fix(server): a background Claude subagent's work shows while its parent is idle

[Vantrongs]

Problem

A background Claude subagent (Agent with run_in_background) keeps working after its parent's turn ends, but T3 stops showing that work. The subagent's thread and its card in the parent freeze at the last step before the turn ended. Everything the subagent did since then appears at once when its end wakes the parent. In one real session a subagent worked for 86 minutes: its thread showed two steps the whole time, then received 844 items within one second. A step that is running when the turn ends is marked failed by that turn's end, then re-created at the wake as a generic tool with empty input. Reproduction and details: #16484.

Change

All in ClaudeAdapterV2:

• While the root has no active turn, a running subagent's own frames are handled at once, the same way as during a turn, through the context of the turn that settled last. These are its assistant and user frames, resolved through the session subagent registry, and its task_progress. Root frames, task_started, task_notification and results still go to the wake buffer, so wake detection and the continuation run don't change. The run that launched the subagent already keeps ingesting while the subagent runs, and it owns the child thread, so these events are stored as they happen.
• While a subagent's task_started waits in the wake buffer, that subagent's own frames, and the result of the Agent call that launched it, go to the buffer behind it; its progress meanwhile is dropped, and the next one replaces it. That task_started registers or re-opens its subagent only when the continuation drains it, and only that run stores what follows. Other subagents' work still shows at once. This covers a resume (SendMessage) whose task_started arrives after settle, and a nested subagent that a running subagent starts while the root is idle.
• A subagent's tool calls live in session scope instead of the turn context. A turn that completes while one of them runs leaves it open, and its result finds it in a later turn. These calls still end with a turn that is interrupted or fails. They also end with any turn once their subagent has stopped or belongs to an earlier CLI process, and with the CLI process if it exits while the root is idle, or when Stop gives up waiting for it to exit.
• Pending subagent launches move to session scope for the same reason. A running subagent's own Agent call can now be handled while the root is idle, while the nested subagent's task_started is drained into the continuation turn. Without this, the nested subagent was attached to the continuation's root instead of the subagent that started it; the claude_nested_background_subagent_wake replay fixture caught that.

What clients receive doesn't change. A thread's items still go only to clients subscribed to that thread, so a client that isn't showing the subagent's thread gets them when it opens the thread.

Scope and approval

Bug report: #16484. This is one problem: the wake buffer held a running subagent's own frames. Moving the tool-call and launch state is what keeps those frames correct across the turn boundary.

Verification

• New adapter test streams a background subagent's work while the root turn is idle. The root settles while the subagent's Bash call runs. Then, with no wake yet, the call's result, a new message with another Bash call, and a task_progress arrive. All of it is projected before any continuation request. The call that spans the turn end goes running → completed as a command_execution, and after the wake nothing is projected twice. On main the test fails: the second Bash call doesn't appear before the wake.
• Two cases keep the old buffering, each pinned by a test that passes on main: the existing re-opens a resumed subagent whose task_started races past settle now also sends the resumed run's own text and Bash call, and checks that the text is projected once, after the drain re-opens the subagent; the new keeps a nested subagent's launch in order while the root turn is idle checks that a nested subagent's Agent call never becomes a plain tool row, that the nested subagent hangs off the one that started it, and that the outer subagent's progress and own work still show meanwhile (the last check fails if any buffered start holds every subagent's frames).
• New test ends a subagent's open call when the CLI exits while the root turn is idle: the call stays running when the root completes, and the SDK stream's end marks it failed once. New test ends a subagent's open call when Stop's close of the CLI times out: when Stop's close doesn't end the stream within its 10 s timeout, the call is marked interrupted; without this the old stream's exit no longer owns the query and the call stayed running.
• claude_background_subagent_after_root replay fixture (a recorded Claude session) gets a new assertion: the subagent's first command is stored as completed before the continuation run starts. On main the command is stored after the continuation starts (event 66, after event 49), so the assertion fails; with this change it passes.
• vp test run on ClaudeAdapterV2.test.ts and the Claude and orchestrator replay fixture suites: 292 passed. The whole apps/server/src/orchestration-v2 directory: 1768 passed.
• tsc --noEmit -p apps/server/tsconfig.json: no new errors (the 10 in process/externalLauncher.test.ts are also on main). vp fmt --check and vp lint on the changed files: clean, apart from the existing unused layer warning.
• Not checked: a live run of the desktop app with this build.

