Write the loader fixture suite, valid and malformed

18 golden fixture boards as real on-disk trees under Fixtures/ — ten
valid/tolerated cases (rich board, interrupted create, non-UUID strays,
stray files, tombstones, tie-breaks, unknown-key order, coercion,
last-wins duplicates, board-level deleted) and eight fail-fast cases,
each pinned to its exact error reason and path; the rich board's whole
tree round-trips byte-identically. Pins two contract subtleties now
recorded in the design: tombstone flags are not inherited (renderers
walk ancestors) and last-wins resolves before order strictness. README
gains the storage-foundation feature entry. 146 tests total.

Claude-Session: https://claude.ai/code/session_018BjQRYBR6jQja3jCRi5S3A

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/attachments/sketch.png

@@ -0,0 +1 @@
+not-a-real-png-just-a-placeholder-attachment

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/comments/60000000-0000-4000-8000-000000000006/index.md

@@ -0,0 +1,8 @@
+---
+schema: 1
+author: rzen
+created: 2026-07-21T08:30:00Z
+---
+Comments are enhanced-schema and out of scope for this version — this
+folder is here only to prove it's preserved verbatim and never descended
+into (cards are leaves; the loader never scans past index.md).

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/30000000-0000-4000-8000-000000000003/index.md

@@ -0,0 +1,17 @@
+---
+schema: 1
+title: "Design the fixture taxonomy"
+order: 1024
+created: 2026-07-20T10:15:00Z
+modified: 2026-07-26T20:07:30Z
+modified-by: claude
+source: DESIGN/01-storage-format.md   # inline comment on a plain scalar
+project: lanework
+sphere: work
+labels: [m1-storage-read]
+---
+Enumerate every fail-fast and tolerated case from the storage format and
+build one golden fixture board per case.
+
+- attachments/ holds a sketch
+- comments/ holds a placeholder future-comment folder

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/40000000-0000-4000-8000-000000000004/index.md

@@ -0,0 +1,9 @@
+---
+schema: 1
+title: Wire up the loader's stray tolerance
+order: 2048
+background: coral
+icon: flag.fill
+iconColor: orange
+---
+Plain, unquoted title this time — mixing styles on purpose.

Fixtures/Valid/rich-board.kanban/10000000-0000-4000-8000-000000000001/index.md

@@ -0,0 +1,10 @@
+---
+schema: 1
+order: 1024
+title: Doing
+width: 2
+background: '#3478F6'
+icon: hammer.fill
+iconColor: blue
+---
+WIP limit: 3 cards. Pull from Backlog only when there's room.