Add canonical transport permalinks

[saagpatel]

Summary

• Add canonical ?t= permalinks for reader-initiated transport changes.
• Preserve unrelated query parameters and hashes with replace-history semantics.
• Keep playback, automatic scene seeks, and programmatic scene interactions URL-silent.
• Add focused coverage for scrubbing, event stepping, keyboard positioning, history, fallback, and rehydration.

Verification

• pnpm test — 160 passed, 1 skipped.
• pnpm typecheck.
• pnpm build.
• pnpm test:e2e — 52 passed.
• pnpm guard — 103 targets clean.
• Direct headless Chrome readback for URL preservation, replacement history, keyboard updates, playback silence, and invalid-link fallback.

Scope

Local/source implementation only. Deployment and human accessibility validation are not claimed.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-02T11:21:13.559608Z	dae1eff	PR opened

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