fix(dub): Export-step language tabs switch the transcript segments too (#1148)

Owner request with screenshot: the Original/Bengali/German/… pills above a
finished dub only swapped the preview VIDEO; the segment list kept showing
the last generated/edited language — German audio playing over Bengali text.

The pills now also route through switchDubLangCode (the P1.2 user-driven
language switch: outgoing text snapshotted into translations[prev], incoming
swapped in, non-destructive when no saved entry exists) plus setDubLang —
exactly what the language dropdown and the multi-language generate loop
already do, so fingerprint/staleness semantics are identical. The Original
pill deliberately leaves the editing language untouched: there is no
'original' editing language, and every row already renders the original
line under its translation.

Tests: clicking the German pill swaps segment text to the stored German
translation, snapshots the outgoing Bengali, and sets dubLangCode; the
Original pill leaves dubLangCode alone. Fail-before verified (wiring
stashed → text swap test fails). Full frontend suite: 1251 passed.

Co-authored-by: mergetest <nizam4103@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -16,6 +16,8 @@ The bundled TTS model package (`pyproject.toml`) is versioned independently.
 
 ### Fixed
 
+- **The Export step's language tabs now switch the transcript too.** Clicking Bengali/German/Hindi… above the finished dub swapped the *video* but left the segment list showing whichever language you generated last — German audio over Bengali text. The tabs now also swap every segment's text to that language (through the same per-language store the language picker uses, so nothing is lost when you switch back); the Original tab keeps your editing language as-is, since each row already shows the original line beneath its translation. (#1148)
+
 - **A "backend crashed" notice can no longer outlive the update that fixed the crash — and the desktop shell's self-repair paths are now pinned by tests that CI actually runs.** Crash notices now record which app version wrote them, and a notice left behind by an older version is ignored and cleaned up after you upgrade instead of resurfacing as if the new build had crashed. The Windows blank-window repair (the one-click WebView cache fix after a BSOD) also gets regression tests pinning its safety contract — one attempt per request, never touches anything unasked, never blocks startup on a locked cache — and CI now runs the desktop shell's entire Rust unit-test suite on macOS, Windows, and Linux, which it previously never executed at all. (#1145)
 
 - **The MLX-Audio phonemizer's language model now ships with the app environment instead of being fetched mid-generation.** Follow-up to the pip fix: with the installer present, the first English MLX-Audio generation would auto-download a small model straight from GitHub — an outbound request that bypasses the app's mirror system (a problem on restricted networks) and fails offline. The model is now a pinned dependency of the managed environment: it arrives at install/update time through the normal dependency flow, and first generation works fully offline. (#1146)

frontend/src/components/dub/DubLeftColumn.jsx

@@ -223,7 +223,18 @@ export default function DubLeftColumn({
                 role="radio"
                 aria-checked={previewMode === code}
                 className={`dub-lang-pill ${previewMode === code ? 'is-active' : ''}`}
-                onClick={() => setPreviewMode(code)}
+                onClick={() => {
+                  setPreviewMode(code);
+                  // The transcript/segment list follows the previewed track:
+                  // swap segment texts to this language's saved translations
+                  // (the P1.2 per-language store — non-destructive, exactly
+                  // what the language dropdown and multi-language generate
+                  // already do). Without this, previewing German played
+                  // German audio over, say, Bengali segment text.
+                  const st = useAppStore.getState();
+                  st.setDubLang(label);
+                  st.switchDubLangCode(code);
+                }}
                 title={trackTooltip(code)}
               >
                 {label}

frontend/src/test/dubPreviewTabTranscriptSync.test.jsx

@@ -0,0 +1,99 @@
+import React, { createRef } from 'react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/react';
+import i18n from '../i18n';
+
+// Preview-tab ↔ transcript sync: clicking a dubbed-language pill on the
+// Export step must ALSO switch the segment texts to that language (the P1.2
+// per-language translations store) — previously the tabs only swapped the
+// video, so previewing German played German audio over Bengali segment text.
+
+vi.mock('../components/WaveformTimeline', () => ({ default: () => <div data-testid="wf" /> }));
+vi.mock('../components/MultiLangPicker', () => ({ default: () => <div data-testid="mlp" /> }));
+vi.mock('react-hot-toast', () => ({
+  default: { error: vi.fn(), success: vi.fn(), loading: vi.fn() },
+}));
+const dubListTracks = vi.hoisted(() => vi.fn());
+vi.mock('../api/dub', () => ({ dubListTracks: (...a) => dubListTracks(...a) }));
+
+import DubLeftColumn from '../components/dub/DubLeftColumn';
+import { useAppStore } from '../store';
+
+const t = i18n.t.bind(i18n);
+
+function makeProps(over = {}) {
+  return {
+    hasDubbedTrack: true,
+    t,
+    i18n,
+    previewMode: 'bn',
+    setPreviewMode: vi.fn(),
+    dubTracks: ['bn', 'de'],
+    videoSrc: '',
+    waveformRef: createRef(),
+    dubJobId: 'job1',
+    dubSegments: [{ id: '1', text: 'hi' }],
+    timelineOnsets: [],
+    timelineSelSegId: null,
+    setTimelineSelSegId: vi.fn(),
+    incrementalPlan: null,
+    segmentMoveResize: vi.fn(),
+    segmentDelete: vi.fn(),
+    onTimelinePreviewSegment: vi.fn(),
+    dubStep: 'done',
+    dubProgress: { current: 0, total: 0, text: '' },
+    fmtDur: (s) => `${s}s`,
+    genElapsed: 0,
+    genRemaining: null,
+    speakerClones: {},
+    setDubSegments: vi.fn(),
+    profiles: [],
+    settingsOpen: false,
+    setSettingsOpen: vi.fn(),
+    dubLang: 'Bengali',
+    dubLangCode: 'bn',
+    translateQuality: 'fast',
+    activeEngineUnavailable: false,
+    translateProvider: 'google',
+    dubInstruct: '',
+    setDubInstruct: vi.fn(),
+    handleTranslateAll: vi.fn(),
+    isTranslating: false,
+    editSegments: vi.fn(),
+    ...over,
+  };
+}
+
+beforeEach(() => {
+  dubListTracks.mockResolvedValue({ tracks: {} });
+  useAppStore.setState({
+    dubLangCode: 'bn',
+    dubLang: 'Bengali',
+    dubSegments: [
+      {
+        id: '1',
+        text: 'বাংলা লাইন',
+        text_original: 'the original line',
+        translations: { bn: 'বাংলা লাইন', de: 'die deutsche Zeile' },
+      },
+    ],
+  });
+});
+
+describe('preview tab → transcript language sync', () => {
+  it('clicking a language pill swaps segment text to that language', () => {
+    render(<DubLeftColumn {...makeProps()} />);
+    fireEvent.click(screen.getByRole('radio', { name: /german|deutsch/i }));
+    const st = useAppStore.getState();
+    expect(st.dubLangCode).toBe('de');
+    expect(st.dubSegments[0].text).toBe('die deutsche Zeile');
+    // Outgoing language snapshotted, not lost.
+    expect(st.dubSegments[0].translations.bn).toBe('বাংলা লাইন');
+  });
+
+  it('the Original pill leaves the editing language untouched', () => {
+    render(<DubLeftColumn {...makeProps()} />);
+    fireEvent.click(screen.getByRole('radio', { name: /original/i }));
+    expect(useAppStore.getState().dubLangCode).toBe('bn');
+  });
+});