v0.2.90

Cargo.lock

@@ -2674,7 +2674,7 @@ dependencies = [
 
 [[package]]
 name = "rustpad"
-version = "0.2.89"
+version = "0.2.90"
 dependencies = [
  "argon2",
  "aws-config",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rustpad"
-version = "0.2.89"
+version = "0.2.90"
 edition = "2024"
 rust-version = "1.94"
 description = "Collaborative Markdown notepad built with Axum, WebSockets and SQLite, PostgreSQL and MySQL"

src/assets.rs

@@ -20,6 +20,7 @@ const MODULES: &[&str] = &[
     "collaboration",
     "collaboration-session",
     "connection-state",
+    "dom-reconcile",
     "editor-format",
     "emoji-data",
     "emoji-groups",

static/css/styles.css

@@ -6318,6 +6318,13 @@ dialog::backdrop {
   }
 }
 
+/* The author labels scroll as one layer; clipping still belongs to .owner-labels. */
+.owner-labels-canvas {
+  position: absolute;
+  inset: 0;
+  pointer-events: none;
+}
+
 .owner-label-group {
   position: absolute;
   right: calc(var(--editor-rendered-font-size, 14px) * .57);

static/js/authorship.js

@@ -116,13 +116,34 @@ export function authorshipOwners(model) {
 }
 
 export function lineAuthors(content, model) {
+  const spans = model?.spans || [];
   const starts = [0];
   for (let i = 0; i < content.length; i++) if (content.charCodeAt(i) === 10) starts.push(i + 1);
+
+  // Parsed authorship spans are sorted and non-overlapping. Retain the old
+  // result for non-canonical callers instead of silently changing semantics.
+  let canonical = true;
+  for (let i = 0, previousEnd = 0; i < spans.length; i++) {
+    const span = spans[i];
+    if (!Number.isFinite(span?.start) || !Number.isFinite(span?.end)
+        || span.start < previousEnd || span.end < span.start) {
+      canonical = false;
+      break;
+    }
+    previousEnd = span.end;
+  }
+
+  let cursor = 0;
   return starts.map((start, index) => {
     const end = index + 1 < starts.length ? starts[index + 1] : content.length;
     const totals = new Map();
     const representatives = new Map();
-    for (const span of model?.spans || []) {
+    if (canonical) {
+      while (cursor < spans.length && spans[cursor].end <= start) cursor++;
+    }
+    for (let i = canonical ? cursor : 0; i < spans.length; i++) {
+      const span = spans[i];
+      if (canonical && span.start >= end) break;
       const overlap = Math.max(0, Math.min(end, span.end) - Math.max(start, span.start));
       if (!overlap) continue;
       const identity = ownerIdentity(span.owner);

static/js/dom-reconcile.js

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2026 Mateusz Gruszczynski @linuxiarz.pl
+ * Source-Available Code / Dual-Licensed.
+ * See LICENSE.md for terms.
+ */
+
+// Preserve existing nodes. Remove stale entries first: otherwise deleting a
+// user near the start of a 1000-person list would move every following node.
+// `desired` must contain each node at most once.
+export function reconcileChildren(container, desired) {
+  const retained = new Set(desired);
+  for (const node of [...container.childNodes]) {
+    if (!retained.has(node)) node.remove();
+  }
+  let cursor = container.firstChild;
+  for (const node of desired) {
+    if (node === cursor) cursor = cursor.nextSibling;
+    else container.insertBefore(node, cursor);
+  }
+}

static/js/markdown.js

@@ -420,11 +420,12 @@ export function alignPreviewLineNumbers(root) {
   const styles = getComputedStyle(root);
   const targetLeft = parseFloat(styles.paddingLeft || "0") - 50;
   const rootLeft = root.getBoundingClientRect().left;
+  const positions = [];
+  // Finish all geometry reads before writing CSS properties. Interleaved
+  // reads and writes force a full layout for each source line in Chromium.
   root.querySelectorAll(".preview-source-line").forEach(line => {
     const lineRect = line.getBoundingClientRect();
     const lineLeft = lineRect.left - rootLeft + root.scrollLeft;
-    line.style.setProperty("--preview-line-left", `${targetLeft - lineLeft}px`);
-
     const textRect = firstRenderedTextRect(line);
     const lineStyles = getComputedStyle(line);
     const gutterStyles = getComputedStyle(line, "::before");
@@ -432,9 +433,16 @@ export function alignPreviewLineNumbers(root) {
     const textLineHeight = textRect?.height || 0;
     const borderTop = parseFloat(lineStyles.borderTopWidth) || 0;
     const textTop = textRect ? textRect.top - lineRect.top - borderTop : 0;
-    const gutterTop = Math.max(0, textTop + (textLineHeight - gutterLineHeight) / 2);
+    positions.push({
-    line.style.setProperty("--preview-line-top", `${gutterTop}px`);
+      line,
+      left: `${targetLeft - lineLeft}px`,
+      top: `${Math.max(0, textTop + (textLineHeight - gutterLineHeight) / 2)}px`,
+    });
   });
+  for (const position of positions) {
+    position.line.style.setProperty("--preview-line-left", position.left);
+    position.line.style.setProperty("--preview-line-top", position.top);
+  }
 }
 
