🤖 fix: retry workspace onChat subscription after disconnect

[ammar-agent]

Fixes a class of "UI got stuck" issues when the renderer misses workspace chat events (e.g. compaction delete/rewrite) and only catches up after a restart.

What changed

• Make the renderer's workspace.onChat subscription resilient: if the async iterator ends or errors unexpectedly, automatically resubscribe with backoff.
• Before resubscribing, clear derived per-workspace chat state so the replay rebuilds from the backend source of truth (prevents stale messages from persisting in-memory).

Why

If the UI misses the compaction delete + summary replay, it may still show the old /compact message. Editing that message then fails server-side because the message ID no longer exists in persisted history.

Validation

• bun test src/browser/stores/WorkspaceStore.test.ts
• make typecheck
• make static-check

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