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fix(provider-acp): retire Copilot tasks when their runtime ends - #32476
When a Copilot ACP runtime exits or is replaced, retained background subagents can remain marked running. Reusing the same native session then carries old tasks into another runtime, and stale raw child events can route its output to an old task.
Change
Retire Copilot's carried and active native subagents at termination and before replacing their runtime, including rollback. Each task receives one interrupted update. Old callbacks are invalidated before a restart, and Copilot's raw attribution maps now belong to each runtime so replacement output cannot enter a retired task's thread.
Callback generation invalidation applies to ACP runtime restarts. Task retirement and routing isolation are specific to Copilot. Other ACP flavors retain their existing task carryover behavior; detached shell commands are untouched.
Scope and approval
This uses CONTRIBUTING.md's exception for a small, focused fix of an obvious bug: a discarded runtime must not leave its process-owned native subagents running in T3. No maintainer approval is claimed. Runtime-specific routing is needed to prevent replacement output from reaching a retired task.
Related open PR #29361 handles Devin background shells at the same lifecycle hooks, so these changes may conflict. PR #27380 handles Copilot Autopilot reply summaries and touches the same event router. Neither implements this Copilot subagent lifetime fix.
Verification
Extended the existing runtime replacement regression with termination, active-prompt termination, and rollback cases. The active-prompt case carries a subagent from the previous turn, terminates the runtime before the prompt returns, and checks immediate retirement with exactly one interrupted update. It also checks that root command tools are not interrupted by subagent retirement. A disabled-ownership row keeps tasks alive for flavors whose work can survive the transport. Removing the ownership guard makes that row fail by assertion. The termination and rollback cases failed before the earlier review fixes: termination still reported pending work through the adapter probe enabled by the fixture, and rollback omitted the interrupted task update. Both now pass. The cases check one interrupted update across retirement and the next turn, and inject an old callback while the replacement turn is active. Temporarily removing generation invalidation caused stale text to enter the replacement turn, so the callback assertion detects the regression.
The fixture enables the pending-work probe to distinguish immediate retirement from cleanup at the next turn. It uses a mock ACP subprocess for session setup, stubbed prompts and injected Copilot events. It also checks that raw child attribution cannot cross runtimes. Manual app testing and live Copilot process-termination testing were not performed.
vp run check:changed passed on e03a0e0adeae with upstream main a9e709f15f82 included. It ran 105 tests in 2 files and affected package typechecks, plus format, lint, knip and GraphQL checks.
CodeRabbit subsequently identified active-turn tasks missing from termination cleanup. An earlier shape of that regression failed before the fix because pending background work remained true. It passes with active subagents retired in the termination callback.
Independent Opus review identified missing immediate-termination and rollback cleanup, plus an ineffective callback assertion. All three were addressed. The follow-up review by Claude Opus 5.5 High found no blocking issues. It noted that the fixture enables a liveness probe that production Copilot currently does not expose; that limitation is stated above. The independent follow-up review at e03a0e0adeae found no blocking issues. Its test-name and description wording corrections are included.
Implemented by GPT-6.1 Terra High and GPT-6.1 Sol High through Codex in T3 Code. Reviewed by Claude Opus 5.5 High through Claude Code in T3 Code.
Macroscope's review found this PR approvable — Copilot task attribution is now isolated per runtime, and outstanding task statuses are retired when that runtime ends or is replaced. The change is bounded lifecycle bookkeeping, with other providers retaining their existing retirement behavior.
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No actionable comments were generated in the recent review.
Walkthrough
The adapter now scopes Copilot session attribution to the runtime that produced each notification. It retires runtime-owned subagents during termination and replacement. Tests cover termination and rollback, including stale runtime events and replacement-runtime output.
The Copilot flavor declares that subagents are runtime-owned. The adapter retires those subagents during runtime termination and replacement. Tests cover termination and rollback, including stale runtime events and replacement output.
pingdotgg/t3code#29211 — The adapter retires carried Copilot subagents when their runtime terminates or is replaced, addressing the stale running state reported when an ACP session closes. The supplied changes do not establish that the issue’s separate follow-up or session-load replay behavior is fixed.
Possibly related PRs
pingdotgg/t3code#21767 — This PR also changes runtime replacement behavior and the runtime-termination test, including cleanup and replacement semantics.
Suggested reviewers:juliusmarminge
Merge Risk: Minimal · up to 81d13
Copilot background subagents are now marked interrupted when their runtime ends or is replaced, and stale events from old runtimes are ignored. No actionable merge-blocking risk remains. Live Copilot process termination was not manually tested.
Pre-merge checks: 4
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Title check
The title names the main change: retiring Copilot background tasks when their ACP runtime ends. The raw summary and objectives confirm the changes cover runtime termination and replacement, including …
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Check skipped because no linked issues were found for this pull request.
