fix(#137): address review findings in docmap.go

- Fix package comment collision: convert to file comment (not package doc)
- Add debug log for directory expansion failure before single-file fallback
- Add validateDocPath: reject absolute paths and '..' segments (security #3)
- Update globMatch comment to say 'filepath.Match' not 'path.Match' (gpt nit #3)
- Add duplication note to truncateUTF8 explaining why it's kept separate (sonnet #2)

review/docmap.go

@@ -1,5 +1,4 @@
-// Package review provides doc-map parsing and doc injection for path-scoped
-// design document context in AI code reviews.
+// doc-map parsing and doc injection for path-scoped design document context in AI code reviews.
 package review
 
 import (
@@ -106,7 +105,7 @@ func mappingMatches(patterns, files []string) bool {
 
 // globMatch matches a path against a glob pattern that may contain **.
 // It supports:
-//   - Standard path.Match patterns (*, ?, [range])
+//   - filepath.Match patterns (*, ?, [range])
 //   - ** as a path segment that matches zero or more segments
 //   - Trailing /** to match a directory and all its contents
 //
@@ -246,9 +245,13 @@ type docEntry struct {
 // If the path is a directory, all .md files under it are returned.
 // If it's a file, a single entry is returned.
 func loadDocEntries(ctx context.Context, fetcher DocFetcher, owner, repo, docPath string) ([]docEntry, error) {
+	if err := validateDocPath(docPath); err != nil {
+		return nil, fmt.Errorf("doc path %q rejected: %w", docPath, err)
+	}
+
 	// Try directory expansion first.
-	files, err := fetcher.GetAllFilesInPath(ctx, owner, repo, docPath)
-	if err == nil && len(files) > 0 {
+	files, dirErr := fetcher.GetAllFilesInPath(ctx, owner, repo, docPath)
+	if dirErr == nil && len(files) > 0 {
 		// Filter for .md files only.
 		var entries []docEntry
 		for path, content := range files {
@@ -261,6 +264,11 @@ func loadDocEntries(ctx context.Context, fetcher DocFetcher, owner, repo, docPat
 		return entries, nil
 	}
 
+	// Directory expansion returned nothing; log and fall through to single-file fetch.
+	if dirErr != nil {
+		slog.Debug("doc-map: directory expansion failed, trying as single file", "path", docPath, "error", dirErr)
+	}
+
 	// Try as a single file.
 	content, fileErr := fetcher.GetFileContent(ctx, owner, repo, docPath)
 	if fileErr != nil {
@@ -290,8 +298,29 @@ func readFileBytes(path string) ([]byte, error) {
 	return os.ReadFile(path)
 }
 
+// validateDocPath rejects doc paths that could cause path traversal via the
+// VCS API (absolute paths, any ".." segment). Defense-in-depth: the VCS API
+// should already scope paths to the repo, but we validate locally to avoid
+// any quirk in backend path handling.
+func validateDocPath(p string) error {
+	if filepath.IsAbs(p) {
+		return fmt.Errorf("absolute paths not allowed")
+	}
+	for _, segment := range strings.Split(p, "/") {
+		if segment == ".." {
+			return fmt.Errorf("path traversal ('..' segment) not allowed")
+		}
+	}
+	return nil
+}
+
 // truncateUTF8 truncates s to at most maxBytes without splitting multi-byte
 // UTF-8 characters. Returns a valid UTF-8 string of at most maxBytes bytes.
+//
+// Note: an identical implementation exists in budget/budget.go. The two
+// packages are intentionally separate (review does not import budget), so
+// the duplication is accepted rather than introducing a shared internal
+// package for a single small function.
 func truncateUTF8(s string, maxBytes int) string {
 	if len(s) <= maxBytes {
 		return s