Investigate the Safari-only "Lost connection to the AI provider" mid-stream
disconnect (Chrome unaffected). Pure instrumentation, no behavior change:
the 15s heartbeat interval and all stream callbacks are unchanged.
- sse-resilience.ts: startSseHeartbeat() gains an optional onBeat hook fired
after each successfully written ping (beat counter).
- ai-chat.service.ts: track stream start, first-chunk latency, model-silent
gap and heartbeat count; log them on finish/error/abort to classify the
drop (idle-gap vs hard wall-clock cap vs slow first chunk).
- ai-chat.controller.ts: append elapsed-since-request to the disconnect warn.
All blocks tagged "DIAGNOSTIC ... temporary" for easy removal once the Safari
failure mode is identified.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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