fix(app): keep live session updates responsive

Cache timeline DOM indexes and memoize the timeline so progress and flap updates avoid rescanning or rerendering old messages. Preserve scroll anchors and disclosure state across targeted live message replacements.

app/src/renderer/src/session-view-state.mjs

@@ -9,6 +9,71 @@ function scrollItems(detail) {
   return arrayFrom(detail?.querySelectorAll?.(SCROLL_ITEM_SELECTOR));
 }
 
+export function createSessionDomIndex(detail) {
+  const items = scrollItems(detail);
+  const byUuid = new Map();
+  const byMessageUuid = new Map();
+  for (const item of items) {
+    const uuid = item.dataset?.uuid;
+    const messageUuid = item.dataset?.messageUuid || uuid;
+    if (uuid) byUuid.set(uuid, item);
+    if (!messageUuid) continue;
+    const roots = byMessageUuid.get(messageUuid) || [];
+    roots.push(item);
+    byMessageUuid.set(messageUuid, roots);
+  }
+  return { items, byUuid, byMessageUuid };
+}
+
+function applyDisclosureState(element, state) {
+  element.classList?.add(...state.classes);
+  if (!state.rawOpen) return;
+  element.querySelector?.('.toolcall-raw')?.classList?.add('show');
+  element.querySelector?.('.toolcall-pretty')?.classList?.add('hidden');
+  element.querySelector?.('.raw-toggle')?.classList?.add('active');
+}
+
+function viewElements(root) {
+  const elements = [];
+  if (root?.matches?.('[data-view-key]')) elements.push(root);
+  elements.push(...arrayFrom(root?.querySelectorAll?.('[data-view-key]')));
+  return elements;
+}
+
+export function createSessionDisclosureRegistry() {
+  const states = new Map();
+  return {
+    remember(element) {
+      const key = element?.dataset?.viewKey;
+      if (!key) return;
+      const messageRoot = element.closest?.('[data-message-uuid]');
+      const messageUuid = messageRoot?.dataset?.messageUuid;
+      if (!messageUuid) return;
+      const classes = DISCLOSURE_CLASSES.filter(className => element.classList?.contains(className));
+      const rawOpen = Boolean(element.querySelector?.('.toolcall-raw')?.classList?.contains('show'));
+      if (!classes.length && !rawOpen) {
+        states.delete(key);
+        return;
+      }
+      states.set(key, { messageUuid, classes, rawOpen });
+    },
+    reconcile(domIndex, { updatedIds = [], removedIds = [] } = {}) {
+      const removed = new Set(removedIds);
+      for (const [key, state] of states) {
+        if (removed.has(state.messageUuid)) states.delete(key);
+      }
+      for (const messageUuid of updatedIds) {
+        for (const root of domIndex?.byMessageUuid?.get(messageUuid) || []) {
+          for (const element of viewElements(root)) {
+            const state = states.get(element.dataset?.viewKey);
+            if (state?.messageUuid === messageUuid) applyDisclosureState(element, state);
+          }
+        }
+      }
+    },
+  };
+}
+
 export function isFollowingSessionTail(wrap, bottomThreshold = 50) {
   if (!wrap) return false;
   return wrap.scrollHeight - wrap.scrollTop - wrap.clientHeight < bottomThreshold;
@@ -19,22 +84,30 @@ export function restoreSessionTail({ wrap, followTail, restoreScroll = true } =
   wrap.scrollTop = wrap.scrollHeight;
 }
 
-export function captureSessionViewState({ wrap, detail, bottomThreshold = 50 } = {}) {
+function firstMessageEndingBelowIndex(messages, line) {
+  let low = 0;
+  let high = messages.length;
+  while (low < high) {
+    const middle = Math.floor((low + high) / 2);
+    if (messages[middle].getBoundingClientRect().bottom > line) {
+      high = middle;
+    } else {
+      low = middle + 1;
+    }
+  }
+  return low;
+}
+
+export function captureSessionViewState({ wrap, domIndex, bottomThreshold = 50 } = {}) {
   if (!wrap) return null;
   const followTail = isFollowingSessionTail(wrap, bottomThreshold);
   const wrapTop = wrap.getBoundingClientRect?.().top || 0;
+  const anchorIndex = followTail
+    ? -1
+    : firstMessageEndingBelowIndex(domIndex?.items || [], wrapTop);
   const anchorElement = followTail
     ? null
-    : scrollItems(detail).find(element => element.getBoundingClientRect().bottom > wrapTop);
+    : domIndex?.items?.[anchorIndex];
-
-  const disclosures = [];
-  for (const element of arrayFrom(detail?.querySelectorAll?.('[data-view-key]'))) {
-    const key = element.dataset?.viewKey;
-    if (!key) continue;
-    const classes = DISCLOSURE_CLASSES.filter(className => element.classList?.contains(className));
-    const rawOpen = Boolean(element.querySelector?.('.toolcall-raw')?.classList?.contains('show'));
-    if (classes.length || rawOpen) disclosures.push({ key, classes, rawOpen });
-  }
 
