fix(acp): child/subagent session permission requests no longer hang forever

[aiken884]

Issue for this PR

Closes #12133

Type of change

• Bug fix

What does this PR do?

Child sessions spawned server-side by the task tool are never registered in the ACP session store (only session/new/load/resume/fork register one). When such a session raises a permission.asked event, acp/permission.ts's Handler.process() calls session.tryGet() on that unregistered id, gets undefined, and just returns — the underlying Permission.ask Deferred is never resolved, so under an "ask" ruleset the whole session/prompt call hangs forever.

This is exactly #12133. That issue shows as closed via #13222, but #13222's actual diff (util/git.ts, snapshot/index.ts) fixes a Windows-only git-subprocess stdin-inheritance deadlock — it never touches acp/permission.ts or acp/session.ts. The PR description lists several "ACP hangs forever" issues together and #12133 looks like it got swept into that list without the actual root cause being addressed. I hit the same hang on current dev with a real subprocess.

Fix: resolveAncestor() (new, in acp/session.ts) walks the SDK's parentID chain for a session id that isn't in the ACP store, until it finds an ancestor that is registered. permission.ts's Handler.process() uses this instead of a bare tryGet(), so a child session's permission ask still routes through the connection. If no ancestor can be resolved at all, it now replies with an active reject instead of silently returning, so the Deferred is never left hanging either way.

How did you verify your code works?

Added test/cli/acp/child-session-permission.test.ts: drives a real opencode acp subprocess through a task-tool delegation under an edit:"ask" ruleset and asserts the session/prompt call resolves instead of hanging. Confirmed it fails (20s timeout) on dev without this change, passes (~2.5s) with it.

Also reproduced this against real acpx + a real model outside the test suite: with a strict permission policy, the model chose on its own to delegate a file-write to a Task subagent, and the whole invocation hung past a 90s timeout with the same symptom.

Ran the full existing acp + permission suite (249 tests) — all pass, no regressions. tsgo --noEmit clean.

Checklist

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

[roamiiing]

Independent confirmation from another ACP client integration.

Environment:

• OpenCode 1.15.10 and 1.17.11
• macOS arm64
• ACP protocol v1
• No relevant plugins

I reproduced this deterministically with:

OPENCODE_PERMISSION='{"*":"ask","task":"allow"}' \
  opencode acp --print-logs

The ACP client:

1. initializes and creates a session;
2. sends a prompt that starts exactly one explore task;
3. asks the child to read a file inside the session cwd;
4. automatically approves every session/request_permission that reaches the wire.

task: allow ensures that the parent task itself does not require permission. The wildcard ask ensures that the child read does.

Observed on both 1.15.10 and 1.17.11:

• the child session is created with parentID=;
• stderr reaches permission=read ... asking for the child;
• the ACP wire receives zero session/request_permission calls;
• session/prompt remains pending until explicitly cancelled.

Result from both runs:

  {
    "childReadAskObserved": true,
    "parentPermissionRequestCount": 0,
    "childPermissionRequestCount": 0,
    "promptSettledBeforeCancel": false,
    "routing": "missing-from-acp-wire"
  }

This independently confirms that #12133 is still reproducible and was not fixed by #13222. The resolveAncestor() approach in this PR targets the exact failing path.

It would also be useful to keep coverage for nested subagents and simultaneous permission requests from multiple children sharing the same ACP parent.