[frenchie4111]

Hotfix candidate for 2.18.1.

Symptom

In 2.18, switching tabs or creating a tab on a remote takes minutes or looks broken. It shows up in both "All" (Fleet) mode and single-host mode with a remote active.

Root cause

Logs from an affected remote (agentjesus):

• harness-server was at 335% CPU and 5.4 GB of memory.
• About 2,000 worktree:isDirty requests were sent in one burst. Each took 7+ minutes to answer.
• The server's event loop was freezing for 8–20 s at a time.
• The client renderer sat at 2–3% CPU the whole time, so it was just waiting on the server.

Fleet view (#344) feeds App from getMergedWorktrees. Its cache is keyed on each backend's whole AppState, which is a new object after every event, so the merge reruns on every streamed token. Every output (flatWorktrees, the owner maps, and so on) came back as a new array or map each time, even when nothing in it had changed.

Cleanup.tsx's dirty-scan effect depended on that array. While the modal was open, every token re-sent a git status for every worktree, and every deletion made from the modal re-sent the whole sweep again. On the remote, each of those git calls stalls the event loop while it starts, so tab switches and new tabs queued behind thousands of reads. Cleanup also sent every check to the active backend rather than the one hosting each worktree.

Fix

• merge-backend-states.ts: each merged output keeps its previous reference unless its contents changed, and the whole result does too when nothing did. Every other consumer of these lists also stops re-firing on every token.
• Cleanup.tsx: each worktree is checked once per open, isDirty and getBranchCommits go through backendFor(path), and the activity log loads once instead of on every update.
• Server (main/index.ts): concurrent isDirty requests for the same path and priority share one git call, so a client still on 2.18 can't overwhelm an updated server.

Testing

• npm run typecheck, npx electron-vite build and npx vitest run (2238 tests) all pass.
• Three new tests in merge-backend-states.test.ts cover reference reuse.
• Not reproduced end to end in the app. The diagnosis comes from the remote's perf.log and the code.

A remote that is already stuck has to have harness-server restarted to clear its backlog.

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