   return {
     followTail,
@@ -42,32 +115,16 @@ export function captureSessionViewState({ wrap, detail, bottomThreshold = 50 } =
     anchor: anchorElement?.dataset?.uuid
       ? {
           uuid: anchorElement.dataset.uuid,
+          messageUuid: anchorElement.dataset.messageUuid || anchorElement.dataset.uuid,
           offset: anchorElement.getBoundingClientRect().top - wrapTop,
         }
       : null,
-    disclosures,
   };
 }
 
-export function restoreSessionViewState(snapshot, { wrap, detail, restoreScroll = true } = {}) {
+export function restoreSessionViewState(snapshot, { wrap, domIndex, restoreScroll = true } = {}) {
   if (!snapshot || !wrap) return;
 
-  const disclosuresByKey = new Map(
-    arrayFrom(detail?.querySelectorAll?.('[data-view-key]'))
-      .filter(element => element.dataset?.viewKey)
-      .map(element => [element.dataset.viewKey, element]),
-  );
-
-  for (const disclosure of snapshot.disclosures || []) {
-    const element = disclosuresByKey.get(disclosure.key);
-    if (!element) continue;
-    element.classList?.add(...disclosure.classes);
-    if (!disclosure.rawOpen) continue;
-    element.querySelector?.('.toolcall-raw')?.classList?.add('show');
-    element.querySelector?.('.toolcall-pretty')?.classList?.add('hidden');
-    element.querySelector?.('.raw-toggle')?.classList?.add('active');
-  }
-
   if (!restoreScroll) return;
 
   if (snapshot.followTail) {
@@ -78,9 +135,8 @@ export function restoreSessionViewState(snapshot, { wrap, detail, restoreScroll
   wrap.scrollTop = snapshot.scrollTop;
   if (!snapshot.anchor) return;
   const wrapTop = wrap.getBoundingClientRect?.().top || 0;
-  const anchorElement = scrollItems(detail).find(
+  const anchorElement = domIndex?.byUuid?.get(snapshot.anchor.uuid)
-    element => element.dataset?.uuid === snapshot.anchor.uuid,
+    || domIndex?.byMessageUuid?.get(snapshot.anchor.messageUuid)?.[0];
-  );
   if (!anchorElement) return;
   const currentOffset = anchorElement.getBoundingClientRect().top - wrapTop;
   wrap.scrollTop += currentOffset - snapshot.anchor.offset;
@@ -88,17 +144,5 @@ export function restoreSessionViewState(snapshot, { wrap, detail, restoreScroll
 
 export function findLastMessageAtOrAbove(messages, bottomLine) {
   if (!messages?.length) return -1;
-  let low = 0;
+  return Math.max(0, firstMessageEndingBelowIndex(messages, bottomLine) - 1);
-  let high = messages.length - 1;
-  let result = 0;
-  while (low <= high) {
-    const middle = Math.floor((low + high) / 2);
-    if (messages[middle].getBoundingClientRect().bottom <= bottomLine) {
-      result = middle;
-      low = middle + 1;
-    } else {
-      high = middle - 1;
-    }
-  }
-  return result;
 }

app/src/renderer/src/views/SessionDetail.vue

@@ -9,6 +9,8 @@ import { getArgPreview, getToolIcon, renderTerminalTool } from '../tool-renderer
 import FlapNumber from '../components/FlapNumber.vue';
 import {
   captureSessionViewState,
+  createSessionDisclosureRegistry,
+  createSessionDomIndex,
   findLastMessageAtOrAbove,
   isFollowingSessionTail,
   restoreSessionTail,
@@ -41,6 +43,8 @@ let scrollRevision = 0;
 // DOM refs
 const wrapRef = ref(null);
 const detailRef = ref(null);
+let sessionDomIndex = createSessionDomIndex(null);
+let disclosureRegistry = createSessionDisclosureRegistry();
 
