Fix critical P0 database reinitialization bug (bd-130)

Fixes silent data loss when .beads/ directory removed and daemon auto-starts.

Root cause: checkGitForIssues() hardcoded 'issues.jsonl' but git tracks 'beads.jsonl'

Changes:
- Fix A (bd-131): checkGitForIssues() tries beads.jsonl first, then issues.jsonl
- Fix B (bd-132): Immediate export after import in bd init to prevent daemon race
- Fix C (bd-133): Safety check that fails loudly if import fails
- Fix D (bd-134): Daemon startup auto-import when DB empty but git has issues
- Tests (bd-135): Comprehensive integration test suite

Oracle-recommended improvements:
- Export to exact git-relative path (prevents path drift)
- filepath.ToSlash for Windows git compatibility
- 64MB scanner buffer for large JSONL lines
- Improved safety check messages (only suggest local file if exists)

All tests passing. No regressions.

Amp-Thread-ID: https://ampcode.com/threads/T-0e31dc6a-a0d9-46c6-87b2-cfdebe829a52
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/autoimport.go

@@ -58,7 +58,7 @@ func checkAndAutoImport(ctx context.Context, store storage.Storage) bool {
 	return true
 }
 
-// checkGitForIssues checks if git has issues in HEAD:.beads/issues.jsonl
+// checkGitForIssues checks if git has issues in HEAD:.beads/beads.jsonl or issues.jsonl
 // Returns (issue_count, relative_jsonl_path)
 func checkGitForIssues() (int, string) {
 	// Try to find .beads directory
@@ -67,32 +67,37 @@ func checkGitForIssues() (int, string) {
 		return 0, ""
 	}
 
-	// Construct relative path to issues.jsonl from git root
+	// Construct relative path from git root
 	gitRoot := findGitRoot()
 	if gitRoot == "" {
 		return 0, ""
 	}
 
-	relPath, err := filepath.Rel(gitRoot, filepath.Join(beadsDir, "issues.jsonl"))
+	relBeads, err := filepath.Rel(gitRoot, beadsDir)
 	if err != nil {
 		return 0, ""
 	}
 
-	// Check if git has this file with content
-	cmd := exec.Command("git", "show", fmt.Sprintf("HEAD:%s", relPath))
-	output, err := cmd.Output()
-	if err != nil {
-		// File doesn't exist in git or other error
-		return 0, ""
+	// Try canonical JSONL filenames in precedence order
+	candidates := []string{
+		filepath.Join(relBeads, "beads.jsonl"),
+		filepath.Join(relBeads, "issues.jsonl"),
 	}
 
-	// Count lines (rough estimate of issue count)
-	lines := bytes.Count(output, []byte("\n"))
-	if lines == 0 {
-		return 0, ""
+	for _, relPath := range candidates {
+		// Use ToSlash for git path compatibility on Windows
+		gitPath := filepath.ToSlash(relPath)
+		cmd := exec.Command("git", "show", fmt.Sprintf("HEAD:%s", gitPath))
+		output, err := cmd.Output()
+		if err == nil && len(output) > 0 {
+			lines := bytes.Count(output, []byte("\n"))
+			if lines > 0 {
+				return lines, relPath
+			}
+		}
 	}
 
-	return lines, relPath
+	return 0, ""
 }
 
 // findBeadsDir finds the .beads directory in current or parent directories
@@ -131,8 +136,9 @@ func findGitRoot() string {
 
 // importFromGit imports issues from git HEAD
 func importFromGit(ctx context.Context, dbFilePath string, store storage.Storage, jsonlPath string) error {
-	// Get content from git
-	cmd := exec.Command("git", "show", fmt.Sprintf("HEAD:%s", jsonlPath))
+	// Get content from git (use ToSlash for Windows compatibility)
+	gitPath := filepath.ToSlash(jsonlPath)
+	cmd := exec.Command("git", "show", fmt.Sprintf("HEAD:%s", gitPath))
 	jsonlData, err := cmd.Output()
 	if err != nil {
 		return fmt.Errorf("failed to read from git: %w", err)
@@ -140,6 +146,8 @@ func importFromGit(ctx context.Context, dbFilePath string, store storage.Storage
 
 	// Parse JSONL data
 	scanner := bufio.NewScanner(bytes.NewReader(jsonlData))
+	// Increase buffer size to handle large JSONL lines (e.g., big descriptions)
+	scanner.Buffer(make([]byte, 0, 1024*1024), 64*1024*1024) // allow up to 64MB per line
 	var issues []*types.Issue
 
 	for scanner.Scan() {