A new post opens up instead of appearing.

A post let in at the top of an open feed was there on the next paint —
one frame nothing, the next a whole row, the page shoved down by that
much. Now it opens over a third of a second: height from nothing to its
own, fading in as it goes, and a repaint mid-way resumes where it was.
The same happens to the posts the pill lets in.

That needed the morph to know which row is which. Children were matched
by position, so a new first row was patched onto the old first row's
node and every row below onto its neighbour's — the node the new post
was built as never reached the page. A list whose every child carries a
data-key is now reconciled by key: new rows are inserted as themselves,
the rest keep their nodes and move. Feed rows and their hairlines carry
the post id. Partially keyed lists keep the positional rule.

feed-live-test catches the arriving row mid-animation: shorter than it
will be, one animation running, and settled clean afterwards.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01QYJfZ4A1TDCEY4Foq3CApR

1 files changed, 46 insertions, 2 deletions

diff --git a/src/features/messages.js b/src/features/messages.js
index 3328d74..11f1a42 100644
--- a/src/features/messages.js
+++ b/src/features/messages.js
@@ -2849,6 +2849,45 @@ export function messagesFeature(ctx) {
   }
   const notesReady = (evs) => { const deadline = Date.now() + READY_MS; return Promise.all(evs.map((e) => noteReady(e, deadline))); };
 
+  // ---- new posts open up rather than appear ------------------------------
+  // A post let in at the top of an open feed used to simply be there on the
+  // next paint — one frame nothing, the next frame a whole row, and the rest
+  // of the page shoved down by exactly that much. Now it opens: height from
+  // nothing to its own, fading in as it goes, over a third of a second. The
+  // feed is rebuilt on every render, so the moment a post was let in is
+  // remembered per id and a repaint mid-way resumes the animation where it
+  // was instead of starting it again.
+  const keyed = (node, key) => { node.setAttribute('data-key', key); return node; };
+  const ENTER_MS = 380;
+  const feedEntered = new Map(); // note id -> ms its row first painted (0: not yet)
+  function noteEntering(evs) {
+    if (!(ui.chatOpen && ui.msgView === 'feed')) return; // nobody is watching
+    for (const e of evs) feedEntered.set(e.id, 0);
+  }
+  function enterRow(node, id) {
+    if (!feedEntered.has(id)) return node;
+    // the clock starts at the first paint, not at admission: a repaint can
+    // trail the merge by longer than the animation itself
+    const at = feedEntered.get(id) || (feedEntered.set(id, Date.now()), Date.now());
+    const elapsed = Date.now() - at;
+    if (elapsed >= ENTER_MS || typeof node.animate !== 'function') { feedEntered.delete(id); return node; }
+    // measured once it is in the page; the row keeps its own padding, which
+    // opens with it so the words don't sit on the hairline for a beat
+    setTimeout(() => {
+      if (!node.isConnected) return;
+      const box = node.getBoundingClientRect().height;
+      const pad = 10; // the row's vertical padding, see noteRow
+      node.style.overflow = 'hidden';
+      const anim = node.animate([
+        { height: '0px', paddingTop: '0px', paddingBottom: '0px', opacity: 0 },
+        { height: Math.max(0, box - 2 * pad) + 'px', paddingTop: pad + 'px', paddingBottom: pad + 'px', opacity: 1 },
+      ], { duration: ENTER_MS, easing: 'cubic-bezier(.2,.7,.2,1)', fill: 'backwards' });
+      anim.currentTime = Math.min(ENTER_MS, Date.now() - at);
+      anim.onfinish = anim.oncancel = () => { node.style.overflow = ''; feedEntered.delete(id); };
+    }, 0);
+    return node;
+  }
+
   // Posts at the door: filtered in synchronously, so the same note from a
   // second relay is dropped while the first copy is still warming.
   const feedStaged = new Set();
@@ -2868,6 +2907,7 @@ export function messagesFeature(ctx) {
       return true;
     }
     c.notes = [...c.notes, ...add].sort((a, b) => b.created_at - a.created_at).slice(0, FEED_KEEP);
+    if (opts.live) noteEntering(add);
     // posts arriving at the TOP shouldn't cost you the ones you'd scrolled to
     const fresh = add.filter((e) => e.created_at >= (c.notes[0] || {}).created_at).length;
     if (fresh) c.shown = Math.min((c.shown || FEED_PAGE) + fresh, c.notes.length);
@@ -2882,6 +2922,7 @@ export function messagesFeature(ctx) {
     if (!c || !(c.pending || []).length) return;
     const add = c.pending;
     c.pending = [];
+    noteEntering(add);
     const seen = new Set(c.notes.map((e) => e.id));
     c.notes = [...c.notes, ...add.filter((e) => !seen.has(e.id))]
       .sort((a, b) => b.created_at - a.created_at).slice(0, FEED_KEEP);
@@ -4243,9 +4284,12 @@ export function messagesFeature(ctx) {
     const c = feedNow();
     const authors = feedAuthors();
     const visible = c.notes.filter((ev) => !isMuted(ev.pubkey));
+    // Every child keyed by its post, hairlines included, so the morph
+    // reconciles the list by post: a new one at the top is inserted as its
+    // own node (and can open itself up), the rest keep theirs.
     const rows = visible.slice(0, c.shown || FEED_PAGE).flatMap((ev, i) => [
-      i ? h('div', { style: 'height:1px;background:var(--border,rgba(128,128,128,.18));margin:0 -14px' }) : null,
-      noteRow(ev.pubkey, ev, displayName(ev.pubkey)),
+      i ? h('div', { 'data-key': 'hr:' + ev.id, style: 'height:1px;background:var(--border,rgba(128,128,128,.18));margin:0 -14px' }) : null,
+      enterRow(keyed(noteRow(ev.pubkey, ev, displayName(ev.pubkey)), ev.id), ev.id),
     ]);
     // Posts that arrived while you were reading, waiting to be let in. A
     // floating pill rather than an insertion: it says how many, and the tap