Keep captions moving.

Reuse the caption engine between yaps and recover from startup failures automatically.

In this release

Improved
A healthy caption engine stays available while the app is in the foreground instead of expiring after 30 seconds. Backgrounding or disabling captions releases it.
Recovery
Caption startup gets one delayed automatic recovery attempt. Repeated failures stop launching workers for each clip, while completed captions remain saved.
Diagnostics
Reports track engine starts and stops and distinguish memory allocation, growth, and access errors.
Validation
222 tests and real desktop browser transcription checks pass. Consecutive-yap testing on affected iPhones remains necessary.