fix: address GhostMaps resource and source ownership review findings

docs/CURRENT-STATE.md

@@ -5133,6 +5133,7 @@ are omitted rather than framing the wrong part of the globe.
   - The layer reloads only products whose blob changed. The new edition's data source is added before the old one is removed. A product that leaves the catalog leaves the globe.
   - The row reads `LIVE` while the stream is open. A five-minute catalog read is the backstop.
 - **Files.** `/api/ghostmaps/file/{product}` serves only catalog products. Files are downloaded by commit-pinned raw URLs, so a CDN cannot return an older edition. They are cached on disk by blob sha, and blobs no current product uses are pruned. A request whose `?v=` names the current blob is `immutable`. Repository paths never reach the page.
+- **Source ownership.** The application catalog receives `sources['s2-ghostmaps']` through the shared source contracts; an omitted or null source stays unavailable without opening a stream or fetching. The standalone source factory supplies the same-origin implementation and accepts replacements. Packed-image URLs are released on cancelled or failed product construction, and remain owned by a successfully loaded product until it is removed.
 - **Rendering.** The page parses the KMZ with the import module's zip, KMZ and XML helpers into one `CustomDataSource` per product.
   - Points become ground-clamped billboards with the depth test off, so they never sink into terrain or 3D tiles. Because the Google 3D map hides the globe, nothing else would stop far-side pins drawing through the planet. Pins are therefore horizon-culled with Street Level's `createHorizonCull` before their first frame and again whenever the camera moves.
   - Lines and polygon outlines are ground-clamped polylines.