test: prove failed revision resync clears count

[Chris0Jeky]

Refs #2579

Summary

• Extend the existing Review polling: the active proposal can change under a live reviewer (focus/hotkeys, stale diff, stale revision state) — from PR #2208 #2215 M-1 failed revision-resync regression with the missing non-authoritative count assertion.
• Confirm a failed resync clears revisionCount while leaving revisionsLoaded false and the silent-toast contract intact.

Verification

• useProposalRevisions.spec.ts: 31/31
• Frontend typecheck: passed
• File-scoped ESLint: passed
• Mutation check: removing the guarded production count reset failed the new assertion with �xpected 0, received 1; production code was restored.
• git diff --check: passed

Two coordinator review passes completed for state-machine proof and scope/lineage.

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, add credits to your account and enable them for code reviews in your settings.