fix(server): child threads no longer flood the mobile thread list

[lukemaj]

Closes #59.

The store T3 Code mobile app has no Agents panel, so every child thread spawned through spawn_thread or Prism landed in its thread list and buried the threads the user started.

The server now leaves child threads (sub.<parent>.<suffix>) out of the shell it sends to mobile connections (clientSurface=mobile):

• WebSocket subscribeShell: snapshot, replayed and live shell events.
• getArchivedShellSnapshot.
• HTTP /api/orchestration/shell, which looks up the surface the session last reported on its WebSocket connect (clients connect the socket before loading the shell over HTTP).

Web and desktop still receive child threads for the Agents panel. No mobile build is needed: a phone drops cached children on its next connection, because new sessions reload the HTTP snapshot. The client only dedupes shell events by sequence, so skipped events are safe.

Tradeoff: until upstream Orchestrator V2 (pingdotgg/t3code#2829) ships, child threads cannot be opened on mobile. They stay reachable from web and desktop. V2's mobile app hides subagent threads natively, so this goes away with the V2 port.

Proof

• vp test run src/mcp/toolkits/threads/mobileShell.test.ts: 3 passed (stream filtering per surface, session surface lookup against SQLite).
• vp test run src/server.test.ts -t "hides child threads from mobile": passes; fails with the ws.ts change reverted.
• apps/server typecheck clean; lint on changed files has no errors; scripts/fork-check.sh OK.
• Not verified on a real phone yet.

Done by Claude Opus 5.5 in Claude Code.

🤖 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	13.5 KiB	13.5 KiB	+27 B (+0.2%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−4 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+31 B (+0.5%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.3 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−1 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	0 B (0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 19a04dc · PR result: c209717 · Source CI: failure

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: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

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