Media pager: the slide meant stays on screen through a resize, from the first moment. The pager's resize handler re-showed pager.cur, which the slide observer sets a frame after the pager opens — so a resize in that first frame (the page going full screen for the pager, as the player's full-screen button does: a taller window, the address bar gone) had nothing to re-show, and the pager was left to the browser's re-snap. Now the slide meant is an anchor: the start slide the moment the pager opens, then each slide arrived at; a resize re-shows it (or the tail, when the reader is waiting there), and an arrival the observer reports at a size other than the one the pager last laid out at is taken as the resize's doing, not the reader's: the anchor goes back instead. Hardening: Adam's full-screen button on a clip 23 posts down showed another post's still, which a headless run of the same path (a user-gesture requestFullscreen on the feed clip) and tools/pager-resize-test.js (the window grows as the pager opens, shrinks and grows again, changes shape) did not reproduce; the recorder on his tab is for the next time.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01J1Kon8bxJoHRpJdSzshCkp

2 files changed, 140 insertions, 1 deletions

diff --git a/src/features/messages.js b/src/features/messages.js
index ae801cd..55deaa1 100644
--- a/src/features/messages.js
+++ b/src/features/messages.js
@@ -12746,6 +12746,7 @@ export function messagesFeature(ctx) {
         if (pager.fromFeed && video) el.classList.remove('show');
       }
       pager.cur = slide;
+      pager.anchor = slide;
       pager.curAt = Date.now();
       pagerArrows(slide);
       if (pager.fromFeed) { const row = feedNow().notes.find((x) => x.id === slide._rowId); markSeen(row || slide._ev); }
@@ -12759,6 +12760,8 @@ export function messagesFeature(ctx) {
       for (const e of entries) {
         if (!e.isIntersecting || e.intersectionRatio < 0.6 || !pager) continue;
         if (pager.flying) continue; // passing, not arriving: the landing is pagerFly's
+        // a slide the screen's new size put there, not the reader: the anchor goes back
+        if (pager.screenH && scroller.clientHeight !== pager.screenH) { pager.onResize(); continue; }
         pager.arrive(e.target);
       }
     }, { root: scroller, threshold: [0.6] });
@@ -12767,6 +12770,8 @@ export function messagesFeature(ctx) {
     document.documentElement.classList.add('no-scroll');
     const first = pagerSlides().find((s) => s.getAttribute('data-k') === want.start) || pagerSlides()[0];
     if (first) pagerShow(first);
+    pager.anchor = first; // the slide meant to be on screen, from the first moment
+    pager.screenH = scroller.clientHeight;
     // the clip on screen's seek bar, every frame (timeupdate comes a few times a second)
     if (video) {
       const p = pager;
@@ -12774,7 +12779,20 @@ export function messagesFeature(ctx) {
       p.raf = requestAnimationFrame(frame);
     }
     // turned on its side (or back), the slides change height: stay on this one
-    pager.onResize = () => { if (pager && pager.cur) pagerShow(pager.cur); };
+    // The screen changed size — a turn of the phone, or the page going full
+    // screen for the pager (the address bar and tabs gone: a taller window).
+    // The posts are a screen tall each, so a scroll position in pixels
+    // deep in the pager now sits in a different post: put the one meant
+    // back on screen. The slide meant is the anchor, set the moment the
+    // pager opens (cur is set by the observer a frame later, and the full
+    // screen's resize beat it: Adam's full-screen button on a clip 23 posts
+    // down landed him on another post's picture) and on each arrival.