 function stripFenceIndent(line, columns) {

static/js/note-editor.js

@@ -22,6 +22,7 @@ import { createMentionNavigator } from "@rustpad/mention-navigation";
 import { updateImageAliasInLineBySource } from "@rustpad/image-alias";
 import { previewEditingHost } from "@rustpad/preview-edit";
 import { createRenderQueue } from "@rustpad/render-queue";
+import { reconcileChildren } from "@rustpad/dom-reconcile";
 import { alignPreviewLineNumbers, renderMarkdown, setMarkdownFiles, setMarkdownMentions, unresolvedMarkdownFileAliases } from "@rustpad/markdown";
 import { getNickname, getGuestId, getAuthToken, getAccessToken, setAccessToken } from "@rustpad/session";
 import { bindIdentityDialog, validateCurrentSession } from "@rustpad/auth-ui";
@@ -323,7 +324,44 @@ export function startNoteEditor(adapter) {
     syncMobileEditorControls();
     updateCurrentUser(); return info;
   }
-  function updatePresence(users) { const entries = Array.isArray(users) ? users : []; presenceUsers = entries.map(entry => typeof entry === "string" ? { name: entry, color: "" } : entry || {}); roomCount.textContent = t(entries.length === 1 ? "editor.user" : "editor.users", { count: entries.length }, `${entries.length} ${entries.length === 1 ? "user" : "users"}`); roomUsers.replaceChildren(...presenceUsers.map(user => { const li = document.createElement("li"), dot = document.createElement("span"), label = document.createElement("span"); li.className = "room-user"; dot.className = "room-user__dot"; dot.style.setProperty("--owner", /^#[0-9a-f]{6}$/i.test(user.color || "") ? user.color : defaultColorFor(user.name)); label.textContent = user.name || t("editor.guest", {}, "Guest"); li.title = label.textContent; li.append(dot, label); return li; })); if (!entries.length) { const li = document.createElement("li"); li.textContent = t("editor.noActiveUsers", {}, "No active users"); roomUsers.append(li); } renderGutter(); }
+  // Presence is independent of document text, authorship spans and the gutter.
+  // Match by name, preserving duplicates and their DOM nodes between snapshots.
+  function updatePresence(users) {
+    const entries = Array.isArray(users) ? users : [];
+    presenceUsers = entries.map(entry => typeof entry === "string" ? { name: entry, color: "" } : entry || {});
+    roomCount.textContent = t(entries.length === 1 ? "editor.user" : "editor.users", { count: entries.length }, `${entries.length} ${entries.length === 1 ? "user" : "users"}`);
+    const existing = new Map();
+    for (const li of roomUsers.children) {
+      if (li.dataset.presenceName === undefined) continue;
+      const bucket = existing.get(li.dataset.presenceName) || [];
+      bucket.push(li);
+      existing.set(li.dataset.presenceName, bucket);
+    }
+    const nodes = presenceUsers.map(user => {
+      const name = String(user.name || "");
+      const bucket = existing.get(name);
+      const li = bucket?.shift() || document.createElement("li");
+      const color = /^#[0-9a-f]{6}$/i.test(user.color || "") ? user.color : defaultColorFor(name);
+      const displayName = name || t("editor.guest", {}, "Guest");
+      if (!li.classList.contains("room-user")) {
+        li.className = "room-user";
+        li.append(document.createElement("span"), document.createElement("span"));
+        li.firstElementChild.className = "room-user__dot";
+      }
+      li.dataset.presenceName = name;
+      if (li.firstElementChild.style.getPropertyValue("--owner") !== color) li.firstElementChild.style.setProperty("--owner", color);
+      if (li.lastElementChild.textContent !== displayName) li.lastElementChild.textContent = displayName;
+      if (li.title !== displayName) li.title = displayName;
+      return li;
+    });
+    if (!nodes.length) {
+      const empty = document.createElement("li");
+      empty.textContent = t("editor.noActiveUsers", {}, "No active users");
+      nodes.push(empty);
+    }
+    reconcileChildren(roomUsers, nodes);
+    renderParticipantBadges(authorshipColorsEnabled ? renderedAuthorshipOwners : []);
+  }
   function updateLatency(ms) {
     const text = Number.isFinite(ms) ? `${ms} ms` : "— ms";
     socketLatency.textContent = text;
@@ -476,6 +514,7 @@ export function startNoteEditor(adapter) {
   }
   async function renderCodeHighlight() { const nodes = preview.querySelectorAll('pre code[class^="language-"]:not(.language-mermaid)'); if (!nodes.length) return; try { const hljs = await loadHighlight(); nodes.forEach(node => { const lines = node.querySelectorAll(".code-line"); if (!lines.length) { hljs.highlightElement(node); return; } const language = [...node.classList].find(name => name.startsWith("language-"))?.slice(9); lines.forEach(line => { try { line.innerHTML = hljs.highlight(line.textContent, { language, ignoreIllegals: true }).value; } catch { line.innerHTML = hljs.highlightAuto(line.textContent).value; } }); node.classList.add("hljs"); }); } catch { } }
   async function renderMediaPlayers() { const nodes = preview.querySelectorAll("[data-rustpad-player]"); if (!nodes.length) return; try { const { hydrateMediaPlayers } = await loadMediaPlayer(); hydrateMediaPlayers(preview); } catch { } }
+  let renderedAuthorshipOwners = [];
   function renderParticipantBadges(owners) {
     if (!participantBadges) return;
     const people = new Map();
@@ -487,19 +526,26 @@ export function startNoteEditor(adapter) {
     }
     participantBadges.hidden = authorshipMode !== "simple" || people.size < 2;
     const compact = people.size > 4;
-    participantBadges.replaceChildren(...[...people.values()].map(person => {
+    const previous = new Map([...participantBadges.children].map(badge => [badge.dataset.personName, badge]));
-      const badge = document.createElement("span");
+    const nodes = [...people.values()].map(person => {
+      const badge = previous.get(person.name) || document.createElement("span");
+      const label = compact && person.compactName ? person.compactName : person.name;
       badge.className = "participant-badge";
-      badge.style.setProperty("--owner", person.color);
+      badge.dataset.personName = person.name;
-      badge.textContent = compact && person.compactName ? person.compactName : person.name;
+      if (badge.style.getPropertyValue("--owner") !== person.color) badge.style.setProperty("--owner", person.color);
-      badge.title = person.name;
+      if (badge.textContent !== label) badge.textContent = label;
+      if (badge.title !== person.name) badge.title = person.name;
       return badge;
-    }));
+    });
+    reconcileChildren(participantBadges, nodes);
   }
   function syncOwnerLabels() {
-    ownerLabels.querySelectorAll(".owner-label-group[data-content-top]").forEach(group => {
+    // One composited transform instead of rewriting every author's position
-      group.style.top = `${Number(group.dataset.contentTop) - editor.scrollTop}px`;
+    // on every scroll event (important for thousands of distinct authors).
-    });
+    const canvas = ownerLabels.firstElementChild;
+    if (canvas?.classList.contains("owner-labels-canvas")) {
+      canvas.style.transform = `translate3d(0, ${-editor.scrollTop}px, 0)`;
+    }
   }
 
