fix(server): stop a hung provider interrupt from blocking every other command

[tachytelicdetonation]

Refs #12136.

A provider interrupt that never settled held the shared command worker, leaving later turns on other threads or providers pending. Interrupts now run in a managed FiberSet, following the existing sendTurn pattern, so the worker can continue processing commands. The test-only drain still waits for interrupts and their recovery.

Recovery checks session identity before applying lifecycle changes and again after awaiting stopSession, so a late failure cannot overwrite a replacement session. Failures while recording recovery state or activity are logged.

This addresses the shared-worker barrier from the issue triage. The adapter's unbounded OpenCode cancellation is a separate concern tracked by #12003.

Verification

• All 75 ProviderCommandReactor tests pass; server typecheck passed and targeted lint found no new issues.
• The hanging-interrupt regression failed before the worker change and passes with it: a second thread reaches provider startup and delivery while the first interrupt remains pending.
• Three review regressions failed before 244076098 and pass after it: replacement during stopSession, session persistence failure during recovery, and activity persistence failure during recovery.

Server-only change; no UI screenshots required.

Original implementation: Claude Fable 5.1 in Claude Code. Review fixes and verification: GPT-6 in Codex.

Summary by CodeRabbit

• Bug Fixes

  • Improved provider interrupt handling so delayed or failing interrupts no longer block session startup or turn delivery on other threads.
  • Prevented late interrupt failures from affecting replacement sessions on the same thread.
  • Ensured the correct session is stopped after lifecycle updates, while preserving newer sessions.
  • Ensured pending interrupts finish processing before shutdown or draining completes.
  • Logged failures encountered while recovering interrupted sessions.

• Tests

  • Added regression coverage for concurrent interrupts, session replacement, lifecycle updates, and recovery failures.

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a focused server-side bug fix that moves hanging provider interrupts off the shared command worker while preserving drain tracking, with live regression coverage for unrelated-thread progress. An unresolved high-severity finding identifies a possible same-thread stale recovery race, leaving a material correctness risk for separate resolution.

Not approved because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

^{Adjust the Minimum Blocking Severity for this repo — including turning it Off — in Settings. You can add or adjust custom eligibility rules. Learn more.}

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Reviewing files that changed from the base of the PR and between 6ed3a90 and 2440760.

📒 Files selected for processing (2)

• apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
• apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

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📝 Walkthrough

Walkthrough

The reactor now runs provider interrupts outside the shared command worker, waits for them during drain, and uses session identity changes to handle late interrupt failures. Tests cover concurrency, session replacement, lifecycle rewrites, and recovery-failure logging.

Changes

Provider interrupt execution

Layer / File(s)	Summary
Detached interrupt execution apps/server/src/orchestration/Layers/ProviderCommandReactor.ts, apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts	Provider interrupts run in a dedicated FiberSet. drain waits for pending interrupts. Tests verify that a pending interrupt does not block work on another thread.
Session race protection and validation apps/server/src/orchestration/Layers/ProviderCommandReactor.ts, apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts	Recovery checks provider instance, active turn, and restart changes instead of updatedAt. Tests verify protection of newer sessions, replacement during stopping, and recovery after an updatedAt-only rewrite.
Recovery failure logging apps/server/src/orchestration/Layers/ProviderCommandReactor.ts, apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts	Non-interrupt recovery failures are logged without escaping the interrupt fiber. Tests inject persistence failures and verify the log message contains the thread id and error.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant ThreadA
  participant ProviderCommandReactor
  participant interruptFibers
  participant ThreadB
  participant SessionStore
  ThreadA->>ProviderCommandReactor: Request provider interrupt
  ProviderCommandReactor->>interruptFibers: Run interrupt asynchronously
  ThreadB->>ProviderCommandReactor: Start session and send turn
  interruptFibers-->>ProviderCommandReactor: Interrupt failure
  ProviderCommandReactor->>SessionStore: Read latest session
  ProviderCommandReactor-->>ThreadB: Preserve newer session when replaced

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Suggested reviewers: t3dotgg

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing a hung provider interrupt from blocking the shared command worker.
Description check	✅ Passed	The description explains what changed, why it changed, recovery behavior, verification results, and that UI changes do not apply. It does not reproduce the checklist headings, but it provides the requ…

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Actionable comments posted: 3

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Inline comments:
In `@apps/server/src/orchestration/Layers/ProviderCommandReactor.ts`:
- Line 1549: Update interrupt recovery around recoverInterruptFailure so it does
not use updatedAt as the OrchestrationSession identity. Capture and compare a
stable provider-session identity at interrupt time, or only skip recovery when
the captured session was replaced or stopped, ensuring stopSession and
provider.turn.interrupt.failed still execute for lifecycle timestamp updates on
the same active session.
- Around line 1608-1613: Update the interrupt handling around
ProviderService.interruptTurn and the turn-start path to track in-flight
interrupts by threadId, await the matching thread’s interrupt before calling
sendTurn, and retain concurrency for different threads. Preserve
recoverInterruptFailure handling and ensure interrupt completion is removed from
the per-thread tracking state.
- Around line 1608-1613: Update the interrupt fiber pipeline at the FiberSet.run
call to add a second catchCause after recoverInterruptFailure. Suppress causes
containing only interrupts, and log non-interrupt residual failures with
Effect.logWarning, including the threadId and a readable Cause.pretty value.

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• apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
• apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

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[tachytelicdetonation]

Fixed recovery-failure logging and a reproduced race that could overwrite a replacement session in 2440760. The three regressions fail before the fix and pass after it; all 75 reactor tests pass.