feat(runtime): add TanStack AI stream converter and barrel export

Add convertTanStackStream async generator that converts TanStack AI
stream chunks (TEXT_MESSAGE_CONTENT, TOOL_CALL_START/ARGS/END) into
AG-UI events. Create converters/index.ts barrel that re-exports both
AI SDK and TanStack converters.

Author: AlemTuzlak

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

@@ -0,0 +1,2 @@
+export { convertAISDKStream } from "./aisdk";
+export { convertTanStackStream } from "./tanstack";

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

@@ -0,0 +1,62 @@
+import {
+  BaseEvent,
+  EventType,
+  TextMessageChunkEvent,
+  ToolCallArgsEvent,
+  ToolCallEndEvent,
+  ToolCallStartEvent,
+} from "@ag-ui/client";
+import { randomUUID } from "crypto";
+
+/**
+ * Converts a TanStack AI stream into AG-UI `BaseEvent` objects.
+ *
+ * This is a pure converter — it does NOT emit lifecycle events
+ * (RUN_STARTED / RUN_FINISHED / RUN_ERROR). The caller (Agent class)
+ * is responsible for those.
+ */
+export async function* convertTanStackStream(
+  stream: AsyncIterable<unknown>,
+  abortSignal: AbortSignal,
+): AsyncGenerator<BaseEvent> {
+  const messageId = randomUUID();
+
+  for await (const chunk of stream) {
+    if (abortSignal.aborted) break;
+
+    const raw = chunk as Record<string, unknown>;
+    const type = raw.type as string;
+
+    if (type === "TEXT_MESSAGE_CONTENT" && raw.delta) {
+      const textEvent: TextMessageChunkEvent = {
+        type: EventType.TEXT_MESSAGE_CHUNK,
+        role: "assistant",
+        messageId,
+        delta: raw.delta as string,
+      };
+      yield textEvent;
+    } else if (type === "TOOL_CALL_START") {
+      const startEvent: ToolCallStartEvent = {
+        type: EventType.TOOL_CALL_START,
+        parentMessageId: messageId,
+        toolCallId: raw.toolCallId as string,
+        toolCallName: raw.toolCallName as string,
+      };
+      yield startEvent;
+    } else if (type === "TOOL_CALL_ARGS") {
+      const argsEvent: ToolCallArgsEvent = {
+        type: EventType.TOOL_CALL_ARGS,
+        toolCallId: raw.toolCallId as string,
+        delta: raw.delta as string,
+      };
+      yield argsEvent;
+    } else if (type === "TOOL_CALL_END") {
+      const endEvent: ToolCallEndEvent = {
+        type: EventType.TOOL_CALL_END,
+        toolCallId: raw.toolCallId as string,
+      };
+      yield endEvent;
+    }
+    // Unknown chunk types are silently ignored
+  }
+}