diff --git a/src/lib/queries.ts b/src/lib/queries.ts
new file mode 100644
index 0000000..ebf4ee5
--- /dev/null
+++ b/src/lib/queries.ts
@@ -0,0 +1,229 @@
+/**
+ * TanStack Query data fetching layer.
+ *
+ * Handles async data fetching, caching, and invalidation for:
+ * - Lore status (GitLab integration health)
+ * - Bridge status (mapping counts, sync times)
+ * - Sync/reconcile mutations
+ *
+ * Query keys are centralized here for consistent invalidation.
+ */
+
+import { useEffect } from "react";
+import {
+  QueryClient,
+  useQuery,
+  useMutation,
+  useQueryClient,
+  type UseQueryResult,
+  type UseMutationResult,
+} from "@tanstack/react-query";
+import { invoke } from "@tauri-apps/api/core";
+import { listen, type UnlistenFn } from "@tauri-apps/api/event";
+import type {
+  LoreStatus,
+  BridgeStatus,
+  SyncResult,
+  McError,
+} from "@/lib/types";
+
+// --- Query Keys ---
+
+export const queryKeys = {
+  loreStatus: ["lore-status"] as const,
+  bridgeStatus: ["bridge-status"] as const,
+} as const;
+
+// --- QueryClient Factory ---
+
+/**
+ * Create a configured QueryClient instance.
+ *
+ * Default options:
+ * - retry: 1 (one retry on failure)
+ * - refetchOnWindowFocus: true (refresh when user returns)
+ */
+export function createQueryClient(): QueryClient {
+  return new QueryClient({
+    defaultOptions: {
+      queries: {
+        retry: 1,
+        refetchOnWindowFocus: true,
+      },
+    },
+  });
+}
+
+// --- Event-Based Invalidation Hook ---
+
+/**
+ * Hook to set up query invalidation on Tauri events.
+ *
+ * Listens for:
+ * - lore-data-changed: Invalidates lore and bridge status
+ * - sync-status (completed): Invalidates lore and bridge status
+ */
+export function useQueryInvalidation(): void {
+  const queryClient = useQueryClient();
+
+  useEffect(() => {
+    let cancelled = false;
+    const unlisteners: Promise<UnlistenFn>[] = [];
+
+    // Invalidate on lore data changes
+    const loreUnlisten = listen("lore-data-changed", () => {
+      queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+      queryClient.invalidateQueries({ queryKey: queryKeys.bridgeStatus });
+    });
+    unlisteners.push(loreUnlisten);
+
+    // Invalidate on sync completion
+    const syncUnlisten = listen<{ status: string; message?: string }>(
+      "sync-status",
+      (event) => {
+        if (event.payload.status === "completed") {
+          queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+          queryClient.invalidateQueries({ queryKey: queryKeys.bridgeStatus });
+        }
+      }
+    );
+    unlisteners.push(syncUnlisten);
+
+    return () => {
+      cancelled = true;
+      // Cleanup all listeners
+      Promise.all(unlisteners).then((fns) => {
+        if (!cancelled) return;
+        for (const fn of fns) {
+          fn();
+        }
+      });
+    };
+  }, [queryClient]);
+}
+
+// --- Query Hooks ---
+
+/**
+ * Fetch lore integration status.
+ *
+ * Returns health, last sync time, and summary counts.
+ * Stale time: 30 seconds (fresh data is important but not real-time)
+ */
+export function useLoreStatus(): UseQueryResult<LoreStatus, McError> {
+  const queryClient = useQueryClient();
+
+  // Set up event-based invalidation
+  useEffect(() => {
+    let cancelled = false;
+    let unlisten: UnlistenFn | undefined;
+
+    listen("lore-data-changed", () => {
+      queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+    }).then((fn) => {
+      if (cancelled) {
+        fn();
+      } else {
+        unlisten = fn;
+      }
+    });
+
+    // Also listen for sync completion
+    let syncUnlisten: UnlistenFn | undefined;
+    listen<{ status: string }>("sync-status", (event) => {
+      if (event.payload.status === "completed") {
+        queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+      }
+    }).then((fn) => {
+      if (cancelled) {
+        fn();
+      } else {
+        syncUnlisten = fn;
+      }
+    });
+
+    return () => {
+      cancelled = true;
+      if (unlisten) unlisten();
+      if (syncUnlisten) syncUnlisten();
+    };
+  }, [queryClient]);
+
+  return useQuery({
+    queryKey: queryKeys.loreStatus,
+    queryFn: () => invoke<LoreStatus>("get_lore_status"),
+    staleTime: 30 * 1000, // 30 seconds
+  });
+}
+
+/**
+ * Fetch bridge status (mapping counts, sync times).