Maintainer update

Rebased onto main (bfec238) with the four commits above unchanged, plus two:

• Replay fixture now pins when the work is stored (681afcd). claude_background_subagent_after_root asserts, by event order, that the subagent's three texts, both completed commands and both task_progress updates are stored before continuation run 2 reaches starting, and that nothing more lands in the child thread afterwards. With main's adapter it fails at event 58 vs 49. The fixture's input comment no longer describes the old buffering. No recorded transcript has a call that spans the turn end, so that case stays on the adapter test.
• Nested Agent result while the root is idle (aad1557). Found in review: an outer subagent launches a nested Agent in one turn, a later root turn settles, and the nested Agent's tool_result arrives while the root is idle. The tool-result loop looked the subagent up only in the settled turn's own map, missed it, and stored a generic tool row with empty input in the outer subagent's thread. It now resolves through the session registry (resolveSubagentByToolUseId). The tracked-call guard still keeps a SendMessage acknowledgement from ending the subagent. New test ends an earlier turn's nested subagent while the root turn is idle fails without it.

Re-run in a PID-namespace sandbox: ClaudeAdapterV2.test.ts 148, ClaudeReplayFixtures 3, orchestrator replays -t claude 33, RunExecutionService 48, BackgroundWorkStop 11, all passing. tsc is clean.

Not covered here, and tracked separately: a subagent that resumes on its own while the root is idle still shows its resumed work only at the next wake, because this change holds those frames behind the buffered resume task_started (relevant to #16609).

Follow-up: frame order and open calls (4b619b8, 3af93e4)

Three more cases found in review on aad1557, each with a test that fails without its fix:

• A subagent's frames overtook each other when its owner was named late. task_started.tool_use_id is optional in the SDK. Without it, a subagent's frames that arrive while the root is idle have no known owner and went to the wake buffer; once a task_progress named the tool use, the later frames were handled at once and overtook them, so a Bash result could come before its call (a synthetic completed row, then the real call re-run at the drain and marked failed). Such frames now wait in the hold used during a turn (pendingSubagentFramesByToolUseId), keyed by their own tool use, which releases them in order when the owner is named. A buffered start without a tool_use_id no longer claims them. Test: keeps a subagent's frames in order when a late progress names its tool use while the root is idle, alone and with another subagent's start without a tool_use_id buffered before or between its frames.
• A resuming SendMessage was marked failed when the CLI exited before the drain. Its result names the buffered resume task_started's tool use, so it waited behind it; the exit ended the call as failed, and the drain then read the result as the resumed subagent's. A result frame whose calls already show as rows is now handled at once. Test: ends a subagent's SendMessage with its result when the CLI exits while the resume waits. keeps a subagent call's result when the CLI exits before the drain pins the neighbouring case, with the Bash result before or after a nested launch result.
• A background subagent's open WebFetch or Write stayed running forever when the subagent stopped or failed. The run that launched the subagent stops taking its thread's events once the subagent ends, and the continuation run doesn't own that thread, so the end emitted at the next root turn end was never stored. updateClaudeSubagentNode now ends a subagent's open calls when the subagent ends (interrupted if it was stopped, failed otherwise), just before its own end. Test: 8 cases in OrchestratorReplayFixtures.integration.test.ts: WebFetch or Write, opened before or after the root settles, stopped or failed.

Left as is, because the CLI doesn't produce these shapes: with two buffered starts that both lack a tool_use_id, a frame carrying one's launch result can be handled before that subagent registers; and a user message carrying both a SendMessage result and an Agent launch result still waits whole. In the recorded transcripts all 18 subagent starts carry a tool_use_id and each of the 52 result messages holds one result; two weeks of local Claude Code transcripts have 113,190 result messages, each with one result.

vp test run src/orchestration-v2: 1805 passed. tsc --noEmit: clean. vp fmt --check and vp lint on the changed files: clean, apart from the existing unused layer.

Model and harness: Claude Opus 5.5, Claude Code in T3 Code

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This targeted server fix changes production Claude event routing and cross-turn lifecycle state: idle subagent work is emitted immediately, tool calls survive turn settlement, and nested or resumed launches are re-attributed. Extensive tests reduce risk, but the asynchronous state changes and cleanup behavior warrant human review.

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📝 Walkthrough

Walkthrough

The Claude adapter retains subagent calls and launch metadata across root turns. It routes eligible child activity while the root is idle, handles nested and resumed subagents, and ends remaining calls when the CLI stream or query ends.

