Snapshot restore from a subdirectory can overwrite sibling files

Description

Reverting or unreverting a session started in a subdirectory can overwrite an unrelated edit in a sibling directory. Snapshot restore applies its whole shared snapshot index with checkout-index -a -f instead of restoring only the session directory.

Plugins

None

OpenCode version

dev (7565e035)

Steps to reproduce

1. Create a Git repository with frontend/ and backend/ files.
2. Start a session in frontend/, create a snapshot, and change a frontend file.
3. Make an unrelated edit to a backend file, then revert or unrevert the session.

The backend edit is restored from the snapshot. Only files under frontend/ should change.

Screenshot and/or share link

None

Operating System

macOS

Terminal

Ghostty