+ *
+ * Stale time: 30 seconds
+ */
+export function useBridgeStatus(): UseQueryResult<BridgeStatus, McError> {
+  const queryClient = useQueryClient();
+
+  // Set up event-based invalidation
+  useEffect(() => {
+    let cancelled = false;
+    let unlisten: UnlistenFn | undefined;
+
+    listen("lore-data-changed", () => {
+      queryClient.invalidateQueries({ queryKey: queryKeys.bridgeStatus });
+    }).then((fn) => {
+      if (cancelled) {
+        fn();
+      } else {
+        unlisten = fn;
+      }
+    });
+
+    return () => {
+      cancelled = true;
+      if (unlisten) unlisten();
+    };
+  }, [queryClient]);
+
+  return useQuery({
+    queryKey: queryKeys.bridgeStatus,
+    queryFn: () => invoke<BridgeStatus>("get_bridge_status"),
+    staleTime: 30 * 1000, // 30 seconds
+  });
+}
+
+// --- Mutation Hooks ---
+
+/**
+ * Trigger an incremental sync (process since_last_check events).
+ *
+ * On success, invalidates lore and bridge status queries.
+ */
+export function useSyncNow(): UseMutationResult<SyncResult, McError, void> {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: () => invoke<SyncResult>("sync_now"),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+      queryClient.invalidateQueries({ queryKey: queryKeys.bridgeStatus });
+    },
+  });
+}
+
+/**
+ * Trigger a full reconciliation pass.
+ *
+ * On success, invalidates lore and bridge status queries.
+ */
+export function useReconcile(): UseMutationResult<SyncResult, McError, void> {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: () => invoke<SyncResult>("reconcile"),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: queryKeys.loreStatus });
+      queryClient.invalidateQueries({ queryKey: queryKeys.bridgeStatus });
+    },
+  });
+}
diff --git a/tests/lib/queries.test.tsx b/tests/lib/queries.test.tsx
new file mode 100644
index 0000000..7c6e99c
--- /dev/null
+++ b/tests/lib/queries.test.tsx
@@ -0,0 +1,513 @@
+/**
+ * Tests for TanStack Query data fetching layer.
+ *
+ * Tests query hooks for lore data, bridge status, and mutations
+ * for sync/reconcile operations.
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { renderHook, waitFor, act } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { type ReactNode } from "react";
+import {
+  useLoreStatus,
+  useBridgeStatus,
+  useSyncNow,
+  useReconcile,
+  createQueryClient,
+} from "@/lib/queries";
+import {
+  invoke,
+  resetMocks,
+  setMockResponse,
+  simulateEvent,
+} from "../mocks/tauri-api";
+import type { LoreStatus, BridgeStatus, SyncResult } from "@/lib/types";
+
+// --- Test Fixtures ---
+
+const mockLoreStatus: LoreStatus = {
+  last_sync: "2026-02-26T10:00:00Z",
+  is_healthy: true,
+  message: "Synced successfully",
+  summary: {
+    open_issues: 5,
+    authored_mrs: 3,
+    reviewing_mrs: 2,
+  },
+};
+
+const mockBridgeStatus: BridgeStatus = {
+  mapping_count: 42,
+  pending_count: 3,
+  suspect_count: 1,
+  last_sync: "2026-02-26T10:00:00Z",
+  last_reconciliation: "2026-02-25T08:00:00Z",
+};
+
+const mockSyncResult: SyncResult = {
+  created: 5,
+  skipped: 10,
+  closed: 2,
+  healed: 1,
+  errors: [],
+};
+
+// --- Test Wrapper ---
+
+function createTestQueryClient(): QueryClient {
+  return new QueryClient({
+    defaultOptions: {
+      queries: {
+        retry: false,
+        gcTime: Infinity,
+      },
+      mutations: {
+        retry: false,
+      },
+    },
+  });
+}
+
+function createWrapper(queryClient: QueryClient) {
+  return function Wrapper({ children }: { children: ReactNode }) {
+    return (
+      <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
+    );
+  };
+}
+
+// --- QueryClient Setup Tests ---
+
+describe("createQueryClient", () => {
+  it("creates a QueryClient with appropriate defaults", () => {
+    const client = createQueryClient();
+    expect(client).toBeInstanceOf(QueryClient);
+
+    const defaults = client.getDefaultOptions();
+    expect(defaults.queries?.retry).toBe(1);
+    expect(defaults.queries?.refetchOnWindowFocus).toBe(true);
+  });
+});
+
+// --- useLoreStatus Tests ---
+
+describe("useLoreStatus", () => {
+  let queryClient: QueryClient;
+
+  beforeEach(() => {
+    queryClient = createTestQueryClient();
+    resetMocks();
+  });
+
+  afterEach(() => {
+    queryClient.clear();
+  });
+
+  it("fetches lore status successfully", async () => {
+    setMockResponse("get_lore_status", mockLoreStatus);
+
+    const { result } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    expect(result.current.data).toEqual(mockLoreStatus);
+    expect(invoke).toHaveBeenCalledWith("get_lore_status");
