feat(FN-3243): add tasks column/updatedAt index and debounce detail fetches

Merges a batch of five commits delivering dashboard performance optimizations (new composite indexes on `tasks.column`/`tasks.updatedAt` and debounced detail fetches), hardened chat SSE parsing with new test coverage, restored typecheck gates, split-pane task-link navigation (FN-3191), and research

Fusion-Task-Id: FN-3243

packages/dashboard/app/api/__tests__/legacy-chat-stream.test.ts

@@ -0,0 +1,70 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { streamChatResponse } from "../legacy";
+
+function createChunkedStream(chunks: string[]): ReadableStream<Uint8Array> {
+  const encoder = new TextEncoder();
+  return new ReadableStream<Uint8Array>({
+    start(controller) {
+      for (const chunk of chunks) {
+        controller.enqueue(encoder.encode(chunk));
+      }
+      controller.close();
+    },
+  });
+}
+
+describe("streamChatResponse SSE parser", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("reconstructs text/done events split across arbitrary chunks", async () => {
+    const fetchMock = vi.spyOn(globalThis, "fetch").mockResolvedValue(
+      new Response(
+        createChunkedStream([
+          "event: text\n",
+          "data: \"Hel",
+          "lo \"\n\n",
+          "event: text\n",
+          "data: \"world\"\n\n",
+          "event: done\n",
+          "data: {\"messageId\":\"msg-1\"}\n\n",
+        ]),
+        { status: 200 },
+      ),
+    );
+
+    const textChunks: string[] = [];
+    const doneIds: string[] = [];
+
+    streamChatResponse("s-1", "hi", {
+      onText: (data) => textChunks.push(data),
+      onDone: (data) => doneIds.push(data.messageId),
+      onError: vi.fn(),
+    });
+
+    await vi.waitFor(() => {
+      expect(textChunks.join("")).toBe("Hello world");
+      expect(doneIds).toEqual(["msg-1"]);
+    });
+
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("handles done events that have no data payload", async () => {
+    vi.spyOn(globalThis, "fetch").mockResolvedValue(
+      new Response(createChunkedStream(["event: done\n\n"]), { status: 200 }),
+    );
+
+    const donePayloads: Array<{ messageId: string }> = [];
+
+    streamChatResponse("s-1", "hi", {
+      onDone: (data) => donePayloads.push(data),
+      onError: vi.fn(),
+    });
+
+    await vi.waitFor(() => {
+      expect(donePayloads).toEqual([{ messageId: "" }]);
+    });
+  });
+});

packages/dashboard/app/api/legacy.ts

@@ -7838,7 +7838,7 @@ export function streamChatResponse(
   let closedByUser = false;
 
   const dispatchEvent = (eventName: string, rawData: string): void => {
-    if (!eventName || !rawData) {
+    if (!eventName) {
       return;
     }