feat(shell): add managed background mode

[FernandoMrq]

Issue for this PR

Closes #29822, #28654, #24658

Type of change

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

What does this PR do?

Adds managed background shell execution across the core bash tool and the opencode shell tool surface.

In packages/core this introduces managed shell jobs, background status/log/wait/cancel tools, auto background mode, and process handling hardening so long-running
commands can detach cleanly while still being observable.

In packages/opencode this exposes the managed background shell tools in the registry, updates shell prompting/schema to support the new mode, and registers the CLI
spinner earlier so background shell activity reports correctly.

How did you verify your code works?

• cd packages/core && bun typecheck
• cd packages/core && bun test test/shell-background.test.ts test/shell-job.test.ts test/tool-bash.test.ts
• cd packages/opencode && bun typecheck
• cd packages/opencode && bun test test/tool/registry.test.ts
• cd packages/opencode && bun test test/session/prompt.test.ts still had 3 local timeout failures around queued callers / shell coordination.
• cd packages/opencode && bun test test/tool/shell.test.ts is not green locally on this machine; several Windows cases assume WINDIR is set and multiple legacy
  shell cases timed out.

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:

Based on my search, I found one potentially related PR:

Related PR:

• feat(core): add V2 background task tool #31173 - feat(core): add V2 background task tool (feat(core): add V2 background task tool #31173)
  • This appears to be related as it also adds background task functionality to the core package. You may want to check if this PR is already merged or if there are any overlapping implementation details with the managed background mode feature you're adding.

The search primarily returned the current PR itself (#32675). The other results don't appear to be duplicates of the background shell execution feature you're implementing.

[FernandoMrq]

Hey @adamdotdevin , could you approve the workflow runs on this PR? Thanks!

[FernandoMrq]

Hona @Hona Brendonovich @Brendonovich adamdotdevin @adamdotdevin - ready for review!

[github-actions]

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

[github-actions]

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