Cache zeroperl.wasm in the ExifTool worker after first fetch.

Avoid repeat multi-megabyte downloads when Tor/Firefox do not HTTP-cache worker WASM responses.

frontend/src/workers/exiftoolWorker.ts

@@ -6,8 +6,31 @@ import type { ExiftoolWorkerJob } from '@/types/workers/exiftoolWorkerJob';
 import { resolveErrorMessage } from '@/utils/resolveErrorMessage';
 import { toArrayBuffer } from '@/utils/toArrayBuffer';
 
+let cachedZeroperlWasm: ArrayBuffer | null = null;
+
+/**
+ * Load `zeroperl.wasm` once per worker lifetime. Tor/Firefox often skip HTTP cache for
+ * worker fetches and may not store responses above the memory-cache entry size limit.
+ */
+const fetchZeroperlWasm = async (): Promise<Response> => {
+    if (!cachedZeroperlWasm) {
+        const response = await fetch(zeroperlWasmUrl);
+
+        if (!response.ok) {
+            throw new Error(`Failed to load zeroperl.wasm: HTTP ${response.status}`);
+        }
+
+        cachedZeroperlWasm = await response.arrayBuffer();
+    }
+
+    return new Response(cachedZeroperlWasm, {
+        status: 200,
+        headers: { 'Content-Type': 'application/wasm' }
+    });
+};
+
 /** Custom fetch function for `@uswriting/exiftool` to load `zeroperl.wasm` from the worker. */
-const exiftoolParseOptions = { fetch: () => fetch(zeroperlWasmUrl) };
+const exiftoolParseOptions = { fetch: fetchZeroperlWasm };
 
 const jobQueue: ExiftoolWorkerJob[] = [];
 let drainPromise: Promise<void> | null = null;
@@ -137,11 +160,7 @@ const processJob = async (job: ExiftoolWorkerJob): Promise<void> => {
         try {
             await initializeWorker();
 
-            const result = await writeMetadata(
-                job.file,
-                {},
-                { args: ['-all='], ...exiftoolParseOptions }
-            );
+            const result = await writeMetadata(job.file, {}, { args: ['-all='], ...exiftoolParseOptions });
 
             if (!result.success) {
                 const message = result.error ?? 'Could not strip image metadata';