Changes

Claude subagent processing

Layer / File(s)	Summary
Session state and idle frame routing apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts	Subagent launch metadata and tool calls use session-level maps. Eligible subagent frames use the last settled turn for routing while the root is idle.
Turn and query call finalization apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts	Successful turn completion preserves open calls from running subagents and finalizes other calls. Query closure, stream exit, and close timeout end remaining calls with failed or interrupted status.
Idle routing and replay coverage apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts, apps/server/src/orchestration-v2/testkit/fixtures/claude_background_subagent_after_root/*, apps/server/src/orchestration-v2/testkit/OrchestratorReplayFixtures.integration.test.ts	Tests cover idle, nested, delayed, and resumed subagent frames, open-call replay, and terminal states. Fixture and integration assertions check projection timing, replay ordering, and child-node completion.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant ClaudeCLI
  participant ClaudeAdapterV2
  participant SettledTurn
  participant ChildThread
  ClaudeCLI->>ClaudeAdapterV2: Send subagent frames while root is idle
  ClaudeAdapterV2->>SettledTurn: Resolve eligible running subagent
  SettledTurn-->>ClaudeAdapterV2: Provide routing context
  ClaudeAdapterV2->>ChildThread: Project subagent messages and tool activity

Loading

Suggested reviewers: maria-rcks

Merge Risk: 🔵 Low · up to 3af93

Background subagent work now shows while the parent is idle, and one subagent's pending start no longer holds back another subagent's ordinary output. One narrow case is left: if a subagent's start arrives without its launch ID, another subagent's tool output can wait until the next wake. The fix is mergeable; the owner should know about this edge case.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 3af93

Background work now remains visible after the parent turn ends. Ownership and shutdown checks limit the risk, and no new permission bypass was established. Some identifier-reuse and concurrent recovery guarantees remain unverified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The demonstrated new reach is earlier mutation of execution records within one provider session and its owned child threads. The inspected changes do not establish additional filesystem, network, credential, or cross-session authority.

Trust Boundaries and Controls

• observed — Provider-supplied identities select registered child ownership. Child calls retain their child thread and null run ownership; downstream routing accepts child events only for owned child threads. Frames from a query that no longer owns the live-query slot are rejected.

Resilience and Maintainability Implications

• inferred — The ownership guards and cleanup paths reduce stale-stream mutation and stranded execution-state risk. They are not a complete proof of atomic or exactly-once behavior under concurrent replacement, interruption, or native identifier reuse.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the main change: showing a background Claude subagent’s work while its parent is idle.
Description check	✅ Passed	The description covers the problem, change, scope and approval, and verification. It reports focused tests and their results, identifies checks that were not performed, and includes the model and harn…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Approvability	✅ Passed	The diff changes only ClaudeAdapterV2 and its orchestration-v2 tests and fixtures. It fixes background subagent frame handling; it does not add a product workflow, change a default, or refactor acro…

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• 🪄 Fix CodeRabbit comments on this PR

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Review comments at
@apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts:
- Around line 7397-7407: In the test around `reopenIndex`, assert that
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`RESUMED_WORK` message position, so the test fails when no matching running
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🟡 Minor · Finalize retained calls in the close-timeout path. · ClaudeAdapterV2.ts:7340-7358

apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:7340-7358
🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Finalize retained calls in the close-timeout path.

When a runtime-restart stop follows a completed turn, closeLiveQueryForNativeThread can time out before the old query’s exit callback claims ownership. The timeout clears queryContext, so the callback skips the new subagent-call drain. Calls retained for running child threads can remain open until a later result or turn finalizer handles them. Ensure the timeout path finalizes those calls before it drops query ownership.

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Review comment at @apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
around lines 7340 - 7358:
Update the timeout path in closeLiveQueryForNativeThread to finalize retained
subagentToolCalls before clearing queryContext, since the old query’s exit
callback may no longer own the query and skip its drain. Reuse the existing
settledTurnByNativeThread and endToolCalls flow shown in the exit callback, then
clear the retained calls.

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Review comments at
@apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:
- Around line 7340-7358: Update the timeout path in
closeLiveQueryForNativeThread to finalize retained subagentToolCalls before
clearing queryContext, since the old query’s exit callback may no longer own the
query and skip its drain. Reuse the existing settledTurnByNativeThread and
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[Vantrongs]

@coderabbitai The outside-diff finding on closeLiveQueryForNativeThread is valid: after the timeout clears queryContext, the old stream's exit no longer owns the query and skipped the drain, and the orchestrator's Stop follow-up only settles the parent thread's items, so the subagent's call stayed running. Fixed in f94f179: both paths now call one helper, endSubagentCallsOfClosedQuery, and the timeout path marks the calls interrupted. The new test ends a subagent's open call when Stop's close of the CLI times out fails without the fix.

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🟠 Major · Limit the buffered-start gate to the frame’s subagent. · ClaudeAdapterV2.ts:5641

apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:5641
🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Limit the buffered-start gate to the frame’s subagent.

