number of additional lines to scan beyond what's already cached
+/// in a single `get_line()` call.  Prevents O(N) blocking when the user
+/// jumps far ahead (e.g. `G` to end-of-file) during the Loading state.
+const SCAN_AHEAD_LIMIT: usize = 10_000;
+
 pub struct ProgressiveFileReader {
     path: PathBuf,
     pub state: ReaderState,
@@ -512,32 +594,23 @@ impl ProgressiveFileReader {
                 let mut newlines = scanned_newlines.borrow_mut();
                 let mut up_to = scanned_up_to.borrow_mut();
 
-                // We need `idx + 1` newlines to have `idx` lines available.
-                // Line i starts after the i-th newline (or at byte 0 for line 0)
-                // and ends at the (i+1)-th newline (or end of file).
-                // So to return line `idx`, we need at least `idx + 1` newline positions
-                // (the idx-th newline marks end of line idx-1/start of line idx,
-                //  and the (idx+1)-th newline marks end of line idx).
-                // Actually: line 0 starts at byte 0, ends at newline[0].
-                //           line 1 starts at newline[0]+1, ends at newline[1].
-                //           line i starts at newline[i-1]+1, ends at newline[i].
-                // So to serve line idx, we need newline positions up to index idx.
+                let scan_limit = newlines.len() + SCAN_AHEAD_LIMIT;
 
-                // Extend scan if needed
-                while newlines.len() <= idx && *up_to < mmap_data.len() {
+                // Extend scan if needed, but stop at scan_limit to avoid O(N) blocking
+                while newlines.len() <= idx
+                    && newlines.len() < scan_limit
+                    && *up_to < mmap_data.len()
+                {
                     let remaining = &mmap_data[*up_to..];
                     if let Some(rel_pos) = memchr::memchr(b'\n', remaining) {
                         newlines.push(*up_to + rel_pos);
                         *up_to += rel_pos + 1;
                     } else {
-                        // No more newlines; rest of file is the last line
                         *up_to = mmap_data.len();
                         break;
                     }
                 }
 
-                // Check if line idx is beyond what's available
-                // If idx == newlines.len(), it's the last line (after last newline, no trailing \n)
                 if idx > newlines.len() {
                     return None;
                 }
@@ -660,10 +733,10 @@ impl ProgressiveFileReader {
         }
     }
 
-    pub fn update_for_append(&mut self) -> Result<u64> {
+    pub fn update_for_append(&mut self) -> Result<AppendStatus> {
         match &mut self.state {
             ReaderState::Ready { reader, .. } => reader.update_for_append(),
-            _ => Ok(0),
+            _ => Ok(AppendStatus::Unchanged),
         }
     }
 
@@ -1197,18 +1270,20 @@ mod tests {
         let (_cancel_tx, cancel_rx) = crossbeam_channel::bounded(1);
 
         let rx = spawn_indexer(temp.path().to_path_buf(), 1, 80, false, cancel_rx);
-        let msg = rx.recv_timeout(std::time::Duration::from_secs(10)).unwrap();
-
-        match msg {
-            IndexerMessage::Complete {
-                visual_height_index,
-                ..
-            } => {
-                let idx = visual_height_index.expect("should have visual height index");
-                assert_eq!(idx.visual_height_of_line(0), 1);
-                assert_eq!(idx.visual_height_of_line(1), 1);
+        loop {
+            match rx.recv_timeout(std::time::Duration::from_secs(10)).unwrap() {
+                IndexerMessage::Progress { .. } => continue,
+                IndexerMessage::Complete {
+                    visual_height_index,
+                    ..
+                } => {
+                    let idx = visual_height_index.expect("should have visual height index");
+                    assert_eq!(idx.visual_height_of_line(0), 1);
+                    assert_eq!(idx.visual_height_of_line(1), 1);
+                    break;
+                }
+                other => panic!("expected Complete, got {:?}", other),
             }
-            other => panic!("expected Complete, got {:?}", other),
         }
     }
 
@@ -1262,6 +1337,72 @@ mod tests {
         idx.extend_from_heights(&[1, 2, 3]);
 
         assert_eq!(idx.total_visual_rows(), 6);
-        assert_eq!(idx.line_count(), 3);
+    }
+
+    #[test]
+    fn test_spawn_indexer_file_truncated_during_scan() {
+        let mut content = Vec::new();
+        for i in 0..100_000 {
+            writeln!(content, "line number {:08}", i).unwrap();
+        }
+        let f = create_temp_file(&content);
+        let (_cancel_tx, cancel_rx) = crossbeam_channel::bounded(1);
+
+        let rx = spawn_indexer(f.path().to_path_buf(), 1, 80, false, cancel_rx);
+
+        {
+            use std::io::Write;
+            let _ = std::fs::OpenOptions::new()
+                .write(true)
+                .truncate(true)
+                .open(f.path())
+                .unwrap();
+        }
+
+        let result = rx.recv_timeout(std::time::Duration::from_secs(10));
+        match result {
+            Ok(IndexerMessage::Complete { reader, .. }) => {
+                assert!(reader.line_count() <= 100_000);
+            }
+            Ok(IndexerMessage::Error { .. }) => {}
+            Err(crossbeam_channel::RecvTimeoutError::Disconnected) => {}
+            Err(crossbeam_channel::RecvTimeoutError::Timeout) => {}
+            other => panic!("unexpected: {:?}", other),
+        }
+    }
+
+    #[test]
+    fn test_spawn_visual_height_rebuild_line_count_mismatch_discards() {
+        let content = b"line0\nline1\nline2\n";
+        let f = create_temp_file(content);
+        let data = std::fs::read(f.path()).unwrap();
+        let index = LineIndex::from_bytes(&data);
+        IndexCache::save(f.path(), &index).unwrap();
+
+        {
+            use std::io::Write;
+            let mut file = std::fs::OpenOptions::new()
+                .write(true)
+                .truncate(true)
+                .open(f.path())
+                .unwrap();
+            file.write_all(b"only_one_line\n").unwrap();
+        }
+
+        let (_cancel_tx, cancel_rx) = crossbeam_channel::bounded(1);
+        let rx = spawn_visual_height_rebuild(
+            f.path().to_path_buf(),
+            1,
+            80,
+            false,
+            cancel_rx,
+        );
+
+        let result = rx.recv_timeout(std::time::Duration::from_secs(5));
+        match result {
+            Err(crossbeam_channel::RecvTimeoutError::Disconnected) => {}
+            Err(crossbeam_channel::RecvTimeoutError::Timeout) => {}
+            Ok(_) => panic!("should have been discarded due to line count mismatch"),
+        }
     }
 }