 // --- Load session on mount or when id changes ---
 const FONT_SIZE_KEY = 'obelisk:session-font-size';
@@ -138,6 +142,7 @@ onUnmounted(() => {
 watch(() => props.id, async (newId, oldId) => {
   if (newId && newId !== oldId) {
     messages.value = [];
+    disclosureRegistry = createSessionDisclosureRegistry();
     progressPct.value = 0;
     currentMsgIdx.value = 0;
     await loadMessages({ force: consumeGlobalSessionDirty(newId) });
@@ -167,7 +172,7 @@ async function loadMessages({ force = false } = {}) {
       if (hadContent && !reconciliation.tailOnly) {
         viewState = captureSessionViewState({
           wrap: wrapRef.value,
-          detail: detailRef.value,
+          domIndex: sessionDomIndex,
         });
       }
       messages.value = reconciliation.messages;
@@ -182,7 +187,8 @@ async function loadMessages({ force = false } = {}) {
   }
 
   await nextTick();
-  syncTotalMessages();
+  syncTimelineDom();
+  disclosureRegistry.reconcile(sessionDomIndex, reconciliation);
   if (!state.pendingFocusUuid) {
     if (reconciliation.tailOnly) {
       restoreSessionTail({
@@ -193,7 +199,7 @@ async function loadMessages({ force = false } = {}) {
     } else {
       restoreSessionViewState(viewState, {
         wrap: wrapRef.value,
-        detail: detailRef.value,
+        domIndex: sessionDomIndex,
         restoreScroll: scrollRevision === scrollRevisionBeforePatch,
       });
     }
@@ -231,9 +237,9 @@ const totalMsgs = ref(0);
 let navLock = false;
 let scrollFrame = null;
 
-function syncTotalMessages() {
+function syncTimelineDom() {
-  const msgs = detailRef.value?.querySelectorAll('.msg, .wf-card, .skill-card');
+  sessionDomIndex = createSessionDomIndex(detailRef.value);
-  totalMsgs.value = msgs?.length || 0;
+  totalMsgs.value = sessionDomIndex.items.length;
 }
 
 function onScroll(event) {
@@ -252,8 +258,8 @@ function setMessagePosition(index, total) {
 }
 
 function updateScrollProgress() {
-  if (!wrapRef.value || !detailRef.value) return;
+  if (!wrapRef.value) return;
-  const msgs = detailRef.value.querySelectorAll('.msg, .wf-card, .skill-card');
+  const msgs = sessionDomIndex.items;
   if (!msgs.length) {
     currentMsgIdx.value = 0;
     progressPct.value = 0;
@@ -268,8 +274,8 @@ function updateScrollProgress() {
 }
 
 function navTo(target) {
-  if (!wrapRef.value || !detailRef.value) return;
+  if (!wrapRef.value) return;
-  const msgs = detailRef.value.querySelectorAll('.msg, .wf-card, .skill-card');
+  const msgs = sessionDomIndex.items;
   if (!msgs.length) return;
   let idx;
   if (target === 'first') idx = 0;
@@ -290,24 +296,11 @@ function navTo(target) {
 }
 
 // --- Toggle helpers ---
-function toggleToolCall(event) {
+function toggleDisclosure(event, selector, className = 'open') {
-  const btn = event.currentTarget;
+  const element = event.currentTarget?.closest(selector);
-  btn.closest('.msg-tool').classList.toggle('open');
+  if (!element) return;
-}
+  element.classList.toggle(className);
-
+  disclosureRegistry.remember(element);
-function toggleSummary(event) {
-  const btn = event.currentTarget;
-  btn.closest('.msg-summary').classList.toggle('open');
-}
-
-function toggleThinking(event) {
-  const btn = event.currentTarget;
-  btn.closest('.msg-thinking').classList.toggle('open');
-}
-
-function toggleMeta(event) {
-  const btn = event.currentTarget;
-  btn.closest('.msg-meta-collapsed').classList.toggle('open');
 }
 
 // --- Full text loading ---
@@ -576,17 +569,13 @@ function toggleRaw(event) {
   const showing = raw.classList.toggle('show');
   pretty.classList.toggle('hidden', showing);
   btn?.classList.toggle('active', showing);
+  disclosureRegistry.remember(body.closest('[data-view-key]'));
 }
 
 function getSkillMd(msg) {
   return msg?._skillMd || null;
 }
 
-function toggleSkillMd(event) {
-  const card = event.target.closest('.skill-card');
-  if (card) card.classList.toggle('skill-md-open');
-}
-
 function getToolCallParsedInput(tc) {
   try {
     return JSON.parse(tc.input_json || '{}');
@@ -637,14 +626,14 @@ function getToolCallParsedInput(tc) {
         </div>
 
