Collapsible lanes — frontmatter-backed slim strips outside the width division

A lane folds to a fixed slim vertical strip carrying its glyph, its card-count
badge and its title turned on its side, and the strip is deliberately not part
of the window's division: the expanded lanes' units divide what is left once
each folded strip's fixed width has come off the top, so folding a lane is a
re-divide trigger of the Show/Hide Trash family — the window never moves and
the siblings grow into what the lane gave up.

The state is a first-class lane frontmatter key, `collapsed: true`, and
document state exactly as `width` is: the files are the board, so an agent
folds a lane by writing one key. Absent means expanded, expanding removes the
key rather than writing `false` (the remove-at-default family beside a
one-unit `width`, the empty rename's `title` and the None well's
`background`), and the lane's `width` rides along untouched so expanding
restores the lane the user had. The read is `width`'s leniency one type over —
a boolean scalar or a quoted boolean word reads as itself, everything else has
no reading at all and renders as expanded, bytes preserved either way.

Toggling is the header's always-visible collapse chevron, the lane context
menu's single Collapse Lane / Expand Lane row, and a plain click anywhere on
the strip; a modified click on the strip stays the ordinary selection grammar,
so a folded lane is still selectable by pointer. The title reads bottom-up and
is justified to the top of the room below the strip's chrome (owner ruling
2026-08-08), truncating against the strip's own height.

While folded the lane draws no cards at all, which is what makes every
exclusion true by construction rather than by a guard per gesture: no card
face means no marquee target and no navigation frame, and no registered grid
means the masonry's drop zones have nothing to resolve against. What did need
code is the half that names absolute destinations — the option-arrow jumps and
the arrow seed scan past a folded lane, the lane domain's down-arrow is inert
on one, and New Card skips it (a selection inside one falls through to the
last-active lane, the stale selection's rule). A drop on the strip appends at
the lane's end, cards and Finder files alike, with an accent edge standing in
for the shadow the strip has no masonry to open; there is no hover-to-auto-
expand yet. Lane reorder works on the strip, and a dragged folded lane carries
its fold, so its shadow and its replica are the strip rather than its units.

The write is `writeLaneWidths` clause for clause — one `updateIndex` bracket,
the same stamp behaviour, the same three do-nothing paths — with two new
`WriteOperation` cases and two new undo verbs rather than one of each, because
a banner or an Edit-menu row that said "resize" after Collapse Lane would name
a control the user never touched.