   function syncEditorLayers() {
@@ -508,6 +554,9 @@ export function startNoteEditor(adapter) {
     syncOwnerLabels();
   }
 
+  let gutterLineCount = 0;
+  let gutterLineHeight = 0;
+  let highlightedGutterLine = null;
   function renderGutter() {
     document.body.classList.toggle("hide-editor-line-numbers", !lineToggle.checked);
     document.body.classList.toggle("hide-preview-line-numbers", !previewLineToggle.checked);
@@ -517,6 +566,7 @@ export function startNoteEditor(adapter) {
     const lineCount = Math.max(1, (editor.value.match(/\n/g) || []).length + 1);
     const lines = Array.from({ length: lineCount });
     const owners = authorshipOwners(authorship);
+    renderedAuthorshipOwners = owners;
     const showAuthorship = authorshipColorsEnabled && owners.length > 0;
     const authorsByLine = showAuthorship ? lineAuthors(editor.value, authorship) : [];
     const full = authorshipMode === "full";
@@ -527,12 +577,27 @@ export function startNoteEditor(adapter) {
     editorWorkspace.dataset.authorshipMode = authorshipMode;
     const style = getComputedStyle(editor), lineHeight = parseFloat(style.lineHeight) || 29, fontSize = parseFloat(style.fontSize) || 14, paddingTop = parseFloat(style.paddingTop) || 24, paddingBottom = parseFloat(style.paddingBottom) || 24;
     gutter.style.paddingTop = `${paddingTop}px`; gutter.style.paddingBottom = `${paddingBottom}px`; gutter.style.lineHeight = `${lineHeight}px`;
-    gutter.innerHTML = lines.map((_, i) => `<div class="line-number-row" style="height:${lineHeight}px"><button class="line-number-button" type="button" tabindex="-1" data-line="${i + 1}" aria-label="Copy link to line ${i + 1}">${i + 1}</button></div>`).join("");
+    // Physical rows represent sequential line numbers, not specific text lines.
+    // Reuse them across character edits and add/remove only the changed tail.
+    if (gutterLineHeight !== lineHeight) {
+      for (const row of gutter.children) row.style.height = `${lineHeight}px`;
+      gutterLineHeight = lineHeight;
+    }
+    if (lineCount > gutterLineCount) {
+      let html = "";
+      for (let i = gutterLineCount; i < lineCount; i++) {
+        html += `<div class="line-number-row" style="height:${lineHeight}px"><button class="line-number-button" type="button" tabindex="-1" data-line="${i + 1}" aria-label="Copy link to line ${i + 1}">${i + 1}</button></div>`;
+      }
+      gutter.insertAdjacentHTML("beforeend", html);
+    } else if (lineCount < gutterLineCount) {
+      for (let i = gutterLineCount; i > lineCount; i--) gutter.lastElementChild?.remove();
+    }
+    gutterLineCount = lineCount;
     ownerLabels.style.setProperty("--editor-line-height", `${lineHeight}px`);
     ownerLabels.style.setProperty("--editor-rendered-font-size", `${fontSize}px`);
     if (full) {
       let previousAuthorSignature = null;
-      ownerLabels.innerHTML = lines.map((_, i) => {
+      ownerLabels.innerHTML = `<div class="owner-labels-canvas">${lines.map((_, i) => {
         const authors = authorsByLine[i] || [];
         if (!authors.length) return "";
         const top = paddingTop + i * lineHeight + lineHeight / 2;
@@ -540,13 +605,17 @@ export function startNoteEditor(adapter) {
         if (signature === previousAuthorSignature) return "";
         previousAuthorSignature = signature;
         const badges = authors.map(owner => `<span class="owner-label" style="--owner:${colorFor(owner)}">${escapeHtml(ownerName(owner))}</span>`).join("");
-        return `<span class="owner-label-group" data-content-top="${top}">${badges}</span>`;
+        return `<span class="owner-label-group" style="top:${top}px">${badges}</span>`;
-      }).join("");
+      }).join("")}</div>`;
     } else ownerLabels.replaceChildren();
     if (showAuthorship) renderAuthorshipLayer(authorshipLayer, editor, authorship, colorFor);
     else authorshipLayer.replaceChildren();
     const linkedLine = lineFromHash(location.hash, lineCount);
-    gutter.querySelector(`[data-line="${linkedLine}"]`)?.classList.add("is-linked");
+    if (highlightedGutterLine !== linkedLine) {
+      gutter.querySelector(`[data-line="${highlightedGutterLine}"]`)?.classList.remove("is-linked");
+      gutter.querySelector(`[data-line="${linkedLine}"]`)?.classList.add("is-linked");
+      highlightedGutterLine = linkedLine;
+    }
     syncEditorLayers();
   }
 
