fix(agent): surface retries and honor Retry-After

[GitGeniusX]

Summary

When a provider turn fails transiently, the harness currently stays silent until the full retry budget is exhausted. For Azure Foundry that can leave a healthy, online agent visibly unresponsive for about 25 minutes. The generic OpenAI-compatible transport also ignores the provider's Retry-After hint on HTTP 429, so its three attempts can land inside the same throttle window.

This change:

• posts one immediate user-visible notice on the first generic retry, while preserving the existing final dead-letter notice
• suppresses repeated notices on later exponential-backoff attempts
• honors bounded Retry-After hints on the generic OpenAI-compatible transport used by Azure Foundry, falling back to existing jittered backoff
• logs only the retry delay metadata, not response content

Related issue

Closest existing issue: #5196. Related: #5557 and #5918 / #5975.

This is complementary rather than duplicate work: #5557 is the relay HTTP publish path; this PR changes the buzz-agent provider transport. #5975 parks recognized multi-hour subscription-limit errors; this PR gives immediate feedback for the generic retry path and does not change retry/dead-letter policy.

Testing

• regression test proves the generic OpenAI-compatible transport waits for Retry-After before its successful retry
• queue regression test proves the first-failure counter increments and resets after completion
• cargo test -p buzz-agent -p buzz-acp
• cargo clippy -p buzz-agent -p buzz-acp --all-targets -- -D warnings
• cargo fmt --all -- --check
• full just ci (workspace lint/tests, desktop, web, Tauri, and 1,465 mobile tests)

No desktop or mobile UI changes.

Follow-up

After merge and an upstream image release, downstream deployments can pin the released digest; no deployment-specific fork is required.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Surface the first recently-active hard-timeout retry

When the first failure is TimeoutKind::Hard { recently_active: true }, the preceding branch requeues the batch without posting the new notice. Because that increments the channel's retry count, this check also suppresses the notice if a later attempt fails through the generic branch. Repeated recently-active hard timeouts can therefore leave the user without feedback until final dead-lettering, contrary to the change's retry-visibility goal; emit the one-shot notice for this retry path as well or track notice delivery separately from the retry count.

AGENTS.md reference: AGENTS.md:L13-L18

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