fix(panels): a collapsed window keeps its chosen height; handle early tile failures

- A floating portable panel saved its measured box, so dragging a
  collapsed window stored its 50 px header strip and a reload clamped it
  to the minimum. It now saves the inline size the user chose. A unit
  test and a collapse -> drag -> reload -> expand step in the panel gate
  pin it.
- Coverage awaits the tile fetch and the one-time terrain table load
  together, so a tile that fails before the table loads is reported at
  once instead of surfacing as an unhandled rejection.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/providers/mapillary/coverage.js

@@ -510,12 +510,14 @@ export function createCoverage({ state, source }) {
     state.coverage.pending.set(key, controller);
     notify();
     try {
-      // Fetch and the one-time terrain-height table load run side by side.
-      const fetching = source.getTile('coverage', tile.z, tile.x, tile.y, {
-        signal: controller.signal,
-      });
-      if (kind === 'sequence') await ensureTerrainReady();
-      const bytes = await fetching;
+      // Fetch and the one-time terrain-height table load run side by side,
+      // both handled from the start so an early tile failure is not unhandled.
+      const [bytes] = await Promise.all([
+        source.getTile('coverage', tile.z, tile.x, tile.y, {
+          signal: controller.signal,
+        }),
+        kind === 'sequence' ? ensureTerrainReady() : null,
+      ]);
       // Only an abort, a retire, a clear or a newer request for this tile
       // discards the bytes; a refresh that still wants the tile keeps them.
       const current = () =>