crates/core/src/io/read_cache.rs

@@ -0,0 +1,435 @@
+// NOTE: This module is implemented and tested but not yet integrated into
+// the production read path (FileReader uses mmap for line access).
+// It is kept as a building block for a future pread-based reader that
+// would avoid the SIGBUS risk of mmap.
+// ─── read_cache.rs ─────────────────────────────────────────────────────────
+// 16-slot LRU read cache with 4KB page-aligned keys.
+// Reduces syscalls by caching recently-read 4KB blocks.
+// Cross-block reads are handled via a spill buffer (not cached).
+// ──────────────────────────────────────────────────────────────────────────
+
+use std::fs::File;
+use std::io;
+use std::os::unix::fs::FileExt;
+
+const LRU_SLOTS: usize = 16;
+pub const BLOCK_ALIGN: usize = 4096;
+
+struct CacheSlot {
+    buf: Vec<u8>,
+    block_offset: u64,
+    len: usize,
+    last_access: u64,
+}
+
+pub struct LruReadCache {
+    slots: [CacheSlot; LRU_SLOTS],
+    spill_buf: Vec<u8>,
+    spill_len: usize,
+    tick: u64,
+}
+
+pub type ReadCache = LruReadCache;
+
+impl Default for LruReadCache {
+    fn default() -> Self {
+        Self {
+            slots: std::array::from_fn(|_| CacheSlot {
+                buf: vec![0u8; BLOCK_ALIGN],
+                block_offset: 0,
+                len: 0,
+                last_access: 0,
+            }),
+            spill_buf: Vec::new(),
+            spill_len: 0,
+            tick: 0,
+        }
+    }
+}
+
+impl LruReadCache {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Read `len` bytes starting at `offset`. Returns a slice into the cache
+    /// on a hit, or fills a cache slot on a miss. Cross-block reads go through
+    /// the spill buffer and are not cached.
+    pub fn get(&mut self, file: &File, offset: u64, len: usize) -> io::Result<&[u8]> {
+        let aligned_key = offset & !(BLOCK_ALIGN as u64 - 1);
+        let request_end = offset.saturating_add(len as u64);
+        let block_end = aligned_key + BLOCK_ALIGN as u64;
+
+        if request_end > block_end {
+            self.spill_buf.resize(len, 0);
+            let bytes_read = file.read_at(&mut self.spill_buf[..len], offset)?;
+            if bytes_read == 0 {
+                return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "read 0 bytes"));
+            }
+            if bytes_read < len {
+                return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "short read"));
+            }
+            self.spill_len = len;
+            return Ok(&self.spill_buf[..len]);
+        }
+
+        let hit_idx = self.slots.iter().position(|slot| {
+            slot.block_offset == aligned_key && request_end <= slot.block_offset + slot.len as u64
+        });
+
+        if let Some(idx) = hit_idx {
+            self.slots[idx].last_access = self.tick;
+            self.tick += 1;
+            let start = (offset - self.slots[idx].block_offset) as usize;
+            return Ok(&self.slots[idx].buf[start..start + len]);
+        }
+
+        let mut evict_idx = 0;
+        let mut min_access = self.slots[0].last_access;
+        for (i, slot) in self.slots.iter().enumerate() {
+            if slot.last_access < min_access {
+                min_access = slot.last_access;
+                evict_idx = i;
+            }
+        }
+
+        let slot = &mut self.slots[evict_idx];
+        let bytes_read = file.read_at(&mut slot.buf, aligned_key)?;
+
+        // Note: get(file, 0, 0) on an empty file now returns Err (old code returned Ok(&[])).
+        // No callers pass len == 0, so this is a safe semantic change.
+        if bytes_read == 0 {
+            return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "read 0 bytes"));
+        }
+
+        slot.block_offset = aligned_key;
+        slot.len = bytes_read;
+        slot.last_access = self.tick;
+        self.tick += 1;
+
+        if request_end > aligned_key + bytes_read as u64 {
+            return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "short read"));
+        }
+
+        let start = (offset - slot.block_offset) as usize;
+        Ok(&slot.buf[start..start + len])
+    }
+
+    /// Invalidate all cache slots and the spill buffer.
+    pub fn clear(&mut self) {
+        for slot in &mut self.slots {
+            slot.len = 0;
+        }
+        self.spill_len = 0;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+    use tempfile::NamedTempFile;
+
+    fn make_file(data: &[u8]) -> NamedTempFile {
+        let mut f = NamedTempFile::new().unwrap();
+        f.write_all(data).unwrap();
+        f.flush().unwrap();
+        f
+    }
+
+    #[test]
+    fn cache_hit_returns_same_data() {
+        // Read the same range twice — second read should be a cache hit.