+    pager.onResize = () => {
+      if (!pager) return;
+      pager.screenH = pager.scroller.clientHeight;
+      if (pager.onTail) pager.scroller.scrollTop = pager.tail.offsetTop;
+      else if (pager.anchor) pagerShow(pager.anchor);
+    };
     window.addEventListener('resize', pager.onResize);
     // new posts land in the feed while the pager is open; counts move
     pager.tick = setInterval(() => { if (pager) { growPager(); pagerFeedAhead(); if (el.classList.contains('show')) pagerCounts(pager.cur); } }, 1500);
diff --git a/tools/pager-resize-test.js b/tools/pager-resize-test.js
new file mode 100644
index 0000000..7e4cfb7
--- /dev/null
+++ b/tools/pager-resize-test.js
@@ -0,0 +1,121 @@
+// The pager keeps its post when the screen changes size: the page going
+// full screen for it (a taller window, the address bar gone), or a turn of
+// the phone. Posts are a screen tall, so a pixel scroll position deep in
+// the pager lands in another post after a resize — Adam's full-screen
+// button on a clip 23 posts down showed him another post's picture. The
+// resize can come before the observer has even named the first slide.
+// Run: bun tools/pager-resize-test.js
+import puppeteer from './puppeteer.js';
+import { cacheKeyFor } from '../src/wallet.js';
+import { generateSecretKey, getPublicKey, finalizeEvent } from 'nostr-tools/pure';
+import { buildHtml } from '../build.js';
+const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
+let ok = true;
+const check = (n, c, d = '') => { console.log(` ${c ? '✓' : '✗'} ${n}${d ? ' — ' + d : ''}`); if (!c) ok = false; };
+const png = (size) => Bun.spawnSync(['ffmpeg', '-loglevel', 'error', '-f', 'lavfi', '-i', 'testsrc=size=' + size, '-frames:v', '1', '-f', 'image2', '-c:v', 'png', 'pipe:1']).stdout;
+const PICS = { a1: png('400x300'), a2: png('300x400'), b: png('320x320'), d: png('360x240'), e: png('240x180') };
+
+const SK = generateSecretKey(), AUTHOR = getPublicKey(SK);
+const now = Math.floor(Date.now() / 1000);
+const post = (content, ago) => finalizeEvent({ kind: 1, created_at: now - ago, tags: [], content }, SK);
+const html = await buildHtml({ minify: true, pwa: false });
+const server = Bun.serve({ port: 0, fetch: (req) => {
+  const path = new URL(req.url).pathname;
+  if (path.startsWith('/punks')) return new Response(Bun.file('dist' + path));
+  const m = /^\/(a1|a2|b|d|e)\d*\.png$/.exec(path);
+  if (m) return new Response(PICS[m[1]], { headers: { 'content-type': 'image/png' } });
+  return new Response(html, { headers: { 'content-type': 'text/html' } });
+} });
+const U = (n) => server.url.origin + '/' + n + '.png';
+const seeded = [
+  post('two pictures ' + U('a1') + ' ' + U('a2'), 100),
+  post('one picture ' + U('b'), 200),
+  post('only words here, nothing to look at', 300),
+  post('a last picture ' + U('d'), 400),
+  ...Array.from({ length: 12 }, (_, i) => post('more ' + i + ' ' + U('e' + i), 500 + i * 60)), // a dozen more, one picture each, for a flight
+];
+
+const browser = await puppeteer.launch({ executablePath: '/usr/bin/google-chrome', headless: 'new', args: ['--no-sandbox', '--blink-settings=primaryHoverType=2,availableHoverTypes=2,primaryPointerType=4,availablePointerTypes=4'] /* a pointer that hovers: headless has none */ });
+const page = await browser.newPage();
+const errs = [];
+page.on('pageerror', (e) => errs.push(String(e)));
+const click = (t) => page.evaluate((x) => { const e = [...document.querySelectorAll('button')].find((n) => n.textContent.trim().toLowerCase().includes(x)); if (e) { e.click(); return true; } return false; }, t);
+const waitText = async (x, ms = 25000) => { for (let i = 0; i < ms / 250; i++) { if ((await page.evaluate(() => document.body.innerText)).toLowerCase().includes(x)) return true; await sleep(250); } return false; };
