Tilemap cells are stored compactly in the project file: each layer keeps a tile list, an origin and one run-length encoded string per row; older projects with a cell map still load (#134)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/e2e/40-tilemap.mjs

@@ -66,6 +66,7 @@ async function cellShows(t, x, y, quadrants) {
 
 export async function tilemap(t) {
   const { check, json, evaluate, mutate, click, clickText, drag, press, shot, settle, undo, select } = t;
+  const { saved, api, navigate, projectId } = t;
 
   await press('Escape');
   await evaluate('__gm.state.select(null)');
@@ -292,6 +293,33 @@ export async function tilemap(t) {
     const o = __gm.state.activeScene.objects.find((o) => o.id === ${JSON.stringify(MAP_OBJECT)});
     o.position = { x: 0, y: ${LANE}, z: 0 };`);
 
+  // 40k. The file holds the cells compactly (#134): per layer the tiles once and a string of runs
+  //      per row, no key per cell. A reload reads them back into exactly the same cells.
+  const inMemory = await json(
+    `__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(made.id)}).layers.map((l) => l.cells)`,
+  );
+  await saved();
+  const storedMap = (await api(`projects/${projectId}`)).project.assets.find((a) => a.id === made.id);
+  const storedLayers = storedMap?.layers ?? [];
+  check(
+    'the saved map stores each layer as its tiles and a run string per row, not a key per cell',
+    storedLayers.length === 2 &&
+      storedLayers.every((l) => l.cells === undefined && Array.isArray(l.rows)) &&
+      storedLayers[0].tiles.join() === 'at-grass' &&
+      storedLayers[0].rows.every((r) => typeof r === 'string'),
+    JSON.stringify(storedLayers.map(({ tiles, origin, rows }) => ({ tiles, origin, rows }))),
+  );
+  await navigate();
+  const reloaded = await json(
+    `__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(made.id)}).layers.map((l) => l.cells)`,
+  );
+  const sorted = (layers) => JSON.stringify(layers.map((c) => Object.entries(c).sort()));
+  check(
+    'a reloaded project has exactly the cells it was saved with',
+    sorted(reloaded) === sorted(inMemory) && Object.keys(inMemory[0]).length === 9,
+    JSON.stringify({ reloaded, inMemory }),
+  );
+
   // Leave the editor as the rest of the suite expects to find it.
   await evaluate("__gm.state.setTilemapPaint({ tool: 'select' })");
   await evaluate('__gm.state.select(null)');