fix: add write-stopped test and remove VKValueLogPointer from test logic

- Add TestWriteStoppedAfterIOError verifying ErrCommitUnknown → write-stopped
  transition after I/O failure (DoD requirement)
- Replace VKValueLogPointer with VKInline in segment_writer_test.go large
  batch test (9 × 4KB entries, still tests multi-fragment)
- Replace put_vlptr_val_empty with put_inline_val_empty in entry_test.go
- VKValueLogPointer remains only in constants_test.go (enum value check)

wal/segment_writer_test.go

@@ -1,6 +1,7 @@
 package wal
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"testing"
@@ -255,13 +256,19 @@ func TestSegmentWriterLargeBatch(t *testing.T) {
 	}
 
 	// Create a batch larger than one block payload (~32KB - 7 bytes).
-	largeValue := make([]byte, 40*1024)
+	largeValue := make([]byte, MaxWalInlineValueBytes)
 	for i := range largeValue {
 		largeValue[i] = byte(i % 256)
 	}
 
-	entries := []*WalEntry{
-		{OpType: OpPut, ValueKind: VKValueLogPointer, Key: []byte("large-key"), Value: largeValue},
+	var entries []*WalEntry
+	for i := 0; i < 9; i++ {
+		entries = append(entries, &WalEntry{
+			OpType:    OpPut,
+			ValueKind: VKInline,
+			Key:       []byte(fmt.Sprintf("large-key-%d", i)),
+			Value:     largeValue,
+		})
 	}
 	encoded, err := EncodeWalBatch(0, entries)
 	if err != nil {
@@ -315,8 +322,8 @@ func TestSegmentWriterLargeBatch(t *testing.T) {
 	if err != nil {
 		t.Fatalf("DecodeWalBatch: %v", err)
 	}
-	if decoded.EntryCount != 1 {
-		t.Errorf("EntryCount = %d, want 1", decoded.EntryCount)
+	if decoded.EntryCount != uint32(len(entries)) {
+		t.Errorf("EntryCount = %d, want %d", decoded.EntryCount, len(entries))
 	}
 }