+        let f = make_file(b"Hello, World! This is a test of the cache.");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let first = cache.get(&file, 0, 13).unwrap().to_vec();
+        let second = cache.get(&file, 0, 13).unwrap().to_vec();
+        assert_eq!(first, second);
+        assert_eq!(&first, b"Hello, World!");
+    }
+
+    #[test]
+    fn cache_miss_reads_correct_data() {
+        // Two non-overlapping ranges — both must be misses but return correct data.
+        let data = b"0123456789ABCDEFGHIJ";
+        let f = make_file(data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let a = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&a, b"0123456789");
+
+        let b = cache.get(&file, 10, 10).unwrap().to_vec();
+        assert_eq!(&b, b"ABCDEFGHIJ");
+    }
+
+    #[test]
+    fn cross_block_read_uses_spill_buffer() {
+        // Read spanning a 4KB block boundary uses spill buffer, not cache.
+        let data = vec![0xABu8; 8192];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // First, cache block 0.
+        let a = cache.get(&file, 0, 100).unwrap().to_vec();
+        assert_eq!(a, vec![0xABu8; 100]);
+
+        // Now read spanning the boundary: offset=4000, len=200 spans [0,4096) and [4096,8192).
+        let b = cache.get(&file, 4000, 200).unwrap().to_vec();
+        assert_eq!(b, vec![0xABu8; 200]);
+    }
+
+    #[test]
+    fn empty_file_read_fails() {
+        let f = make_file(b"");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Reading 1 byte from empty file should fail.
+        let result = cache.get(&file, 0, 1);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn clear_invalidates_cache() {
+        let data = b"original data here";
+        let f = make_file(data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Populate cache.
+        let first = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&first, b"original d");
+
+        // Invalidate.
+        cache.clear();
+
+        // After clear, reading same range should still work (re-reads from file).
+        let after = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&after, b"original d");
+    }
+
+    // ─── New LRU-specific tests ───────────────────────────────────────────
+
+    #[test]
+    fn lru_multi_block_hit() {
+        // Read 3 different aligned blocks, verify re-reading each hits cache.
+        let data = vec![0u8; BLOCK_ALIGN * 4];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Write distinct patterns to each block.
+        drop(file);
+        {
+            use std::io::Seek;
+            let mut f2 = std::fs::OpenOptions::new()
+                .write(true)
+                .open(f.path())
+                .unwrap();
+            f2.seek(std::io::SeekFrom::Start(0)).unwrap();
+            f2.write_all(&[1u8; BLOCK_ALIGN]).unwrap();
+            f2.seek(std::io::SeekFrom::Start(BLOCK_ALIGN as u64))
+                .unwrap();
+            f2.write_all(&[2u8; BLOCK_ALIGN]).unwrap();
+            f2.seek(std::io::SeekFrom::Start((BLOCK_ALIGN * 2) as u64))
+                .unwrap();
+            f2.write_all(&[3u8; BLOCK_ALIGN]).unwrap();
+        }
+        let file = File::open(f.path()).unwrap();
+
+        let block0 = cache.get(&file, 0, 16).unwrap().to_vec();
+        let block1 = cache.get(&file, BLOCK_ALIGN as u64, 16).unwrap().to_vec();
+        let block2 = cache
+            .get(&file, (BLOCK_ALIGN * 2) as u64, 16)
+            .unwrap()
+            .to_vec();
+
+        assert_eq!(block0, vec![1u8; 16]);
+        assert_eq!(block1, vec![2u8; 16]);
+        assert_eq!(block2, vec![3u8; 16]);
+
+        // Re-read — should hit cache and return same data.
+        let block0_again = cache.get(&file, 0, 16).unwrap().to_vec();
+        let block1_again = cache.get(&file, BLOCK_ALIGN as u64, 16).unwrap().to_vec();
+        let block2_again = cache
+            .get(&file, (BLOCK_ALIGN * 2) as u64, 16)
+            .unwrap()
+            .to_vec();
+
+        assert_eq!(block0_again, block0);
+        assert_eq!(block1_again, block1);
+        assert_eq!(block2_again, block2);
+    }
+
+    #[test]
+    fn lru_eviction_order() {
+        // Fill all 16 slots, re-access slot 0, add 17th block,
+        // verify slot at offset 4096 (slot 1) evicted, not slot 0.
+        let data = vec![0u8; BLOCK_ALIGN * 20];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Fill all 16 slots with blocks 0..16.
+        for i in 0..16u64 {
+            cache.get(&file, i * BLOCK_ALIGN as u64, 1).unwrap();
+        }
+
+        // Re-access block 0 so it's not the LRU.
+        cache.get(&file, 0, 1).unwrap();
+
+        // Add 17th block — should evict block 1 (offset 4096), which is the oldest
+        // since block 0 was re-accessed.
