feat: add useApiSSE helper for Server-Sent Events connections

web/src/composables/useApi.ts

@@ -18,3 +18,33 @@ export async function useApiFetch<T>(
     return { data: null, error: { kind: 'network', message: String(e) } }
   }
 }
+
+/**
+ * Open an SSE connection. Returns a cleanup function.
+ * onEvent receives each parsed JSON payload.
+ * onComplete is called when the server sends a {"type":"complete"} event.
+ * onError is called on connection error.
+ */
+export function useApiSSE(
+  url: string,
+  onEvent: (data: Record<string, unknown>) => void,
+  onComplete?: () => void,
+  onError?: (e: Event) => void,
+): () => void {
+  const es = new EventSource(url)
+  es.onmessage = (e) => {
+    try {
+      const data = JSON.parse(e.data) as Record<string, unknown>
+      onEvent(data)
+      if (data.type === 'complete') {
+        es.close()
+        onComplete?.()
+      }
+    } catch { /* ignore malformed events */ }
+  }
+  es.onerror = (e) => {
+    onError?.(e)
+    es.close()
+  }
+  return () => es.close()
+}