@@ -1062,7 +1131,30 @@ export function startNoteEditor(adapter) {
     };
   }
 
+  let previewPositionCache = null;
+  let cachedPreviewHeight = -1;
+  let cachedPreviewWidth = -1;
+  function invalidatePreviewPositions() { previewPositionCache = null; }
+  // The (rect.top - container.top + scrollTop) coordinates are invariant to
+  // scrolling; only rebuild them when layout/content actually changes.
+  if (typeof ResizeObserver !== "undefined") {
+    new ResizeObserver(invalidatePreviewPositions).observe(preview);
+  }
+  if (typeof MutationObserver !== "undefined") {
+    new MutationObserver(invalidatePreviewPositions).observe(preview, {
+      subtree: true, childList: true, characterData: true,
+      attributes: true, attributeFilter: ["open", "src", "class"],
+    });
+  }
+  preview.addEventListener("toggle", invalidatePreviewPositions, true);
+  preview.addEventListener("load", invalidatePreviewPositions, true);
+  window.addEventListener("resize", invalidatePreviewPositions);
+  document.fonts?.addEventListener?.("loadingdone", invalidatePreviewPositions);
   function previewLinePositions() {
+    // Height/width checks catch dynamic embeds that change geometry without
+    // a DOM mutation (e.g. a media player expanding after initialization).
+    const height = preview.scrollHeight, width = preview.clientWidth;
+    if (previewPositionCache && cachedPreviewHeight === height && cachedPreviewWidth === width) return previewPositionCache;
     const previewRect = preview.getBoundingClientRect();
     const positions = [];
     preview.querySelectorAll(".preview-source-line[data-source-line]").forEach(node => {
@@ -1084,7 +1176,10 @@ export function startNoteEditor(adapter) {
         bottom: rect.bottom - previewRect.top + preview.scrollTop,
       });
     });
-    return positions.sort((left, right) => left.top - right.top || left.sourceLine - right.sourceLine);
+    previewPositionCache = positions.sort((left, right) => left.top - right.top || left.sourceLine - right.sourceLine);
+    cachedPreviewHeight = height;
+    cachedPreviewWidth = width;
+    return previewPositionCache;
   }
 
   function previewScrollAnchor() {
@@ -1215,34 +1310,51 @@ export function startNoteEditor(adapter) {
     preview.scrollTop = Math.max(0, Math.min(range, snapshot.scrollTop || 0));
   }
 
