Closes#50185
Two independent gaps let a transient Photon/Spectrum upstream overflow
degrade message delivery and amplify gRPC pressure:
1. _is_retryable_error did not recognise Photon- or Envoy-specific error
strings ("internal sidecar error", "upstream connect error",
"reset reason: overflow"), so _send_with_retry fell through to the
plain-text fallback immediately instead of backing off and retrying.
2. send_typing had no rate gate, so a burst of typing-indicator calls
during an overflow event kept hitting the upstream gRPC connection and
widened the failure window.
Fix:
- Add _PHOTON_RETRYABLE_PATTERNS with the three high-specificity Envoy /
sidecar substrings and override _is_retryable_error on PhotonAdapter to
check them after delegating to the base-class patterns. base.py and all
other adapters are untouched.
- Add a 5 s per-chat cooldown in send_typing backed by _typing_last_sent.
stop_typing clears the entry so the next start after a completed turn
fires immediately — only rapid consecutive starts without a stop are
suppressed.
- Reduce PhotonAdapter._send_with_retry default max_retries from 2 to 1
(single 2 s back-off check) — enough to confirm whether the Envoy
circuit-breaker has opened, without adding unnecessary latency.
All changes are scoped to plugins/platforms/photon/adapter.py.
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