         <!-- Message timeline -->
-        <div class="timeline">
+        <div class="timeline" v-memo="[messages, state.query]">
           <template v-for="msg in messages" :key="msg.uuid" v-memo="[msg, state.query]">
 
             <!-- Meta messages: collapsed system indicator -->
             <template v-if="msg.is_meta === 1">
-              <div class="msg meta" :data-uuid="msg.uuid">
+              <div class="msg meta" :data-uuid="msg.uuid" :data-message-uuid="msg.uuid">
                 <div class="msg-meta-collapsed" :data-view-key="`meta:${msg.uuid}`">
-                  <button class="meta-toggle" @click="toggleMeta">
+                  <button class="meta-toggle" @click="toggleDisclosure($event, '.msg-meta-collapsed')">
                     <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                     <span class="meta-label">System</span>
                     <span class="meta-preview">{{ (msg.text || '').replace(/<[^>]+>/g, '').slice(0, 80) }}</span>
@@ -664,7 +653,7 @@ function getToolCallParsedInput(tc) {
             <!-- Workflow card (standalone, outside assistant bubble) -->
             <template v-else-if="!msg.type || msg.type !== 'user' ? (msg.tool_calls || []).find(tc => tc.name === 'Workflow' && tc.workflow) : false">
               <template v-if="(() => { const wfCall = (msg.tool_calls || []).find(tc => tc.name === 'Workflow' && tc.workflow); return wfCall && msg.type !== 'user'; })()">
-                <div class="wf-card" :data-uuid="msg.uuid">
+                <div class="wf-card" :data-uuid="msg.uuid" :data-message-uuid="msg.uuid">
                   <div class="wf-card-header">
                     <span class="wf-card-icon">&#x2699;</span>
                     <span class="wf-card-name">{{ ((msg.tool_calls || []).find(tc => tc.name === 'Workflow' && tc.workflow)).workflow.workflow_name || 'Workflow' }}</span>
@@ -705,12 +694,12 @@ function getToolCallParsedInput(tc) {
                 </div>
                 <!-- Other tool calls (non-workflow) for this message -->
                 <template v-if="(msg.tool_calls || []).filter(tc => !(tc.name === 'Workflow' && tc.workflow)).length > 0">
-                  <div class="msg assistant" :data-uuid="msg.uuid + '-tools'">
+                  <div class="msg assistant" :data-uuid="msg.uuid + '-tools'" :data-message-uuid="msg.uuid">
                     <div class="msg-tools">
                       <template v-for="tc in (msg.tool_calls || []).filter(tc2 => !(tc2.name === 'Workflow' && tc2.workflow))" :key="tc.id">
                         <!-- Render non-workflow tool calls -->
                         <div class="msg-tool" :class="{ 'is-error': tc.result && tc.result.is_error }" :data-view-key="`tool:${tc.id}`">
-                          <button class="toolcall-toggle" @click="toggleToolCall">
+                          <button class="toolcall-toggle" @click="toggleDisclosure($event, '.msg-tool')">
                             <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                             <span v-if="getToolIcon(tc.name)" class="tool-icon" v-html="getToolIcon(tc.name)"></span>
                             <span class="tool-name">{{ tc.name }}</span>
@@ -743,7 +732,7 @@ function getToolCallParsedInput(tc) {
 
             <!-- Skill card (standalone, like workflow) -->
             <template v-else-if="msg.type === 'assistant' && (msg.tool_calls || []).length === 1 && msg.tool_calls[0].name === 'Skill' && !msg.text">
-              <div class="skill-card" :data-uuid="msg.uuid" :data-view-key="`skill:${msg.uuid}`">
+              <div class="skill-card" :data-uuid="msg.uuid" :data-message-uuid="msg.uuid" :data-view-key="`skill:${msg.uuid}`">
                 <div class="skill-card-icon">
                   <svg viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="1.4" stroke-linejoin="round" stroke-linecap="round"><rect x="2" y="3" width="12" height="10" rx="1.5"/><path d="M5 6.5h6M5 9h4"/></svg>
                 </div>
@@ -754,7 +743,7 @@ function getToolCallParsedInput(tc) {
                   </div>
                   <div class="skill-card-args">{{ getToolCallParsedInput(msg.tool_calls[0]).args || '' }}</div>
                   <div v-if="getSkillMd(msg)" class="skill-card-md">
-                    <button class="skill-md-toggle" @click="toggleSkillMd">
+                    <button class="skill-md-toggle" @click="toggleDisclosure($event, '.skill-card', 'skill-md-open')">
                       <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                       <span>SKILL.md</span>
                     </button>
@@ -766,9 +755,9 @@ function getToolCallParsedInput(tc) {
 
