fix: v3.5.10 — engine fallback installer (#39), German AI-analysis, install heartbeat

[DozaVisuals]

Reliability fixes for the issues that surfaced right after v3.5.9 — the open GitHub issue #39 plus the two follow-ups from the Reddit thread (install hang, AI-analysis empty results). Root-caused with a multi-agent investigation + adversarial verification; ships only the load-bearing fixes (a couple of initially-proposed changes were dropped after verification flagged one as a regression and one as targeting an unreachable path).

1. #39 — "No transcription engine found" (the open issue)

English jobs try Parakeet first. When Parakeet crashes/fails on a file (the issue #23 Metal-crash class — certain MXF/AVC and some mp4 inputs), it falls back to WhisperX/Whisper, which isn't bundled on a fresh DMG. That dead-ended with a bare pip install … 500 and no in-app installer — the same dead-end class as #36, but for English.

• app.py /transcribe except handler now offers the same on-demand Whisper installer for any language once every engine is exhausted (gated on the No transcription engine found signal and _whisper_ready()), and keeps the project at status='uploaded' so the banner survives a reload.
• The pre-flight guard is deliberately left English-bypassed (English may still succeed via Parakeet).
• Frontend banner copy is now language-agnostic (English users were being told their audio was "non-English").

Once the user installs Whisper once, future Parakeet crashes silently fall back to it — no more dead-end.

2. AI Analysis "produced no results" on German / long interviews

Ollama (format='json') truncates output at num_predict (done_reason='length'); token-verbose languages (German ≈ 40–50% more tokens for the same verbatim quotes) overflow routinely. _repair_truncated_json was closing braces at the raw cut point, leaving a dangling key/value → invalid JSON → the whole reply (including its complete leading items) was discarded → all categories empty → the misleading "the model may need to be restarted" message (a restart never helped).

• Rewrote _repair_truncated_json to rewind to the last fully-formed element of the deepest still-open container and close the rest — every complete item survives, only the half-written trailing one is dropped. Idempotent on valid JSON.
• Raised the analysis num_predict ceiling 4096 → 8192 so most passes never truncate.
• Replaced the misleading error message with an honest, actionable one.
• Guarded b-roll partials (no timecode → skip).

3. Install stuck on "Starting install…"

The installer's progress only updated on a newline boundary, so pip piped to a non-TTY and the ~1.6 GB model download could go quiet for minutes inside a blocking read, leaving the banner frozen.

• Background heartbeat in _stream_subprocess (elapsed clock) that runs independently of the read, so the banner always moves while the worker is alive.
• elapsed field on the status poll; frontend shows it and surfaces "lost contact" after repeated poll failures instead of freezing silently.

4. Hardening (from the completeness audit)

An interrupted model download leaves a truncated large-v3-turbo.pt at the final path, which the filename-only check reported as "ready" (re-introducing the #13/#36 silent-redownload symptom).

• _whisper_model_cached() now requires a full-size file (≥1.5 GB floor).
• The worker deletes the undersized partial on failure so "Try again" re-downloads cleanly.

Tests

• tests/test_whisper_install_guard.py: English no-engine → installer; non-engine English errors still 500; model size-floor rejects truncated .pt; install heartbeat fires during a quiet child.
• tests/test_json_repair.py (new): all canonical truncation shapes parse, complete items survive, nested arrays preserved, valid JSON untouched, end-to-end through _parse_json_response.

All new/extended tests pass. The 18 pre-existing failures on main (chat-prompt / editorial-DNA suites) are unrelated to this change and reproduce on the base branch.

Note: the actual 3.5.10 DMG still needs the local signed/notarized build + GitHub release.

🤖 Generated with Claude Code

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Status	Name	Latest Commit	Updated (UTC)
❌ Deployment failed View logs	doza-assist	ae7606c	Jun 09 2026, 03:30 PM