+const waitFor = async (fn, arg, ms = 10000) => { for (let i = 0; i < ms / 100; i++) { if (await page.evaluate(fn, arg)) return true; await sleep(100); } return false; };
+// the slide the pager rests on, by its picture
+const curPic = () => page.evaluate(() => {
+  const sc = document.querySelector('.mp-scroll'); if (!sc) return null;
+  const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; });
+  return s ? s.getAttribute('data-k').split('|')[1].split('/').pop() : 'between';
+});
+const resting = async (name) => rested(name).then(async (r) => { await sleep(260); return r; }); // a breath after: the wheel's gate between steps
+const rested = async (name) => waitFor((n) => { const sc = document.querySelector('.mp-scroll'); if (!sc) return false; const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; }); return !!s && s.getAttribute('data-k').endsWith('/' + n); }, name, 4000);
+const openPic = async (word) => {
+  await page.evaluate((w) => { const r = [...document.querySelectorAll('.notes-feed [data-key]')].find((n) => n.textContent.includes(w)); r.scrollIntoView({ block: 'center' }); }, word);
+  await sleep(400);
+  const at = await page.evaluate((w) => { const r = [...document.querySelectorAll('.notes-feed [data-key]')].find((n) => n.textContent.includes(w)); const i = r.querySelector('img.note-img').getBoundingClientRect(); return { x: i.x + i.width / 2, y: i.y + i.height / 2, y0: window.scrollY }; }, word);
+  await page.mouse.click(at.x, at.y);
+  await waitFor(() => !!document.querySelector('.media-pager'), null, 4000);
+  return at.y0;
+};
+const tapPager = async () => { const at = await page.evaluate(() => { const sc = document.querySelector('.mp-scroll'); const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; }) || sc.firstChild; const r = s.querySelector('img.mp-media').getBoundingClientRect(); return { x: r.x + r.width / 2, y: r.y + r.height / 2 }; }); await page.mouse.click(at.x, at.y); };
+const rowTop = (word) => page.evaluate((w) => { const r = [...document.querySelectorAll('.notes-feed [data-key]')].find((n) => n.textContent.includes(w)); return r ? Math.round(r.getBoundingClientRect().top) : null; }, word);
+
+try {
+  await page.setViewport({ width: 1280, height: 900 });
+  await page.goto(server.url.href, { waitUntil: 'domcontentloaded' });
+  await page.evaluate(() => localStorage.setItem('btc-wallet-network', 'regtest'));
+  await page.reload({ waitUntil: 'domcontentloaded' });
+  await sleep(400);
+  await click('create a new wallet'); await sleep(600);
+  await page.waitForSelector('.words .w .t');
+  const mn = (await page.$$eval('.words .w .t', (l) => l.map((e) => e.textContent.trim()))).join(' ');
+  await click('skip verification');
+  await waitText('receive', 20000);
+  const base = cacheKeyFor(mn + '\n');
+  await page.evaluate(([k, pk, ns]) => {
+    localStorage.setItem(k + ':follows', JSON.stringify({ tags: [['p', pk]], c: '', at: Math.floor(Date.now() / 1000) }));
+    localStorage.setItem(k + ':feedNotes', JSON.stringify(ns));
+    localStorage.setItem(k + ':profiles', JSON.stringify({ [pk]: { name: 'Picture Poster', t: Date.now() } }));
+    localStorage.setItem('btc-wallet-feed:' + k, 'following');
+  }, [base, AUTHOR, seeded]);
+  await page.reload({ waitUntil: 'domcontentloaded' });
+  await waitText('receive', 20000);
+  await page.evaluate(() => document.querySelector('.app-nav-button[aria-label="Feed"]').click());
+  check('the pictures are in the feed', await waitFor(() => document.querySelectorAll('.notes-feed img.note-img').length >= 4, null, 20000));
+  const cdp = await page.target().createCDPSession();
+  // a trackpad's run: small deltas, page-side — a CDP mouseWheel is always a 120-unit notch to Chrome
