The wheel coasts over a video and on a thread, and a turn back against a coast is a gentler half push that winds up again from the next notch.

A notch with the pointer over a clip fell to the browser's single-notch scroll: video and audio were on the wheel handler's hands-off list from the first commit, though the wheel does nothing to a player itself. The thread page was outside the handler's scope altogether, so a thread scrolled plain while the feed coasted. Both coast now, like the words around them (Adam, 2026-10-16).

A reversal was a full notch the other way followed by two notches without wind-up, and felt like an overshoot. It is now half a notch's travel at half the speed, so the reader who flew past a post settles back onto it; the next notch the same way is a plain one, winding up from whatever speed the half push left, so a spin on after a reversal gets going at once. (The five-notch quarter-size hunt stays gone.)

feed-wheel-reverse-test: the half push, the wind-up from the second notch, a notch over a video / audio / a thread coasts, one in a text box or the pager does not; the fixture's target can sit inside a given element and on a thread page.

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

2 files changed, 62 insertions, 36 deletions

diff --git a/src/app.js b/src/app.js
index dae7b17..96c6af1 100644
--- a/src/app.js
+++ b/src/app.js
@@ -6617,13 +6617,17 @@ if (INTENT_URI) {
 // selection, and a drag that moved isn't a click on what it started on.
 (() => {
   if (typeof window === 'undefined' || matchMedia('(prefers-reduced-motion: reduce)').matches) return;
-  const SCOPE = '.feed-page, .notes-feed';
+  const SCOPE = '.feed-page, .notes-feed, .thread-page'; // a thread scrolls the same as a feed (Adam, 2026-10-16)
   const TAU = 325; // ms: how quickly a coast dies down (the phone's feel)
   const VMAX = 16; // px/ms
   const inScope = (t) => {
     const el = t && t.closest ? t : t && t.parentElement;
     if (!el || !el.closest(SCOPE)) return false;
-    if (el.closest('input, textarea, select, video, audio, [contenteditable], .feed-chips, .lightbox, .media-pager')) return false;
+    // (A video or an audio player is part of the feed: a notch over a clip
+    // coasts like one over the words — the wheel does nothing to a player
+    // itself, so there is nothing to leave it. Adam, 2026-10-16: "over a
+    // video it doesn't initiate a coast, just a single notch".)
+    if (el.closest('input, textarea, select, [contenteditable], .feed-chips, .lightbox, .media-pager')) return false;
     // something inside that scrolls on its own (a caption, a list) keeps its wheel
     for (let n = el; n && n !== document.body; n = n.parentElement) {
       if (n.scrollHeight > n.clientHeight + 1 && /(auto|scroll)/.test(getComputedStyle(n).overflowY)) return false;
@@ -6653,16 +6657,19 @@ if (INTENT_URI) {
     if (!raf && v) { last = performance.now(); raf = requestAnimationFrame(tick); }
   };
   // ---- the wheel
-  // A turn back against the coast catches the page at once and is a plain
-  // notch from rest — no flight the other way, since the next couple of
-  // notches after a reversal (CALM) don't wind the speed up, so a couple of
-  // correcting notches travel a couple of notches; a spin that keeps going
-  // winds up again from the third. (A spell of quarter-size "hunting"
-  // notches ramping back up was tried here and felt like a stutter and a
-  // slow patch; a 700 ms spell without wind-up after a reversal was tried
-  // too and a spin begun inside it felt slow — Adam, 2026-10-16.)
-  const CALM = 2; // notches after a reversal without wind-up
-  let calmLeft = 0; // (lastDir/lastMoveAt: the tick's, above)
+  // A turn back against the coast catches the page at once and is a gentler
+  // push the other way — half a notch's travel, at half the speed — so the
+  // reader who overshot a post settles back onto it instead of flying past
+  // it the other way. The next notch the same way is a plain one, winding
+  // up from whatever speed the half push left, so a spin on after a
+  // reversal gets going again at once. (A spell of quarter-size "hunting"
+  // notches ramping back up over five turns was tried here and felt like a
+  // stutter and a slow patch; a full notch then two without wind-up felt
+  // like an overshoot — Adam, 2026-10-16: "could the first coast in the
