feat: poll server data so shared pages stay near-live

Refetch the current page every 15s while the tab is visible, gated by a
pure refresh policy: edit pages, hidden or offline tabs and in-flight
navigations are left alone. Replaces refresh-on-refocus with auto-refresh.

1 files changed, 31 insertions, 0 deletions

diff --git a/src/lib/shared/refresh-policy.ts b/src/lib/shared/refresh-policy.ts
new file mode 100644
index 0000000..d79e6b7
--- /dev/null
+++ b/src/lib/shared/refresh-policy.ts
@@ -0,0 +1,31 @@
+/**
+ * Routes whose page data must not be refetched in the background: edit pages
+ * hold in-progress work, and refreshing the login form is pointless.
+ */
+export const EXCLUDED_ROUTES: Record<string, true> = {
+	'/login': true,
+	'/grocery/[id]': true,
+	'/projects/[projectId]/routine/[routineId]': true,
+};
+
+export interface RefreshConditions {
+	/** `$page.route.id`; null when no route matched yet. */
+	routeId: string | null | undefined;
+	/** Document is visible (not a backgrounded tab). */
+	visible: boolean;
+	/** Browser reports a network connection. */
+	online: boolean;
+	/** A navigation or form action is already in flight. */
+	navigating: boolean;
+}
+
+/** A background refetch may re-run the page load only if nothing is at stake. */
+export function shouldAutoRefresh({
+	routeId,
+	visible,
+	online,
+	navigating,
+}: RefreshConditions): boolean {
+	if (!routeId || routeId in EXCLUDED_ROUTES) return false;
+	return visible && online && !navigating;
+}