             <!-- Standalone thinking message -->
             <template v-else-if="msg.type === 'assistant' && msg.content_type === 'thinking'">
-              <div class="msg assistant" :data-uuid="msg.uuid">
+              <div class="msg assistant" :data-uuid="msg.uuid" :data-message-uuid="msg.uuid">
                 <div class="msg-thinking" :data-view-key="`thinking:${msg.uuid}`">
-                  <button class="thinking-toggle" @click="toggleThinking">
+                  <button class="thinking-toggle" @click="toggleDisclosure($event, '.msg-thinking')">
                     <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                     <span class="thinking-label">Thinking</span>
                   </button>
@@ -783,6 +772,7 @@ function getToolCallParsedInput(tc) {
                 class="msg"
                 :class="msg.type === 'user' ? 'user' : 'assistant'"
                 :data-uuid="msg.uuid"
+                :data-message-uuid="msg.uuid"
               >
                 <!-- Message header -->
                 <div class="msg-head">
@@ -792,7 +782,7 @@ function getToolCallParsedInput(tc) {
 
                 <!-- Attached thinking block (merged from preceding thinking messages) -->
                 <div v-if="msg._thinking" class="msg-thinking" :data-view-key="`thinking:${msg.uuid}`">
-                  <button class="thinking-toggle" @click="toggleThinking">
+                    <button class="thinking-toggle" @click="toggleDisclosure($event, '.msg-thinking')">
                     <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                     <span class="thinking-label">Thinking</span>
                   </button>
@@ -827,7 +817,7 @@ function getToolCallParsedInput(tc) {
                     <!-- Agent/Task tool call (subagent) -->
                     <template v-else-if="tc.name === 'Agent' || tc.name === 'Task'">
                       <div class="msg-tool agent-call" :data-view-key="`tool:${tc.id}`">
-                        <button class="toolcall-toggle" @click="toggleToolCall">
+                        <button class="toolcall-toggle" @click="toggleDisclosure($event, '.msg-tool')">
                           <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                           <span class="tool-name">{{ getToolCallParsedInput(tc).subagent_type || getToolCallParsedInput(tc).agentType || 'Agent' }}</span>
                           <span class="tool-arg">{{ getToolCallParsedInput(tc).description || (getToolCallParsedInput(tc).prompt || '').slice(0, 80) }}</span>
@@ -854,7 +844,7 @@ function getToolCallParsedInput(tc) {
                     <!-- Workflow tool call (inside assistant bubble) -->
                     <template v-else-if="tc.name === 'Workflow'">
                       <div class="msg-tool agent-call" :data-view-key="`tool:${tc.id}`">
-                        <button class="toolcall-toggle" @click="toggleToolCall">
+                        <button class="toolcall-toggle" @click="toggleDisclosure($event, '.msg-tool')">
                           <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                           <span class="tool-name">Workflow</span>
                           <span class="tool-arg">{{ tc.workflow?.workflow_name || getToolCallParsedInput(tc).name || 'Workflow' }}</span>
@@ -902,7 +892,7 @@ function getToolCallParsedInput(tc) {
                     <!-- Generic tool call -->
                     <template v-else>
                       <div class="msg-tool" :class="{ 'is-error': tc.result && tc.result.is_error }" :data-view-key="`tool:${tc.id}`">
-                        <button class="toolcall-toggle" @click="toggleToolCall">
+                        <button class="toolcall-toggle" @click="toggleDisclosure($event, '.msg-tool')">
                           <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                           <span v-if="getToolIcon(tc.name)" class="tool-icon" v-html="getToolIcon(tc.name)"></span>
                           <span class="tool-name">{{ tc.name }}</span>
@@ -933,7 +923,7 @@ function getToolCallParsedInput(tc) {
 