+        cache.get(&file, 16 * BLOCK_ALIGN as u64, 1).unwrap();
+
+        // Reading block 1 (offset 4096) should be a miss (evicted).
+        // We verify by checking the cache slots: block 1 should not be cached.
+        let has_block1 = cache
+            .slots
+            .iter()
+            .any(|s| s.block_offset == BLOCK_ALIGN as u64 && s.len > 0);
+        assert!(!has_block1, "block 1 should have been evicted");
+
+        // Block 0 should still be cached.
+        let has_block0 = cache.slots.iter().any(|s| s.block_offset == 0 && s.len > 0);
+        assert!(has_block0, "block 0 should still be cached");
+    }
+
+    #[test]
+    fn lru_clear_all_slots() {
+        // Fill 3+ slots, call clear(), verify subsequent reads all miss.
+        let data = vec![0x42u8; BLOCK_ALIGN * 4];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Fill 3 slots.
+        cache.get(&file, 0, 1).unwrap();
+        cache.get(&file, BLOCK_ALIGN as u64, 1).unwrap();
+        cache.get(&file, (BLOCK_ALIGN * 2) as u64, 1).unwrap();
+
+        cache.clear();
+
+        // All slots should have len == 0.
+        for slot in &cache.slots {
+            assert_eq!(slot.len, 0);
+        }
+        assert_eq!(cache.spill_len, 0);
+
+        // Re-read should still work (reads from file).
+        let val = cache.get(&file, 0, 1).unwrap();
+        assert_eq!(val[0], 0x42);
+    }
+
+    #[test]
+    fn lru_aligned_keys() {
+        // offset=100 and offset=200 both align to block 0 — should hit same slot.
+        let data = vec![0xEEu8; BLOCK_ALIGN];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let a = cache.get(&file, 100, 10).unwrap().to_vec();
+        assert_eq!(a, vec![0xEEu8; 10]);
+
+        let b = cache.get(&file, 200, 10).unwrap().to_vec();
+        assert_eq!(b, vec![0xEEu8; 10]);
+
+        // Both should be served from the same cache slot (block 0).
+        let slot_count = cache
+            .slots
+            .iter()
+            .filter(|s| s.block_offset == 0 && s.len > 0)
+            .count();
+        assert_eq!(slot_count, 1, "only one slot should hold block 0");
+    }
+
+    #[test]
+    fn lru_cross_block_uses_spill_buffer() {
+        // File [0xAA×4096, 0xBB×4096], get(file, 4090, 20) → [0xAA×6, 0xBB×14].
+        let mut data = vec![0xAAu8; BLOCK_ALIGN];
+        data.extend_from_slice(&vec![0xBBu8; BLOCK_ALIGN]);
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 4090, 20).unwrap().to_vec();
+        assert_eq!(&result[..6], &[0xAAu8; 6]);
+        assert_eq!(&result[6..], &[0xBBu8; 14]);
+
+        // Verify no cache slot holds block 0 or block 1.
+        for slot in &cache.slots {
+            assert!(
+                slot.len == 0,
+                "cross-block data should not be cached in slots"
+            );
+        }
+    }
+
+    #[test]
+    fn lru_partial_last_block() {
+        // 5000 byte file, get(file, 4096, 904) reads last 904 bytes,
+        // then get(file, 4096, 100) hits cache.
+        let data = vec![0x77u8; 5000];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let first = cache.get(&file, 4096, 904).unwrap().to_vec();
+        assert_eq!(first.len(), 904);
+        assert_eq!(first, vec![0x77u8; 904]);
+
+        // Second read of 100 bytes from same block should hit cache.
+        let second = cache.get(&file, 4096, 100).unwrap().to_vec();
+        assert_eq!(second.len(), 100);
+        assert_eq!(second, vec![0x77u8; 100]);
+    }
+
+    #[test]
+    fn lru_short_file_overread() {
+        // 1 byte file, get(file, 0, 100) → Err (not panic).
+        let f = make_file(b"X");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 0, 100);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn lru_empty_file_returns_error() {
+        // Empty file, get(file, 0, 1) → Err.
+        let f = make_file(b"");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 0, 1);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn long_line_spans_multiple_blocks() {
+        // Create file with line >4KB: b'A'×4090 + "\n" + b'B'×4090 + "\n"
+        let mut data = vec![b'A'; 4090];
+        data.push(b'\n');
+        data.extend_from_slice(&vec![b'B'; 4090]);
+        data.push(b'\n');
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Read the first line: offset 0, len 4091 (fits in block 0 since 4091 <= 4096).
+        let line1 = cache.get(&file, 0, 4091).unwrap().to_vec();
+        assert_eq!(&line1[..4090], &[b'A'; 4090]);
+        assert_eq!(line1[4090], b'\n');
+
+        // Read the second line: offset 4091, len 4091 (starts in block 0, ends in block 1 — cross-block).
+        let line2 = cache.get(&file, 4091, 4091).unwrap().to_vec();
+        assert_eq!(&line2[..4090], &[b'B'; 4090]);
+        assert_eq!(line2[4090], b'\n');
+    }
+}

