fix(export): disambiguate export filenames with generation id

[ivancorsetti]

Problem

Export filenames are derived from only the first 30 characters of the generation text:

• backend/routes/history.py — Content-Disposition for /history/{id}/export-audio ({text}.wav) and /history/{id}/export (generation-{text}.voicebox.zip)
• app/src/lib/hooks/useHistory.ts — the filename passed to platform.filesystem.saveFile in both export hooks

When iterating on the same line — a very common workflow — generations share the same 30-char prefix and therefore get identical filenames. Exporting several of them collides on disk: the browser appends (1)/ (2), and users end up opening audio that doesn't match the filename, which looks like the app exported the wrong audio.

Reproduction

Two distinct generations whose text both starts with "Martina se fai la brava stasera puoi rientrare domani…":

Generation	Size	md5	Filename (before)
95ac48a0…	311 KB	63967a68…	Martina se fai la brava staser.wav
4ed9b3cc…	200 KB	0c404d44…	Martina se fai la brava staser.wav

Different audio, identical filename.

Fix

Append the first 8 characters of the generation id to the .wav and .voicebox.zip export filenames, in both the backend Content-Disposition headers and the frontend save-file hooks.

After the fix:

95ac48a0 -> Martina se fai la brava staser-95ac48a0.wav
4ed9b3cc -> Martina se fai la brava staser-4ed9b3cc.wav

Testing

• Verified both /export-audio and /export now return unique Content-Disposition filenames for the colliding pair above, against a running backend.
• tsc -p app/tsconfig.json --noEmit — passes.
• biome lint on the changed file — clean.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Exported Voicebox ZIP and WAV files now include a unique identifier in their filenames.
  • Prevented files from being unintentionally overwritten when exports have similar text or names.

[coderabbitai]

📝 Walkthrough

Walkthrough

Export filenames for voicebox ZIP and audio WAV downloads now combine sanitized text prefixes with the first eight characters of each generation identifier in both frontend and backend history flows.

Changes

Export filename generation

Layer / File(s)	Summary
Add generation identifiers to export filenames backend/routes/history.py, app/src/lib/hooks/useHistory.ts	ZIP and WAV filenames now append generation_id[:8] or its frontend equivalent to the sanitized, truncated text prefix.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding generation-id suffixes to export filenames to avoid collisions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

app/src/lib/hooks/useHistory.ts (1)

50-57: 🎯 Functional Correctness | 🔵 Trivial | ⚡ Quick win

Keep frontend and backend filename sanitization consistent.

The frontend replaces invalid characters with - and lowercases the text, while backend/routes/history.py removes invalid characters and preserves case. The same export can therefore receive different filenames depending on the download path. Reuse a shared convention or explicitly document that these names intentionally differ.

Also applies to: 78-85

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@app/src/lib/hooks/useHistory.ts` around lines 50 - 57, Align the filename
sanitization in the frontend export logic around safeText and filename with the
backend history route’s convention, so both download paths produce identical
names. Reuse a shared sanitization rule where available; otherwise update the
frontend transformations to match the backend behavior and apply the same change
to the additional filename construction.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@app/src/lib/hooks/useHistory.ts`:
- Around line 50-57: Align the filename sanitization in the frontend export
logic around safeText and filename with the backend history route’s convention,
so both download paths produce identical names. Reuse a shared sanitization rule
where available; otherwise update the frontend transformations to match the
backend behavior and apply the same change to the additional filename
construction.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 636d2ac9-d944-49e3-82f1-9c709cc7b422

📥 Commits

Reviewing files that changed from the base of the PR and between 52f8d8d and 9af22ab.

📒 Files selected for processing (2)

• app/src/lib/hooks/useHistory.ts
• backend/routes/history.py