                 <!-- Summary block -->
                 <div v-if="msg.summary" class="msg-summary" :data-view-key="`summary:${msg.uuid}`">
-                  <button class="summary-toggle" @click="toggleSummary">
+                  <button class="summary-toggle" @click="toggleDisclosure($event, '.msg-summary')">
                     <svg class="chevron" viewBox="0 0 8 8" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"><path d="M2.5 1.5l3 2.5-3 2.5"/></svg>
                     <span class="label">Session summary</span>
                     <span class="source">{{ msg.summary.source || '' }}</span>

tests/session-view-state.test.mjs

@@ -4,6 +4,8 @@ import { readFileSync } from 'node:fs';
 
 import {
   captureSessionViewState,
+  createSessionDisclosureRegistry,
+  createSessionDomIndex,
   findLastMessageAtOrAbove,
   isFollowingSessionTail,
   restoreSessionTail,
@@ -52,6 +54,10 @@ function detail(disclosures, scrollItems) {
   };
 }
 
+function domIndex(items) {
+  return createSessionDomIndex(detail([], items));
+}
+
 function wrap({ scrollTop, scrollHeight, clientHeight, top = 0 }) {
   return {
     scrollTop,
@@ -76,39 +82,53 @@ function functionSource(source, name) {
   assert.fail(`${name} should have a complete function body`);
 }
 
-test('session refresh restores disclosure state and the visible scroll anchor', () => {
+test('session refresh restores the visible scroll anchor from cached DOM indexes', () => {
-  const oldTool = disclosure('tool:call-1', ['open'], { rawOpen: true });
   const oldWrap = wrap({ scrollTop: 500, scrollHeight: 2000, clientHeight: 600 });
   const snapshot = captureSessionViewState({
     wrap: oldWrap,
-    detail: detail([oldTool], [scrollItem('msg-1', -20, 180)]),
+    domIndex: domIndex([scrollItem('msg-1', -20, 180)]),
   });
 
-  const newTool = disclosure('tool:call-1');
   const newWrap = wrap({ scrollTop: 0, scrollHeight: 2200, clientHeight: 600 });
   restoreSessionViewState(snapshot, {
     wrap: newWrap,
-    detail: detail([newTool], [scrollItem('msg-1', 80, 280)]),
+    domIndex: domIndex([scrollItem('msg-1', 80, 280)]),
   });
 
-  assert.equal(newTool.classList.contains('open'), true);
-  assert.equal(newTool.raw.classList.contains('show'), true);
-  assert.equal(newTool.pretty.classList.contains('hidden'), true);
-  assert.equal(newTool.button.classList.contains('active'), true);
   assert.equal(newWrap.scrollTop, 600, '100 px inserted above the anchor is compensated');
 });
 
+test('session refresh falls back to the owning message when its rendered root changes', () => {
+  const oldRoot = scrollItem('message-1-tools', -20, 180);
+  oldRoot.dataset.messageUuid = 'message-1';
+  const snapshot = captureSessionViewState({
+    wrap: wrap({ scrollTop: 500, scrollHeight: 2000, clientHeight: 600 }),
+    domIndex: domIndex([oldRoot]),
+  });
+
+  const newRoot = scrollItem('message-1', 80, 280);
+  newRoot.dataset.messageUuid = 'message-1';
+  const newWrap = wrap({ scrollTop: 0, scrollHeight: 2200, clientHeight: 600 });
+  restoreSessionViewState(snapshot, {
+    wrap: newWrap,
+    domIndex: domIndex([newRoot]),
+  });
+
+  assert.equal(snapshot.anchor.messageUuid, 'message-1');
+  assert.equal(newWrap.scrollTop, 600, 'message identity preserves the anchor across render shapes');
+});
+
 test('session refresh follows appended content only when already at the tail', () => {
   const oldWrap = wrap({ scrollTop: 1390, scrollHeight: 2000, clientHeight: 600 });
   const snapshot = captureSessionViewState({
     wrap: oldWrap,
-    detail: detail([], [scrollItem('msg-last', 300, 590)]),
+    domIndex: domIndex([scrollItem('msg-last', 300, 590)]),
   });
   const newWrap = wrap({ scrollTop: 0, scrollHeight: 2400, clientHeight: 600 });
 
   restoreSessionViewState(snapshot, {
     wrap: newWrap,
-    detail: detail([], [scrollItem('msg-last', 300, 590)]),
+    domIndex: domIndex([scrollItem('msg-last', 300, 590)]),
   });
 
   assert.equal(newWrap.scrollTop, 2400);
@@ -142,21 +162,18 @@ test('tail append preserves an active reader and follows only without newer scro
 });
 
 test('session refresh never restores an old anchor over newer user scrolling', () => {
-  const oldTool = disclosure('tool:call-1', ['open']);
   const snapshot = captureSessionViewState({
     wrap: wrap({ scrollTop: 500, scrollHeight: 2000, clientHeight: 600 }),
-    detail: detail([oldTool], [scrollItem('msg-1', -20, 180)]),
+    domIndex: domIndex([scrollItem('msg-1', -20, 180)]),
   });
-  const newTool = disclosure('tool:call-1');
   const userScrolledWrap = wrap({ scrollTop: 800, scrollHeight: 2200, clientHeight: 600 });
 
   restoreSessionViewState(snapshot, {
     wrap: userScrolledWrap,
-    detail: detail([newTool], [scrollItem('msg-1', 80, 280)]),
+    domIndex: domIndex([scrollItem('msg-1', 80, 280)]),
     restoreScroll: false,
   });
 
