fix: Gemma4 worker — catch unhandled rejections + null-check Gemma4 classes

Author: ijbo

ai-worker-gemma4.js

@@ -25,6 +25,19 @@ let processor = null;
 self.postMessage({ type: "status", message: `[Gemma4] Loading transformers.js ${TRANSFORMERS_URL.split('@').pop()}...` });
 console.log(`[Gemma4 worker] TRANSFORMERS_URL = ${TRANSFORMERS_URL}`);
 
+// ── Global safety net ────────────────────────────────────────────────────────
+// Catch any uncaught async rejection (e.g. from the message handler's async fn)
+// and convert it to a postMessage error so the UI shows a readable status
+// instead of firing worker.onerror → "AI Worker error: Event".
+self.addEventListener('unhandledrejection', (event) => {
+    const msg = event.reason && event.reason.message
+        ? event.reason.message
+        : String(event.reason || 'Unknown error in Gemma4 worker');
+    console.error('[Gemma4 worker] Unhandled rejection:', msg);
+    self.postMessage({ type: 'error', message: `Gemma 4 worker error: ${msg}` });
+    event.preventDefault();
+});
+
 // ============================================
 // Progress callback factory
 // ============================================
@@ -73,6 +86,16 @@ async function loadModel() {
         read_audio = transformers.read_audio;
         TextStreamer = transformers.TextStreamer;
 
+        // ── Verify Gemma 4 classes are available in this version ──
+        if (!Gemma4ForConditionalGeneration || !Gemma4Processor) {
+            const ver = TRANSFORMERS_URL.split('@').pop();
+            throw new Error(
+                `Gemma 4 classes not found in transformers.js@${ver}. ` +
+                `The loaded version does not support Gemma 4 yet. ` +
+                `Try clearing site data and reloading.`
+            );
+        }
+
         // 2. WebGPU detection
         let device = "wasm";
         if (typeof navigator !== "undefined" && navigator.gpu) {
@@ -238,36 +261,47 @@ async function generate({ userPrompt, prompt, attachments = [], context, chatHis
 self.addEventListener("message", async (event) => {
     const { type } = event.data;
 
-    switch (type) {
-        case "setModelId":
-            MODEL_ID = event.data.modelId || MODEL_ID;
-            MODEL_LABEL = event.data.modelLabel || MODEL_LABEL;
-            break;
-
-        case "load":
-            await loadModel();
-            break;
-
-        case "generate":
-            await generate(event.data);
-            break;
-
-        // Compatibility alias used by ai-docgen-generate.js
-        case "process":
-            await generate({
-                prompt: event.data.prompt || event.data.task,
-                attachments: event.data.attachments || [],
-                context: event.data.context,
-                messageId: event.data.messageId,
-                options: event.data.options || {},
-            });
-            break;
-
-        case "ping":
-            self.postMessage({ type: "pong" });
-            break;
-
-        default:
-            console.warn("Gemma4 worker — unknown message type:", type);
+    try {
+        switch (type) {
+            case "setModelId":
+                MODEL_ID = event.data.modelId || MODEL_ID;
+                MODEL_LABEL = event.data.modelLabel || MODEL_LABEL;
+                break;
+
+            case "load":
+                await loadModel();
+                break;
+
+            case "generate":
+                await generate(event.data);
+                break;
+
+            // Compatibility alias used by ai-docgen-generate.js
+            case "process":
+                await generate({
+                    prompt: event.data.prompt || event.data.task,
+                    attachments: event.data.attachments || [],
+                    context: event.data.context,
+                    messageId: event.data.messageId,
+                    options: event.data.options || {},
+                });
+                break;
+
+            case "ping":
+                self.postMessage({ type: "pong" });
+                break;
+
+            default:
+                console.warn("Gemma4 worker — unknown message type:", type);
+        }
+    } catch (err) {
+        // Catch synchronous throws from any case and route them as error messages
+        // so they don't escape to worker.onerror (which shows generic "Model unavailable")
+        console.error('[Gemma4 worker] Uncaught in message handler:', err);
+        self.postMessage({
+            type: 'error',
+            message: `Gemma 4 worker error (${type}): ${err.message}`,
+            messageId: event.data.messageId,
+        });
     }
 });

changelogs/CHANGELOG-gemma4-worker-error-handling.md

@@ -0,0 +1,6 @@
+# Gemma4 Worker — Unhandled Rejection Safety Net
+
+- Added `unhandledrejection` listener at worker top level to route async throws to `postMessage({type:"error"})` instead of `worker.onerror`
+- Wrapped message handler switch in try/catch
+- Added null-checks for `Gemma4ForConditionalGeneration` + `Gemma4Processor` with readable error messages
+- Root cause: browser evicted cached model (persistent storage not granted), re-download triggered uncaught async rejection