Investigate the intermittent (~20-30%) long-turn failure
"Lost connection to the AI provider" = AI_RetryError / read ECONNRESET
on the gitmost->z.ai link (browser-agnostic, mid-turn). Pure
instrumentation, no behavior change:
- ai-http-diagnostics.ts: a passive fetch wrapper injected into the
OpenAI-compatible (z.ai) client. Per provider HTTP call it logs
time-to-headers/status on success, and on a pre-response rejection the
latency, error code/cause, request-body size and idle-gap since the
previous call. The Response is returned untouched (streaming intact),
errors rethrown unchanged; no retry/timeout/dispatcher.
- ai.service.ts: wire the instrumented fetch into the openai case only.
Lets us classify the reset as connection-phase vs mid-stream before
choosing a fix, without repeating the reverted RetryAgent (#140).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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