fix(session): abort-safe stream processing and resilient cleanup

[ESRE-dev]

Issue for this PR

Closes#20094

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Fixes three tightly related session processor correctness problems:

1. Abort-safe stream iteration

   • Replaces the blocking stream iteration pattern with an abort-race loop so cancellation can interrupt pending iterator waits immediately.

2. Resilient cleanup finalization

   • Wraps cleanup-time snapshot patching in error handling, so snapshot failures do not skip message/session finalization.

3. Abort-aware doom-loop permission wait

   • Races doom-loop permission prompts against abort so cancellation cannot be blocked by a pending prompt.

This PR is intentionally scoped to stream-loop and cleanup correctness in session/processor.ts.

Related (not duplicates):

• [BUG] Session cancel races cause lost cancels, stale aborts, and dangling waits #20095 (cancel lifecycle + dangling waits)
• [FEATURE]: Runtime watchdog for stuck tool/session recovery (complements #19023 startup recovery) #20099 (runtime watchdog)

How did you verify your code works?

• Added and ran packages/opencode/test/session/iterator-cleanup.test.ts to validate iterator abort and cleanup behavior.
• Ran targeted session reliability tests in the same area (cancel/watchdog/processor paths).
• Manually verified finalization still runs when snapshot patching throws.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

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[github-actions]

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[ESRE-dev]

Closing: Obsoleted by upstream Effect/Stream migration

This PR is no longer needed. The upstream codebase has undergone a major architectural migration to Effect/Stream/Runner that addresses all the race conditions this PR targeted. Our PR branches forked from 0bbf26a1ce (Mar 20) and were pushed Mar 30 — the same day the final migration commit landed, making them effectively obsolete before they were even reviewed.

Upstream commits that supersede this PR

Commit	Date	Description
860531c275	Mar 28	refactor(session): effectify session processor (#19485) — Replaces raw for await iteration with Effect/Stream (Stream.tap → Stream.runDrain), making stream interruption native via Fiber.interrupt. The cleanup() function handles all dangling state (currentText, reasoningMap, pending tool parts).
c5442d418d	Mar 30	refactor(session): effectify SessionPrompt service (#19483) — Introduces the Runner state machine with SynchronizedRef-based atomic state transitions. Runner.cancel → Fiber.interrupt propagates cleanly through the stream processing chain.

What this PR did vs what upstream now handles

Our fix	Upstream solution
Promise.race([iter.next(), aborted]) to prevent for await hang	Effect/Stream with Stream.runDrain — interruption is native via Fiber.interrupt
abortChildren() to kill child tool fibers	cleanup() in processor.ts marks all pending tools as error on abort
sweep() for dangling state	cleanup() handles currentText, reasoningMap, and pending tool parts

Related: #20095, #20094
Superseded by: #19485, #19483