Move sequence-array publication off participant startup's critical path

[JackWilb]

Summary

• key sequence artifacts and build records by config hash
• atomically coordinate deterministic seeds and bounded publication leases across Firebase and Supabase
• derive sequence arrays locally so participant assignment can continue while the lease owner publishes in the background
• retain legacy arrays and prior config artifacts for existing participant sessions
• attach immutable cache metadata during the initial canonical artifact upload

Why

The first participant after a config change previously generated and uploaded the full sequence array before participant initialization could continue. It also deleted the prior mutable artifact, which made artifact lifetime depend on the active config rather than participant sessions.

This change establishes a small transactional build record first. Concurrent clients derive the same array from its seed, while only the lease owner uploads the canonical artifact. Failed or abandoned publishers can be replaced without changing the seed.

Closes #1319.

Validation

• yarn install --frozen-lockfile
• yarn unittest --run (2,036 tests passed, 1 skipped)
• yarn typecheck
• yarn lint
• yarn build
• git diff --check

[github-actions]

A preview of 22d5bb1 is uploaded and can be seen here:

✨ https://revisit.dev/study/PR1370 ✨

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