Add Playwright assistant regression coverage

frontend/e2e/subtitles.ts

@@ -0,0 +1,33 @@
+export interface Clip {
+  title: string;
+  caption: string;
+  file: string;
+  startMs: number;
+  endMs: number;
+  narration: { path: string; durationMs: number } | null;
+}
+
+export function msToSrtTimestamp(ms: number): string {
+  const clamped = Math.max(0, Math.round(ms));
+  const hours = Math.floor(clamped / 3_600_000);
+  const minutes = Math.floor((clamped % 3_600_000) / 60_000);
+  const seconds = Math.floor((clamped % 60_000) / 1000);
+  const millis = clamped % 1000;
+  const pad = (n: number, len = 2) => String(n).padStart(len, "0");
+  return `${pad(hours)}:${pad(minutes)}:${pad(seconds)},${pad(millis, 3)}`;
+}
+
+/** One subtitle cue per step, spanning its full on-screen duration. */
+export function buildSrt(clips: Clip[]): string {
+  return clips
+    .map((clip, i) => {
+      const index = i + 1;
+      return [
+        String(index),
+        `${msToSrtTimestamp(clip.startMs)} --> ${msToSrtTimestamp(clip.endMs)}`,
+        clip.caption,
+        "",
+      ].join("\n");
+    })
+    .join("\n");
+}