Fix connection to find first unoccupied input handle

When connecting to nodes with multiple input handles of the same type,
now finds the first unoccupied handle instead of always targeting the
first one. Returns null if all handles are occupied.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/WorkflowCanvas.tsx

@@ -333,12 +333,22 @@ export function WorkflowCanvas() {
         const nodeData = node.data as { inputSchema?: Array<{ name: string; type: string }> };
         if (nodeData.inputSchema && nodeData.inputSchema.length > 0) {
           if (needInput) {
-            // Find first input handle matching the type
+            // Find input handles matching the type
             const matchingInputs = nodeData.inputSchema.filter(i => i.type === handleType);
-            if (matchingInputs.length > 0) {
-              // Return normalized handle ID, not schema name
-              // Always use indexed IDs (image-0, text-0) for schema inputs for consistency
-              return `${handleType}-0`;
+            const numHandles = matchingInputs.length;
+            if (numHandles > 0) {
+              // Find the first unoccupied indexed handle by checking existing edges
+              for (let i = 0; i < numHandles; i++) {
+                const candidateHandle = `${handleType}-${i}`;
+                const isOccupied = edges.some(
+                  (edge) => edge.target === node.id && edge.targetHandle === candidateHandle
+                );
+                if (!isOccupied) {
+                  return candidateHandle;
+                }
+              }
+              // All handles are occupied
+              return null;
             }
           }
           // Output handle - check for video or image type
@@ -425,7 +435,7 @@ export function WorkflowCanvas() {
         sourceHandleId: fromHandleId,
       });
     },
-    [screenToFlowPosition, nodes, handleConnect]
+    [screenToFlowPosition, nodes, edges, handleConnect]
   );
 
   // Handle the splitGrid action - uses automated grid detection