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Description check
The description follows the repository template closely: it has Problem, Change, Scope and approval, and Verification sections, plus a model/harness attribution at the end. The Problem section states …
Full details: Title check
Explanation
The title names the main change: retiring Copilot background tasks when their ACP runtime ends. The raw summary and objectives confirm the changes cover runtime termination and replacement, including rollback. The title uses the conventional commit form and does not claim more than the changeset delivers.
Full details: Description check
Explanation
The description follows the repository template closely: it has Problem, Change, Scope and approval, and Verification sections, plus a model/harness attribution at the end. The Problem section states the bug and the expected behavior. The Change section explains the fix and why the Copilot-specific routing is needed. The Scope section cites CONTRIBUTING.md's small-fix exception, states that no maintainer approval is claimed, and names related open PRs that may conflict. The Verification section gives concrete tests, observed failures and passes, the check command with its result, and states what was not checked (manual app testing and live Copilot process-termination testing). It is long and includes some review-history narration, which a maintainer may find hard to scan, but all required sections are substantively filled. The one weak point is the scope justification: the author invokes the obvious-bug exception, which the template allows, but the change is substantial (multi-runtime attribution maps, generation invalidation, and subagent retirement in the shared adapter), so a maintainer may still question whether the exception applies. That is a reviewer judgment, not a missing section.
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Actionable comments posted: 1
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @packages/provider-acp/src/server/adapter.ts:
- Line 2322: Update the runtime termination path around retireRuntimeSubagents
so it also retires rehydrated subagents still active in the terminating prompt,
while preserving detached root commands. Add a test that terminates the runtime
during a prompt with a rehydrated subagent and verifies the subagent is no
longer running.
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Problem
When a Copilot ACP runtime exits or is replaced, retained background subagents can remain marked running. Reusing the same native session then carries old tasks into another runtime, and stale raw child events can route its output to an old task.
Change
Retire Copilot's carried and active native subagents at termination and before replacing their runtime, including rollback. Each task receives one interrupted update. Old callbacks are invalidated before a restart, and Copilot's raw attribution maps now belong to each runtime so replacement output cannot enter a retired task's thread.
Callback generation invalidation applies to ACP runtime restarts. Task retirement and routing isolation are specific to Copilot. Other ACP flavors retain their existing task carryover behavior; detached shell commands are untouched.
Scope and approval
This uses CONTRIBUTING.md's exception for a small, focused fix of an obvious bug: a discarded runtime must not leave its process-owned native subagents running in T3. No maintainer approval is claimed. Runtime-specific routing is needed to prevent replacement output from reaching a retired task.
Related open PR #29361 handles Devin background shells at the same lifecycle hooks, so these changes may conflict. PR #27380 handles Copilot Autopilot reply summaries and touches the same event router. Neither implements this Copilot subagent lifetime fix.
Verification
Extended the existing runtime replacement regression with termination, active-prompt termination, and rollback cases. The active-prompt case carries a subagent from the previous turn, terminates the runtime before the prompt returns, and checks immediate retirement with exactly one interrupted update. It also checks that root command tools are not interrupted by subagent retirement. A disabled-ownership row keeps tasks alive for flavors whose work can survive the transport. Removing the ownership guard makes that row fail by assertion. The termination and rollback cases failed before the earlier review fixes: termination still reported pending work through the adapter probe enabled by the fixture, and rollback omitted the interrupted task update. Both now pass. The cases check one interrupted update across retirement and the next turn, and inject an old callback while the replacement turn is active. Temporarily removing generation invalidation caused stale text to enter the replacement turn, so the callback assertion detects the regression.
The fixture enables the pending-work probe to distinguish immediate retirement from cleanup at the next turn. It uses a mock ACP subprocess for session setup, stubbed prompts and injected Copilot events. It also checks that raw child attribution cannot cross runtimes. Manual app testing and live Copilot process-termination testing were not performed.
vp run check:changedpassed one03a0e0adeaewith upstream maina9e709f15f82included. It ran 105 tests in 2 files and affected package typechecks, plus format, lint, knip and GraphQL checks.CodeRabbit subsequently identified active-turn tasks missing from termination cleanup. An earlier shape of that regression failed before the fix because pending background work remained true. It passes with active subagents retired in the termination callback.
Independent Opus review identified missing immediate-termination and rollback cleanup, plus an ineffective callback assertion. All three were addressed. The follow-up review by Claude Opus 5.5 High found no blocking issues. It noted that the fixture enables a liveness probe that production Copilot currently does not expose; that limitation is stated above. The independent follow-up review at
e03a0e0adeaefound no blocking issues. Its test-name and description wording corrections are included.Implemented by GPT-6.1 Terra High and GPT-6.1 Sol High through Codex in T3 Code. Reviewed by Claude Opus 5.5 High through Claude Code in T3 Code.