-  assert.equal(newTool.classList.contains('open'), true, 'disclosure state still restores');
   assert.equal(userScrolledWrap.scrollTop, 800, 'newer user scroll wins over stale refresh state');
 });
 
@@ -173,18 +190,162 @@ test('scroll progress locates the visible message without scanning the full sess
   assert.ok(layoutReads < 20, `expected logarithmic layout reads, got ${layoutReads}`);
 });
 
+test('view-state capture locates its anchor logarithmically from the DOM index', () => {
+  let layoutReads = 0;
+  const items = Array.from({ length: 4096 }, (_, index) => ({
+    dataset: { uuid: `message-${index}` },
+    getBoundingClientRect() {
+      layoutReads++;
+      return { top: index * 20, bottom: (index + 1) * 20 };
+    },
+  }));
+
+  const snapshot = captureSessionViewState({
+    wrap: wrap({ scrollTop: 20000, scrollHeight: 90000, clientHeight: 600, top: 30000 }),
+    domIndex: {
+      items,
+      byUuid: new Map(items.map(item => [item.dataset.uuid, item])),
+      byMessageUuid: new Map(),
+    },
+  });
+
+  assert.equal(snapshot.anchor.uuid, 'message-1500');
+  assert.ok(layoutReads < 20, `expected logarithmic anchor reads, got ${layoutReads}`);
+});
+
+test('session DOM index scans the timeline once and groups roots by message UUID', () => {
+  let queries = 0;
+  const first = scrollItem('render-1', 0, 20);
+  first.dataset.messageUuid = 'message-1';
+  const second = scrollItem('render-2', 20, 40);
+  second.dataset.messageUuid = 'message-2';
+  const secondTools = scrollItem('render-2-tools', 40, 60);
+  secondTools.dataset.messageUuid = 'message-2';
+  const index = createSessionDomIndex({
+    querySelectorAll(selector) {
+      queries++;
+      assert.equal(selector, '.msg[data-uuid], .wf-card[data-uuid], .skill-card[data-uuid]');
+      return [first, second, secondTools];
+    },
+  });
+
+  assert.equal(queries, 1);
+  assert.deepEqual(index.items, [first, second, secondTools]);
+  assert.equal(index.byUuid.get('render-2-tools'), secondTools);
+  assert.deepEqual(index.byMessageUuid.get('message-2'), [second, secondTools]);
+
+  findLastMessageAtOrAbove(index.items, 35);
+  findLastMessageAtOrAbove(index.items, 55);
+  assert.equal(queries, 1, 'scroll reads reuse the index instead of querying the DOM');
+});
+
+test('disclosure registry restores only message roots replaced by the snapshot', () => {
+  const previous = disclosure('tool:call-1', ['open'], { rawOpen: true });
+  previous.closest = selector => selector === '[data-message-uuid]'
+    ? { dataset: { messageUuid: 'message-1' } }
+    : null;
+  const registry = createSessionDisclosureRegistry();
+  registry.remember(previous);
+
+  const replacement = disclosure('tool:call-1');
+  const updatedRoot = {
+    matches: () => false,
+    querySelectorAll(selector) {
+      assert.equal(selector, '[data-view-key]');
+      return [replacement];
+    },
+  };
+  const untouchedRoot = {
+    matches: () => false,
+    querySelectorAll() {
+      assert.fail('unchanged message roots must not be scanned');
+    },
+  };
+
+  registry.reconcile({
+    byMessageUuid: new Map([
+      ['message-1', [updatedRoot]],
+      ['message-2', [untouchedRoot]],
+    ]),
+  }, {
+    updatedIds: ['message-1'],
+    removedIds: [],
+  });
+
+  assert.equal(replacement.classList.contains('open'), true);
+  assert.equal(replacement.raw.classList.contains('show'), true);
+  assert.equal(replacement.pretty.classList.contains('hidden'), true);
+  assert.equal(replacement.button.classList.contains('active'), true);
+});
+
+test('removed messages discard their remembered disclosure state', () => {
+  const previous = disclosure('tool:call-1', ['open']);
+  previous.closest = () => ({ dataset: { messageUuid: 'message-1' } });
+  const registry = createSessionDisclosureRegistry();
+  registry.remember(previous);
+  registry.reconcile({ byMessageUuid: new Map() }, {
+    updatedIds: [],
+    removedIds: ['message-1'],
+  });
+
+  const replacement = disclosure('tool:call-1');
+  registry.reconcile({
+    byMessageUuid: new Map([['message-1', [{
+      matches: () => false,
+      querySelectorAll: () => [replacement],
+    }]]]),
+  }, {
+    updatedIds: ['message-1'],
+    removedIds: [],
+  });
+
+  assert.equal(replacement.classList.contains('open'), false);
+});
+
+test('disclosure registry restores root-level skill cards', () => {
+  const previous = disclosure('skill:message-1', ['skill-md-open']);
+  previous.closest = () => ({ dataset: { messageUuid: 'message-1' } });
+  const registry = createSessionDisclosureRegistry();
+  registry.remember(previous);
+
+  const replacement = disclosure('skill:message-1');
+  replacement.matches = selector => selector === '[data-view-key]';
+  replacement.dataset.messageUuid = 'message-1';
+  registry.reconcile({
+    byMessageUuid: new Map([['message-1', [replacement]]]),
+  }, {
+    updatedIds: ['message-1'],
+    removedIds: [],
+  });
+
+  assert.equal(replacement.classList.contains('skill-md-open'), true);
+});
+
+test('view-state capture and restore do not query the full DOM', () => {
+  const source = readFileSync(new URL('../app/src/renderer/src/session-view-state.mjs', import.meta.url), 'utf8');
+  const capture = functionSource(source, 'captureSessionViewState');
+  const restore = functionSource(source, 'restoreSessionViewState');
+
+  assert.doesNotMatch(capture, /querySelectorAll|scrollItems\(|\bdetail\b/);
+  assert.doesNotMatch(restore, /querySelectorAll|scrollItems\(|\bdetail\b/);
+});
+
 test('SessionDetail isolates unchanged rows and gives tail appends a scan-free path', () => {
   const source = readFileSync(new URL('../app/src/renderer/src/views/SessionDetail.vue', import.meta.url), 'utf8');
   const dataSource = readFileSync(new URL('../app/src/renderer/src/data.js', import.meta.url), 'utf8');
   const loadMessages = functionSource(source, 'loadMessages');
   const getSkillMd = functionSource(source, 'getSkillMd');
+  const toggleDisclosure = functionSource(source, 'toggleDisclosure');
 