+  // opposite direction be smaller/slower than usual? then speed up if we
+  // scroll again in the same direction".)
+  const REVERSE = 0.5; // of a notch: the first push back against a coast
+  // (lastDir/lastMoveAt: the tick's, above)
   let smoothUntil = 0; // a trackpad's events were just seen: hands off
   window.addEventListener('wheel', (e) => {
     if (e.ctrlKey || e.shiftKey || e.defaultPrevented) return;
@@ -6680,19 +6687,19 @@ if (INTENT_URI) {
       // A reversal catches the old coast immediately. Discard its fractional
       // step and frame clock too: after a busy frame, applying the NEW velocity
       // to the OLD elapsed time made the first reverse step jump. Give the
-      // notch a small response now, then coast the rest of its travel.
+      // notch a small response now, then coast the rest of its (half) travel.
       stop();
-      calmLeft = CALM;
-      const first = dir * Math.min(16, Math.abs(px * 3 / TAU) * 16);
+      const travel = px * 3 * REVERSE;
+      const first = dir * Math.min(16, Math.abs(travel / TAU) * 16);
       window.scrollBy({ top: first, behavior: 'instant' });
       lastDir = dir; lastMoveAt = now;
-      coast((px * 3 - first) / TAU, TAU);
+      coast((travel - first) / TAU, TAU);
     } else {
       // A notch into a page already moving pushes harder: the faster it
       // goes, the more each turn adds (up to 2.5x), so keeping the wheel
       // turning winds the speed up instead of settling at a stroll. From
       // rest a notch is the same push as ever.
-      const gain = calmLeft-- > 0 ? 1 : 1 + Math.min(1.5, Math.abs(v) / 4);
+      const gain = 1 + Math.min(1.5, Math.abs(v) / 4);
       coast(v + (px * 3 * gain) / TAU, TAU);
     }
   }, { passive: false });
diff --git a/tools/feed-wheel-reverse-test.js b/tools/feed-wheel-reverse-test.js
index 632bbc6..be5ad54 100644
--- a/tools/feed-wheel-reverse-test.js
+++ b/tools/feed-wheel-reverse-test.js
@@ -5,7 +5,7 @@ const source = await Bun.file('src/app.js').text();
 const start = source.indexOf('(() => {', source.indexOf('// The feed scrolls like a phone'));
 const end = source.indexOf("\nwindow.addEventListener('load'", start);
 assert(start > 0 && end > start);
-function fixture() {
+function fixture(inside = '') {
   let now = 100, id = 0;
   const handlers = new Map(), frames = new Map(), steps = [];
   const window = { scrollY: 5000,
@@ -13,7 +13,8 @@ function fixture() {
     scrollBy: ({ top }) => { steps.push(top); window.scrollY += top; },
   };
   const document = { body: {}, addEventListener() {}, removeEventListener() {} };
-  const target = { closest: (selector) => selector.includes('.feed-page') ? target : null,
+  // the target sits in a feed page (or, for a thread case, a thread page), inside the given element
+  const target = { closest: (selector) => selector.split(/,\s*/).some((p) => p === inside || (p === '.feed-page' && inside !== '.thread-page')) ? target : null,
     scrollHeight: 100, clientHeight: 100, parentElement: document.body };
   runInNewContext(source.slice(start, end), { window, document,
     matchMedia: () => ({ matches: false }), performance: { now: () => now },
@@ -46,29 +47,47 @@ for (const dir of [1, -1]) {
   assert((f.y - reversed) * dir < 0, 'next frame continues in the new direction');
   assert(Math.abs(f.y - reversed) < 20, 'new velocity is not applied to the old frame delay');
   settle(f);
-  // The turn back is a plain notch from rest: its full travel, no flight the other way.
+  // The turn back is a gentler push than a notch: half a notch's travel, so
+  // a reader who overshot settles back rather than flying the other way.
   const back = (before - f.y) * dir;
-  assert(back > 280 && back < 330, 'a reverse notch against a coast travels one notch: ' + back);
-  // For a moment after a reversal notches don't wind the speed up: a
-  // reversal and a quick second notch travel about two notches, not a flight.
-  let calm;
+  assert(back > 130 && back < 170, 'a reverse notch against a coast travels half a notch: ' + back);
+  // The next notch the same way is a plain one again, winding up from the
+  // half push's speed: a reversal and a quick second notch travel about a
+  // notch and a half.
+  let pair;
   { f.wheel(-dir); f.advance(17); f.frame(); f.wheel(-dir); f.advance(120); f.frame(); // coasting again, the other way
-    const y = f.y; f.wheel(dir); f.advance(60); f.frame(); f.wheel(dir); settle(f); calm = (f.y - y) * dir;
