The previous PR (#22993) gave us a structured WARNING per stream drop
but the only diagnostic was 'error_type=APIError error=Network
connection lost.' — same nothing the user started with. To actually
diagnose why subagents drop streams disproportionately we need to know
WHERE the drop happened.
Adds three breadcrumbs to the agent.log WARNING:
1. Inner exception chain. openai SDK wraps httpx errors as
APIConnectionError / APIError so the catch site only sees the
wrapper. _flatten_exception_chain walks __cause__/__context__ up to
4 levels deep and renders 'Outer(msg) <- Inner(msg)' so we can
tell ConnectError vs RemoteProtocolError vs ReadError vs
ProxyError without enabling verbose mode.
2. Upstream HTTP headers. Snapshots cf-ray, x-openrouter-provider,
x-openrouter-model, x-openrouter-id, x-request-id, server, via,
etc. from stream.response immediately after open (so they survive
even when the stream dies before the first chunk). These answer
'is one CF edge / one downstream provider responsible, or random?'
3. Per-attempt counters. bytes streamed, chunk count, elapsed time on
the dying attempt, and time-to-first-byte. Distinguishes 'couldn't
connect at all' (0s, 0 bytes) from 'died after 30s mid-stream'
(very different root causes — first is auth/routing, second is
upstream idle-kill or proxy timeout).
Plumbing:
- _stream_diag_init / _stream_diag_capture_response live on AIAgent
and produce a per-attempt dict held on request_client_holder['diag']
for closure access from the retry block.
- _call_chat_completions and _call_anthropic both initialize the diag
and increment counters per chunk/event (best-effort, never raises in
the streaming hot path).
- _log_stream_retry / _emit_stream_drop accept an optional diag and
render the new fields. Final-exhaustion log goes through the same
helper so it gets the same diagnostic dump.
- UI status line gains a brief 'after Xs' suffix when timing is
available — distinguishes 'connect failed' from 'died mid-stream'
at a glance without grepping logs.
Sample WARNING after this change:
Stream drop mid tool-call on attempt 2/3 — retrying.
subagent_id=sa-2-cafef00d depth=1 provider=openrouter
base_url=https://openrouter.ai/api/v1
error_type=APIError error=Connection error.
chain=APIError(Connection error.) <- RemoteProtocolError(peer
closed connection without sending complete message body)
http_status=200 bytes=12400 chunks=47 elapsed=12.00s ttfb=0.83s
upstream=[cf-ray=8f1a2b3c4d5e6f7g-LAX
x-openrouter-provider=Anthropic
x-openrouter-id=gen-abc123 server=cloudflare]
Tests: 10 covering diag init, header capture (whitelist enforced for
PII), exception-chain walking + depth cap, log content with full diag,
log content without diag (placeholders), UI elapsed-suffix on/off.
126cbffb8a