[Bug]: Grok thread stays running forever after t3_worktree_handoff; later messages stay queued #35274

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Fresh T3 home, Grok provider enabled, a git project.
2. Start a Grok thread and let one turn finish.
3. In the next turn, ask the agent to call t3_worktree_handoff with no continuationPrompt.
4. After the tool returns, send another message.

Expected behavior

The hand-off turn ends, as it does for Codex since #24545, and the next message runs in the new worktree.

Actual behavior

The worktree is created and bound to the thread, but the hand-off run never settles. The thread stays running with the hand-off run active, and every later message stays queued. I watched it for 30+ minutes, reproduced on 3 of 3 fresh threads.

The same test with other providers on the same server:

From the server trace, in this order:

1. mcp.tool.t3_worktree_handoff succeeds.
2. ProviderSessionManager.detach runs. Inside it, AcpAdapterV2.interruptTurn exits Interrupted after about 1.6 s while session/close succeeds.
3. The run's event stream then fails with ProviderAdapterEventStreamError … Workspace changed., logged as "orchestration V2 provider event ingestion failed".
4. The ingestion-failure handler in RunExecutionService.ts (around line 1734) calls session.interruptTurn again with requestRuntimeRestart: true before writing the failed terminal. That second AcpAdapterV2.interruptTurn span never ends, so the terminal write after it never runs.

My guess, which I haven't verified: the first interrupt is cut off while it holds runtimeTransitionPermit, or its transition fiber is forked into the session scope the detach just closed. The second interrupt then waits on the permit forever. Claude and Muse don't hang because their interrupts return, as a success or a failure.

Impact

Major degradation or frequent failure

Version or commit

main at e9e934bb3d, also 65c0195b46

Environment

macOS (Darwin 25.2, arm64), Node 24.18.1, Grok CLI 1.0.77, model grok-4.7-build-fast, full access. Isolated dev server (vp run dev --home-dir <tmp> --no-seed), threads driven with t3 thread start/send.

Logs or stack traces

WARN orchestration V2 provider event ingestion failed
  RunExecutionIngestError: Failed while ingesting orchestration V2 run execution run:thread:mcp%3A…:ordinal:2.
  [cause]: ProviderAdapterEventStreamError: Failed while streaming grok provider session … events.
    [cause]: Error: Workspace changed.

Workaround

None found. I didn't try Stop.

Related: #22971 (the same hand-off ends failed for Claude), #24545 (the fix for Codex), #22825 (a draft that waits for the turn's terminal on detach).