+  let previewStale = true;
+  let forcePreviewRender = false;
   function renderNow() {
     const previewViewport = pendingPreviewViewport;
-    pendingPreviewViewport = null;
+    // In editor-only view this DOM is display:none. Building a full Markdown
-    const openDetailsLines = uiState.mode === "markdown"
+    // tree (and highlighting / Mermaid) on each remote edit is wasted work.
-      ? new Set([...preview.querySelectorAll("details.markdown-details[open][data-source-line]")].map(node => node.dataset.sourceLine))
+    // Keep the exceptional consumers working: heading deep-links and PDF export.
-      : new Set();
+    const headingRevealPending = uiState.mode === "markdown" && location.hash
-    if (uiState.mode === "markdown") {
+      && !/^#L[1-9]\d*$/i.test(location.hash)
-      preview.classList.remove("preview--raw");
+      && lastRevealedHeadingHash !== location.hash;
-      preview.innerHTML = renderMarkdown(editor.value);
+    const previewNeededForPdf = forcePreviewRender || document.querySelector("#pdf-export-dialog")?.open;
-      preview.querySelectorAll("details.markdown-details[data-source-line]").forEach(node => {
+    const buildPreview = activeView() !== "edit" || previewNeededForPdf || headingRevealPending;
-        node.open = openDetailsLines.has(node.dataset.sourceLine);
+    forcePreviewRender = false;
-      });
+    if (buildPreview) {
-      scheduleAliasFileRefresh(editor.value);
+      pendingPreviewViewport = null;
-      document.querySelector("#preview-label").textContent = "Preview (media / mermaid / markdown)";
+      const openDetailsLines = uiState.mode === "markdown"
-      renderMermaid();
+        ? new Set([...preview.querySelectorAll("details.markdown-details[open][data-source-line]")].map(node => node.dataset.sourceLine))
-      renderCodeHighlight();
+        : new Set();
-      renderMediaPlayers();
+      if (uiState.mode === "markdown") {
-    } else {
+        preview.classList.remove("preview--raw");
-      preview.classList.add("preview--raw");
+        preview.innerHTML = renderMarkdown(editor.value);
-      preview.innerHTML = editor.value.split("\n").map((line, index) => `<div class="preview-source-line preview-editable" data-source-line="${index + 1}">${escapeHtml(line) || "<br>"}</div>`).join("");
+        preview.querySelectorAll("details.markdown-details[data-source-line]").forEach(node => {
-      document.querySelector("#preview-label").textContent = "Text preview";
+          node.open = openDetailsLines.has(node.dataset.sourceLine);
-    }
+        });
+        scheduleAliasFileRefresh(editor.value);
+        document.querySelector("#preview-label").textContent = "Preview (media / mermaid / markdown)";
+        if (activeView() !== "edit" || previewNeededForPdf) {
+          renderMermaid();
+          renderCodeHighlight();
+          renderMediaPlayers();
+        }
+      } else {
+        preview.classList.add("preview--raw");
+        preview.innerHTML = editor.value.split("\n").map((line, index) => `<div class="preview-source-line preview-editable" data-source-line="${index + 1}">${escapeHtml(line) || "<br>"}</div>`).join("");
+        document.querySelector("#preview-label").textContent = "Text preview";
+      }
+      previewStale = false;
+      invalidatePreviewPositions();
+    } else previewStale = true;
     mentionNavigator.render({ markdown: uiState.mode === "markdown" });
-    alignPreviewLineNumbers(preview);
+    if (buildPreview && previewLineToggle.checked && activeView() !== "edit") alignPreviewLineNumbers(preview);
     document.querySelector("#characters").textContent = `${editor.value.length} characters`;
     document.querySelector("#words").textContent = `${editor.value.trim() ? editor.value.trim().split(/\s+/).length : 0} words`;
     renderGutter();
-    requestAnimationFrame(() => {
+    if (buildPreview) requestAnimationFrame(() => {
       if (previewViewport) restorePreviewViewport(previewViewport);
       else syncPreviewScroll();
       revealHeadingAnchor();
@@ -1809,7 +1921,7 @@ export function startNoteEditor(adapter) {
   toolbarCollapseToggle?.addEventListener("click", () => { toolbarCollapsed = !toolbarCollapsed; localStorage.setItem(notePreferenceKey("toolbar-collapsed"), toolbarCollapsed ? "on" : "off"); applyUiPreservingScroll(); scheduleEditorSettingsSave({ personal: true }); });
   navbarCollapseToggle?.addEventListener("click", () => { navbarCollapsed = !navbarCollapsed; localStorage.setItem(notePreferenceKey("navbar-collapsed"), navbarCollapsed ? "on" : "off"); if (navbarCollapsed) setHeaderMenuOpen(false); applyUiPreservingScroll(); scheduleEditorSettingsSave({ personal: true }); });
   lineToggle.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("line-numbers"), lineToggle.checked ? "on" : "off"); syncMobileEditorControls(); renderGutter(); scheduleEditorSettingsSave({ personal: true }); });
-  previewLineToggle.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("preview-line-numbers"), previewLineToggle.checked ? "on" : "off"); syncMobileEditorControls(); renderGutter(); alignPreviewLineNumbers(preview); scheduleEditorSettingsSave({ personal: true }); });
+  previewLineToggle.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("preview-line-numbers"), previewLineToggle.checked ? "on" : "off"); syncMobileEditorControls(); renderGutter(); if (previewLineToggle.checked && activeView() !== "edit") alignPreviewLineNumbers(preview); scheduleEditorSettingsSave({ personal: true }); });
   compactToggle.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("compact"), compactToggle.checked ? "on" : "off"); syncMobileEditorControls(); applyUiPreservingScroll(); scheduleEditorSettingsSave({ personal: true }); });
   lineLinksToggle.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("line-links"), lineLinksToggle.checked ? "on" : "off"); syncMobileEditorControls(); renderGutter(); scheduleEditorSettingsSave({ personal: true }); });
   fontFamily.addEventListener("change", () => { localStorage.setItem(notePreferenceKey("font-family"), fontFamily.value); syncMobileEditorControls(); applyUiPreservingScroll(); scheduleEditorSettingsSave({ personal: true }); });
@@ -2047,7 +2159,7 @@ export function startNoteEditor(adapter) {
     }
   }
   window.addEventListener("popstate", () => { const anchor = activeScrollAnchor(); lastRevealedLineHash = ""; lastRevealedHeadingHash = ""; uiState = readEditorState(); applyUi(); restoreScrollAnchor(anchor); requestAnimationFrame(() => { revealLinkedLine(); revealHeadingAnchor(); }); });
-  window.addEventListener("hashchange", () => { lastRevealedLineHash = ""; lastRevealedHeadingHash = ""; renderGutter(); requestAnimationFrame(() => { revealLinkedLine(); revealHeadingAnchor(); }); });
+  window.addEventListener("hashchange", () => { lastRevealedLineHash = ""; lastRevealedHeadingHash = ""; renderGutter(); if (activeView() === "edit" && uiState.mode === "markdown" && location.hash && !/^#L[1-9]\d*$/i.test(location.hash)) render(); requestAnimationFrame(() => { revealLinkedLine(); revealHeadingAnchor(); }); });
   preview.addEventListener("click", event => {
     const link = event.target instanceof Element ? event.target.closest('a[href^="#"]') : null;
     if (!link) return;
@@ -2170,6 +2282,10 @@ export function startNoteEditor(adapter) {
   let pdfExportBound = false;
   let pdfExportLoad = null;
   pdfExportArgs.button?.addEventListener("click", async event => {
+    if (previewStale) {
+      forcePreviewRender = true;
+      render();
+    }
     if (pdfExportBound) return;
     event.stopImmediatePropagation();
     pdfExportLoad ||= import("@rustpad/pdf-export").then(({ bindPdfExport }) => {
@@ -2489,9 +2605,14 @@ export function startNoteEditor(adapter) {
     toast.info("The global profile color is active again.", { title: "Profile color restored" });
   });
   editor.addEventListener("keydown", continueIndentation);
+  let editorScrollFrame = 0;
   editor.addEventListener("scroll", () => {
-    syncEditorLayers();
+    if (editorScrollFrame) return;
-    syncPreviewScroll();
+    editorScrollFrame = requestAnimationFrame(() => {
+      editorScrollFrame = 0;
+      syncEditorLayers();
+      syncPreviewScroll();
+    });
   });
   editor.addEventListener("input", event => {
     if (!canEditDocument() && !applyingRemote) {