crates/core/src/watcher/file_watcher.rs

@@ -1,2 +1,236 @@
-pub struct FileWatcher {/* TODO */}
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex};
+
+use crossbeam_channel::{bounded, Receiver, Sender};
+use notify::{Event, EventKind, RecommendedWatcher, RecursiveMode, Watcher};
+
+use crate::error::Result;
+
+// ─── FileEvent ──────────────────────────────────────────────────────────────
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum FileEvent {
+    Appended { new_size: u64 },
+    Truncated { new_size: u64 },
+    Rotated { new_inode: u64 },
+    Removed,
+}
+
+// ─── get_inode ──────────────────────────────────────────────────────────────
+
+#[cfg(unix)]
+fn get_inode(path: &Path) -> std::io::Result<u64> {
+    use std::os::unix::fs::MetadataExt;
+    Ok(std::fs::metadata(path)?.ino())
+}
+
+#[cfg(not(unix))]
+fn get_inode(_path: &Path) -> std::io::Result<u64> {
+    Ok(0) // rotation detection not supported on non-Unix
+}
+
+// ─── WatchState ─────────────────────────────────────────────────────────────
+struct WatchState {
+    last_size: u64,
+    last_inode: u64,
+}
+
+// ─── FileWatcher ────────────────────────────────────────────────────────────
+pub struct FileWatcher {
+    rx: Receiver<FileEvent>,
+    _watcher: RecommendedWatcher,
+}
+
+impl FileWatcher {
+    pub fn watch(path: &Path) -> Result<Self> {
+        let (tx, rx): (Sender<FileEvent>, Receiver<FileEvent>) = bounded(100);
+
+        let initial_size = std::fs::metadata(path)?.len();
+        let initial_inode = get_inode(path).unwrap_or(0);
+        let state = Arc::new(Mutex::new(WatchState {
+            last_size: initial_size,
+            last_inode: initial_inode,
+        }));
+        let watch_path: PathBuf = path.to_path_buf();
+
+        let mut watcher =
+            notify::recommended_watcher(move |res: std::result::Result<Event, notify::Error>| {
+                let event = match res {
+                    Ok(e) => e,
+                    Err(_) => return,
+                };
+
+                match event.kind {
+                    EventKind::Modify(_) | EventKind::Create(_) | EventKind::Any => {}
+                    EventKind::Remove(_) => {
+                        let _ = tx.try_send(FileEvent::Removed);
+                        return;
+                    }
+                    _ => return,
+                }
+
+                if !event.paths.iter().any(|p| p == &watch_path) {
+                    return;
+                }
+
+                let current_inode = get_inode(&watch_path).unwrap_or(0);
+                let current_size = std::fs::metadata(&watch_path).map(|m| m.len()).unwrap_or(0);
+
+                let mut st = state.lock().unwrap_or_else(|poison| {
+                    // Recover from poisoned mutex — state only tracks last_size
+                    // and last_inode for event dedup. Stale values at worst
+                    // cause a duplicate event, which is harmless.
+                    poison.into_inner()
+                });
+
+                if current_inode != 0 && st.last_inode != 0 && current_inode != st.last_inode {
+                    let _ = tx.try_send(FileEvent::Rotated {
+                        new_inode: current_inode,
+                    });
+                    st.last_inode = current_inode;
+                    st.last_size = current_size;
+                } else if current_size > st.last_size {
+                    let _ = tx.try_send(FileEvent::Appended {
+                        new_size: current_size,
+                    });
+                    st.last_size = current_size;
+                    st.last_inode = current_inode;
+                } else if current_size < st.last_size {
+                    let _ = tx.try_send(FileEvent::Truncated {
+                        new_size: current_size,
+                    });
+                    st.last_size = current_size;
+                    st.last_inode = current_inode;
+                }
+            })?;
+
+        watcher.watch(path, RecursiveMode::NonRecursive)?;
+
+        Ok(Self {
+            rx,
+            _watcher: watcher,
+        })
+    }
+
+    pub fn try_recv(&self) -> Option<FileEvent> {
+        self.rx.try_recv().ok()
+    }
+}
+
+// ─── SmartFollow ────────────────────────────────────────────────────────────
+
 pub struct SmartFollow {/* TODO */}
+
+// ─── Tests ──────────────────────────────────────────────────────────────────
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+    use std::thread;
+    use std::time::Duration;
+
+    fn collect_events(watcher: &FileWatcher, timeout_ms: u64) -> Vec<FileEvent> {
+        let mut events = Vec::new();
+        let deadline = std::time::Instant::now() + Duration::from_millis(timeout_ms);
+        while std::time::Instant::now() < deadline {
+            if let Some(e) = watcher.try_recv() {
+                events.push(e);
+            }
+            thread::sleep(Duration::from_millis(50));
+        }
+        // final drain
+        while let Some(e) = watcher.try_recv() {
+            events.push(e);
+        }
+        events
+    }
+
+    #[test]
+    fn test_watcher_append() {
+        let dir = tempfile::tempdir().expect("create temp dir");
+        let path = dir.path().join("test.log");
+
+        std::fs::write(&path, b"hello\n").expect("write initial");
+
+        let watcher = FileWatcher::watch(&path).expect("start watcher");
+
+        {
+            let mut f = std::fs::OpenOptions::new()
+                .append(true)
+                .open(&path)
+                .expect("open for append");
+            f.write_all(b"world\n").expect("append data");
+        }
+
+        let events = collect_events(&watcher, 1000);
+        let appended: Vec<&FileEvent> = events
+            .iter()
+            .filter(|e| matches!(e, FileEvent::Appended { .. }))
+            .collect();
+        assert!(
+            !appended.is_empty(),
+            "should detect append event, got: {events:?}"
+        );
+    }
+
+    #[test]
+    fn test_watcher_truncate() {
+        let dir = tempfile::tempdir().expect("create temp dir");
+        let path = dir.path().join("test.log");
+
+        std::fs::write(&path, b"hello world this is a long line\n").expect("write initial");
+
+        let watcher = FileWatcher::watch(&path).expect("start watcher");
+
+        // File::create truncates to 0 bytes
+        let _ = std::fs::File::create(&path).expect("truncate file");
+
+        let events = collect_events(&watcher, 1000);
+        let truncated: Vec<&FileEvent> = events
+            .iter()
+            .filter(|e| matches!(e, FileEvent::Truncated { .. }))
+            .collect();
+        assert!(
+            !truncated.is_empty(),
+            "should detect truncate event, got: {events:?}"
+        );
+    }
+
+    #[test]
+    fn test_watcher_idle() {
+        let dir = tempfile::tempdir().expect("create temp dir");
+        let path = dir.path().join("idle.log");
+
+        std::fs::write(&path, b"static content\n").expect("write");
+
+        let watcher = FileWatcher::watch(&path).expect("start watcher");
+
+        thread::sleep(Duration::from_millis(300));
+        assert_eq!(watcher.try_recv(), None, "no events on idle file");
+    }
+
+    #[test]
+    fn test_get_inode() {
+        let dir = tempfile::tempdir().expect("create temp dir");
+        let path = dir.path().join("inode_test.txt");
+        std::fs::write(&path, b"test").expect("write file");
+
+        let inode = get_inode(&path).expect("get inode");
+        #[cfg(unix)]
+        assert!(inode > 0, "inode should be positive on Unix");
+        #[cfg(not(unix))]
+        assert_eq!(inode, 0, "inode should be 0 on non-Unix");
+    }
+
+    #[test]
+    fn test_file_event_equality() {
+        let a = FileEvent::Appended { new_size: 100 };
+        let b = FileEvent::Appended { new_size: 100 };
+        assert_eq!(a, b);
+
+        let c = FileEvent::Truncated { new_size: 0 };
+        assert_ne!(a, c);
+
+        let d = FileEvent::Rotated { new_inode: 42 };
+        assert_ne!(a, d);
+    }
+}

crates/tui/Cargo.toml

@@ -10,6 +10,7 @@ clap.workspace = true
 anyhow.workspace = true
 log-viewer-core.workspace = true
 serde_json.workspace = true
+crossbeam-channel.workspace = true
 
