🤖 fix: stabilize retry barrier visibility and manual retry feedback

[ibetitsmike]

Summary
This PR stabilizes the bottom-of-chat retry UI by keeping the Retry barrier visible across auto-retry start/fail loops, and adds immediate manual-click feedback for the Retry button so users get instant acknowledgement before stream events arrive.

Background
The retry footer could still visually churn when retry attempts toggled stream-start without visible output yet. Separately, manual Retry clicks had no immediate pending state for non-auto-retryable errors, which made the button feel unresponsive until backend events landed.

After adding manual pending state, we found a remaining UX jump: clicking Retry briefly removed the error-details row because manual retry clears retryState.lastError immediately, shrinking the yellow box before it re-expanded on the next failure.

Implementation

• ChatPane
  • Reads persisted retry attempt state via getRetryStateKey(...).
  • Computes retry visibility using getInterruptionContext(...) plus shouldKeepRetryBarrierVisibleDuringRetry(...).
  • Keeps retry barrier visible during retry-loop stream starts (before visible token output).
  • Suppresses StreamingBarrier whenever retry barrier UI is active to avoid footer swapping.
• RetryBarrier
  • Adds a local isManualRetryInFlight state for immediate click feedback.
  • Shows spinner + Retrying... label and temporarily disables the manual Retry button.
  • Keeps the most recent error details visible while manual retry is pending, so the banner height stays stable instead of collapsing/re-expanding.
  • Clears the local pending state when retry transitions into normal auto-retry UI, stream start, or a new error state.
• retryEligibility
  • Uses the sticky retry predicate to keep the banner stable through retry-loop TTFT gaps.

Validation

• bun test src/browser/utils/messages/retryEligibility.test.ts
• make static-check

Risks

• Low-to-moderate UI-state risk in chat footer transitions.
• Scope is constrained to retry/stream barrier presentation logic and manual retry button state.
• Existing retry eligibility tests cover sticky-visibility paths; static checks are green.

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[chatgpt-codex-connector]

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[ibetitsmike]

@codex review

Addressed the TTFT regression by restoring the !canInterrupt gate for the hasInterruptedStream(...) branch and expanding the retry-sticky predicate to cover the common case where no assistant DisplayedMessage exists until the first delta.

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Codex Review: Didn't find any major issues. Can't wait for the next one!

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