fix: address 5 code review findings across execution and UI code

- TutorialOverlay: move completeCurrentStep() inside setTimeout to prevent
  cleanup from clearing the advance timeout, fixing stuck tutorial steps
- useStitchVideos: push silent AudioBuffer for clips with no/incompatible
  audio instead of skipping, preventing audio-video timeline desync
- generate3dExecutor: clear savedFilename/savedFilePath on new generation
  to prevent stale save metadata from previous runs
- pollTaskCompletion: restructure abort listener/timer cleanup to prevent
  listener accumulation across polling iterations
- connectedInputs: exclude loop edges in validateWorkflowPure checks for
  nanoBanana/generateVideo text inputs, matching runtime behavior

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/onboarding/TutorialOverlay.tsx

@@ -112,12 +112,15 @@ export function TutorialOverlay() {
     }
 
     if (actionCompleted) {
-      completeCurrentStep();
-      // Advance to next step after configurable delay (default 1000ms)
+      // Advance to next step after configurable delay (default 1000ms).
+      // Both completeCurrentStep() and nextTutorialStep() are called inside
+      // the timeout so that the state update doesn't trigger a re-render
+      // whose cleanup would clear the pending timeout.
       const delay = currentStep.advanceDelay !== undefined ? currentStep.advanceDelay : 1000;
       if (advanceTimeoutRef.current) clearTimeout(advanceTimeoutRef.current);
       advanceTimeoutRef.current = setTimeout(() => {
         advanceTimeoutRef.current = null;
+        completeCurrentStep();
         nextTutorialStep();
       }, delay);
     }

src/hooks/useStitchVideos.ts

@@ -224,13 +224,14 @@ export async function stitchVideosAsync(
         try {
           const blobSource = new BlobSource(videoBlobs[i]);
           const input = new Input({ source: blobSource, formats: ALL_FORMATS });
+          let extractedAudio = false;
           try {
+            const clipDuration = await input.computeDuration();
             const audioTracks = await input.getAudioTracks();
             if (audioTracks.length > 0) {
               const audioTrack = audioTracks[0];
               const sink = new AudioBufferSink(audioTrack);
-              const duration = await input.computeDuration();
-              for await (const wrapped of sink.buffers(0, duration)) {
+              for await (const wrapped of sink.buffers(0, clipDuration)) {
                 if (referenceSampleRate === null) {
                   referenceSampleRate = wrapped.buffer.sampleRate;
                   referenceChannels = wrapped.buffer.numberOfChannels;
@@ -240,9 +241,21 @@ export async function stitchVideosAsync(
                   wrapped.buffer.numberOfChannels === referenceChannels
                 ) {
                   allAudioBuffers.push(wrapped.buffer);
+                  extractedAudio = true;
                 }
               }
             }
+            // If no audio was extracted (no tracks or incompatible params),
+            // push a silent buffer to maintain timeline alignment
+            if (!extractedAudio && referenceSampleRate && referenceChannels && clipDuration > 0) {
+              const silentSamples = Math.max(1, Math.floor(clipDuration * referenceSampleRate));
+              const silentBuffer = new AudioBuffer({
+                length: silentSamples,
+                numberOfChannels: referenceChannels,
+                sampleRate: referenceSampleRate,
+              });
+              allAudioBuffers.push(silentBuffer);
+            }
           } finally {
             input.dispose();
           }

src/store/execution/generate3dExecutor.ts

@@ -137,6 +137,8 @@ export async function executeGenerate3D(
           output3dUrl: result.model3dUrl,
           status: "complete",
           error: null,
+          savedFilename: null,
+          savedFilePath: null,
         });
 
         // Track cost if applicable

src/store/execution/pollTaskCompletion.ts

@@ -50,19 +50,16 @@ export async function pollGenerateTask(
 
     // Wait before polling
     await new Promise<void>((resolve, reject) => {
-      const timer = setTimeout(resolve, interval);
+      const onAbort = () => {
+        clearTimeout(timer);
+        reject(new DOMException("The operation was aborted.", "AbortError"));
+      };
+      const timer = setTimeout(() => {
+        if (signal) signal.removeEventListener("abort", onAbort);
+        resolve();
+      }, interval);
       if (signal) {
-        const onAbort = () => {
-          clearTimeout(timer);
-          reject(new DOMException("The operation was aborted.", "AbortError"));
-        };
         signal.addEventListener("abort", onAbort, { once: true });
-        // Clean up listener when timer fires
-        const origResolve = resolve;
-        resolve = () => {
-          signal.removeEventListener("abort", onAbort);
-          origResolve();
-        };
       }
     });
 

src/store/utils/connectedInputs.ts

@@ -403,11 +403,13 @@ export function validateWorkflowPure(
   }
 
   // Check each Nano Banana node has required inputs (text required, image optional)
+  // Loop edges are excluded because they carry no data on the first iteration.
   nodes
     .filter((n) => n.type === "nanoBanana")
     .forEach((node) => {
       const textConnected = edges.some(
         (e) => e.target === node.id &&
+               !e.data?.isLoop &&
                (e.targetHandle === "text" || e.targetHandle?.startsWith("text-"))
       );
       if (!textConnected) {
@@ -421,6 +423,7 @@ export function validateWorkflowPure(
     .forEach((node) => {
       const textConnected = edges.some(
         (e) => e.target === node.id &&
+               !e.data?.isLoop &&
                (e.targetHandle === "text" || e.targetHandle?.startsWith("text-"))
       );
       if (!textConnected) {