fix(tui): harden disposal recovery — bounded retry, session re-sync, fresh context, conditional event stream

[sjawhar]

Issue for this PR

Closes #16545

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When the backend Instance is disposed while the TUI is active, several recovery bugs can cause a blank screen or infinite retry loops. This PR fixes all six identified issues:

sync.tsx — Disposal recovery hardening:

• Saves active session IDs before clearing fullSyncedSessions, then re-syncs them after successful re-bootstrap so the user's current view refreshes automatically instead of showing stale data
• Caps re-bootstrap retries at 5 with exponential backoff (2s → 4s → 8s → 16s → 30s) — previously retried infinitely with fixed 2s delay
• Adds a generation counter so that when a newer disposal arrives, stale retry chains from earlier disposals cancel themselves instead of racing
• Replaces manual new Promise(r => setTimeout(r, 2000)) with sleep() from node:timers/promises to match the rest of the codebase

worker.ts — Event stream lifecycle:

• Moves Instance.provide() inside the while loop so each reconnect iteration gets fresh context — previously a single Instance.provide() wrapped the entire loop, so after disposal the reconnect used a stale context
• Removes the unconditional startEventStream(process.cwd()) at module load and adds an events RPC method so the thread controls when and where to start the stream
• Tracks eventStream.directory so reload() can abort the stream and conditionally restart it, rather than relying on timing-sensitive SSE reconnect

thread.ts — Transport-aware event stream startup:

• Calls worker.events({ directory }) only when not in external transport mode (!external guard) — previously the event stream started regardless of transport
• Adds proper .catch() handler on the checkUpgrade call (was silently swallowing errors with empty .catch(() => {}))

How did you verify your code works?

• bun run typecheck passes from packages/opencode
• Structural grep verification of all six fixes (Instance.provide position, events RPC existence, transport guard, sleep import, generation counter, resync logic)
• Reviewed the diff to confirm no changes to instance.ts or server.ts (those belong to the separate idle timeout PR)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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