tests/frontend-optimizations-browser.py

@@ -0,0 +1,157 @@
+#!/usr/bin/env python3
+"""Isolated browser tests of DOM reconciliation, preview alignment and owner labels.
+Run from the repository root. Does not emulate the server or OT protocol.
+"""
+from __future__ import annotations
+
+import base64
+from pathlib import Path
+
+from playwright.sync_api import sync_playwright
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def module_url(content: str) -> str:
+    return "data:text/javascript;base64," + base64.b64encode(content.encode()).decode()
+
+
+def main():
+    reconcile = (ROOT / "static/js/dom-reconcile.js").read_text()
+    editor_source = (ROOT / "static/js/note-editor.js").read_text()
+    presence_source = editor_source.split("  function updatePresence(users) {", 1)[1].split("  function updateLatency", 1)[0]
+    presence_source = "function updatePresence(users) {" + presence_source
+    badges_source = editor_source.split("  let renderedAuthorshipOwners = [];", 1)[1].split("  function syncOwnerLabels()", 1)[0]
+    badges_source = "let renderedAuthorshipOwners = [];" + badges_source
+    geometry_source = "let previewPositionCache = null;" + editor_source.split("  let previewPositionCache = null;", 1)[1].split("  function previewScrollAnchor()", 1)[0]
+    markdown = (ROOT / "static/js/markdown.js").read_text()
+    markdown = "const EMOJI_SHORTCODES = {}; const t = (key, v, fallback) => fallback; const parseImageAlias = () => null;\n" + "\n".join(
+        line for line in markdown.splitlines() if not line.startswith("import ")
+    ) + "\nexport { firstRenderedTextRect };\n"
+    html = '''<!doctype html><html><head><meta charset="utf-8"><style>
+    .owner-labels { position: relative; height: 100px; width: 250px; overflow:hidden; }
+    .owner-labels-canvas { position:absolute;inset:0; }
+    .owner-label-group { position:absolute;right:12px;transform:translateY(-50%); }
+    #preview, #original { width:600px; height: 350px; overflow:auto; padding:24px; border:1px solid #ccc; }
+    .preview-source-line {display:block; position:relative; min-height: 24px; }
+    .preview-source-line::before {content:attr(data-source-line); position:absolute;left:-50px;line-height:16px;font-size:13px;}
+    </style></head><body>
+    <ul id="users"></ul><span id="room-count"></span><ul id="room-users"></ul><div id="participant-badges"></div>
+    <div id="owner-labels" class="owner-labels"><div class="owner-labels-canvas"><span class="owner-label-group" style="top:250px">Alice</span></div></div>
+    <article id="preview"></article><article id="original"></article>
+    <script type="module">
+    import { reconcileChildren } from "__RECONCILE__";
+    import { alignPreviewLineNumbers, firstRenderedTextRect } from "__MARKDOWN__";
+    const roomCount=document.querySelector('#room-count');
+    const roomUsers=document.querySelector('#room-users');
+    const participantBadges=document.querySelector('#participant-badges');
+    let presenceUsers=[];
+    const authorshipColorsEnabled=true, authorshipMode='simple';
+    const t=(key, vars, fallback)=>fallback;
+    const defaultColorFor=()=> '#444444';
+    const ownerName=value=>String(value).split('\u001f')[0];
+    const colorFor=()=> '#aabbcc';
+    function renderGutter() { throw new Error('Presence must not cause a gutter rebuild'); }
+    __BADGES_SOURCE__
+    __PRESENCE_SOURCE__
+    function check(result, label) {if (!result) throw new Error(label);}
+    const list = document.querySelector('#users');
+    const a = document.createElement('li'), b=document.createElement('li'), c=document.createElement('li'), d=document.createElement('li');
+    a.textContent='A';b.textContent='B';c.textContent='C';d.textContent='D';
+    list.append(a,b,c);
+    reconcileChildren(list,[c,a,d]);
+    check(list.children.length===3 && list.children[0]===c && list.children[1]===a && list.children[2]===d, 'reordering/removal/insertion');
+    const observer = new MutationObserver(()=>{});
+    observer.observe(list,{childList:true});
+    reconcileChildren(list,[c,a,d]);
+    check(observer.takeRecords().length === 0, 'unchanged list should not mutate the DOM');
+    observer.disconnect();
+    const participants=Array.from({length:1000},(_,i)=>({name:`User ${i}`,compact_name:`U${i}`,color:'#abcdef'}));
+    updatePresence(participants);
+    check(roomUsers.children.length===1000 && participantBadges.children.length===1000, '1000 participants rendered');
+    const rowRefs=Array.from(roomUsers.children);
+    const badgeRefs=Array.from(participantBadges.children);
+    updatePresence([...participants,{name:'New person',color:'#123456'}]);
+    check(roomUsers.children.length===1001 && roomUsers.children[0]===rowRefs[0] && roomUsers.children[999]===rowRefs[999], 'presence DOM reused');
+    check(participantBadges.children[0]===badgeRefs[0] && participantBadges.children[999]===badgeRefs[999], 'badge DOM reused');
+    const presenceMutations=new MutationObserver(()=>{});
+    presenceMutations.observe(roomUsers,{childList:true});
+    updatePresence([...participants.slice(1),{name:'New person',color:'#123456'}]);
+    const changes=presenceMutations.takeRecords();
