fix(tui): add retry backoff for event subscription to prevent CPU spin

[SunandRiver]

Problem

When the server shuts down unexpectedly, the TUI attach client enters a tight retry loop causing 100% CPU usage. This happens because the event subscription loop in sdk.tsx lacks error handling and backoff.

Reproduction:

1. Run opencode spawn
2. Kill the spawn process (Ctrl+C or kill)
3. The attach subprocess continues running at 100% CPU, trying to reconnect indefinitely

Solution

• Add try-catch around sdk.event.subscribe()
• Implement exponential backoff: 1s → 2s → 4s → ... → 30s max
• Add random jitter to prevent thundering herd
• Give up after 10 consecutive failures with error message

Testing

Manually tested by killing the server process and observing the attach client behavior - it now backs off exponentially and eventually exits gracefully instead of spinning the CPU.

Fixes #7645

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[SunandRiver]

Hi @aidenpcline @maintainers,

I noticed that the check is failing, but this appears to be due to a CI configuration issue rather than a problem with my code changes.

Error details:

Root cause:
Commit changed the GraphQL field from to in , but is not a valid field in the GitHub GraphQL API.

My PR status:

• ✅ Title format: (follows conventional commits)
• ✅ Code changes: Add exponential backoff retry logic to prevent CPU spinning when server shuts down
• ✅ Problem addressed: Fixes 100% CPU usage in TUI attach client during server shutdown
• ❌ CI cannot check for linked issue due to API field error

Suggested fix:
Revert back to or use another valid field from the GitHub GraphQL API documentation.

Next steps from my side:

1. I'll resolve the merge conflicts with the branch
2. Keep the PR ready for review/merge

Thanks for looking into this!

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[SunandRiver]

Related issue: #7645 (TUI client CPU 100% when server shuts down)