refactor(dashboard): thin page orchestrator + consume server bands and batched series

Extract the pure first-paint / skeleton-reservation gates
(resolveDashboardFirstPaintGate, resolveConfiguredTileCount,
resolveChartRowPlaceholderCount + their widget-id sets) into
components/dashboard/dashboard-gates; page.tsx re-exports them so the
existing unit-test imports stay valid. Wire the page to read the
server-computed targetBands when snapshot mode is on (legacy client
compute kept for the snapshot-off fallback) and to issue one
series-batch fetch for the visible non-sleep charts, threading each
chart its slice via preloadedSeries.

src/components/dashboard/dashboard-gates.ts

@@ -0,0 +1,119 @@
+/**
+ * v1.18.6 — dashboard first-paint / skeleton-reservation gates.
+ *
+ * Extracted verbatim from `src/app/page.tsx` so the page component reads
+ * as a thinner orchestrator and these pure helpers (already unit-tested)
+ * live in one cohesive module. `page.tsx` re-exports them so the existing
+ * `../page` test imports stay valid.
+ */
+import type { DashboardLayout } from "@/lib/dashboard-layout";
+
+/**
+ * v1.7.0 — first-paint gate for the dashboard tile strip.
+ *
+ * `primaryLoading` must come from whichever query actually drives the
+ * tiles: the snapshot cell by default, the slim analytics cell when
+ * `NEXT_PUBLIC_DASHBOARD_SNAPSHOT=false`. A disabled TanStack query reports
+ * `isLoading: false` (idle fetch status), so keying off the wrong
+ * source flashes the empty state for the whole fetch. Pure + exported
+ * so the gate has direct unit coverage without mounting the page.
+ */
+export function resolveDashboardFirstPaintGate(input: {
+  trendCardCount: number;
+  chartCount: number;
+  configuredTileCount: number;
+  primaryLoading: boolean;
+}): { showTileStripSkeleton: boolean; showEmptyState: boolean } {
+  const showTileStripSkeleton =
+    input.trendCardCount === 0 &&
+    input.primaryLoading &&
+    input.configuredTileCount > 0;
+  const showEmptyState =
+    input.trendCardCount === 0 &&
+    input.chartCount === 0 &&
+    !showTileStripSkeleton &&
+    !input.primaryLoading;
+  return { showTileStripSkeleton, showEmptyState };
+}
+
+/**
+ * v1.16.8 — widget ids that actually paint a tile in the strip on the
+ * web dashboard, mirrored from the per-id render blocks below.
+ * `medications` / `recentWorkouts` / `achievements` carry NO strip tile
+ * (chart-row cards only), and the iOS-pin-only ids have no web render
+ * path at all — counting any of them over-reserved the loading
+ * silhouette and made the strip reshuffle when the data landed.
+ */
+const TILE_CAPABLE_WIDGET_IDS = new Set<string>([
+  "weight",
+  "bp",
+  "pulse",
+  "bodyFat",
+  "mood",
+  "sleep",
+  "steps",
+  "glucose",
+  "bpInTarget",
+  "vo2Max",
+]);
+
+/**
+ * v1.16.8 — silhouette count for the tile-strip skeleton: one card per
+ * tile-capable, tile-visible widget. `bp` paints TWO tiles (sys + dia,
+ * see the render block below) so it counts double; `glucose` can fan
+ * out to one tile per logged context, but the contexts are unknown
+ * until the snapshot lands, so it reserves one card (the sane floor).
+ * Pure + exported for direct unit coverage.
+ */
+export function resolveConfiguredTileCount(layout: DashboardLayout): number {
+  let count = 0;
+  for (const widget of layout.widgets) {
+    if (!TILE_CAPABLE_WIDGET_IDS.has(widget.id)) continue;
+    if (!(widget.tileVisible ?? widget.visible)) continue;
+    count += widget.id === "bp" ? 2 : 1;
+  }
+  return count;
+}
+
+/**
+ * v1.16.8 — widget ids with a chart-row surface on the web dashboard,
+ * mirrored from the `charts[]` entries below. The achievements +
+ * recent-workouts cards stay out: they self-skeleton, carry no
+ * chart-shaped footprint, and gate on `layoutResolved`.
+ */
+const CHART_CAPABLE_WIDGET_IDS = new Set<string>([
+  "weight",
+  "bp",
+  "pulse",
+  "bodyFat",
+  "mood",
+  "sleep",
+  "steps",
+  "medications",
+  // v1.18.2 — Vorsorge preventive-care summary card (chart-row only).
+  "vorsorge",
+]);
+
+/**
+ * v1.16.8 — expected chart-row card count while the snapshot is still
+ * in flight. Every chart gate below needs `count > 0` from snapshot
+ * data, so the cold page used to render NO chart row at all and then
+ * grow ~1000 px when the snapshot landed. The best available signal
+ * before data arrives is the layout config (the user's saved layout
+ * when cached, the default otherwise): one card per chart-visible
+ * widget, plus the BMI card that rides the weight gate when the
+ * profile carries a height. Pure + exported for direct unit coverage.
+ */
+export function resolveChartRowPlaceholderCount(
+  layout: DashboardLayout,
+  opts?: { hasHeightCm?: boolean },
+): number {
+  let count = 0;
+  for (const widget of layout.widgets) {
+    if (!CHART_CAPABLE_WIDGET_IDS.has(widget.id)) continue;
+    if (!widget.visible) continue;
+    count += 1;
+    if (widget.id === "weight" && opts?.hasHeightCm) count += 1;
+  }
+  return count;
+}