-    assert(calm > 540 && calm < 700, 'a reversal and a quick second notch: about two notches of travel: ' + calm); }
-  // From rest, well after, the wind-up is back: the same two quick notches go further.
-  { f.advance(2500); const y = f.y; f.wheel(dir); f.advance(60); f.frame(); f.wheel(dir); settle(f); const s = (f.y - y) * dir; assert(s > calm + 40, 'two quick notches with the wind-up go further: ' + s + ' vs ' + calm); }
-  // A spin that keeps going after a reversal winds up again from its third
-  // notch: a reversal plus four quick notches goes well past five plain ones.
+    const y = f.y; f.wheel(dir); f.advance(60); f.frame(); f.wheel(dir); settle(f); pair = (f.y - y) * dir;
+    assert(pair > 440 && pair < 560, 'a reversal and a quick second notch: about a notch and a half: ' + pair); }
+  // From rest the same two quick notches go further: a full first push, and the wind-up.
+  { f.advance(2500); const y = f.y; f.wheel(dir); f.advance(60); f.frame(); f.wheel(dir); settle(f); const s = (f.y - y) * dir; assert(s > pair + 100, 'two quick notches from rest go further: ' + s + ' vs ' + pair); }
+  // A spin that keeps going after a reversal winds up from its second
+  // notch: a reversal plus four quick notches goes well past four plain ones.
   let spin;
   { f.wheel(-dir); f.advance(17); f.frame(); f.wheel(-dir); f.advance(120); f.frame();
     const y = f.y; f.wheel(dir); for (let i = 0; i < 4; i++) { f.advance(60); f.frame(); f.wheel(dir); } settle(f); spin = (f.y - y) * dir;
-    assert(spin > 5 * 300 + 150, 'a spin on after a reversal winds up again: ' + spin); }
-  // ...and the same five quick notches from rest go about as far (the two calm ones cost little).
+    assert(spin > 4 * 300 + 150, 'a spin on after a reversal winds up again: ' + spin); }
+  // ...and the same five quick notches from rest go about as far (the half push costs little).
   { f.advance(2500); const y = f.y; f.wheel(dir); for (let i = 0; i < 4; i++) { f.advance(60); f.frame(); f.wheel(dir); } settle(f); const s = (f.y - y) * dir;
-    assert(s < spin * 1.25, 'five from rest vs five after a reversal: ' + s + ' vs ' + spin); settle(f, 200); }
+    assert(s < spin * 1.3, 'five from rest vs five after a reversal: ' + s + ' vs ' + spin); settle(f, 200); }
   // From rest a notch either way is a full push.
   { f.advance(2500); const y = f.y; f.wheel(dir); settle(f); const s = (f.y - y) * dir; assert(s > 280 && s < 330, 'from rest a notch either way is a full push: ' + s); }
-  // A turn back against a coast that only just died is a reversal too (caught, no wind-up).
-  { f.wheel(dir); settle(f, 40); f.advance(100); const y = f.y; f.wheel(-dir); f.advance(60); f.frame(); f.wheel(-dir); settle(f); const s = (y - f.y) * dir; assert(s > 520 && s < 700, 'reversing right after the coast dies: no wind-up: ' + s); }
+  // A turn back against a coast that only just died is a reversal too: the half push.
+  { f.wheel(dir); settle(f, 40); f.advance(100); const y = f.y; f.wheel(-dir); settle(f); const s = (y - f.y) * dir; assert(s > 130 && s < 170, 'reversing right after the coast dies is the half push: ' + s); }
+  // Well after the coast died it is a plain notch from rest, whichever way.
+  { f.advance(2500); const y = f.y; f.wheel(-dir); settle(f); const s = (y - f.y) * dir; assert(s > 280 && s < 330, 'a notch the other way from rest is a full push: ' + s); }
 }
-console.log('✓ immediate reversal both ways, stale frame timestamps, busy frame recovery, a reversal is a plain notch, two calm notches, then the wind-up is back');
+// A notch over a video (or an audio player) in the feed coasts like any
+// other — the wheel does nothing to a player itself — and so does one on a
+// thread page.
+for (const sel of ['video', 'audio', '.thread-page']) {
+  const f = fixture(sel);
+  const y = f.y; f.wheel(1); settle(f);
+  assert(f.y - y > 280 && f.y - y < 330, 'a notch over ' + sel + ' coasts a full push: ' + (f.y - y));
+}
+// ...while a notch in a text box, or in the media pager, is left alone.
+for (const sel of ['textarea', '.media-pager']) {
+  const f = fixture(sel);
+  const y = f.y; f.wheel(1); settle(f);
+  assert.equal(f.y, y, 'a notch in ' + sel + ' is not ours');
+}
+console.log('✓ immediate reversal both ways, stale frame timestamps, busy frame recovery, a reversal is a half push that winds up again from the next notch, videos and threads coast');