fix: harden AI subtitle fix response parsing

launcher/youtube/subtitle-fix-ai.test.ts

@@ -0,0 +1,126 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import { applyFixedCueBatch, parseAiSubtitleFixResponse } from './subtitle-fix-ai';
+import { parseSrt } from './srt';
+
+test('applyFixedCueBatch accepts content-only fixes with identical timing', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんいちは
+
+2
+00:00:03,000 --> 00:00:04,000
+世界
+`);
+  const fixed = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんにちは
+
+2
+00:00:03,000 --> 00:00:04,000
+世界
+`);
+
+  const merged = applyFixedCueBatch(original, fixed);
+  assert.equal(merged[0]?.text, 'こんにちは');
+});
+
+test('applyFixedCueBatch rejects changed timestamps', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんいちは
+`);
+  const fixed = parseSrt(`1
+00:00:01,100 --> 00:00:02,000
+こんにちは
+`);
+
+  assert.throws(() => applyFixedCueBatch(original, fixed), /timestamps/i);
+});
+
+test('parseAiSubtitleFixResponse accepts valid SRT wrapped in markdown fences', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんいちは
+
+2
+00:00:03,000 --> 00:00:04,000
+世界
+`);
+
+  const parsed = parseAiSubtitleFixResponse(
+    original,
+    '```srt\n1\n00:00:01,000 --> 00:00:02,000\nこんにちは\n\n2\n00:00:03,000 --> 00:00:04,000\n世界\n```',
+  );
+
+  assert.equal(parsed[0]?.text, 'こんにちは');
+  assert.equal(parsed[1]?.text, '世界');
+});
+
+test('parseAiSubtitleFixResponse accepts text-only one-block-per-cue output', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんいちは
+
+2
+00:00:03,000 --> 00:00:04,000
+世界
+`);
+
+  const parsed = parseAiSubtitleFixResponse(
+    original,
+    `こんにちは
+
+世界`,
+  );
+
+  assert.equal(parsed[0]?.start, '00:00:01,000');
+  assert.equal(parsed[0]?.text, 'こんにちは');
+  assert.equal(parsed[1]?.end, '00:00:04,000');
+  assert.equal(parsed[1]?.text, '世界');
+});
+
+test('parseAiSubtitleFixResponse rejects unrecoverable text-only output', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんいちは
+
+2
+00:00:03,000 --> 00:00:04,000
+世界
+`);
+
+  assert.throws(
+    () => parseAiSubtitleFixResponse(original, 'こんにちは\n世界\n余分です'),
+    /cue block|cue count/i,
+  );
+});
+
+test('parseAiSubtitleFixResponse rejects language drift for primary Japanese subtitles', () => {
+  const original = parseSrt(`1
+00:00:01,000 --> 00:00:02,000
+こんにちは
+
+2
+00:00:03,000 --> 00:00:04,000
+今日はいい天気ですね
+`);
+
+  assert.throws(
+    () =>
+      parseAiSubtitleFixResponse(
+        original,
+        `1
+00:00:01,000 --> 00:00:02,000
+Hello
+
+2
+00:00:03,000 --> 00:00:04,000
+The weather is nice today
+`,
+        'ja',
+      ),
+    /language/i,
+  );
+});