+    check(changes.length===1 && changes[0].removedNodes.length===1, 'single early removal does not move remaining users');
+    presenceMutations.disconnect();
+    updatePresence([{name:'Duplicate',color:'#abcdef'},{name:'Duplicate',color:'#123456'}]);
+    check(roomUsers.children.length===2 && participantBadges.children.length===1, 'same-name participants count preserved, badge deduplicated');
+    updatePresence([{name:'<script>alert(1)<'+'/script>',color:'red'}]);
+    check(roomUsers.querySelector('script')===null && participantBadges.querySelector('script')===null, 'text remains escaped');
+    const ownerLabels=document.querySelector('#owner-labels');
+    const canvas=ownerLabels.firstElementChild;
+    const group=canvas.firstElementChild;
+    canvas.style.transform='translate3d(0,-170px,0)';
+    let top=group.getBoundingClientRect().top-ownerLabels.getBoundingClientRect().top;
+    check(Math.abs(top - (250 - 170 - group.getBoundingClientRect().height/2)) < 1, 'owner labels scroll as one canvas');
+    function oldAlign(root) {
+      const styles=getComputedStyle(root), targetLeft=parseFloat(styles.paddingLeft||'0')-50;
+      const rootLeft=root.getBoundingClientRect().left;
+      root.querySelectorAll('.preview-source-line').forEach(line=>{
+        const lineRect=line.getBoundingClientRect();
+        const lineLeft=lineRect.left-rootLeft+root.scrollLeft;
+        line.style.setProperty('--preview-line-left', `${targetLeft - lineLeft}px`);
+        const textRect=firstRenderedTextRect(line);
+        const lineStyles=getComputedStyle(line), gutterStyles=getComputedStyle(line,'::before');
+        const gutterLineHeight=parseFloat(gutterStyles.lineHeight)||parseFloat(gutterStyles.fontSize)||0;
+        const textLineHeight=textRect?.height||0;
+        const borderTop=parseFloat(lineStyles.borderTopWidth)||0;
+        const textTop=textRect?textRect.top-lineRect.top-borderTop:0;
+        line.style.setProperty('--preview-line-top', `${Math.max(0,textTop+(textLineHeight-gutterLineHeight)/2)}px`);
+      });
+    }
+    const preview=document.querySelector('#preview'), original=document.querySelector('#original');
+    const rows=Array.from({length:150},(_,i)=>`<p class="preview-source-line" data-source-line="${i+1}">Row ${i} some text</p>`).join('');
+    preview.innerHTML=rows;original.innerHTML=rows;
+    oldAlign(original);
+    alignPreviewLineNumbers(preview);
+    const oldRows=original.querySelectorAll('.preview-source-line');
+    const newRows=preview.querySelectorAll('.preview-source-line');
+    for(let i=0;i<newRows.length;i++) {
+      for(const prop of ['--preview-line-left','--preview-line-top']) {
+        const before=parseFloat(oldRows[i].style.getPropertyValue(prop));
+        const after=parseFloat(newRows[i].style.getPropertyValue(prop));
+        check(Math.abs(before-after)<0.05, 'alignment parity at '+i+' '+prop+': '+before+' != '+after);
+      }
+    }
+    // Cached source geometry must not be remeasured during scroll, but must
+    // rebuild when the preview DOM/layout changes.
+    __GEOMETRY_SOURCE__
+    const firstPositions=previewLinePositions();
+    check(previewLinePositions()===firstPositions, 'preview geometry cached');
+    preview.scrollTop=100;
+    check(previewLinePositions()===firstPositions, 'scroll does not discard geometry');
+    preview.insertAdjacentHTML('beforeend','<p class="preview-source-line" data-source-line="151">Last line</p>');
+    await new Promise(resolve=>setTimeout(resolve,50));
+    const changedPositions=previewLinePositions();
+    check(changedPositions!==firstPositions && changedPositions.length===firstPositions.length+1, 'DOM mutation invalidates geometry');
+    window.frontendTestsPassed=true;
+    </script></body></html>'''.replace("__RECONCILE__", module_url(reconcile)).replace("__MARKDOWN__", module_url(markdown)).replace("__BADGES_SOURCE__", badges_source).replace("__PRESENCE_SOURCE__", presence_source).replace("__GEOMETRY_SOURCE__", geometry_source)
+    with sync_playwright() as playwright:
+        browser = playwright.chromium.launch(executable_path="/usr/bin/chromium", args=["--no-sandbox", "--disable-dev-shm-usage"])
+        try:
+            page = browser.new_page(viewport={"width": 1100, "height": 780})
+            errors = []
+            page.on("pageerror", lambda error: errors.append(str(error)))
+            page.set_content(html)
+            try:
+                page.wait_for_function("window.frontendTestsPassed===true", timeout=15000)
+            except Exception:
+                raise AssertionError(f"Browser errors: {errors}")
+            assert not errors, errors
+            print("PASS: keyed DOM list updates preserve node identity; identical list has zero mutations")
+            print("PASS: real presence update handles 1000 users with row/badge reuse, duplicates and XSS-safe text")
+            print("PASS: owner-label canvas transforms; preview alignment parity for 150 lines in Chromium")
+            print("PASS: preview geometry cache reuses measurements on scroll and invalidates on content change")
+        finally:
+            browser.close()
+
+
+if __name__ == "__main__":
+    main()

