fix(tui): surface sub-agent provider errors in parent task flow

[LucasSantana-Dev]

Issue for this PR

Closes #17583

Type of change

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

What does this PR do?

This ensures sub-agent provider failures are visible in the parent task flow. The task tool previously returned normally even when the sub-agent ended with an assistant API error, which made the parent flow appear successful with no clear failure signal.

Now the task tool surfaces non-abort sub-agent assistant errors as tool failures (Sub-agent failed: ...). This makes rate-limit/provider failures visible in the primary flow instead of being silently swallowed.

How did you verify your code works?

• cd packages/opencode && bun test test/tool/task.test.ts
• cd packages/opencode && bun run typecheck
• Added regression test for a mocked sub-agent 429/API error propagation path

Screenshots / recordings

Not a UI layout change. TUI behavior change validated by test coverage.

Checklist

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

Related: #5204

[github-actions]

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

I found some potentially related PRs:

Related PRs:

1. PR fix: Fixes race conditions and missing error handling that cause subagents to hang indefinitely when errors occur. #18389 - "fix: Fixes race conditions and missing error handling that cause subagents to hang indefinitely when errors occur"

   • Appears to address similar subagent error handling issues in a recent PR

2. PR fix(opencode): propagate subagent errors to parent session #13422 - "fix(opencode): propagate subagent errors to parent session"

   • Directly related to error propagation from subagents to parent sessions, similar to PR fix(tui): surface sub-agent provider errors in parent task flow #18444's goal

3. PR fix: robust subagent completion propagation #13321 - "fix: robust subagent completion propagation"

   • Also addresses subagent propagation concerns

Why they're related: These PRs all deal with error handling and propagation from sub-agents/subagents to parent tasks/sessions. PR #18444 specifically focuses on surfacing terminal provider/API errors from SessionPrompt.prompt() up the chain, which overlaps conceptually with these other error propagation fixes. PR #18389 in particular seems very recent and might warrant checking for overlap.

[github-actions]

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

[elmagow]

Any update on this?

[LucasSantana-Dev]

Rebased on upstream/dev (HEAD: ffa2bff). CI re-running.

[LucasSantana-Dev]

Already on upstream/dev. HEAD: ffa2bff

[rekram1-node]

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