Street Level: Panoramax review follow-ups (gekh, #1134)

Image loading (photoViewer.js)
- One AbortController per open: a new open, close or unmount stops the
  previous photo's first and sharper downloads (an <img> by src = '').
  A collapsed viewer never falls back to the original; Panoramax's flat
  fallback is the thumbnail. A superseded open resolves quietly.
- Flat HD tracked as "loading" and "shown" apart: a discarded response no
  longer blocks later upgrades, and resizes while it loads ask once.
- No upgrade of the photo still shown while another opens.
- Size limits before decoding: imageSize.js reads JPEG/PNG/WebP/GIF
  headers; more than 64 MP or 16,384 px a side is refused undecoded, an
  <img> that decodes larger is refused and let go, flat HD needs a known
  width of at most 8,192 px, and panoramas always decode with a resize.

Panoramax provider
- Retry-After parsed as seconds or an HTTP date; the browser cannot read
  it here, so busy answers back off 5 s doubling to 300 s, reset once
  answered.
- Headers timed, then the body by an idle timeout (15 s of silence), so a
  slow link still gets its megabyte tiles.
- Cones centre only on the picture shown (onShowing), never on a late
  lookup; lookups nobody waits for are aborted (shared, refcounted).
- onReopen: a GPU reset redraws in the viewer, not through the core.
- Cones draw the home z15 tile at once and add neighbours as they arrive;
  a neighbour that failed is not counted as drawn.
- Coverage tiles decode in ~8 ms slices (a 2 MB z10 tile over Paris was
  one ~85-200 ms task); sorted by measured length without a Map.
- Box search asks for 20, not 100 (the API returns them nearest first).
- looksLikeEmail checks every '@'; creatorOf de-duplicates with a Set.

lineCoverage.js
- A redraw while a swap still builds keeps what is on screen (the swap's
  old lines and its ready new ones) and drops only the unready ones.

Tests for each (mutation-checked), two vacuous tests made real, the
cones' pictures lane and readable()'s busy/timeout paths covered; the
fixture's box search is nearest first. Docs: README filters and share
links, CHANGELOG HD wording, CURRENT-STATE.

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

src/layers/streetLevel/lineCoverage.js

@@ -247,7 +247,6 @@ export function createLineCoverage({
     entry.castRequested = false;
     entry.meshParts = null;
     if (swap && entry.kind === 'sequence' && entry.primitives?.length) {
-      finishSwap(entry);
       redrawTile(entry);
       return;
     }
@@ -373,7 +372,22 @@ export function createLineCoverage({
 
   /** Rebuild a tile's lines; the old ones stay up until the new are ready. */
   function redrawTile(entry) {
-    const previous = entry.primitives;
+    let previous = entry.primitives;
+    if (entry.swap) {
+      // A swap still building: what is on screen is its old lines and
+      // whichever new ones are ready. Those stay; the rest never showed.
+      const shown = [...entry.swap.old];
+      const building = [];
+      for (const record of previous)
+        (record.primitive.ready && !record.primitive.isDestroyed?.()
+          ? shown
+          : building
+        ).push(record);
+      entry.swap.stop();
+      entry.swap = null;
+      removePrimitives(building);
+      previous = shown;
+    }
     entry.primitives = [];
     attachPrimitive(entry);
     removeWhenReady(entry, previous);