feat(session): add support for per-session working directories

[ssmirr]

What does this PR do?

Adds Session.directory.get()/.set() so sessions can have their own working directory instead of always using Instance.directory. This enables plugins to customize where each session operates, supporting use cases like:

• Git worktrees (isolated branches per session)
• Sandboxed environments
• Custom project layouts
  Updates all tools (bash, edit, write, grep, glob, ls, lsp, apply_patch) to use the session's directory.

Changes

• session/index.ts: Add Session.directory accessor with get() and set() methods
• All tools: Update to use Session.directory.get() instead of Instance.directory
• prompt.ts: Set Session.directory at the start of prompt loop and shell command execution
• system.ts: Show Session.directory in environment info
• compaction.ts: Use Session.directory in path.cwd

Backward Compatibility

Session.directory.get() falls back to Instance.directory if not set, so existing behavior is unchanged.

Note

This PR works standalone but is designed to pair with a session.creating plugin hook (#9361), which would allow plugins to set custom directories during session creation.

How did you verify your code works?

1. Added unit tests in packages/opencode/test/session/directory.test.ts
2. Manual testing with a plugin that sets custom session directories
3. Verified tools operate in the correct directory
4. Verified sessions without a custom directory still default to Instance.directory

closes #9366

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

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

Based on my search, I found one related PR that is closely connected to the current PR:

Related PR (Companion Feature):

• #9361: feat(plugin): add session.creating hook for customizing session creation
  • This is the companion hook mentioned in your PR description. While not a duplicate, these two PRs are designed to work together. PR feat(plugin): add session.creating hook for customizing session creation #9361 would allow plugins to set custom directories during session creation, which complements the per-session directory support in this PR.

No duplicate PRs found addressing the same feature.

[simonsmallchua]

Fully support/keen on this feature.
(Not sure if this is the right place to put a comment like this)

[MrTravisB]

This would be a great feature to have to be able to do soemthing like /new /new/working/directory

I know +1 comments not great but want to bump this up.

[yanhao98]

建议也更新 skill 系统的目录获取逻辑。