fix(street-level): KartaView PR review — context loss mid-load, chunked reads, source switches, a11y

From the IC8 review of #1121 (2 P2, 7 P3; each with a test that fails on
the old code):

P2
- A WebGL context lost while a newer panorama loaded left a black viewer
  and a 'successful' open: the panorama now builds on the new canvas (or
  falls back to its front view).
- The streaming body read every real answer takes was tested with one
  chunk only: answers split mid-character are reassembled; the shared test
  fake now streams, so every source test runs the production path.

P3
- Lighting another source by its chip (params) now stops a running lookup
  and clears its spinner and error, as setProviderEnabled did; a restore
  that changes nothing leaves them alone.
- Panoramas decode off the main thread (ImageBitmap, RGBA upload: ~90 ms →
  ~15 ms at 4,096 px on a phone-class CPU) and are 2,048 px docked, 4,096
  once the viewer grows; a closed viewer keeps a 1×1 texture.
- The lit KARTAVIEW chip label is #8f8aff (~6:1; #635bff was 3.7:1).
- The viewer's keyboard focus ring is drawn above the photo.
- Tests: a second context loss and a drag on the new canvas; the look
  direction kept across a loss; a page's 30 s first try.
- The browser gate loses a real WebGL context in the 360° step and checks
  the 429 lookup was asked again (the fixture counter is reset first).

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

src/layers/streetLevel/providers/kartaview/panorama.js

@@ -179,7 +179,17 @@ export function createPanoramaRenderer(canvas) {
       gl.activeTexture(gl.TEXTURE0);
       gl.bindTexture(gl.TEXTURE_2D, texture);
       gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, false);
-      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);
+      // RGBA: the format a decoded ImageBitmap uploads without conversion.
+      gl.texImage2D(
+        gl.TEXTURE_2D,
+        0,
+        gl.RGBA,
+        gl.RGBA,
+        gl.UNSIGNED_BYTE,
+        image,
+      );
+      // The pixels are on the GPU now; a bitmap's copy can go.
+      image.close?.();
       // Linear only: a mipmapped lookup draws a seam where longitude wraps.
       gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
       gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
@@ -205,6 +215,19 @@ export function createPanoramaRenderer(canvas) {
     hasImage: () => loaded,
     clear() {
       loaded = false;
+      // Hand the 32 MB texture back: a closed viewer keeps only 1×1.
+      gl.bindTexture(gl.TEXTURE_2D, texture);
+      gl.texImage2D(
+        gl.TEXTURE_2D,
+        0,
+        gl.RGBA,
+        1,
+        1,
+        0,
+        gl.RGBA,
+        gl.UNSIGNED_BYTE,
+        new Uint8Array(4),
+      );
       scheduleRender();
     },
     destroy() {