feat(sidepanel): enhance welcome pane with action groups and link cards

- Refactored WelcomePane to include structured action groups for prompts, understanding, questioning, and library suggestions.
- Introduced LinkCardsBlock component to display link card groups with expandable sections.
- Updated session storage to handle pinned and archived states for sessions.
- Added utility functions for title generation retry logic.
- Removed unused SourcesBlock component.
- Implemented tests for title generation retry state management.

Co-authored-by: Copilot <copilot@github.com>

Author: lcomplete

app/extension/src/__tests__/sidepanelSessions.test.ts

@@ -109,4 +109,78 @@ describe("sidepanel session helpers", () => {
       "older-message",
     ]);
   });
+
+  it("sorts pinned sessions above unpinned ones regardless of last-message time", () => {
+    const ordered = sortSessionMetadataByActivity([
+      createSession("newer-unpinned", {
+        lastMessageAt: "2026-04-22T08:00:00.000Z",
+      }),
+      createSession("older-pinned", {
+        lastMessageAt: "2026-04-20T08:00:00.000Z",
+        pinned: true,
+        pinnedAt: "2026-04-21T08:00:00.000Z",
+      }),
+    ]);
+
+    expect(ordered.map((session) => session.id)).toEqual([
+      "older-pinned",
+      "newer-unpinned",
+    ]);
+  });
+
+  it("orders multiple pinned sessions by most recently pinned", () => {
+    const ordered = sortSessionMetadataByActivity([
+      createSession("pinned-early", {
+        pinned: true,
+        pinnedAt: "2026-04-20T08:00:00.000Z",
+      }),
+      createSession("pinned-latest", {
+        pinned: true,
+        pinnedAt: "2026-04-22T08:00:00.000Z",
+      }),
+    ]);
+
+    expect(ordered.map((session) => session.id)).toEqual([
+      "pinned-latest",
+      "pinned-early",
+    ]);
+  });
+
+  it("exposes pinned and archived metadata when building from session data", () => {
+    const metadata = buildSessionMetadata(
+      createSessionData("session-pin", {
+        pinned: true,
+        pinnedAt: "2026-04-22T08:00:00.000Z",
+        archived: true,
+        archivedAt: "2026-04-22T08:05:00.000Z",
+      })
+    );
+
+    expect(metadata.pinned).toBe(true);
+    expect(metadata.pinnedAt).toBe("2026-04-22T08:00:00.000Z");
+    expect(metadata.archived).toBe(true);
+    expect(metadata.archivedAt).toBe("2026-04-22T08:05:00.000Z");
+  });
+
+  it("defaults pinned and archived fields to false when not set", () => {
+    const metadata = buildSessionMetadata(createSessionData("session-default"));
+
+    expect(metadata.pinned).toBe(false);
+    expect(metadata.archived).toBe(false);
+    expect(metadata.pinnedAt).toBeUndefined();
+    expect(metadata.archivedAt).toBeUndefined();
+  });
+
+  it("reconciles metadata when pinned or archived flags diverge from the session", () => {
+    const metadata = createSession("session-flip");
+    const session = createSessionData("session-flip", {
+      pinned: true,
+      pinnedAt: "2026-04-22T08:00:00.000Z",
+    });
+
+    const repaired = reconcileSessionMetadata(metadata, session);
+
+    expect(repaired.pinned).toBe(true);
+    expect(repaired.pinnedAt).toBe("2026-04-22T08:00:00.000Z");
+  });
 });

app/extension/src/__tests__/sidepanelTitleGenerationRetry.test.ts

@@ -0,0 +1,57 @@
+import {
+  getNextTitleGenerationRetryState,
+  hasTitleGenerationAttemptsRemaining,
+  resetTitleGenerationRetryState,
+} from "../sidepanel/utils/titleGenerationRetry";
+
+describe("sidepanel title generation retry helpers", () => {
+  it("starts a new request at the first attempt", () => {
+    const next = getNextTitleGenerationRetryState(
+      resetTitleGenerationRetryState(),
+      "session-1:message-1"
+    );
+
+    expect(next).toEqual({
+      requestKey: "session-1:message-1",
+      attempts: 1,
+    });
+  });
+
+  it("increments attempts for the same request", () => {
+    const first = getNextTitleGenerationRetryState(
+      resetTitleGenerationRetryState(),
+      "session-1:message-1"
+    );
+    const second = getNextTitleGenerationRetryState(
+      first,
+      "session-1:message-1"
+    );
+
+    expect(second).toEqual({
+      requestKey: "session-1:message-1",
+      attempts: 2,
+    });
+  });
+
+  it("resets attempts when the latest message changes", () => {
+    const current = getNextTitleGenerationRetryState(
+      resetTitleGenerationRetryState(),
+      "session-1:message-1"
+    );
+    const next = getNextTitleGenerationRetryState(
+      current,
+      "session-1:message-2"
+    );
+
+    expect(next).toEqual({
+      requestKey: "session-1:message-2",
+      attempts: 1,
+    });
+  });
+
+  it("stops retrying once the attempt budget is exhausted", () => {
+    expect(hasTitleGenerationAttemptsRemaining(1, 3)).toBe(true);
+    expect(hasTitleGenerationAttemptsRemaining(2, 3)).toBe(true);
+    expect(hasTitleGenerationAttemptsRemaining(3, 3)).toBe(false);
+  });
+});