fix(opencode): harden nested request discovery

[samiralibabic]

Issue for this PR

Fixes anomalyco#13715 when merged with the parent branch.

Builds on anomalyco#41496 rather than creating a competing upstream PR.

Type of change

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

What does this PR do?

This adds two cherry-pickable follow-ups to the nested-request fix:

• surface SDK error responses while collecting descendant sessions instead of treating a failed branch as an empty leaf
• lock in breadth-first traversal order and session identity in the TUI helper test

No source-attribution UI or permission-approval semantics are included, so the parent PR remains focused on request discovery.

How did you verify your code works?

• packages/opencode: 38 targeted CLI tests and package typecheck
• packages/tui: 8 subtree tests and package typecheck
• packages/app: 15 permission auto-response tests
• Changed-file Prettier and git diff --check
• Pre-push workspace typecheck (30 packages passed)

Screenshots / recordings

N/A. This does not change the UI.

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

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[NaturalSelect]

By the way, would you be interested in developing a Go-based agent? https://github.com/NaturalSelect/angela

[samiralibabic]

After a deeper review, I am withdrawing this follow-up. Treating one descendant session.children API error as fatal would abort the entire opencode run transport, which is too aggressive for a best-effort bootstrap path. The extra breadth-first order/identity assertion also constrains incidental behavior without directly testing prompt visibility.

The parent PR already contains the essential nested-request fix, so keeping this open would add risk rather than useful scope. Thanks for allowing me to build on the branch, and apologies for opening the follow-up before completing that review.