fix(task): propagate subagent provider errors to orchestrator

[Haohao-end]

Problem

Provider/model failures inside subagent sessions were not reaching the primary orchestrator, so the parent could continue spinning instead of surfacing the real error.

Root cause

TaskTool.execute() treated the child session result as a successful assistant text response and ignored childAssistant.info.error, which downgraded provider failures into empty task results.

Fix

After SessionPrompt.prompt(...) returns, TaskTool.execute() now checks for info.error and throws a normal Error with the child error message. Successful child responses still follow the existing task_id + <task_result> path unchanged.

Validation

• Added focused regression tests for successful subagent output propagation
• Added focused regression tests for provider-error propagation from subagent to parent
• Verified with:
  • bun test test/tool/task.test.ts

[github-actions]

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[github-actions]

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[github-actions]

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

Potential Duplicate PRs Found

#18444 - fix(tui): surface sub-agent provider errors in parent task flow

• Directly related: This PR appears to address the same issue of surfacing subagent provider errors to the parent, but from a TUI perspective. This might be a duplicate or closely related fix addressing the same root cause.

#17577 - feat(opencode): add model override for task tool subagents

• Related feature: While this is a feature rather than a fix, it involves task tool subagent handling and might have context on the error propagation mechanism.

#13321 - fix: robust subagent completion propagation

• Historical context: This older PR also dealt with subagent result propagation issues and may be relevant for understanding the context.

I recommend reviewing #18444 most closely as it appears to be addressing the same issue from a different angle.

[Haohao-end]

CI is currently failing on unrelated existing typecheck errors in packages/app:

• src/components/dialog-connect-provider.tsx:386
• src/components/dialog-custom-provider.tsx:134

My change only touches:

• packages/opencode/src/tool/task.ts
• packages/opencode/test/tool/task.test.ts

Local validation for this fix:

• bun test test/tool/task.test.ts

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

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