fix(cli-run): prevent premature exit when background tasks are active

[CHLK]

Summary

• Prevent opencode run from exiting prematurely when background tasks are active but no todos exist
• Use the existing run-continuation-state marker system to signal active background tasks across the process boundary
• Fix BG task status checks to include "pending" alongside "running" so queued tasks are not invisible

Problem

When running opencode run, the agent would exit immediately after dispatching background tasks because:

1. Agent dispatches background task(s) → finishes response → session.idle fires
2. checkCompletionConditions() sees no todos, no active children → returns true
3. pollForCompletion() returns exit code 0 → process exits
4. Background tasks are orphaned/aborted during shutdown

PR #217 partially addressed this but only when todos exist. The todo-continuation-enforcer returns early at idle-event.ts:110-114
when there are no todos, bypassing the background task check entirely.

Solution

File	Change
src/features/run-continuation-state/types.ts	Add "background-task" to ContinuationMarkerSource
src/features/background-agent/manager.ts	Add updateBackgroundTaskMarker() — writes/clears marker on task lifecycle events
(launch, tryCompleteTask, cancelTask, failCrashedTask)
src/cli/run/continuation-state.ts	Add hasActiveBackgroundTaskMarker field
src/cli/run/completion.ts	Check background-task marker in checkCompletionConditions()
src/hooks/todo-continuation-enforcer/idle-event.ts	Include "pending" in BG task status check
src/hooks/todo-continuation-enforcer/continuation-injection.ts	Include "pending" in BG task status check

Testing

• bun run typecheck — Pass
• bun test — 171 relevant tests pass, 0 fail
• Manual: opencode run with 1 background task — process waits for completion, exits normally
• Manual: opencode run with 2 parallel background tasks — process waits for both, agent provides final summary

Closes #3452

---

Summary by cubic

Fixes premature exit in opencode run when background tasks are active. The CLI now waits for running or pending tasks before exiting. Closes #3452.

• Bug Fixes
  • Added "background-task" continuation marker and hasActiveBackgroundTaskMarker; completion check blocks exit when active.
  • Background manager updates the marker on lifecycle and terminal paths (launch, complete, cancel, crash, start errors, non-retryable session errors, stale prune) to avoid stale markers.
  • Treats "pending" as active alongside "running" so queued tasks keep the process alive.

^{Written for commit eaa3837. Summary will update on new commits.}

[github-actions]

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_{Posted by the CLA Assistant Lite bot.}

[CHLK]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

1 issue found across 6 files

Confidence score: 3/5

• There is a concrete regression risk in src/features/background-agent/manager.ts: terminal error/interrupt paths may leave a stale active continuation marker, which can block CLI run completion.
• Given the issue is severity 7/10 with high confidence (8/10) and affects completion behavior, this is more than a minor edge case and adds meaningful merge risk.
• Pay close attention to src/features/background-agent/manager.ts - ensure all terminal exit paths clear or reconcile the continuation marker consistently.

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/features/background-agent/manager.ts">

<violation number="1" location="src/features/background-agent/manager.ts:375">
P1: The new background-task continuation marker is set on enqueue, but some terminal error/interrupt paths do not update it, which can leave a stale `active` marker and block CLI run completion.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[CHLK]

Has anyone reviewed this PR? Happy to help test or document it.

[mrosnerr]

When task-poller.ts cancels a stale task, it mutates task.status directly but never calls updateBackgroundTaskMarker(). If that was the last active task, the marker stays active and checkCompletionConditions() will block exit indefinitely.

With this one additional change, I think it should be in pretty good shape to get in 👍