feat(opencode): run bash commands in background

[Rejudge-F]

Issue for this PR

Closes #1970

Type of change

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

What does this PR do?

Adds an explicit opt-in background mode for the opencode bash tool.

When the model calls bash with run_in_background: true (or the background alias), the command is registered with the existing BackgroundJob service and the tool returns immediately with a job id and output path. The command keeps running outside the original tool call, writes its final output to the output path, and injects a synthetic completion message back into the parent session when it exits.

This also adds bash_kill so agents can cancel bash background jobs by id. It checks the job type before canceling so it cannot stop non-bash background jobs such as subagent tasks.

This is intentionally narrower than a full shell job manager: it does not add mid-flight detach, automatic backgrounding, or a TUI keybind.

How did you verify your code works?

• cd packages/opencode && bun typecheck
• cd packages/opencode && bun test test/tool/shell.test.ts test/tool/parameters.test.ts
• cd packages/opencode && bun test test/tool/ --timeout 60000
• bun run typecheck
• bun run lint — 0 errors, existing warnings only

Screenshots / recordings

N/A

Checklist

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

[github-actions]

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

Potential Related PR Found:

• PR feat(shell): add managed background mode #32675: "feat(shell): add managed background mode"
  • URL: feat(shell): add managed background mode #32675
  • This appears to be related as it also addresses background execution for shell/bash commands. It may be addressing the same issue (Feature Request: Add Background Bash Execution (Like Claude Code’s Ctrl+b) #1970) or a similar feature for managing background processes.

Please review PR #32675 to confirm whether it's a duplicate or addresses the same underlying feature request.

[github-actions]

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