 [dev-dependencies]
 tempfile = { workspace = true }

crates/tui/src/main.rs

@@ -1,3 +1,6 @@
+use std::time::Duration;
+
+use anyhow::Context;
 use clap::Parser;
 
 mod app;
@@ -11,42 +14,93 @@ struct Cli {
     files: Vec<String>,
 }
 
+// ── RAII terminal guard ────────────────────────────────────────────
+//
+// Holds the ratatui Terminal and guarantees terminal state restoration
+// (disable raw mode, leave alternate screen, show cursor) on **every**
+// exit path: normal return, `?` error propagation, and panic unwind.
+//
+// IMPORTANT: `Drop` does **not** run on `std::process::exit` or
+// `panic = "abort"`.  Therefore we must never call `process::exit`
+// inside the guarded scope — use `?` to return `Err` instead.
+
+type Backend = ratatui::backend::CrosstermBackend<std::io::Stdout>;
+
+struct TerminalGuard {
+    terminal: ratatui::Terminal<Backend>,
+}
+
+impl TerminalGuard {
+    /// Enable raw mode, enter alternate screen, and create the terminal.
+    /// On partial failure, rolls back any steps that already succeeded.
+    fn enter() -> anyhow::Result<Self> {
+        crossterm::terminal::enable_raw_mode()
+            .map_err(|e| anyhow::anyhow!("enable_raw_mode: {e}"))?;
+
+        let mut stdout = std::io::stdout();
+        if let Err(e) = crossterm::execute!(stdout, crossterm::terminal::EnterAlternateScreen) {
+            let _ = crossterm::terminal::disable_raw_mode();
+            return Err(anyhow::anyhow!("EnterAlternateScreen: {e}"));
+        }
+
+        let backend = ratatui::backend::CrosstermBackend::new(stdout);
+        match ratatui::Terminal::new(backend) {
+            Ok(terminal) => Ok(Self { terminal }),
+            Err(e) => {
+                // Roll back: leave alternate screen + disable raw mode
+                let _ = crossterm::execute!(
+                    std::io::stdout(),
+                    crossterm::terminal::LeaveAlternateScreen
+                );
+                let _ = crossterm::terminal::disable_raw_mode();
+                Err(anyhow::anyhow!("Terminal::new: {e}"))
+            }
+        }
+    }
+
+    fn terminal(&mut self) -> &mut ratatui::Terminal<Backend> {
+        &mut self.terminal
+    }
+}
+
+impl Drop for TerminalGuard {
+    fn drop(&mut self) {
+        // Best-effort cleanup; suppress errors (Drop must not panic).
+        let _ = crossterm::terminal::disable_raw_mode();
+        let _ = crossterm::execute!(
+            self.terminal.backend_mut(),
+            crossterm::terminal::LeaveAlternateScreen
+        );
+        let _ = self.terminal.show_cursor();
+    }
+}
+
+// ── main ───────────────────────────────────────────────────────────
+
 fn main() -> anyhow::Result<()> {
     let cli = Cli::parse();
 
-    crossterm::terminal::enable_raw_mode()?;
-    let mut stdout = std::io::stdout();
-    crossterm::execute!(stdout, crossterm::terminal::EnterAlternateScreen)?;
-    let backend = ratatui::backend::CrosstermBackend::new(stdout);
-    let mut terminal = ratatui::Terminal::new(backend)?;
-
+    let mut guard = TerminalGuard::enter()?;
     let mut app = app::App::new();
     app.color_config = log_viewer_core::config::ColorConfig::load();
 
-    if let Some(file) = cli.files.first()
-        && let Err(e) = app.load_file(file)
-    {
-        eprintln!("Error loading file: {e}");
-        std::process::exit(1);
+    if let Some(file) = cli.files.first() {
+        app.load_file(file)
+            .with_context(|| format!("loading file {file}"))?;
     }
 
     while !app.should_quit {
-        terminal.draw(|frame| ui::render(frame, &mut app))?;
-        if crossterm::event::poll(std::time::Duration::from_millis(100))? {
+        app.poll_background_indexer();
+        app.poll_file_watcher();
+        guard.terminal().draw(|frame| ui::render(frame, &mut app))?;
+        if crossterm::event::poll(Duration::from_millis(100))? {
             match crossterm::event::read()? {
                 crossterm::event::Event::Key(key) => app.handle_key(key),
-                crossterm::event::Event::Resize(_w, _h) => {}
+                crossterm::event::Event::Resize(_, _) => {}
                 _ => {}
             }
         }
     }
 
