Rule the session-commit await, switch-clears-stacks, and skip-purge decoupling

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

DESIGN/13-native-undo.md

@@ -17,7 +17,7 @@ The undo/redo substrate for **every board without app-managed git, in every tier
 
 ⌫'s undo is the move back — a delete is a move into `.trash/` (cards resettled 2026-07-28; lanes rejoined 2026-07-29), so its undo is the ordinary inverse move, returning a card to its source lane and rank, a lane to its strip position (subtree intact — it never left the folder); a restore-by-move undoes the same way in reverse. The stack and the trash never conflict — they are the same folder moves addressed by recency instead of by selection. The old lane-delete recreate-from-capture inverse is **retired** — no destructive delete remains outside a trash, so nothing needs byte capture. A **permanent delete registers no step** — the trash's Delete and Empty Trash are not undoable (Rules above), lanes and their freight included; the confirm is the safety.
 
-**Comments keep the no-capture rule true — on the window stack** (re-ruled 2026-07-31, superseding the board-stack routing): a comment delete is a move into the card's `comments/.trash/` (01-storage-format.md ▸ Enhanced schema — the materialized-trash pattern one level down), its inverse the ordinary move back, and the step lives on the **card window's own stack** (Rules above) — the board stack never carries a granular comment step, so the old stale-after-close skip scenario cannot arise. **The purge of `comments/.trash/` defers with the coarse step** (re-ruled 2026-07-31, superseding purge-at-close): the coarse close step's undo restores deleted comments, so their backing lives as long as the step does — the purge runs when the coarse step leaves the board stack (undone-and-superseded, dropped off the end, or gone stale) or the board session ends; crash residue still sweeps at the next card-window open — **and residue is defined by the purge-deferral condition itself** (ruled 2026-07-31): `comments/.trash/` content referenced by a live coarse step on the board stack is a step's backing, not residue — the open-time sweep consults the stack and skips owned content, re-arming when the owning step leaves the stack (which is exactly when the deferred purge wanted to run; one condition, two consumers). Reopening a window can therefore never destroy its prior session's undo backing. Unowned content sweeps as before, armed-then-cleared like every heal memo. On Pro the substrate is history: the close commit nets delete-plus-purge to a removal, revert restores it, so purge rides the close flush there as before — purge timing follows the undo substrate's need.
+**Comments keep the no-capture rule true — on the window stack** (re-ruled 2026-07-31, superseding the board-stack routing): a comment delete is a move into the card's `comments/.trash/` (01-storage-format.md ▸ Enhanced schema — the materialized-trash pattern one level down), its inverse the ordinary move back, and the step lives on the **card window's own stack** (Rules above) — the board stack never carries a granular comment step, so the old stale-after-close skip scenario cannot arise. **The purge of `comments/.trash/` defers with the coarse step** (re-ruled 2026-07-31, superseding purge-at-close): the coarse close step's undo restores deleted comments, so their backing lives as long as the step does — the purge runs when the coarse step leaves the board stack **cleanly** — undone-and-superseded, or dropped off the end — or when the board session ends; **a stale-skipped step's backing instead survives to board-session end** (ruled 2026-07-31, decoupling skip from purge): the skip banner says nothing was applied, and an irreversible purge riding that gesture would be surprise loss — the skip is exactly when the user may want to inspect what the collision left; crash residue still sweeps at the next card-window open — **and residue is defined by the purge-deferral condition itself** (ruled 2026-07-31): `comments/.trash/` content referenced by a live coarse step on the board stack is a step's backing, not residue — the open-time sweep consults the stack and skips owned content, re-arming when the owning step leaves the stack (which is exactly when the deferred purge wanted to run; one condition, two consumers). Reopening a window can therefore never destroy its prior session's undo backing. Unowned content sweeps as before, armed-then-cleared like every heal memo. On Pro the substrate is history: the close commit nets delete-plus-purge to a removal, revert restores it, so purge rides the close flush there as before — purge timing follows the undo substrate's need.
 
 ## Out of scope