Detect the language once for auto-detect file passes on the chunked path (D-053)

Transformers.js has no Whisper language detection and silently decoded
Danish as English whenever "Skip silence" was off or unavailable.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/WorkBreakdown.md

@@ -441,7 +441,7 @@ Found in spec 001 workstream 6 (D-046), open:
       this repo has.
 
 Found while building the long-form pipeline (spec 001 Goal 3, D-049), 2026-10-29:
-- [ ] "Auto-detect" on the default (chunked) file path does not detect: with no
+- [x] "Auto-detect" on the default (chunked) file path does not detect: with no
       `language`, Transformers.js 4.2 logs "No language specified - defaulting to
       English" and decodes Danish audio as an English translation (da_festuge WER
       0.94 vs 0.14 with `da`). Long-form ("Skip silence") detects once and pins
@@ -449,6 +449,11 @@ Found while building the long-form pipeline (spec 001 Goal 3, D-049), 2026-10-29
 - [ ] Spec 001's measurement fallback mentions a hint list of the names in
       `en_alien`'s reference; `tests/meetingFixture.ts` returns audio + reference
       only. Add the list when the vocabulary hint (workstream 2) lands.
+      — Fixed for file passes: detect once on the first 30 s and pin (D-053).
+- [ ] "Auto-detect" on **live** passes (browser engine) still decodes as English:
+      each live pass would need its own detection (an extra encoder run per
+      pass). Needs a once-per-session design (detect on the first committed
+      segment, then pin) — D-053.
 
 - [ ] Parakeet v3 also transcribes 24 other European languages, Danish included, but the app
       offers it English-only (spec 001) — unmeasured on `da_festuge`. Candidate for a later spec.