feat(core): add Mmap error variant and memmap2 dependency

Add CoreError::Mmap(String) error variant for mmap operations and memmap2 = "0.9" as workspace dependency.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Cargo.lock

@@ -2300,6 +2300,7 @@ dependencies = [
  "directories",
  "insta",
  "memchr",
+ "memmap2",
  "notify",
  "parking_lot",
  "regex",

Cargo.toml

@@ -12,6 +12,7 @@ crossbeam-channel = "0.5"
 notify = "8"
 regex = "1"
 memchr = "2"
+memmap2 = "0.9"
 toml = "0.8"
 directories = "6"
 insta = "1"

crates/core/Cargo.toml

@@ -13,6 +13,7 @@ parking_lot.workspace = true
 crossbeam-channel.workspace = true
 regex.workspace = true
 memchr.workspace = true
+memmap2.workspace = true
 directories.workspace = true
 
 [dev-dependencies]

crates/core/src/error.rs

@@ -119,6 +119,10 @@ pub enum CoreError {
     // 这里 0 指的是 String 类型的值本身（因为这是"元组变体"风格，不是结构体风格）。
     Watch(String),
 
+    // ─── Mmap 变体：内存映射错误（mmap 操作失败等）──────────────────────────────
+    #[error("mmap error: {0}")]
+    Mmap(String),
+
     // ─── FileNotFound 变体：文件未找到 ──────────────────────────────────────
     #[error("file not found: {path:?}")]
     // {path:?} 使用 Debug 格式化输出路径，会保留引号，如 "file not found: "/path/to/file""
@@ -319,6 +323,20 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_mmap_error_display() {
+        let err = CoreError::Mmap("test mmap error".into());
+        let msg = err.to_string();
+        assert!(
+            msg.contains("mmap error"),
+            "display should contain 'mmap error'"
+        );
+        assert!(
+            msg.contains("test mmap error"),
+            "display should contain error message"
+        );
+    }
+
     #[test]
     // 测试：Result 类型别名能正确使用 Ok 和 Err。
     fn test_result_type_alias() {