On-disk content and thumbnail cache with per-photo fetch and prefetch (closes #46)

Adds the on-disk content and thumbnail cache keyed by fileID: originals/ and thumbnails/ under cacheDirectory, present-means-complete (streaming atomic rename), orphan temp reaping on open. Photo.original/thumbnail return a cached path with no network when present, else fetch through the shared request pool; thumbnails.ensure drives the thumbnail pool with priority, dedup and AbortSignal. One shared RequestPools set serves both the ML fetch and the content cache. Content-hash integrity is deferred (#68); authenticated streaming decrypt guarantees integrity now.

Model: opus-4-8

src/library/records.ts

@@ -166,11 +166,20 @@ const toAlbumRecord = (
     };
 };
 
+// The cache paths known for a file, so the projection can expose them on the
+// record without the read layer reaching into the content cache itself.
+export type CachedPathLookup = (fileID: number) => {
+    originalPath?: string;
+    thumbnailPath?: string;
+};
+
 // Project the decrypted collections and file memberships into by-id records.
 // `files` is every membership (a file appears once per collection it is in).
+// `cachedPaths`, when given, fills each record's cache paths.
 export const deriveRecords = (
     collections: Collection[],
     files: EnteFile[],
+    cachedPaths?: CachedPathLookup,
 ): DerivedRecords => {
     const byFileID = new Map<number, EnteFile[]>();
     for (const f of files) {
@@ -183,6 +192,13 @@ export const deriveRecords = (
     const takenAtByFile = new Map<number, number>();
     for (const [fileID, memberships] of byFileID) {
         const record = toPhotoRecord(fileID, memberships);
+        if (cachedPaths) {
+            const paths = cachedPaths(fileID);
+            if (paths.originalPath !== undefined)
+                record.originalPath = paths.originalPath;
+            if (paths.thumbnailPath !== undefined)
+                record.thumbnailPath = paths.thumbnailPath;
+        }
         photos.set(fileID, record);
         takenAtByFile.set(fileID, record.takenAt);
     }