fix(background-agent): force-deliver parent wakes held past a stale tool-call ceiling

[andrei-kiparuk]

Problem

Background-task completion notifications can be starved forever by the stale tool-call deferral, leaving a fully idle parent session that never resumes work.

When the latest assistant turn in the parent session ends with an unresolved tool part, getParentWakeSessionHistoryDeferralDecision holds the wake (admitting it as a noReply deposit at most) and waits for "the idle/consumption machinery" to resume. That is correct while the turn is genuinely mid-flight, but there is no upper bound on the hold. If the blocking tool part can never resolve — e.g. a bash tool left at state.status: "running" after its stream died mid-tool — the state is permanent:

• the zombie assistant turn keeps latestAssistantTurnBlocksInternalPrompt true forever,
• every future flush hits deferReplyWakeWhileUnsafe and reschedules,
• no new internal prompt (or anything else) ever starts a stream again.

Observed in production

From a single real session (ses_fda080e47…):

[20:39:42] Sent deferred parent wake
[20:39:47] Requeued dispatched parent wake after no assistant output (retryCount: 1)
[20:39:48] Sent deferred parent wake
[20:39:52 → 20:52:46+] Holding parent wake during stale tool-call deferral   ← every ~1s, 13+ min and counting
[20:39:52 → 20:52:46+] Deferred retained reply-required parent wake until parent session is safe

209 hold events across two sessions on one day. The session history confirmed the blocker: the latest assistant message had finish: null, 0 tokens, and exactly one part — a bash tool stuck at "running" (a gh run watch) from hours earlier. Every background task had long since completed; the parent just sat idle.

Fix

Cap the hold with PARENT_WAKE_STALE_TOOL_BLOCK_MAX_HOLD_MS (60s), wired through as an optional staleToolBlockMaxHoldMs option:

• Before the ceiling: behavior is unchanged — hold, admit-only deposits, reply liveness retained. A live-but-quiet turn (long silent tools are legitimate) still gets its full grace window, preserving the intent of the ses_14a3ab27bffe fix.
• At/after the ceiling: the wake is force-delivered (defer: false). Sixty seconds of zero activity across message time, part time, and tool-state timestamps overwhelmingly indicates a dead turn rather than a quiet one, and unbounded starvation is worse than the residual fork risk of dispatching into an idle-status session.
• toolCallDeferralStartedAt is deliberately not cleared on the escape path so the pre-dispatch confirmation re-check reaches the same decision instead of re-arming the deferral.
• No ceiling configured (undefined) preserves the historical unbounded hold for existing callers.

Also marks the admit-only/noReply wake text part as synthetic: true, so deferred notifications no longer render as raw <system-reminder> user messages in the TUI while they sit deposited during the hold window.

Test updates

Two tests in task-completion-cleanup.test.ts pinned the unbounded-hold behavior at a 60s-stale zombie tool block ("admitted as noReply with reply liveness retained"). That exact scenario is the starvation case this PR fixes, so they now assert the post-ceiling contract: force-delivered reply dispatch, pending wake consumed. Sub-ceiling admission behavior remains covered by the untouched neighboring tests plus three new cases in parent-wake-history-deferral.test.ts (held under ceiling → still held; past ceiling → delivered, including confirmation re-check convergence; no ceiling configured → historical hold preserved).

Testing

• bun test packages/omo-opencode/src/features/background-agent/ → 746 pass, 0 fail
• tsgo --noEmit -p packages/omo-opencode/tsconfig.json → clean

---

Summary by cubic

Stops indefinite starvation of background-task completion notifications by capping the stale tool-call deferral and force-delivering the parent wake after 60s. Previously we held reply-required wakes indefinitely when the last assistant turn had a zombie tool; now we hold under the ceiling and dispatch after it. Deferred noReply deposits are marked synthetic to avoid TUI noise.

• Adds optional staleToolBlockMaxHoldMs through ParentWakeNotifier and ParentWakeSessionInspector; BackgroundManager sets it to 60_000 ms. Omitting it preserves the legacy unbounded hold for other callers.
• Leaves toolCallDeferralStartedAt set on escape so pre-dispatch confirmation re-checks converge on delivery.
• Marks admit-only/noReply text parts synthetic to hide raw system-reminder messages in the TUI.
• Updates tests to expect force-delivery past the ceiling and adds history-deferral coverage.

^{Written for commit c92f51a. Summary will update on new commits.}

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[andrei-kiparuk]

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