If subagent B has a buffered task_started, this condition sends subagent A’s assistant and tool-result frames to the wake buffer too. A start or assistant frame alone does not request a continuation, so A’s work can remain invisible while B runs. Resolve each frame’s task ID before applying the gate. Defer only frames whose own task has a buffered start.

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Review comment at @apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
at line 5641:
Update the buffered-start gate using bufferedStarts so every frame is checked
against its own resolved task ID, rather than allowing buffered starts from
other tasks to gate assistant or tool-result frames. Defer a frame only when its
task has a buffered task_started.

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Review comments at
@apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:
- Line 5641: Update the buffered-start gate using bufferedStarts so every frame
is checked against its own resolved task ID, rather than allowing buffered
starts from other tasks to gate assistant or tool-result frames. Defer a frame
only when its task has a buffered task_started.

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🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail
ast-grep outline apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts --match 'closeLiveQueryForNativeThread|endSubagentCallsOfClosedQuery' --items all
rg -n -C 35 '\bendSubagentCallsOfClosedQuery\b|\bcloseLiveQueryForNativeThread\b' apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
ast-grep outline apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts --match 'Stop|close|subagent' --items all
rg -n -B 5 -A 180 "ends a subagent's open call when Stop's close of the CLI times out" apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts

Length of output: 31697

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@Vantrongs Thanks for the fix and explanation. I verified that both paths call endSubagentCallsOfClosedQuery. The timeout path marks open subagent calls interrupted only when it still owns the query.

The new test asserts running → interrupted after the 10-second Stop timeout. This addresses the finding. I inspected the code and test but did not run the test.

---

✏️ Learnings added

Learnt from: Vantrongs
URL: https://github.com/pingdotgg/t3code/pull/16486

Timestamp: 2026-10-06T15:26:17.866Z
Learning: In apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts, clearing queryContext during closeLiveQueryForNativeThread's timeout causes the old stream's exit to skip cleanup because it no longer owns the query. The orchestrator's Stop follow-up settles only the parent thread's items, not subagent items. Both stream exit and the ownership-guarded close timeout must call endSubagentCallsOfClosedQuery; the Stop timeout ends open subagent calls with interrupted status.

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[Vantrongs]

@coderabbitai The outside-diff finding on the buffered-start gate is valid: any buffered subagent task_started held every subagent's frames, so an outer subagent that launched a nested one stayed invisible until the next wake. Fixed in 1e479b2: a frame waits only if its own subagent's start is buffered (the resume case) or it carries the result of the Agent call that launched a buffered subagent, so that call never becomes a plain tool row. If a buffered start has no tool_use_id, every frame carrying a tool result waits. keeps a nested subagent's launch in order while the root turn is idle now also checks that the outer subagent's own work shows while the nested start waits; that check fails with the old gate.

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🏁 Script executed:

#!/bin/bash
set -euo pipefail
ast-grep outline apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts --items all --match 'buffer|Buffer|handle.*Message'
rg -n -C 24 'tool_use_id|task_started' apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts | tail -n 320
ast-grep outline apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts --items all --match 'nested|idle'
rg -n -B 5 -A 240 "keeps a nested subagent's launch in order while the root turn is idle" apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts

Length of output: 27800

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🏁 Script executed:

#!/bin/bash
set -euo pipefail
rg -n -C 32 'buffered.*[Ss]tart|[Ss]tart.*buffered|wakeBuffer|wakeBuffered|bufferedMessages' apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts

Length of output: 39386

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@Vantrongs Thanks for the fix and explanation. I inspected settledTurnForSubagentFrame and the updated test.

The gate now holds only the affected subagent’s frames or frames carrying its launch call’s result. If a buffered start has no tool_use_id, the gate holds every frame carrying a tool result.

The test asserts that OUTER_WORKING appears before any continuation request. It also checks that the nested Agent call never becomes a plain tool row. This addresses the finding. I did not run the test.

---

✏️ Learnings added

Learnt from: Vantrongs
URL: https://github.com/pingdotgg/t3code/pull/16486

Timestamp: 2026-10-06T15:40:37.858Z
Learning: In apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts, settledTurnForSubagentFrame must not block all subagent frames when a subagent task_started is buffered. Hold only frames belonging to that subagent or frames carrying the result whose tool_use_id matches the buffered start's launching call. If a buffered start lacks tool_use_id, conservatively hold every frame carrying a tool result. This preserves resume attribution and prevents a nested Agent launch from becoming a plain tool row while allowing the outer subagent's own work to remain visible during root idle. The test "keeps a nested subagent's launch in order while the root turn is idle" in apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts covers outer work appearing before a continuation request and the absence of a plain tool row for the nested Agent call.

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