fix(opencode): reconcile agent selection during TUI startup

[sjawhar]

Issue for this PR

Fixes #16034

Type of change

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

What does this PR do?

Fix agent selection reconciliation during TUI startup to prevent stale/missing agent state. Ensures the agent selector reflects actual available agents after plugin loading completes.

How did you verify your code works?

• Ran bun typecheck from packages/opencode
• Ran targeted unit tests
• Tested with custom binary build

Checklist

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

[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

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[github-actions]

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

Based on my search, I found potential related PRs:

1. PR Fix/issue 16982 agent current undefined #17015 - "Fix/issue 16982 agent current undefined"

   • May be related to similar agent state issues during initialization

2. PR fix:Guard against missing agent, add warning & fallbacks, and fix dialog mouse selection handling #19685 - "fix: Guard against missing agent, add warning & fallbacks, and fix dialog mouse selection handling"

   • Addresses missing agent handling and agent selection in the TUI, which could overlap with agent selection reconciliation

These PRs deal with agent state management and selection in the TUI context. However, they appear to be addressing specific issues rather than the same reconciliation problem during startup that PR #20674 is targeting. The most relevant one is #19685 given its focus on agent selection handling.

[github-actions]

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