fix(opencode): include partial bash output on abort

[jakvbs]

Summary

• Include bounded partial bash output in tool error text when execution is aborted, so the model can reason from already-produced logs.
• Keep existing behavior unchanged for non-bash tools and non-abort errors.
• Add tests for both normal partial output and whitespace-only partial output on abort.

Fixes #13809

Verification

• bun test test/session/message-v2.test.ts
• bun run typecheck

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.