[regnull]

Summary

Port OpenCode's MIT-licensed snapshot approach (snapshot/ service) so every run records which workspace files it changed and a unified diff — all without touching the workspace's own .git.

Closes #257.

How It Works

Each workspace gets a dedicated, bare git repository under .openbot/snapshots/<sha256-of-workspace-path>. Before a run, the runner fingerprints the workspace with git add -A && git write-tree against that store; after the run ends (completed / failed / cancelled / undeliverable human question), it captures a second tree and diffs the two with git diff-tree --name-status -r -z (for the file list) and git diff-tree -p (for the unified diff).

The store's index is rebuilt from the worktree on every capture — three concurrent bots editing the same workspace never interleave writes because captures are serialized per-storedir (in-process asyncio.Lock), and git itself provides index.lock for cross-process safety.

What Changed

Layer	File	Change
New	backend/openbot/runtime/snapshot.py	SnapshotStore class + store_for_run helper — entire snapshot/diff engine (credit comment links OpenCode MIT source)
New	backend/openbot/db/migrations/versions/0023_run_snapshots.py	Adds changed_files (JSON) and diff (Text) columns to runs
New	backend/tests/test_snapshot.py	7 tests: store init, capture+diff, gitignore/OOB exclusion, deletions, no-change empty diff, full runner wiring with actual tool calls
Modified	backend/openbot/db/models.py	Run.changed_files + Run.diff mapped columns
Modified	backend/openbot/api/schemas.py	RunOut.changed_files + RunOut.diff
Modified	backend/openbot/runtime/runner.py	_snapshot_capture_before, _snapshot_store_after, _snapshot_attach_terminal methods; wired into execute() at start and all terminal paths (completed / cancelled / failed / undeliverable ask_human)
Modified	backend/openbot/runtime/cli_agents/run.py	CLI agent path now calls _snapshot_attach_terminal instead of _set_status for its terminal status
Modified	frontend/src/api/types.ts	Run interface gets changed_files?: string[] | null + diff?: string | null
Modified	frontend/src/components/RunCard.tsx	New "Changed" section: file count, up to 4 filename badges, "+N more", collapsible <details> unified diff

Design Decisions

• No revert. Several bots share one workspace; reverting one run's snapshot would clobber other bots' edits.
• Best-effort, never blocking. A failed snapshot capture or diff is logged as a warning and the run proceeds normally — changed_files simply stays None.
• Gitignore-respecting. The store inherits the workspace's own .gitignore, .git/info/exclude, and global excludes. .openbot is additionally always excluded via the store's info/exclude, so OpenBot state is never recorded as a run's changes.
• Rename detection disabled. --no-renames on diff-tree matches OpenCode's behavior: one run's delete+recreate of a file shows as delete+add, which is clearer in a per-run audit.
• Before-tree persists across resumes. A run paused on ask_human re-enters execute() on resume; its original before-tree is keyed in self._snapshot_before so the final diff spans the entire multi-segment run.

Test Results

• Backend: 848 passed (841 base + 7 new), 30 deselected, 0 failures — ruff check clean
• Frontend: 349/351 passed — 2 pre-existing failures in electron/main.test.ts (unrelated --root-directory test, also fails on main), tsc --noEmit clean, pnpm lint 0 errors (1 pre-existing set-state-in-effect warning)