fix(opencode): prevent /undo from using unsafe root pathspecs

[himax12]

Fixes #25400

/undo can receive snapshot patch entries that resolve to an unsafe target (for example worktree root).
When that reaches git checkout pathspec handling, it can broaden the checkout scope and touch unrelated files.

What changed:

• normalize revert targets against the active worktree
• skip unsafe targets (worktree root or outside worktree)
• use normalized relative pathspecs for checkout calls
• add a regression test that verifies worktree-root targets are ignored

Verification:

• bun --cwd packages/opencode test test/snapshot/snapshot.test.ts -t revert --timeout 120000
• bun --cwd packages/opencode test test/session/revert-compact.test.ts --timeout 120000

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[Copilot]

Pull request overview

Hardens snapshot revert (used by /undo) to prevent unsafe git checkout pathspecs (e.g., worktree root) from expanding the checkout scope and touching unrelated files/mtimes.

Changes:

• Normalize revert targets against the active worktree and skip unsafe targets (worktree root / outside worktree).
• Use normalized relative pathspecs for git checkout during revert (single + batched paths).
• Add a regression test asserting that worktree-root targets are ignored (no mtime churn).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/opencode/src/snapshot/index.ts	Adds worktree-based normalization/filtering and switches revert checkout to relative pathspecs.
packages/opencode/test/snapshot/snapshot.test.ts	Adds regression coverage for ignoring worktree-root revert targets.

Comments suppressed due to low confidence (1)

packages/opencode/src/snapshot/index.ts:415

• Switching git checkout to use op.rel introduces Git pathspec parsing (e.g. pathspec magic like :(exclude) / :(icase) and globbing) for any revert target that starts with : or contains pattern characters. That can broaden the checkout scope again despite the root/outside filtering. To ensure the argument is treated as a literal path, consider enabling literal pathspecs for these invocations (e.g. pass --literal-pathspecs to git, or prefix each pathspec with :(literal)), and apply the same treatment to the ls-tree probe below.

                log.info("reverting", { file: op.file, hash: op.hash })
                const result = yield* git([...core, ...args(["checkout", op.hash, "--", op.rel])], {
                  cwd: state.worktree,
                })
                if (result.code === 0) return
                const tree = yield* git([...core, ...args(["ls-tree", op.hash, "--", op.rel])], {
                  cwd: state.worktree,
                })

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[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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[jasonwch]

please reopenand review this fix!