perf: reuse progressive live snapshot during hydration (Closes #1405)

frontend/context-poller.js

@@ -166,9 +166,47 @@ function createContextPoller({
     return refresh({ force: true });
   }
 
+  function adopt(snapshot) {
+    if (
+      stopped || activeRequest || retainedSnapshot || !snapshot ||
+      typeof snapshot !== 'object' ||
+      !Object.prototype.hasOwnProperty.call(snapshot, 'context')
+    ) return false;
+    retainedSnapshot = { ...snapshot };
+    revisions = { ...(snapshot.revisions || {}) };
+    failureStreak = 0;
+    lastSuccessAt = Date.now();
+    nextDelayMs = snapshotDelay(snapshot);
+    const changedSections = ['context', 'events', 'notifications'].filter(
+      section => Object.prototype.hasOwnProperty.call(snapshot, section)
+    );
+    onSnapshot(retainedSnapshot, changedSections);
+    schedule(nextDelayMs);
+    return true;
+  }
+
+  async function adoptPending(snapshotPromise) {
+    if (!snapshotPromise || typeof snapshotPromise.then !== 'function') return false;
+    let deadline = null;
+    const timeout = new Promise(resolve => {
+      deadline = setDeadlineTimer(() => resolve(null), timeoutMs);
+    });
+    try {
+      const snapshot = await Promise.race([
+        Promise.resolve(snapshotPromise).catch(() => null),
+        timeout,
+      ]);
+      return adopt(snapshot);
+    } finally {
+      clearDeadlineTimer(deadline);
+    }
+  }
+
   return {
     start: refresh,
     refresh,
+    adopt,
+    adoptPending,
     setVisible,
     getState() {
       return {

frontend/dashboard.js

@@ -8441,9 +8441,12 @@
     if (!deviceSetup) await (await ensureDeviceSetup()).open(event);
   });
   pushControllerReady.then(ensureDeviceSetup).catch(console.warn);
-  await load();
+  let adoptedProgressiveSnapshot = contextPoller.adopt(progressiveWorkHandoff?.liveSnapshot);
+  if (!adoptedProgressiveSnapshot && progressiveWorkHandoff?.liveSnapshotPromise) {
+    adoptedProgressiveSnapshot = await contextPoller.adoptPending(progressiveWorkHandoff.liveSnapshotPromise);
+  }
+  if (!adoptedProgressiveSnapshot) await load();
   await appShortcut.run();
-  contextPoller.start();
   document.addEventListener('visibilitychange', () => {
     contextPoller.setVisible(!document.hidden);
     if (!document.hidden) deviceSetup?.render();

frontend/progressive-my-work.js

@@ -7,6 +7,8 @@ function createProgressiveMyWork({ document, fetchSnapshot }) {
   let active = 'all';
   let stopped = false;
   let selectedByUser = false;
+  let liveSnapshot = null;
+  let liveSnapshotPromise = null;
   const deferredQueues = {
     today:'Today', agenda:'Agenda', later:'Later', draft:'Drafts',
   };
@@ -59,13 +61,31 @@ function createProgressiveMyWork({ document, fetchSnapshot }) {
 
   return {
     handoff() {
-      return { selectedFilter:selectedByUser ? active : null };
+      const state = { selectedFilter:selectedByUser ? active : null };
+      if (liveSnapshot) {
+        state.liveSnapshot = liveSnapshot;
+        liveSnapshot = null;
+        liveSnapshotPromise = null;
+      } else if (liveSnapshotPromise) {
+        state.liveSnapshotPromise = liveSnapshotPromise;
+        liveSnapshotPromise = null;
+      }
+      return state;
     },
     async start() {
       if (status) status.textContent = 'Loading assigned work…';
+      const request = Promise.resolve().then(() => fetchSnapshot());
+      liveSnapshotPromise = request.then(snapshot => (
+        snapshot && typeof snapshot === 'object' &&
+        Object.prototype.hasOwnProperty.call(snapshot, 'context') ? snapshot : null
+      ), () => null);
       try {
-        const snapshot = await fetchSnapshot();
+        const snapshot = await request;
         if (stopped) return false;
+        const transferable = snapshot && typeof snapshot === 'object' &&
+          Object.prototype.hasOwnProperty.call(snapshot, 'context');
+        if (transferable) liveSnapshot = snapshot;
+        else liveSnapshotPromise = null;
         const context = snapshot?.context || snapshot || {};
         items = buildMyWork({ ...context, notifications:snapshot?.notifications || context.notifications || [] });
         updateCounts();