[Bug]: A Claude subagent waiting on its own background command or Monitor shows as finished, and its commands aren't shown #27700

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. In a Claude Agent thread, have the agent launch a background subagent: Agent with run_in_background: true (here also isolation: "worktree").
2. In the subagent, start a long shell command with Bash run_in_background: true (here a multi-minute cargo test run), arm a Monitor on it, and end the subagent's turn. The parent receives a task_notification (status completed) whose summary says the agent is "waiting on its own background work".
3. While that command is still running, look at the parent thread.
4. Send the subagent a message with SendMessage, which resumes it.

Timeline from one thread (native subagent id ae822370b88798e95, times UTC, approximate):

• 14:47: the subagent is launched as above.
• Over the next ~2 h it repeats step 2 several times; each time the parent gets a completed notification saying it waits on its own background work.
• ~16:40: Lineage shows no running subagent and there is no "Running N commands" bar. On the machine, the subagent's cargo test and several rustc processes are running, and its log file was written seconds earlier.
• ~16:46: the parent sends SendMessage. Lineage immediately lists the subagent as running, and the bar shows "Running 1 command and 1 monitor" with its new command.

Expected behavior

While a subagent has its own background commands or monitors alive, it stays shown as running (or as waiting on background work), and those commands and monitors are visible in the subagent row or in the parent's command bar.

Actual behavior

Between its turns, the subagent drops out of Lineage's running list and its background command and monitor are not shown anywhere. A subagent doing real work can't be told apart from a stalled thread with nothing running.

Impact

Minor bug or occasional failure

Version or commit

T3 Code (Beta) 0.1.5

Environment

macOS 27.0.1, desktop app, Claude Code 2.1.314, Claude Agent provider, parent claude-opus-5-5, subagent claude-haiku-5-5

Logs or stack traces

No response

Screenshots, recordings, or supporting files

No response

Workaround

Check the subagent's log files or processes on disk, or send it a message to resume it, which makes it visible again. Related: #18966 and #17625 (the same problem for whole threads, both closed), #24337 (the reverse for Claude background subagents: stuck as Running after finishing).