tests/frontend-optimizations-test.mjs

@@ -0,0 +1,74 @@
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { performance } from 'node:perf_hooks';
+
+const source = readFileSync('static/js/authorship.js', 'utf8');
+const { lineAuthors, parseAuthorship } = await import('data:text/javascript;base64,' + Buffer.from(source).toString('base64'));
+
+// Reference implementation from 0.2.89; include it to detect attribution,
+// color and tie-breaking regressions independently of the optimized code.
+function referenceLineAuthors(content, model) {
+  const starts = [0];
+  for (let i = 0; i < content.length; i++) if (content.charCodeAt(i) === 10) starts.push(i + 1);
+  return starts.map((start, index) => {
+    const end = index + 1 < starts.length ? starts[index + 1] : content.length;
+    const totals = new Map();
+    const representatives = new Map();
+    for (const span of model?.spans || []) {
+      const overlap = Math.max(0, Math.min(end, span.end) - Math.max(start, span.start));
+      if (!overlap) continue;
+      const identity = String(span.owner || '').split('\u001f', 1)[0];
+      totals.set(identity, (totals.get(identity) || 0) + overlap);
+      representatives.set(identity, span.owner);
+    }
+    return [...totals.entries()]
+      .sort((a, b) => b[1] - a[1])
+      .map(([identity]) => representatives.get(identity));
+  });
+}
+
+let seed = 42;
+function random(n) { seed = (seed * 1664525 + 1013904223) >>> 0; return seed % n; }
+const owners = ['A\u001f#ff0000', 'B', 'A\u001f#00ff00', 'C', 'D', ''];
+for (let sample = 0; sample < 400; sample++) {
+  const content = Array.from({ length: 1 + random(65) }, (_, i) => {
+    const base = ['text', '', '🙂 éół', '  x', '......'][random(5)];
+    return base + (i ? '\n' : '');
+  }).join('');
+  const spans = [];
+  for (let i = 0; i < 4 + random(100); i++) {
+    const start = random(content.length + 1);
+    spans.push({ start, end: start + random(content.length + 4), owner: owners[random(owners.length)] });
+  }
+  const canonical = parseAuthorship(content, { version: 2, spans });
+  assert.deepEqual(lineAuthors(content, canonical), referenceLineAuthors(content, canonical), `canonical parity sample ${sample}`);
+  assert.deepEqual(lineAuthors(content, { spans }), referenceLineAuthors(content, { spans }), `noncanonical parity sample ${sample}`);
+}
+for (const content of ['', 'a', '\n', '🙂\n\nB\n', 'line1\nline2\n']) {
+  for (const model of [{ spans: [] }, { spans: [{ start: 0, end: 999, owner: 'one' }] }]) {
+    assert.deepEqual(lineAuthors(content, model), referenceLineAuthors(content, model));
+  }
+}
+
+const n = 6000;
+const lines = [], spans = [];
+let offset = 0;
+for (let i = 0; i < n; i++) {
+  const line = `row ${String(i).padStart(5, '0')} lorem ipsum\n`;
+  lines.push(line);
+  spans.push({ start: offset, end: offset + line.length, owner: `user${i % 37}` });
+  offset += line.length;
+}
+const text = lines.join('');
+const model = { version: 2, spans };
+assert.deepEqual(lineAuthors(text, model), referenceLineAuthors(text, model));
+function medianDuration(fn) {
+  const ms = [];
+  for (let i = 0; i < 7; i++) { const start = performance.now(); fn(); ms.push(performance.now() - start); }
+  ms.sort((a, b) => a - b);
+  return ms[3];
+}
+medianDuration(() => lineAuthors(text, model));
+const oldMs = medianDuration(() => referenceLineAuthors(text, model));
+const newMs = medianDuration(() => lineAuthors(text, model));
+console.log(`PASS: 400 randomized canonical + noncanonical parity cases; 6000 lines, 6000 spans: reference ${oldMs.toFixed(2)} ms; optimized ${newMs.toFixed(2)} ms; ${(oldMs / newMs).toFixed(1)}x`);