Merge work/dose-taken-lag

src/lib/queries/__tests__/use-dashboard-snapshot.test.tsx

@@ -194,6 +194,53 @@ describe("prefetchDashboardSnapshot — hydration-safe promise handoff", () => {
     expect(fetchMock).not.toHaveBeenCalled();
   });
 
+  it("a cell that already carries data never parks a response, so a write's refetch reads the server as it is AFTER the write", async () => {
+    // The read-after-write rule for the handoff. A parked response is a copy of
+    // the server from the moment it was requested; handing it to a later
+    // `queryFn` run serves pre-write data to a refetch whose entire purpose is
+    // to see the write. The dashboard reaches `queryFn` again only via the
+    // 120 s poll, a focus refetch, or the invalidation a mutation fires — never
+    // via a remount (`refetchOnMount: false`) — so every consumer of a parked
+    // response is one of those three.
+    let serverBody: Record<string, unknown> = {
+      layout: { widgets: [] },
+      tiles: {},
+      medsToday: { takenToday: 0 },
+    };
+    const fetchMock = vi
+      .fn()
+      .mockImplementation(() => Promise.resolve(envelopeResponse(serverBody)));
+    vi.stubGlobal("fetch", fetchMock);
+    getQueryDataMock.mockReturnValue({ widgets: [{ id: "existing" }] });
+
+    // The user comes back to the dashboard after a few minutes away. The cell
+    // still holds the pre-write body, so the page paints from it at once.
+    prefetchDashboardSnapshot(
+      fakeQueryClient({
+        data: { tiles: {} },
+        dataUpdatedAt: Date.now() - 5 * 60_000,
+      }),
+    );
+    expect(fetchMock).not.toHaveBeenCalled();
+
+    // They record a dose. The server now reports it taken.
+    serverBody = {
+      layout: { widgets: [] },
+      tiles: {},
+      medsToday: { takenToday: 1 },
+    };
+
+    // The write's invalidation refetches the mounted cell.
+    useDashboardSnapshot();
+    const opts = lastOptsOf(useQueryMock);
+    const snap = await (
+      opts.queryFn as () => Promise<{ medsToday: { takenToday: number } }>
+    )();
+
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    expect(snap.medsToday.takenToday).toBe(1);
+  });
+
   it("falls back to a fresh fetch when the preload failed — the mounted cell owns error surfacing", async () => {
     const layout = { widgets: [] };
     const fetchMock = vi

src/lib/queries/use-dashboard-snapshot.ts

@@ -99,15 +99,25 @@ export function prefetchDashboardSnapshot(queryClient: QueryClient) {
   }
   // A fresh handoff is already in flight / parked.
   if (preloadedSnapshot) return;
-  // Cache already warm (return-to-dashboard within staleTime) — the
-  // mounted cell serves it without ever calling `queryFn`; fetching here
-  // would be a wasted request parked in the slot.
+  // The handoff exists to cut the COLD first-load waterfall, so it is only
+  // ever warranted when no snapshot cell has produced data yet. Once a cell
+  // carries data the page paints from it immediately and there is no waterfall
+  // left to cut — but the parked response would still sit in the slot, because
+  // `refetchOnMount: false` means a remount never calls `queryFn` to consume
+  // it. The next `queryFn` run is then whatever comes along: the 120 s poll, a
+  // focus refetch, or the invalidation that follows the user's own write. All
+  // three exist to fetch data that is NEWER than what the cell holds, and all
+  // three would instead be handed a response whose request was issued BEFORE
+  // the write. That is how a just-recorded dose kept reading as still due
+  // until the following poll cleared it.
+  //
   // v1.21.3 (b) — the live cell is locale-keyed (`["dashboard","snapshot",
   // locale]`), but the preloader runs before the locale context is in scope.
-  // Probe ALL `["dashboard","snapshot"]` cells (prefix) and treat the freshest
-  // as the warm-slot signal: if any locale's cell is fresh, skip the preload;
-  // otherwise warm the request through the handoff and let the mounted cell
-  // commit it under whichever locale the user lands on.
+  // Probe ALL `["dashboard","snapshot"]` cells (prefix): if ANY locale's cell
+  // has data, skip the preload; otherwise warm the request through the handoff
+  // and let the mounted cell commit it under whichever locale the user lands
+  // on. A cell that exists but never resolved (an error slot) reports
+  // `dataUpdatedAt === 0` and correctly still warms.
   const states = queryClient
     .getQueriesData({ queryKey: queryKeys.dashboardSnapshot() })
     .map(([key]) => queryClient.getQueryState(key));
@@ -115,7 +125,7 @@ export function prefetchDashboardSnapshot(queryClient: QueryClient) {
     (max, s) => (s ? Math.max(max, s.dataUpdatedAt) : max),
     0,
   );
-  if (freshest > 0 && Date.now() - freshest < PRELOAD_MAX_AGE_MS) {
+  if (freshest > 0) {
     return;
   }
   const promise = fetchDashboardSnapshot();