opencode-cli serve CPU saturated (200%+) by repeated full-patch generation — only workaround is disabling snapshot #21699

Description

When using OpenCode Desktop App (v1.4.0), the bundled opencode-cli serve backend process consistently exceeds 200% CPU during active agent sessions. The only effective workaround is setting "snapshot": false in config, which disables session change tracking and file revert/undo — a significant feature trade-off.

Root cause (CPU profiled):

• Top frame: vcs.ts:63 accounts for ~65% of total sampled time
• Dominant stack: execEditLength ← structuredPatch ← patch3[vcs.ts:53] ← (anonymous)[vcs.ts:63]
• summarize() generates full unified patches on every file event when it only needs summary statistics

Environment:

Suggested fixes (by priority):

1. Separate summary stats from full patch generation — summarize() only needs additions/deletions/files counts, which git diff --numstat provides cheaply. Generate actual patch strings only on demand when the user expands a specific file in the review UI.
2. Debounce + coalesce refreshVcs() — use a dirty-flag + debounce (300–1000 ms) so a burst of file writes triggers only one diff instead of clearing in-flight dedup state on every event.
3. Use git-native patch output instead of JS-side structuredPatch() — moves the O(N·D) algorithm out of the Node event loop entirely.
4. Cache patches by file content hash — skip re-diffing files whose before/after content hasn't changed.

Related: #21470, #19466

Plugins

oh-my-openagent (local)
[email protected]

OpenCode version

1.4.0 (Desktop App, bundled opencode-cli serve)

Steps to reproduce

1. Open a large project with OpenCode Desktop App (keep the Changes/Review panel visible)
2. Start an agent session that edits files across multiple steps
3. Observe opencode-cli serve process CPU climbing above 200% as the session progresses
4. Set "snapshot": false in config to confirm it stops — this is the only workaround, but disables session change tracking

Screenshot and/or share link

CPU profile files are saved at ~/.local/share/opencode/log/cpu-*.cpuprofile and can be loaded in Chrome DevTools Performance tab.

Operating System

macOS 26.2 (Build 25C56), Apple M4 Max, 128 GB RAM, 4 TB SSD

Terminal

OpenCode Desktop App v1.4.0