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

DESIGN/03-board-ui.md

@@ -21,6 +21,7 @@ Toolbars are **pure enhancement**: every function they host already has a menu i
 - Title bar: leading SF Symbol (the lane's `icon`), title, **card-count badge** (quiet, secondary styling), new-card button. The whole title bar is the lane's drag surface — no separate grip; a plain click (no movement) on it selects the lane (04-interactions.md ▸ Selection). **The lane has one context menu** (settled), invoked on the header or on lane empty space alike — Rename, Style…, the quick-style recents row, the Width stepper, Delete (inventory normative in 11-command-nexus.md ▸ Context menus); a full lane still has its header, so the menu is always reachable. The count reads the search filter like every other surface (04-interactions.md): during a search it shows the visible count, not the total.
 - Body: vertical card stack (masonry grid when wide — settled, the pathfinder's masonry works), scrolls vertically.
 - Right-edge **drag-to-resize** between integer widths (1×, 2×, 3×, … — no cap): shadow snaps at the inter-column gap with 10pt release hysteresis; the window grows/shrinks by one standard width per snap so other lanes keep their exact size. **At the screen's visible frame the window stops and the drag degrades to the re-divide** (settled 2026-08-08, superseding the pathfinder's hard stop): further snaps re-divide the now-fixed width across one more unit each — siblings compress, exactly the stepper's mechanism — so a lane keeps growing at the siblings' expense once the screen is spent; a window with no headroom to begin with (already at the edge, or full screen) re-divides from the first snap. The two regimes meet without a pixel jump — the re-divided standard at the screen fit *is* the frozen standard. Shrinking mirrors it: re-divide back down to the screen fit, then window shrinking resumes (and shrinking is always allowed). The rubber-band feedback (the dragged edge gives a fraction of the overshoot and snaps back, signalling the bound) moves to the true end of travel — the strip's own capacity — and the window still never overflows the screen. The header context menu's Width control (stepper, uncapped) remains the precise control: it never touches the window, it **re-divides** the existing width across the new unit total (siblings compress); the drag now reaches those widths too, but the stepper stays the exact, accessible path. The **Increase/Decrease Lane Width menu items (⌥⌘→/⌥⌘← — 11-command-nexus.md) are this stepper's keyboard face** — same re-divide semantics, never the window's size; window-growing behavior belongs to the drag alone — and they **batch over a multi-lane selection** (settled, the styling precedent): each selected lane steps one unit, one gesture, one commit; the context-menu stepper itself stays single-lane by nature. **A width write landing on 1 removes the `width` key** (settled — the remove-at-default family: the empty rename removes `title`, the None well removes `background`): a default lane's frontmatter stays clean, drag, stepper, and menu items alike; a hand-written `width: 1` is legal and preserved until the app itself next edits width. **A failed width commit at drag release rolls the window back** (settled): the failure surfaces as the ordinary one-shot banner and the window animates back by the uncommitted delta — 02-architecture.md's write-failure honesty (the action visibly doesn't happen) applied to the one control that moves the window.
+- **Collapsed lanes** (settled 2026-08-08): a lane folds to a **fixed slim vertical strip** — its `icon`, its card-count badge, its title rotated a quarter turn **counterclockwise so it reads bottom-up** (the book-spine orientation) and **justified to the top** of the room below that chrome (ruled by the owner 2026-08-08, reversing the top-down reading of the first pass), and its accent band, at a fixed width (~44pt, an em multiple like every other figure) — and **the strip is not part of the width re-division**: the window's width divides across the *expanded* lanes' units alone, with each collapsed strip's fixed width taken off the top, so folding a lane is a re-divide trigger of the Show/Hide Trash family (the window never moves and the siblings grow into what the lane gave up). Persistence is a first-class lane frontmatter key, `collapsed: true` — **document state exactly like `width`**, because the files are the board and an agent must be able to fold a lane by editing frontmatter; absent means expanded, expanding **removes** the key (never writes `false` — the remove-at-default family), and the lane's `width` is preserved untouched while collapsed so expanding restores the lane the user had. **Toggling**: the header's trailing collapse chevron (always visible beside the new-card button — the header has no hover chrome to match), the lane context menu's single **Collapse Lane** / **Expand Lane** row (single-lane like the width stepper, not batched), and a plain click anywhere on the collapsed strip, which expands it; a modified click on the strip stays the ordinary selection grammar, so a folded lane is still selectable by pointer. Rename and the expanded header's double-click behaviours are unchanged. **While collapsed**: no resize handle (the width stepper and ⌥⌘→/⌥⌘← still edit the preserved key), and the lane's cards are **not rendered at all** — which is what excludes them from the marquee sweep, from spatial keyboard navigation, and from the ⌥-arrow jumps (↓ from a folded lane is inert, like an empty one), and what makes ⌘N skip the lane for creation (a selection inside a folded lane falls through to the last-active lane rather than refusing). A drop on the strip **appends at the lane's end**, like an end-of-lane drop, with an accent edge standing in for the shadow the strip has no masonry to open; there is no hover-to-auto-expand in v1 (future work). Lane reorder drag works on the strip, and a folded lane's replica and drop shadow are the strip rather than its units. **Search still matches cards in collapsed lanes** — the badge and the flatten lists count them, since collapse is a presentation fold rather than a filter — but the lane stays folded and shows no match: pointing into a folded lane is not something the current search presentation can do, and the honest minimum is that the query does not fold or unfold anything. The **trash quasi-lane is not collapsible**; multi-select styling and the Style editor are unaffected.
 
 ## Card face