Trash quasi-lane spans a fixed width unit; Show Trash re-divides

Resolves 03's internal conflict: the shown trash consumes one fixed
width unit (no width frontmatter, not resizable) and Show/Hide Trash
joins the re-divide trigger list — lane units + 1 while shown. Small
windows compress like any lane add.

Claude-Session: https://claude.ai/code/session_01HJ7PhFNmQ19bvy9RMD6GSb

DESIGN/03-board-ui.md

@@ -4,7 +4,7 @@ The board window: layout, lanes, cards, and styling. Interaction mechanics (sele
 
 ## Layout — full visibility
 
-- **Every lane is always on screen.** The window width divides across the lanes' width units — no horizontal scroll, no enforced minimum lane width. Resizing the window is the width control. (Settled emphatically in the old app: horizontal scroll strays from what kanban is for.) The degenerate case is accepted, not floored: enough lanes/units in a small window compress every lane, titles and cards truncate gracefully, and the remedy is the user's (fewer units, bigger window). A minimum-width setting that reintroduces scroll was considered in the pathfinder and deliberately rejected. **Lane-count changes re-divide, never resize**: new lane (⇧⌘N), lane paste or cross-board lane drop, lane tombstone, and Put Back all re-divide the existing window width across the new unit total — window-growing behavior belongs to the right-edge drag alone (Lane below).
+- **Every lane is always on screen.** The window width divides across the lanes' width units — no horizontal scroll, no enforced minimum lane width. Resizing the window is the width control. (Settled emphatically in the old app: horizontal scroll strays from what kanban is for.) The degenerate case is accepted, not floored: enough lanes/units in a small window compress every lane, titles and cards truncate gracefully, and the remedy is the user's (fewer units, bigger window). A minimum-width setting that reintroduces scroll was considered in the pathfinder and deliberately rejected. **Lane-count changes re-divide, never resize**: new lane (⇧⌘N), lane paste or cross-board lane drop, lane tombstone, Put Back, and Show/Hide Trash (the quasi-lane's fixed unit joins and leaves the division — Trash below) all re-divide the existing window width across the new unit total — window-growing behavior belongs to the right-edge drag alone (Lane below).
 - A lane spans a **whole number of width units** (`width` frontmatter, ≥ 1, no cap). Cards stay standard width; a wide lane flows them into as many interior masonry columns as it has units.
 - New lanes are created via a **File-menu item** (the one committed surface; ⇧⌘N — 11-command-nexus.md); new cards from the lane (see 04-interactions.md for creation flows).
 
@@ -60,7 +60,7 @@ The window-title widget opens the **board popover** — the one board-level surf
 
 Deletion is a two-stage, Finder-style story: ⌫ tombstones (01-storage-format.md), and the **trash quasi-lane** is where tombstoned items live on screen. It is a **pure view** — tombstoned cards keep their `deleted:` key and stay exactly where they are on disk; nothing about the storage schema is trash-specific.
 
-- **Rendering**: trailing (rightmost) position, visually distinct — dimmed/hatched header, trash SF Symbol, count badge; no new-card button; not draggable, not resizable, excluded from lane reordering and width math.
+- **Rendering**: trailing (rightmost) position, visually distinct — dimmed/hatched header, trash SF Symbol, count badge; no new-card button; not draggable, not resizable, excluded from lane reordering. It spans a **fixed one width unit** — no `width` frontmatter, and neither the stepper nor the edge drag applies — consumed only while shown: Show/Hide Trash is a re-divide trigger (Layout above), dividing the window across lane units + 1. A small window compresses like any lane add — accepted, not floored.
 - **Contents**: the board's tombstoned cards, sorted by `deleted` timestamp (newest first). A tombstoned *lane* appears as a single restorable entry — its cards were hidden with it, not individually tombstoned, and it restores as a whole.
 - **Visibility**: hidden by default; **View ▸ Show Trash** toggles it (⇧⌘T; stable title with checkmark state, per 04-interactions.md's configurable-bindings rules). Transient board-scoped state, held in the BoardStore (02-architecture.md; one board window per board, so board-scoped and per-window coincide today) — resets to hidden on open, not persisted (visiting the trash is an errand, not a layout choice). Hidden trash is invisible to search; shown, it participates in the filter like any lane.
 - **Put Back** (context menu, Finder vocabulary; ⌘⌫ on a tombstoned selection — Finder's own symmetry): removes `deleted:` — the item reappears in its lane at its old `order` (ties break deterministically). Putting back a card whose parent lane is tombstoned restores the lane too. Restore fidelity is perfect because nothing ever moved.