Anchor session undo steps by card identity, not path

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

DESIGN/13-native-undo.md

@@ -4,7 +4,7 @@ The undo/redo substrate for **every board without app-managed git, in every tier
 
 ## Rules
 
-- **Two levels: one stack per board, one per open card window** (re-ruled 2026-07-31 — the session-coarsening model, superseding the pure one-stack rule): the **board stack** is owned by the board session and shared by board surfaces; a **card window owns its own stack** for the session it represents — every gesture issued in that window (comment post/delete/edit, body Edit sessions, style/details changes, attachment ops where undoable) registers there at fine grain, and `window.undoManager` answers with it (standard per-window AppKit scoping). Disk stays live throughout — files-first untouched; this is history granularity only. **Window close coarsens**: the session's net effect registers on the board stack as **one coarse step** ("Edit card 'Fix login'"), values-based, whose undo restores the card subtree to its session-start state — deleted comments included — and whose redo reapplies the net effect; a session with no net change registers nothing. The coarse step is transactional at apply time: staleness validation runs per component (the field-level predicate below), and any stale component skips the whole step — never a partial session revert. 06 ▸ Undo routing applies unchanged — text-editing surfaces get their session-scoped text undo above either stack.
+- **Two levels: one stack per board, one per open card window** (re-ruled 2026-07-31 — the session-coarsening model, superseding the pure one-stack rule): the **board stack** is owned by the board session and shared by board surfaces; a **card window owns its own stack** for the session it represents — every gesture issued in that window (comment post/delete/edit, body Edit sessions, style/details changes, attachment ops where undoable) registers there at fine grain, and `window.undoManager` answers with it (standard per-window AppKit scoping). Disk stays live throughout — files-first untouched; this is history granularity only. **Window close coarsens**: the session's net effect registers on the board stack as **one coarse step** ("Edit card 'Fix login'"), values-based, whose undo restores the card subtree to its session-start state — deleted comments included — and whose redo reapplies the net effect; a session with no net change registers nothing. The coarse step is transactional at apply time: staleness validation runs per component (the field-level predicate below), and any stale component skips the whole step — never a partial session revert. **Session steps anchor by card identity, never by path** (ruled 2026-07-31): the coarse step — and the window's fine steps it folds — stores the card's UUID plus expected values, and apply-time validation resolves the card's *current* folder exactly the way the window itself always resolves its card (the per-snapshot UUID walk; `writeCardBody` already resolves trash locations on purpose). A tracked relocation — a lane move mid-session or after close, a trash move — therefore never stales the step; only genuine content changes do, which is what the validation exists to catch. A card that resolves nowhere (purged, or moved out of the board) is the honest skip. 06 ▸ Undo routing applies unchanged — text-editing surfaces get their session-scoped text undo above either stack.
 - **Registration at the Writer boundary.** Every app-mediated mutation already passes through the Writer as a `WriteOperation` (02-architecture.md) — that closed enum is the exact inventory of undoable operations. Each Writer call site registers the inverse operation, computed from the pre-write snapshot the store already holds: move → move back (original lane, original `order`); reorder → restore original `order`; rename → restore title; restyle → restore prior style; resize → restore prior width; Edit-session body save → restore prior body bytes; card or lane delete (⌫) → move back out of `.trash/` (lanes rejoined the trash 2026-07-29 — the recreate-from-capture inverse retires with the last destructive delete); restore-by-move → move back in; create → remove the created folder.
 - **What is not undoable** (settled): **Permanently delete** (the trash's Delete, Empty Trash) — `purgeIsUnrecoverable` stays true in base, and the existing confirmation rule (03-board-ui.md) already fires on all base boards, since none have git history: the confirm *is* the safety. **The duplicate-id remint** (01-storage-format.md — a silent scheduled heal since 2026-07-29, formerly the user-gated Repair) — heals aren't user gestures, so nothing enters the stack, and undoing one would recreate the duplicate id it exists to remove. Permanently delete matches its existing "destructive, confirmed, final" posture; the remint sits outside undo as all heals do.
 - **Coalescing follows commit granularity** (settled; window scoping added 2026-07-31): one gesture, one undo step — a multi-card move is one step with a plural title; an Edit session is one step, registered at the Edit→Preview flip (the effective Save — 05-card-window.md) **on the card window's stack**, like every window gesture; the window close registers the one coarse session step on the board stack (Rules above); a styling batch is one step (03's one-gesture-one-commit rule, substrate swapped). The 06 vocabulary supplies menu titles ("Undo Move 3 Cards"), via NSUndoManager's dynamic retitling — the same naming machinery both editions use.