+  });
+
+  it("shows loading state initially", () => {
+    const { result } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    expect(result.current.isLoading).toBe(true);
+    expect(result.current.data).toBeUndefined();
+  });
+
+  it("handles lore unavailable error", async () => {
+    const mockError = {
+      code: "LORE_UNAVAILABLE",
+      message: "lore CLI not found",
+      recoverable: true,
+    };
+
+    invoke.mockRejectedValueOnce(mockError);
+
+    const { result } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isError).toBe(true);
+    });
+
+    expect(result.current.error).toEqual(mockError);
+  });
+
+  it("invalidates on lore-data-changed event", async () => {
+    setMockResponse("get_lore_status", mockLoreStatus);
+
+    const { result } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    // Initial fetch
+    expect(invoke).toHaveBeenCalledTimes(1);
+
+    // Simulate event
+    act(() => {
+      simulateEvent("lore-data-changed", undefined);
+    });
+
+    // Should refetch
+    await waitFor(() => {
+      expect(invoke).toHaveBeenCalledTimes(2);
+    });
+  });
+
+  it("uses staleTime of 30 seconds", async () => {
+    setMockResponse("get_lore_status", mockLoreStatus);
+
+    const { result: result1 } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result1.current.isSuccess).toBe(true);
+    });
+
+    // Second hook should use cached data, not refetch
+    const { result: result2 } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    // Data should be immediately available (from cache)
+    expect(result2.current.data).toEqual(mockLoreStatus);
+    // Still only one invoke call
+    expect(invoke).toHaveBeenCalledTimes(1);
+  });
+});
+
+// --- useBridgeStatus Tests ---
+
+describe("useBridgeStatus", () => {
+  let queryClient: QueryClient;
+
+  beforeEach(() => {
+    queryClient = createTestQueryClient();
+    resetMocks();
+  });
+
+  afterEach(() => {
+    queryClient.clear();
+  });
+
+  it("fetches bridge status successfully", async () => {
+    setMockResponse("get_bridge_status", mockBridgeStatus);
+
+    const { result } = renderHook(() => useBridgeStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    expect(result.current.data).toEqual(mockBridgeStatus);
+    expect(invoke).toHaveBeenCalledWith("get_bridge_status");
+  });
+
+  it("shows loading state initially", () => {
+    const { result } = renderHook(() => useBridgeStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    expect(result.current.isLoading).toBe(true);
+  });
+
+  it("handles bridge error", async () => {
+    const mockError = {
+      code: "BRIDGE_LOCKED",
+      message: "Bridge is locked by another process",
+      recoverable: true,
+    };
+
+    invoke.mockRejectedValueOnce(mockError);
+
+    const { result } = renderHook(() => useBridgeStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isError).toBe(true);
+    });
+
+    expect(result.current.error).toEqual(mockError);
+  });
+
+  it("invalidates on lore-data-changed event", async () => {
+    setMockResponse("get_bridge_status", mockBridgeStatus);
+
+    const { result } = renderHook(() => useBridgeStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    expect(invoke).toHaveBeenCalledTimes(1);
+
+    // Simulate event
+    act(() => {
+      simulateEvent("lore-data-changed", undefined);
+    });
+
+    await waitFor(() => {
+      expect(invoke).toHaveBeenCalledTimes(2);
+    });
+  });
+});
+
+// --- useSyncNow Mutation Tests ---
+
+describe("useSyncNow", () => {
+  let queryClient: QueryClient;
+
+  beforeEach(() => {
+    queryClient = createTestQueryClient();
+    resetMocks();
+  });
+
+  afterEach(() => {
+    queryClient.clear();
+  });
+
+  it("triggers sync and returns result", async () => {
+    setMockResponse("sync_now", mockSyncResult);
+
+    const { result } = renderHook(() => useSyncNow(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    expect(result.current.isPending).toBe(false);
+
+    act(() => {
+      result.current.mutate();
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    expect(invoke).toHaveBeenCalledWith("sync_now");
+    expect(result.current.data).toEqual(mockSyncResult);
+  });
+
+  it("invalidates lore and bridge queries on success", async () => {
+    setMockResponse("sync_now", mockSyncResult);
+    setMockResponse("get_lore_status", mockLoreStatus);
+    setMockResponse("get_bridge_status", mockBridgeStatus);
+
+    // First, set up some cached data
+    const { result: loreResult } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(loreResult.current.isSuccess).toBe(true);
