perf: fix ExtractWorkflowNameFromFile regression — stream file instead of slurping

pkg/cli/workflows.go

@@ -362,17 +362,66 @@ func fastParseTitle(content string) (string, error) {
 	return "", nil
 }
 
+// fastParseTitleFromReader scans lines from r for the first H1 header, skipping
+// an optional frontmatter block, without reading the entire file into memory.
+// This is more efficient than fastParseTitle for file-based callers because it
+// stops reading as soon as the title is found.
+//
+// Frontmatter is recognised only when "---" appears on the very first line.
+// Returns the H1 title text, or ("", nil) when no H1 header is present.
+// Returns an error if frontmatter is opened but never closed.
+func fastParseTitleFromReader(r io.Reader) (string, error) {
+	scanner := bufio.NewScanner(r)
+	// Increase the max token size beyond the default 64 KB to handle files with
+	// large frontmatter values or long base64-encoded lines.
+	scanner.Buffer(make([]byte, 64*1024), 1024*1024)
+	firstLine := true
+	inFrontmatter := false
+	for scanner.Scan() {
+		trimmed := strings.TrimSpace(scanner.Text())
+		if firstLine {
+			firstLine = false
+			if trimmed == "---" {
+				inFrontmatter = true
+				continue
+			}
+		} else if inFrontmatter {
+			if trimmed == "---" {
+				inFrontmatter = false
+			}
+			continue
+		}
+		if strings.HasPrefix(trimmed, "# ") {
+			return strings.TrimSpace(trimmed[2:]), nil
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
+
+	// Unclosed frontmatter is an error (consistent with ExtractFrontmatterFromContent).
+	if inFrontmatter {
+		return "", errors.New("frontmatter not properly closed")
+	}
+
+	return "", nil
+}
+
 // extractWorkflowNameFromFile extracts the workflow name from a file's H1 header
 func extractWorkflowNameFromFile(filePath string) (string, error) {
-	content, err := os.ReadFile(filePath)
+	fd, err := os.Open(filePath)
 	if err != nil {
 		return "", err
 	}
 
-	title, err := fastParseTitle(string(content))
+	title, err := fastParseTitleFromReader(fd)
+	closeErr := fd.Close()
 	if err != nil {
 		return "", err
 	}
+	if closeErr != nil {
+		return "", fmt.Errorf("failed to close workflow file %s: %w", filePath, closeErr)
+	}
 	if title != "" {
 		return title, nil
 	}