The board wears a picture — background becomes a mapping, and the window chrome follows it under a thin frost

background is {color:, image:} and only a mapping at every level; the board's image paints the full window under a transparent title bar, with a thin-material frost strip keeping the chrome legible and the standard accommodations intact.

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

DESIGN/01-storage-format.md

@@ -49,7 +49,7 @@ MyBoard.kanban/                                  ← board = the document
 | `created` | ISO-8601 | no | Set at creation, with timezone |
 | `modified` | ISO-8601 | no | Updated on every app write **that rewrites this `index.md`** — see below |
 | `modified-by` | string | no | Self-reported writer identity, set by external writers only; the app clears it on every write — see below |
-| `background` | string | no | Palette name or `#RRGGBB[AA]` — see 03-board-ui.md |
+| `background` | mapping | no | `{color: …, image: …}` — `color` is a palette name or `#RRGGBB[AA]` hex (03-board-ui.md), `image` a file path. Both subkeys optional, either half may stand alone, unknown subkeys preserved verbatim like any unknown key. `image` is a path **relative to the board root** (absolute paths and any path escaping the root resolve to nothing) and is **board-level only**: lanes and cards read `color` and ignore the rest. **A mapping is the only shape** (ruled 2026-08-06, before anything shipped — so no legacy spelling, no version bump, no migration): a bare scalar `background: green` has no reading, rendering as no color, coerce-tier logged, bytes preserved — the standard lenient degrade. |
 | `icon` | string | no | SF Symbol name, per-level defaults |
 | `iconColor` | string | no | Palette name or hex |
 | `kind` | string | no | The object's kind — `board`, `lane`, `card` (`comment` — its storage schema now specified, Enhanced schema below). **Written at creation of every object** (re-ruled 2026-07-29 — consistency across the schema, even where position already answers). The value — never the key's mere presence — names the kind, and consumers that consult it trust the value outright: no stripping, no corroboration machinery. Only consequential inside `.trash/` today, where position can't answer (Deletion below); everywhere else it is redundant with position (level is position) and carried for uniformity. Missing on an older object, it **backfills on touch** — the integrity service's on-touch heal (Validation and healing below), never a scheduled sweep. |

DESIGN/03-board-ui.md

@@ -33,7 +33,7 @@ Toolbars are **pure enhancement**: every function they host already has a menu i
 
 ### Capabilities (settled)
 
-- **`background`** on board / lane / card: palette name (kebab-case, hand-editable) or `#RRGGBB[AA]` hex. Board color paints the board window's content background (the surface behind and between lanes). Lane and card color are **edge accents, not fills** (settled in the pathfinder's treatment shootout — its settings matrix of C-series lane / K-series card variants landed on **C7 · full-column top edge** and **K1 · left edge stripe**): a lane's color paints a full-width band along its top edge, a card's a stripe along its left edge; the surfaces themselves keep the standard chrome, so colored title text never sits on a colored fill.
+- **`background`** on board / lane / card: a mapping, `{color: …, image: …}`, and only a mapping (settled 2026-08-06 — 01-storage-format.md § Frontmatter; a bare scalar has no reading and paints nothing). `color` is a palette name (kebab-case, hand-editable) or a `#RRGGBB[AA]` hex; either subkey may stand alone. Board color paints the board window's content background (the surface behind and between lanes). **A board's background may also carry an image**: the `image` path is relative to the board root so the picture travels with the document. Color and image both paint the **full window** — the content runs under a transparent title bar, with a frosted strip across the title-bar/toolbar band keeping the chrome legible over them; the extended chrome applies only while the board has a background of its own, and a board without one keeps the standard chrome unchanged. The image draws over the color, scaled to fill and cropped, with the color standing in while it loads or if it can't be read; an unresolvable path paints nothing, the lenient degrade an unrecognized color already gets. **There is no in-app control for the image** — the raw file is the escape hatch (the stance custom hex held until the 2026-08-06 combo reversal; for images it stands) — and **the board-level ink rule still derives from the color reading alone**: an image makes no AA claim (10-accessibility.md), since a picture has no single luminance to threshold against. Lane and card color are **edge accents, not fills** (settled in the pathfinder's treatment shootout — its settings matrix of C-series lane / K-series card variants landed on **C7 · full-column top edge** and **K1 · left edge stripe**): a lane's color paints a full-width band along its top edge, a card's a stripe along its left edge; the surfaces themselves keep the standard chrome, so colored title text never sits on a colored fill.
 - **The standard chrome is the pathfinder's surface stack** (settled 2026-08-06): the window keeps the neutral system background; every lane wears a quiet quaternary-wash plate (the trash plate's own figure — translucent, so a board-chosen color shows through and the board-level ink rule keeps its premise; opaque under Reduce Transparency, the trash precedent); every card sits on an opaque `controlBackgroundColor` plate — white over the washed lane in light appearance, a step *darker* than the window in dark. One plate value for every face a card draws (resting, replicas, placeholder, arriving), so a card is the same object wherever it renders.
 - **`icon`**: SF Symbol per item with per-level defaults (board `rectangle.split.3x1`, lane `square.stack`, card `doc.text`).
 - **`iconColor`**: resolved — **schema yes, control no**. The field renders when hand-written (tint palette name or hex); the app offers no control for it (Controls below).