+    });
+
+    const { result: bridgeResult } = renderHook(() => useBridgeStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(bridgeResult.current.isSuccess).toBe(true);
+    });
+
+    // Clear call counts after initial fetches
+    invoke.mockClear();
+
+    // Now trigger sync
+    const { result: syncResult } = renderHook(() => useSyncNow(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await act(async () => {
+      await syncResult.current.mutateAsync();
+    });
+
+    // Should have called sync_now plus refetched both status queries
+    await waitFor(() => {
+      expect(invoke).toHaveBeenCalledWith("sync_now");
+      expect(invoke).toHaveBeenCalledWith("get_lore_status");
+      expect(invoke).toHaveBeenCalledWith("get_bridge_status");
+    });
+  });
+
+  it("handles sync failure", async () => {
+    const mockError = {
+      code: "BRIDGE_SYNC_FAILED",
+      message: "Sync failed",
+      recoverable: true,
+    };
+
+    invoke.mockRejectedValueOnce(mockError);
+
+    const { result } = renderHook(() => useSyncNow(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    act(() => {
+      result.current.mutate();
+    });
+
+    await waitFor(() => {
+      expect(result.current.isError).toBe(true);
+    });
+
+    expect(result.current.error).toEqual(mockError);
+  });
+});
+
+// --- useReconcile Mutation Tests ---
+
+describe("useReconcile", () => {
+  let queryClient: QueryClient;
+
+  beforeEach(() => {
+    queryClient = createTestQueryClient();
+    resetMocks();
+  });
+
+  afterEach(() => {
+    queryClient.clear();
+  });
+
+  it("triggers reconciliation and returns result", async () => {
+    const reconcileResult: SyncResult = {
+      ...mockSyncResult,
+      closed: 5, // More closures in full reconcile
+      healed: 3,
+    };
+    setMockResponse("reconcile", reconcileResult);
+
+    const { result } = renderHook(() => useReconcile(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    act(() => {
+      result.current.mutate();
+    });
+
+    await waitFor(() => {
+      expect(result.current.isSuccess).toBe(true);
+    });
+
+    expect(invoke).toHaveBeenCalledWith("reconcile");
+    expect(result.current.data).toEqual(reconcileResult);
+  });
+
+  it("invalidates queries on success", async () => {
+    setMockResponse("reconcile", mockSyncResult);
+    setMockResponse("get_lore_status", mockLoreStatus);
+    setMockResponse("get_bridge_status", mockBridgeStatus);
+
+    // Set up cached queries
+    const { result: loreResult } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(loreResult.current.isSuccess).toBe(true);
+    });
+
+    invoke.mockClear();
+
+    // Trigger reconcile
+    const { result } = renderHook(() => useReconcile(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await act(async () => {
+      await result.current.mutateAsync();
+    });
+
+    await waitFor(() => {
+      expect(invoke).toHaveBeenCalledWith("reconcile");
+      expect(invoke).toHaveBeenCalledWith("get_lore_status");
+    });
+  });
+
+  it("handles reconcile failure", async () => {
+    const mockError = {
+      code: "LORE_FETCH_FAILED",
+      message: "Failed to fetch from lore",
+      recoverable: true,
+    };
+
+    invoke.mockRejectedValueOnce(mockError);
+
+    const { result } = renderHook(() => useReconcile(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    act(() => {
+      result.current.mutate();
+    });
+
+    await waitFor(() => {
+      expect(result.current.isError).toBe(true);
+    });
+
+    expect(result.current.error).toEqual(mockError);
+  });
+});
+
+// --- Combined Status Hook Tests ---
+
+describe("query invalidation coordination", () => {
+  let queryClient: QueryClient;
+
+  beforeEach(() => {
+    queryClient = createTestQueryClient();
+    resetMocks();
+  });
+
+  afterEach(() => {
+    queryClient.clear();
+  });
+
+  it("sync-status event with completed status invalidates queries", async () => {
+    setMockResponse("get_lore_status", mockLoreStatus);
+    setMockResponse("get_bridge_status", mockBridgeStatus);
+
+    const { result: loreResult } = renderHook(() => useLoreStatus(), {
+      wrapper: createWrapper(queryClient),
+    });
+
+    await waitFor(() => {
+      expect(loreResult.current.isSuccess).toBe(true);
+    });
+
+    invoke.mockClear();
+
+    // Simulate sync completed event
+    act(() => {
+      simulateEvent("sync-status", { status: "completed", message: "Done" });
+    });
+
+    await waitFor(() => {
+      expect(invoke).toHaveBeenCalledWith("get_lore_status");
+    });
+  });
+});