[BUG] /vcs/diff spawns one git show HEAD:<file> process per changed file after large refactors #24739

Description

When the web/desktop review diff state refreshes after a large refactor, OpenCode can spawn hundreds of short-lived Git processes like:

git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:src/features/review/diff-view.ts
git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:src/services/git/diff-cache.ts
git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:test/review-panel/diff-refresh.test.ts

I observed this after a large refactor where many tracked files changed. The process list showed many concurrent/repeated git show HEAD:<path> commands for different files, including repeated paths.

The root cause appears to be the VCS diff path:

• packages/app/src/pages/session.tsx invalidates VCS diff on file.watcher.updated events.
• That triggers /vcs/diff.
• /vcs/diff reaches packages/opencode/src/project/vcs.ts.
• files(...) iterates the changed file list.
• For every non-added tracked file, it calls git.show(cwd, ref, item.file, base).
• git.show(...) runs git show ${ref}:${path} as a separate Git process.

So one VCS diff refresh over N modified/deleted tracked files can spawn roughly N git show HEAD:<file> processes. After a large refactor, watcher-triggered refreshes can multiply that cost.

This is separate from the broader full-context patch/OOM problem tracked in other issues. Even before addressing patch payload size, the current implementation creates avoidable process fan-out while loading the old HEAD contents for changed files.

A more scalable implementation would batch these old blob reads, for example with git cat-file --batch, similar to the existing snapshot diff batching precedent.

Related but not identical:

• High CPU Utilization Due To Repeated Git Process Invocations #9059 reported repeated git show processes, but was closed stale.
• fix(watcher): filter ignored paths before publishing events, handle worktree git dirs #21453 addresses watcher filtering and worktree .git paths.
• .watchman-cookie-* files in git worktrees cause periodic /vcs/diff requests #24357 addresses Watchman cookie files causing periodic /vcs/diff.
• /vcs/diff can OOM in desktop-layout web UI on umbrella workspaces with many nested git repos #24049 / perf: diff pipeline causes severe UI lag on desktop — full-context patches + synchronous parsing on main thread #22650 / TUI hangs indefinitely when resuming sessions with large file diffs (formatPatch/structuredPatch blocks event loop) #23362 track broader /vcs/diff OOM, full-context patches, and UI lag.

Plugins

No response

OpenCode version

Current dev branch / observed locally while working on upstream source.

Steps to reproduce

1. Open a git-backed project in the web/desktop UI.
2. Ensure the review/changes diff state is active or can be refreshed by file watcher events.
3. Make a large refactor touching many tracked files.
4. Observe OS process list while /vcs/diff refreshes.
5. Many commands of this form are spawned:

git ... show HEAD:<changed-file>

Expected behavior: /vcs/diff should not spawn one Git process per changed file. Old blob contents should be loaded in a batched way.

Actual behavior: /vcs/diff fans out to many git show HEAD:<file> processes.

Screenshot and/or share link

Example process list excerpt with generated placeholder file paths:

git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:src/features/review/diff-view.ts
git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:src/services/git/diff-cache.ts
git --no-optional-locks -c core.autocrlf=false -c core.fsmonitor=false -c core.longpaths=true -c core.symlinks=true -c core.quotepath=false show HEAD:test/review-panel/diff-refresh.test.ts
...

Operating System

macOS

Terminal

N/A