web: Review tab stuck loading when session directory is not a git repo

Summary

The web UI Review tab spins forever on "loading changes" when the session directory is not a git repository (e.g. a working directory containing multiple service repos). Both backing APIs return empty data, but the UI never renders an empty state. Related: there is no way to switch the Review scope to a different repo without moving the whole session.

Environment

• opencode version: 2.0.3 (background service, healthy; serve --service, pid confirmed via /api/health)
• OS: Linux 6.18.33.2-microsoft-standard-WSL2 x86_64
• Terminal: TERM=xterm-256color
• Shell: /bin/bash
• Install/channel: latest (npm @opencode/cli); opencode2 beta build also present but the serving instance is 2.0.3
• Active plugins: none found in config

Reproduction

1. Open (or move) a session whose location.directory is a plain directory that is NOT a git repository — e.g. /root/work which contains multiple independent service repos/worktrees (git rev-parse → fatal: not a git repository).
2. Open the web UI (served by the same server, e.g. http://127.0.0.1:49374, Basic auth user opencode) and click the Review tab (审查).
3. The panel shows "loading changes" indefinitely.

Expected Behavior

• When there is nothing to review, the panel should render an empty state (e.g. "no changes") instead of loading forever.
• Ideally the Review scope can be switched to a specific repo (location) without moving the session, since VCS routes are already location-scoped and POST /api/session/{sessionID}/move exists for changing the project directory.

Actual Behavior

• Infinite loading spinner; no empty state, no error.
• Backing API evidence (all via opencode api, which uses the same discovery+auth flow as first-party clients):
  • GET /api/session/{id}/diff → {"data":[]}
  • GET /api/vcs/status → {"location":{...,"directory":"/root",...},"data":[]} (project resolves away from the non-git session dir, empty file list)
  • GET /api/vcs/diff without mode → 400 InvalidRequestError "Missing key at [\"mode\"]" (mode is required: working | branch | committed)

Additional Context

• Frequency: consistent — reproduces every time the session directory has no git repo.
• The empty-data case likely misses an empty-state branch in the web client; the fetch itself succeeds (200 with []), so this looks like a frontend handling gap rather than a server error. No error lines related to vcs/diff in ~/.local/share/opencode/log/opencode.log (role=server).
• Workaround tried: none helps in place; reviewing per-repo requires opening a session scoped to that repo directory (one session per project directory, matching the session/move design) or falling back to git status/git diff in a terminal.
• Related feature ask: allow the Review tab to pick/switch the repo (location) when the session directory spans multiple repos.