-    crossterm::terminal::disable_raw_mode()?;
-    crossterm::execute!(
-        terminal.backend_mut(),
-        crossterm::terminal::LeaveAlternateScreen
-    )?;
-    terminal.show_cursor()?;
-
     Ok(())
 }

crates/tui/src/ui.rs

@@ -1,4 +1,4 @@
-use ratatui::style::{Color, Style};
+use ratatui::style::{Color, Modifier, Style};
 use ratatui::text::{Line, Span};
 
 use crate::app::{App, AppMode};
@@ -42,6 +42,10 @@ pub fn render(frame: &mut ratatui::Frame, app: &mut App) {
     // ── Title bar ──────────────────────────────────────────────────
     let title_text = if app.mode == AppMode::Settings {
         " Color Settings".to_string()
+    } else if app.is_loading() {
+        let name = app.file_name().unwrap_or("unknown");
+        let pct = app.loading_progress().map_or(0, |p| p as usize);
+        format!(" {} [Loading... {}%]", name, pct)
     } else if app.is_loaded() {
         let name = app.file_name().unwrap_or("unknown");
         let cursor_display = if app.total_lines() == 0 {
@@ -61,6 +65,22 @@ pub fn render(frame: &mut ratatui::Frame, app: &mut App) {
     // ── Content area ───────────────────────────────────────────────
     if app.mode == AppMode::Settings {
         render_settings(frame, app, outer[1]);
+    } else if app.is_error() {
+        let msg = app.error_message().unwrap_or_default();
+        let error_lines = vec![
+            Line::from(""),
+            Line::from(""),
+            Line::styled(
+                format!(" Error: {}", msg),
+                Style::default().fg(Color::Red).add_modifier(Modifier::BOLD),
+            ),
+            Line::from(""),
+            Line::styled(" Press q to quit", Style::default().fg(Color::DarkGray)),
+        ];
+        frame.render_widget(Paragraph::new(error_lines).centered(), outer[1]);
+    } else if app.is_loading() {
+        // Show content from sampling during loading
+        render_content(frame, app, outer[1]);
     } else if !app.is_loaded() {
         frame.render_widget(Paragraph::new(" No file loaded"), outer[1]);
     } else {
@@ -70,6 +90,30 @@ pub fn render(frame: &mut ratatui::Frame, app: &mut App) {
     // ── Status bar ─────────────────────────────────────────────────
     let status_text = if app.mode == AppMode::Settings {
         " j/k:navigate  ←/→:change  1-8:jump  Enter:save  Esc:cancel"
+    } else if app.is_error() {
+        " Press q to quit"
+    } else if app.is_loading() {
+        let pct = app.loading_progress().map_or(0, |p| p as usize);
+        let est = app
+            .estimated_lines()
+            .map_or("?".to_string(), |e| format!("~{}", e));
+        let name = app.file_name().unwrap_or("unknown");
+        let status = format!(
+            " Indexing... {}% | {} lines | {} | j/k:scroll q:quit",
+            pct, est, name
+        );
+        frame.render_widget(
+            Paragraph::new(status).style(Style::default().fg(Color::Yellow)),
+            outer[2],
+        );
+        return;
+    } else if app.is_loaded() {
+        let name = app.file_name().unwrap_or("unknown");
+        let total = app.total_lines();
+        let cursor_display = if total == 0 { 0 } else { app.cursor_line + 1 };
+        let status = format!(" {} [{}/{}] | j/k:scroll d/u:half-page f/b:page G/gg:jump Tab:format S:settings q:quit", name, cursor_display, total);
+        frame.render_widget(Paragraph::new(status), outer[2]);
+        return;
     } else {
         " j/k:scroll d/u:half-page f/b:page G/gg:jump Tab:format S:settings q:quit"
     };
@@ -165,8 +209,11 @@ fn render_content(frame: &mut ratatui::Frame, app: &mut App, area: ratatui::layo
     } else {
         0
     };
+
+    let is_loading = app.is_loading();
+    let gutter_prefix_extra = if is_loading { 1 } else { 0 };
     let gutter_width = if total_lines > 0 {
-        line_num_width + 1 + 1
+        line_num_width + gutter_prefix_extra + 1 + 1
     } else {
         0
     };
@@ -177,62 +224,73 @@ fn render_content(frame: &mut ratatui::Frame, app: &mut App, area: ratatui::layo
         return;
     }
 
-    app.recompute_wrap_cache(actual_content_width);
-    let mut visual_acc: usize = 0;
-    let mut start_logical: usize = 0;
-    let mut offset_in_line: usize = 0;
-    let v_offset = app.v_offset;
-
-    for (i, &h) in app.visual_heights.iter().enumerate() {
-        if visual_acc.saturating_add(h) > v_offset {
-            start_logical = i;
-            offset_in_line = v_offset.saturating_sub(visual_acc);
-            break;
-        }
-        visual_acc += h;
-        if i == app.visual_heights.len() - 1 {
-            start_logical = i;
-            offset_in_line = 0;
-        }
-    }
+    let (start_logical, offset_in_line) = app.ensure_viewport_cache(actual_content_width);
 
     let mut lines: Vec<Line> = Vec::new();
     let mut current_visual_offset: usize = 0;
     let available_rows = content_height;
 
-    for logical_line in start_logical..total_lines {
-        let wrapped = &app.wrap_cache[logical_line];
+    let gutter_style = if is_loading {
+        Style::default()
+            .fg(Color::DarkGray)
+            .add_modifier(Modifier::DIM)
+    } else {
+        Style::default().fg(Color::DarkGray)
+    };
+
+    for (entry_idx, entry) in app.viewport_cache.entries.iter().enumerate() {
+        let logical_line = app.viewport_cache.logical_start + entry_idx;
         let start_row = if logical_line == start_logical {
             offset_in_line
         } else {
             0
         };
 
-        for (visual_row, text) in wrapped.iter().enumerate().skip(start_row) {
+        for (visual_row, text) in entry.wrapped_rows.iter().enumerate().skip(start_row) {
             if current_visual_offset >= available_rows {
                 break;
             }
 
             let is_cursor = logical_line == app.cursor_line;
-            let level = app.level_cache.get(logical_line).and_then(|l| l.as_ref());
+            let level = entry.level.as_ref();
+
+            let bg_color = if is_cursor {
+                Color::DarkGray
+            } else {
+                Color::Reset
+            };
+            let level_fg = level_fg(level, &app.color_config).unwrap_or(Color::White);
 
             let gutter_text = if visual_row == 0 {
-                format!(
-                    "{:>width$} \u{2502}",
-                    logical_line + 1,
-                    width = line_num_width
-                )
+                if is_loading {
+                    format!(
+                        "~{:>width$} \u{2502}",
+                        logical_line + 1,
+                        width = line_num_width
+                    )
+                } else {
+                    format!(
+                        "{:>width$} \u{2502}",
+                        logical_line + 1,
+                        width = line_num_width
+                    )
+                }
+            } else if is_loading {
+                format!(" {:width$} \u{2502}", "", width = line_num_width)
             } else {
                 format!("{:width$} \u{2502}", "", width = line_num_width)
             };
 
