feat(kanban): 'shutting down' state for tasks awaiting teardown

[ittaiz]

Problem

There is often a long delay (up to the multi-second worktree/tmux teardown) between clicking "move to complete" and the task actually moving. The teardown runs synchronously in moveTask (destroySession → cleanup script → removeWorktree). Until now the board card sat fully clickable in its column with no indication until it abruptly moved — most visible on the agent-approved completion path (App.tsx onAgentCompletionRequested), which sets no local moving flag.

What this does

Adds a "shutting down" card state — the visual/interaction opposite of the blue todo→in-progress "preparing" loader.

• Backend: moveTask decorates a transient, never-persisted shuttingDown flag onto a taskUpdated push at the start of the teardown branch; the terminal taskUpdated clears it. Works for every client (board + remote browser) and both completion paths.
• Card: muted / grayscale "powering down" overlay — grey spinner, SHUTTING DOWN + Closing session & worktree, no progress bar (teardown duration is unknowable; a draining bar would be fake progress, violating the manifest's forward-only-honesty rule).
• Interaction guard: while shutting down the card is not openable (unlike preparing, which stays openable — here the worktree/session are being destroyed), not draggable, no context menu, no hover preview.

UX plan (via /ux-principal)

Manifest-compliant (Task-card status state, Bible §5/§6/§8/§11, §1.1 honesty) — no new destination/surface/token/object, so zero manifest doc writes. Visual direction ("powering down", muted + indeterminate) confirmed with the requester.

Why transient, not persisted like preparing

See decisions/102-shutting-down-transient-not-persisted.md: a persisted flag could strand a card as "shutting down" after a crash/reload (violates the ~/.dev3.0/ no-stuck-state intent). The flag never reaches data.updateTask.

Tests

• Backend: shuttingDown push fires before teardown (removeWorktree) and is never passed to data.updateTask.
• Card: overlay renders (role=status, aria-busy, no progressbar); click does not open; not draggable.
• Full suite green (mainview 1974 + bun 1779).

Browser QA

Verified in a real browser (headless Chromium) by injecting the state client-side via the real rpc:taskUpdated push path (no backend teardown, no data mutated). Overlay renders muted/greyed with spinner; pointer-events:none; click does not open; no console errors. Screenshots attached to the task.

Test instructions

1. On a project board, take a task with a worktree (in-progress / review) and move it to Completed (drag to the column, or the card status menu → Completed) — or approve an agent's dev3 task move --status completed dialog.
2. Expected: while the worktree/session tear down, the card greys out and shows a small "Shutting down… / Closing session & worktree" overlay with a spinner (no progress bar).
3. Try to click the shutting-down card → nothing opens. Try to drag it → it won't drag. Right-click → no context menu.
4. When teardown finishes, the card moves to Completed and the overlay is gone.
5. Reload mid-teardown (or after a crash): no card is ever stuck in "shutting down".

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