[jayleaton]

Problem

Chats an agent launches sometimes land top-level on the Agents board instead of inside the launching chat's card, on every machine. An audit of real data on the Mac, desktop-pc and dev-box found these causes:

• Cross-machine delegate_task without profileId (rows D1, V1, V2). Over a stored peer link, the other machine sees only the link session, never the calling thread, so the chat was created with no parent. t3_thread_launch sent over a peer link had the same gap.
• Chats launched by a delegate_task helper (a subagent). Their parent is the helper, which is never a card, so the board showed them top-level.
• Captain → Captain launches later detached (rows M1, V3). These were explicit detaches, which older Captain instructions asked for. The launched chat kept a task owned by its launcher while its parent link was null, so the two disagreed.
• Invented parentThreadId (S1–S5). Already rejected since fix(mcp-gateway): chat creation rejects a parentThreadId that isn't a chat #175, which merged after those rows. One related gap remained: a chat naming itself as the parent of a chat on another machine was refused, because the parent was looked up on the target environment.

Explicit parentThreadId: null (S7–S9) stays as a supported opt-out. The tool text does not suggest it, so it is unchanged.

Change

 caller on Mac ──t3_thread_launch / delegate_task──▶ PeerForwarding ──link──▶ box
-                                                      (no caller)              parent: none
+                                                      delegatedFrom = caller   parent: caller @ Mac

• PeerForwarding stamps the calling thread as delegatedFrom on every forwarded t3_thread_launch. The receiving t3_thread_launch handler nests a link-session launch under that thread (parentThreadId + parentEnvironmentId).
• selectAgentSidebarThreads (packages/client-runtime, shared by the web, desktop and mobile boards) lists a chat whose parent is a subagent under that subagent's nearest non-subagent owner.
• The parent link is canonical, and a task follows it.
  • ThreadTaskService reacts to thread.metadata-updated: a reparented child's task moves to the new parent, and a detached child's task is removed (the old owner's delta reads it as a departure).
  • Startup recovery fixes tasks that drifted earlier, such as M1.
  • ThreadTaskStore gains remove, and its cursor also counts departures, so cursors never repeat.
• mcp-gateway t3_create_thread: a parentThreadId equal to the calling chat resolves to the caller's environment.

Scope and approval

Maintainer-requested bug fix (JJ via Captain). One problem: agent-launched chats losing their parent link.

Verification

Each new assertion failed on the base commit (fix reverted, test kept) and passes with the fix:

Test	Before	After
client-runtime agents.test.ts › nests a chat a subagent launched in the card of the subagent's owner	✗ doug-chat, deeper-chat were top-level cards	✓ 44/44 (+ threadRelationships 14/14)
server RemoteDelegation.test.ts › a task delegated to the box… (parent assertion)	✗ parentThreadId: undefined	✓ 27/27
server PeerForwarding.test.ts › launches in a linked environment… (parent assertion)	✗ no parent fields	✓ 42/42 with handlers.test
server ThreadTaskService.test.ts › a task follows its worker's parent…	✗ expected 'captain' to equal 'stranger'	✓ 26/26 (threadTask dir)
mcp-gateway tools.test.ts › parents chats a T3 chat creates on any environment	✗ self-parent on remote refused	✓ 114/114

• Format and lint are clean on the changed files.
• Typecheck passes for client-runtime, mcp-gateway and apps/server.
• Format, lint and the apps/server typecheck ran locally because the Davit box ran out of memory. The tests ran in Davit.
• Not done: a screenshot of the board in a real client. The board change is pure grouping logic, covered by the shared selector test above.

Merge Danger

Door: two-way for the parenting changes. A task removed on detach is not restored by a revert; the worker can be reassigned with t3_task_assign.

Blast Radius: consumers. Affected:

• linked-environment launches and delegates (new parent fields on the remote chat);
• Agents board grouping on web, desktop and mobile;
• t3_task_read for owners whose children were moved or detached.

Model and harness: Claude Opus 5.5 in Claude Code (T3 agent Doug).

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	+29 B (+0.6%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	+29 B (+2.3%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	21.5 KiB	21.6 KiB	+41 B (+0.2%)	24.4 KiB	✅
Codex	Live turn messages	1	2	+1 (+100.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.3 KiB	1.3 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.9 KiB	21.9 KiB	0 B (0.0%)	24.4 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 8d1b3cf · PR result: 769a28c · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.