-            lines.push(build_line_spans(
-                gutter_text,
-                text.clone(),
-                is_cursor,
-                level,
-                &app.color_config,
-            ));
+            let effective_gutter_style = if is_cursor {
+                gutter_style.bg(bg_color)
+            } else {
+                gutter_style
+            };
+
+            lines.push(Line::from(vec![
+                Span::styled(gutter_text, effective_gutter_style),
+                Span::styled(text.clone(), Style::default().fg(level_fg).bg(bg_color)),
+            ]));
 
             current_visual_offset += 1;
         }
@@ -304,4 +362,135 @@ mod tests {
         assert_eq!(line.spans[0].style.bg, Some(Color::Reset));
         assert_eq!(line.spans[1].style.bg, Some(Color::Reset));
     }
+
+    fn render_to_buffer(app: &mut App, width: u16, height: u16) -> ratatui::buffer::Buffer {
+        let backend = ratatui::backend::TestBackend::new(width, height);
+        let mut terminal = ratatui::Terminal::new(backend).unwrap();
+        terminal.draw(|frame| render(frame, app)).unwrap();
+        terminal.backend().buffer().clone()
+    }
+
+    fn make_temp_file(content: &str) -> std::path::PathBuf {
+        use std::sync::atomic::{AtomicU64, Ordering};
+        static COUNTER: AtomicU64 = AtomicU64::new(0);
+        let id = COUNTER.fetch_add(1, Ordering::Relaxed);
+        let dir = std::env::temp_dir();
+        let name = format!("log_viewer_ui_test_{}_{}", std::process::id(), id);
+        let path = dir.join(name);
+        std::fs::write(&path, content).unwrap();
+        path
+    }
+
+    #[test]
+    fn test_render_error_state() {
+        let mut app = App::new();
+        app.set_error_state("file not found");
+
+        let buf = render_to_buffer(&mut app, 80, 24);
+
+        let mut found_error = false;
+        let mut found_quit = false;
+        for row in 0..23 {
+            let content: String = (0..80)
+                .map(|c| buf.cell((c, row)).unwrap().symbol().to_string())
+                .collect();
+            if content.contains("Error") && content.contains("file not found") {
+                found_error = true;
+            }
+            if content.contains("Press q to quit") {
+                found_quit = true;
+            }
+        }
+        assert!(found_error, "content area should show error message");
+        assert!(found_quit, "content area should show quit hint");
+    }
+
+    #[test]
+    fn test_render_loading_state_status_bar() {
+        let path = make_temp_file("line1\nline2\nline3\nline4\nline5\n");
+        let result = std::panic::catch_unwind(|| {
+            let mut app = App::new();
+            app.load_file(path.to_str().unwrap()).unwrap();
+
+            if app.is_loading() {
+                let buf = render_to_buffer(&mut app, 80, 24);
+
+                let status: String = (0..80)
+                    .map(|c| buf.cell((c, 23)).unwrap().symbol().to_string())
+                    .collect();
+                assert!(
+                    status.contains("Indexing"),
+                    "status bar should show 'Indexing', got: {}",
+                    status
+                );
+                assert!(
+                    status.contains("%"),
+                    "status bar should show percentage, got: {}",
+                    status
+                );
+                assert!(
+                    status.contains("~"),
+                    "status bar should show ~ for estimated lines, got: {}",
+                    status
+                );
+            }
+        });
+        let _ = std::fs::remove_file(&path);
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn test_render_loading_gutter_tilde_prefix() {
+        let path = make_temp_file("line1\nline2\nline3\n");
+        let result = std::panic::catch_unwind(|| {
+            let mut app = App::new();
+            app.load_file(path.to_str().unwrap()).unwrap();
+
+            if app.is_loading() {
+                let buf = render_to_buffer(&mut app, 80, 24);
+
+                let first_line: String = (0..10)
+                    .map(|c| buf.cell((c, 1)).unwrap().symbol().to_string())
+                    .collect();
+                assert!(
+                    first_line.contains("~"),
+                    "loading state gutter should have ~ prefix, got: {}",
+                    first_line
+                );
+            }
+        });
+        let _ = std::fs::remove_file(&path);
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn test_render_ready_state_status_bar() {
+        let path = make_temp_file("alpha\nbeta\ngamma\n");
+        let result = std::panic::catch_unwind(|| {
+            let data = std::fs::read(&path).unwrap();
+            let index = log_viewer_core::io::line_index::LineIndex::from_bytes(&data);
+            let _ = log_viewer_core::io::index_cache::IndexCache::save_with_hash(&path, &index, &data);
+
+            let mut app = App::new();
+            app.load_file(path.to_str().unwrap()).unwrap();
+
+            assert!(
+                app.is_loaded() && !app.is_loading(),
+                "should be in Ready state with cache hit"
+            );
+
+            let buf = render_to_buffer(&mut app, 80, 24);
+
+            let status: String = (0..80)
+                .map(|c| buf.cell((c, 23)).unwrap().symbol().to_string())
+                .collect();
+            assert!(
+                status.contains("1/") || status.contains("1/3"),
+                "status bar should show cursor position, got: {}",
+                status
+            );
+        });
+        let _ = std::fs::remove_file(&path);
+        assert!(result.is_ok());
+    }
 }