feat(runtime): emit STATE_DELTA on AGUISendStateDelta in TanStack converter

Author: AlemTuzlak

packages/runtime/src/agent/__tests__/converter-tanstack.test.ts

@@ -340,4 +340,25 @@ describe("TanStack AI converter — state tools", () => {
       snapshot,
     );
   });
+
+  it("emits STATE_DELTA before TOOL_CALL_RESULT for AGUISendStateDelta", async () => {
+    const delta = [{ op: "replace", path: "/counter", value: 7 }];
+    const agent = createAgent("tanstack", [
+      tanstackToolCallStart("call1", "AGUISendStateDelta"),
+      tanstackToolCallEnd("call1"),
+      tanstackToolCallResult("call1", { success: true, delta }),
+    ]);
+    const events = await collectEvents(agent.run(createDefaultInput()));
+
+    expectLifecycleWrapped(events);
+
+    const deltaIdx = events.findIndex((e) => e.type === EventType.STATE_DELTA);
+    const resultIdx = events.findIndex(
+      (e) => e.type === EventType.TOOL_CALL_RESULT,
+    );
+
+    expect(deltaIdx).toBeGreaterThanOrEqual(0);
+    expect(deltaIdx).toBeLessThan(resultIdx);
+    expect(eventField<unknown>(events[deltaIdx], "delta")).toEqual(delta);
+  });
 });

packages/runtime/src/agent/converters/tanstack.ts

@@ -290,6 +290,19 @@ export async function* convertTanStackStream(
         yield stateSnapshotEvent;
       }
 
+      if (
+        toolName === "AGUISendStateDelta" &&
+        parsedContent &&
+        typeof parsedContent === "object" &&
+        "delta" in parsedContent
+      ) {
+        const stateDeltaEvent: StateDeltaEvent = {
+          type: EventType.STATE_DELTA,
+          delta: (parsedContent as Record<string, unknown>).delta as never,
+        };
+        yield stateDeltaEvent;
+      }
+
       let serializedContent: string;
       if (typeof rawContent === "string") {
         serializedContent = rawContent;
@@ -312,10 +325,9 @@ export async function* convertTanStackStream(
       toolNamesById.delete(toolCallId);
     }
     // Unhandled chunk types are silently ignored.
-    // Known gaps: STATE_DELTA and REASONING events are not yet converted from
-    // TanStack streams. Shared state (STATE_SNAPSHOT) is now supported.
+    // Known gap: REASONING events are not yet converted from TanStack streams.
     // Reasoning will not surface when using the TanStack backend.
-    // Use the AI SDK backend if these features are required.
+    // Use the AI SDK backend if reasoning is required.
   }
 }