+  const pad = (dy, n) => page.evaluate(async ([dy, n]) => { const sc = document.querySelector('.mp-scroll'); for (let i = 0; i < n; i++) { const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; }) || sc.firstChild; const ev = new WheelEvent('wheel', { deltaY: dy, deltaX: 0, deltaMode: 0, bubbles: true, cancelable: true, clientX: 640, clientY: 450 }); Object.defineProperty(ev, 'wheelDeltaY', { value: -Math.round(dy * 1.2) }); s.querySelector('img.mp-media').dispatchEvent(ev); await new Promise((r) => setTimeout(r, 16)); } }, [dy, n]);
+  const pos = () => page.evaluate(() => { const sc = document.querySelector('.mp-scroll'); return sc ? Math.round(sc.scrollTop) + '/' + sc.clientHeight + ' glide:' + !!sc._glide + ' snap:' + sc.style.scrollSnapType : 'none'; });
+  const wheel = (dy, { dx = 0, mods = 0 } = {}) => cdp.send('Input.dispatchMouseEvent', { type: 'mouseWheel', x: 640, y: 450, deltaX: dx, deltaY: dy, modifiers: mods });
+  const zoomOf = () => page.evaluate(() => { const sc = document.querySelector('.mp-scroll'); const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; }); const m = /scale\(([\d.]+)\)/.exec(s.querySelector('img.mp-media').style.transform || ''); return m ? Number(m[1]) : 1; });
+  const shiftOf = () => page.evaluate(() => { const sc = document.querySelector('.mp-scroll'); const s = [...sc.querySelectorAll('.mp-slide')].find((x) => { const r = x.getBoundingClientRect(); return Math.abs(r.top) < 4 && Math.abs(r.left) < 4; }); const m = /translate\(([-\d.]+)px, ([-\d.]+)px\)/.exec(s.querySelector('img.mp-media').style.transform || ''); return m ? [Number(m[1]), Number(m[2])] : [0, 0]; });
+
+  console.log('\n[the screen grows right as the pager opens]');
+  // the feed draws a window of rows: scroll down until the post is drawn
+  for (let i = 0; i < 40; i++) {
+    if (await page.evaluate((w) => { const r = [...document.querySelectorAll('.notes-feed [data-key]')].find((n) => n.textContent.includes(w)); if (!r) return false; r.scrollIntoView({ block: 'center' }); return true; }, 'more 8')) break;
+    await page.evaluate(() => window.scrollBy(0, 1500)); await sleep(300);
+  }
+  await sleep(500);
+  const at = await page.evaluate((w) => { const r = [...document.querySelectorAll('.notes-feed [data-key]')].find((n) => n.textContent.includes(w)); const i = r.querySelector('img.note-img').getBoundingClientRect(); return { x: i.x + i.width / 2, y: i.y + i.height / 2 }; }, 'more 8');
+  await page.mouse.click(at.x, at.y);
+  await waitFor(() => !!document.querySelector('.media-pager'), null, 4000);
+  // the window grows (full screen) before the pager's observer has named a slide
+  await page.setViewport({ width: 1280, height: 1040 });
+  check('the pager rests on the picture tapped, eleven posts down', await resting('e8.png'), await curPic() + ' ' + await pos());
+  await sleep(600);
+  check('…and stays there', (await curPic()) === 'e8.png', await curPic());
+  console.log('\n[a later resize]');
+  await page.keyboard.press('ArrowDown'); await resting('e9.png');
+  await page.setViewport({ width: 1280, height: 780 });
+  check('the window shrinks: still on the post the reader moved to', await resting('e9.png'), await curPic() + ' ' + await pos());
+  await page.setViewport({ width: 1280, height: 1100 });
+  check('…and grows again: still there', await resting('e9.png'), await curPic() + ' ' + await pos());
+  await page.keyboard.press('ArrowUp'); await resting('e8.png');
+  await page.setViewport({ width: 900, height: 1200 });
+  check('a different shape: still on the post', await resting('e8.png'), await curPic() + ' ' + await pos());
+  check('no page errors', errs.length === 0, errs.slice(0, 2).join(' | '));
+} catch (e) { console.error(e); ok = false; } finally { await browser.close(); server.stop(true); }
+console.log(ok ? '\n✅ the pager keeps its post through a resize' : '\n❌ failed');
+process.exit(ok ? 0 : 1);