feat(web): implement a plan through the executor, and stop it from the Pair panel

[rynfar]

What

Two additions to the web Pair experience.

• Implementing a plan on a paired thread. The plan card's button reads "Implement with executor", and the implementation message ends with one reminder: write the contract and the failing tests yourself, hand the plan to the executor one step at a time with pair_handoff, verify each step before the next. The recognized prefix stays first, and an unpaired thread sends exactly what it sent before. "Implement in a new thread" is unchanged, since a new thread is not paired.
• Stop executor. The Pair panel shows a "Stop executor" button while the executor holds a turn, including one paused on an approval or a question. It dispatches the existing turn interrupt for the executor thread and reports a failure as a toast.

How

• buildPlanImplementationPrompt(plan, { paired }) and resolvePlanFollowUpSubmission carry the flag; ChatView derives activeThreadPaired from the thread shells it already has.
• ComposerPrimaryActions takes pairedImplement; PairControl takes an optional onStopExecutor, supplied by usePairControl.
• No server or contract changes.

Verification

• vp test run apps/web/src/proposedPlan.test.ts apps/web/src/components/chat: 970 passed. Three tests were written first and seen failing: the exact prompt suffix and that the unpaired prompt is unchanged, the button label in all three states, and the stop button's presence per executor phase and without a handler.
• Typecheck @t3tools/web: 0 errors. vp check on the changed files: no formatting issues, no new lint warnings.
• Not run in a browser.

How it was built

Through pair mode on a real install: Claude lead, Antigravity executor, shared worktree, three test files protected (checked 3, changed []). One executor turn, no corrections.

Part of #622.

Model: Claude Fable 5.1 (lead) with an Antigravity executor, paired in Pylon via the Claude Code harness.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
pylon-marketing	Ready	Preview	Sep 18, 2026 10:44pm UTC

[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	14.0 KiB	13.9 KiB	−8 B (−0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	−6 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−2 B (−0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	−7 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	+7 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−14 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.9 KiB	58.9 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: e397226 · PR result: 8acc575 · 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: 115.6 KiB
• Claude decoded thread snapshot: 116.4 KiB

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