chore: ignore agent scratch directories

[rynfar]

.jcode/ and .playwright-cli/ are agent tool output that lands in the worktree
and is not ignored, so git check-ignore exits 1 on both and a stray git add -A
can commit them. AGENTS.md already says working material stays out of the
worktree; this is the same safety net .plans/ gets.

Caught by an adversarial review pass on #241.

Model: Claude Opus 5 in Claude Code.

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[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	13.6 KiB	13.7 KiB	+170 B (+1.2%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+7 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.8 KiB	+163 B (+2.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.2 KiB	58.7 KiB	+1.5 KiB (+2.6%)	66.4 KiB	✅
Codex	Live turn messages	10	11	+1 (+10.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.8 KiB	+185 B (+1.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	+10 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.8 KiB	+175 B (+2.6%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.1 KiB	59.5 KiB	+1.5 KiB (+2.5%)	66.4 KiB	✅
Claude	Live turn messages	10	11	+1 (+10.0%)	21	✅

Baseline: a509639 · PR result: c89c670 · 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: 109.5 KiB
• Claude decoded thread snapshot: 110.2 KiB

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