Snapshot restore() force-rewrites every worktree file even when content is identical (related: #15391)

Description

When snapshot.restore() runs (revert/unrevert flows), it does read-tree + checkout-index -a -f. The -a -f force-rewrites every file in the index unconditionally, even when the worktree is already byte-identical to the snapshot. All file mtimes in the project get bumped while content stays identical (git status remains clean).

Related: #15391 (closed without a fix — checkout-index -a -f is still in restore() on dev @ 55f9841) and #5840 (mtime side effect).

Evidence from my machine: opencode.log shows restore commit=4ca9cb1a... at 08:48:26Z, and 1012 files had their mtime changed within the same 2-3 seconds. The shadow repo sets autocrlf=false, so rewrites are byte-identical (LF stays LF).

Impact: anything that diffs by mtime misfires. After every opencode session, the Obsidian "Remotely Save" plugin planned to re-upload 657/945 vault files and tripped its own ">=50% changed" safety abort.

Suggested fix: content-compare the worktree against the snapshot first (git diff --name-only <snapshot>) and return early when empty; otherwise proceed as today. Note that plumbing diff-files can't be used for this check after read-tree (the index has no stat cache, so it reports every file) — the porcelain diff is content-aware. Happy to send a PR.

Plugins

No response

OpenCode version

1.14.29

Steps to reproduce

1. Open any git project in opencode, let it edit a file, then run /undo (the session now carries a revert marker)
2. Run /redo (or resume the session) so restore() fires — opencode.log will show restore commit=<hash>
3. Compare file mtimes before/after, e.g. find . -type f -newermt "1 minute ago" | wc -l in a quiet project
4. Every indexed file gets rewritten: all mtimes bump, content is byte-identical, git status stays clean

Screenshot and/or share link

No screenshot — log and mtime evidence:

timestamp=2026-08-24T08:48:26.714Z level=INFO message=restore commit=4ca9cb1a5fb02fddc76e8f07cb01a19d404d5034

Same moment, project root: 1012 files rewritten within 2s (928 content files + 84 .obsidian files), git status clean before and after.

Operating System

Windows 10

Terminal

git bash