Scratch: verify fork runner fallback for pingdotgg/t3code#11438

[Project516]

Temporary PR to run CI in this fork's context for pingdotgg#11438. Will be closed and its base branch deleted after the run.

[project516-review-bot]

This PR adds fork runner fallback by replacing hardcoded Blacksmith runner labels with conditional expressions that select Blacksmith runners for the pingdotgg org and GitHub-hosted runners for forks. The change is applied consistently across ci.yml, mobile-fingerprint-check.yml, and windows-tests.yml. The logic is sound and the runner labels used for GitHub-hosted runners (ubuntu-24.04, macos-26, windows-2025) are valid.

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_{review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.5 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.1 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.4 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	56.2 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	9	—	21	✅
Claude	Total thread wire	—	13.5 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.1 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	57.0 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	9	—	21	✅

Baseline: unavailable · PR result: 164db5a · 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.

[Project516]

Verification for pingdotgg#11438 is done.