[JoaoMarcos44]

Summary

• Prevents overflow promotion when the interrupt recursion cap will defer the current pending event.
• Requeues the pending event through the FIFO path instead of the single-slot overwrite helper.
• Preserves normal promotion when recursion is allowed.
• Adds a regression proving all queued events survive in order.

Problem and impact

The gateway queue uses one adapter slot for the head and SessionState.conversation.queued_events for overflow. At the recursion ceiling, the drain path could lose the next queued message permanently while later messages still ran, creating both data loss and order inversion.

Root cause

The drain popped the overflow head into the adapter slot before checking _MAX_INTERRUPT_DEPTH. The cap branch then called merge_pending_message_event(..., merge_text=False), whose text-only fallback assigns into the slot and overwrites the promoted event.

Implementation decision

When the recursion cap will defer the current event, promotion is deferred too. The current event is then placed back through _enqueue_fifo, leaving the overflow tail untouched. This preserves the existing normal path and avoids merging separate user turns.

Scope and compatibility

• Normal queue promotion is unchanged when recursion is below the cap.
• The fix applies to the drain/re-entry boundary and complements the input-side FIFO fix for Bug: busy_input_mode: queue silently drops messages — single-slot overwrite instead of FIFO #28503.
• No sleeps or timing assumptions are used in the regression.

Files

• gateway/run.py
• tests/gateway/test_queue_consumption.py

Verification

• Local: scripts/run_tests.sh tests/gateway/test_queue_consumption.py -q → 6 passed.
• Local ruff check: passed.
• Local git diff --check: passed.
• Remote required checks: passed at last verification.
• The real pre-fix reproduction lost msg2 from [msg1, msg2, msg3, msg4]; the regression now preserves the full FIFO chain.

Fixes #93871

[alt-glitch]

This was generated by AI during triage.

Duplicate of #78015: both repair the recursion-cap promotion path that overwrites a promoted FIFO event and loses a queued turn.