diff --git a/apps/app/src/components/generative-ui/open-generative-ui/__tests__/open-generative-ui-renderer.test.tsx b/apps/app/src/components/generative-ui/open-generative-ui/__tests__/open-generative-ui-renderer.test.tsx
index 65cdb2a..09d2ee1 100644
--- a/apps/app/src/components/generative-ui/open-generative-ui/__tests__/open-generative-ui-renderer.test.tsx
+++ b/apps/app/src/components/generative-ui/open-generative-ui/__tests__/open-generative-ui-renderer.test.tsx
@@ -647,4 +647,25 @@ describe("OpenGenUIActivityRenderer", () => {
     });
     expect(parsed.success).toBe(true);
   });
+
+  it("waits for complete streamed function source before injection", async () => {
+    const base = { html: ["<body><button onclick='greet()'>Go</button></body>"], htmlComplete: true, generating: true };
+    const partial = "function greet() {";
+    const complete = "function greet() { return 'hi'; }";
+    const { rerender } = renderRenderer({ ...base, jsFunctions: partial, jsFunctionsComplete: false });
+    await flushImport();
+    await resolveSandboxReady();
+    expect(mockRun.mock.calls.some((call) => call[0] === partial)).toBe(false);
+    rerender(rendererElement({ ...base, jsFunctions: complete, jsFunctionsComplete: true }));
+    await flushImport();
+    expect(mockRun.mock.calls.filter((call) => call[0] === complete)).toHaveLength(1);
+  });
+
+  it("does not run incomplete function source when generation stops", async () => {
+    const partial = "function greet() {";
+    renderRenderer({ html: ["<body>Interrupted</body>"], htmlComplete: true, generating: false, jsFunctions: partial, jsFunctionsComplete: false });
+    await flushImport(); await resolveSandboxReady();
+    expect(mockRun.mock.calls.some((call) => call[0] === partial)).toBe(false);
+  });
+
 });
diff --git a/apps/app/src/components/generative-ui/open-generative-ui/renderer.tsx b/apps/app/src/components/generative-ui/open-generative-ui/renderer.tsx
index 4fb3a40..f11d03f 100644
--- a/apps/app/src/components/generative-ui/open-generative-ui/renderer.tsx
+++ b/apps/app/src/components/generative-ui/open-generative-ui/renderer.tsx
@@ -326,7 +326,14 @@ const OpenGenUIActivityRendererInner = React.memo(
 
     // Effect 2 — jsFunctions injection (once per final sandbox)
     useEffect(() => {
-      if (!content.jsFunctions || jsFunctionsInjectedRef.current) return;
+      // Partial function source cannot run until the middleware completes it.
+      // Completed activities without the flag remain compatible.
+      if (
+        !content.jsFunctions ||
+        content.jsFunctionsComplete === false ||
+        (content.jsFunctionsComplete !== true && content.generating !== false) ||
+        jsFunctionsInjectedRef.current
+      ) return;
       jsFunctionsInjectedRef.current = true;
 
       const sandbox = sandboxRef.current;
@@ -335,7 +342,7 @@ const OpenGenUIActivityRendererInner = React.memo(
       } else {
         pendingQueueRef.current.push(content.jsFunctions);
       }
-    }, [content.jsFunctions]);
+    }, [content.jsFunctions, content.jsFunctionsComplete, content.generating]);
 
     // Effect 3 — jsExpressions execution (arrival order, sequential await)
     useEffect(() => {