   assert.match(source, /import\s*\{[^}]*shallowRef[^}]*\}\s*from ['"]vue['"]/s);
   assert.match(source, /const messages = shallowRef\(\[\]\)/);
   assert.match(source, /applySnapshot/);
   assert.match(source, /isFollowingSessionTail/);
   assert.match(source, /captureSessionViewState/);
+  assert.match(source, /createSessionDomIndex/);
+  assert.match(source, /createSessionDisclosureRegistry/);
   assert.match(source, /restoreSessionViewState/);
+  assert.match(source, /class="timeline"\s+v-memo="\[messages, state\.query\]"/);
   assert.match(source, /:key="msg\.uuid"\s+v-memo=/);
   assert.match(source, /v-memo="\[msg, state\.query\]"/);
   assert.match(source, /loading\.value\s*=\s*!hadContent/);
@@ -193,6 +354,8 @@ test('SessionDetail isolates unchanged rows and gives tail appends a scan-free p
   assert.match(source, /requestAnimationFrame/);
   assert.match(source, /findLastMessageAtOrAbove/);
   assert.match(loadMessages, /if \(hadContent && !reconciliation\.tailOnly\)/);
+  assert.match(loadMessages, /domIndex:\s*sessionDomIndex/);
+  assert.match(loadMessages, /disclosureRegistry\.reconcile\(sessionDomIndex, reconciliation\)/);
   assert.match(loadMessages, /if \(!reconciliation\.changed\)/);
   assert.ok(
     loadMessages.indexOf('applySnapshot(') < loadMessages.indexOf('captureSessionViewState('),
@@ -212,20 +375,29 @@ test('SessionDetail isolates unchanged rows and gives tail appends a scan-free p
   );
   assert.doesNotMatch(getSkillMd, /messages\.value/);
   assert.match(source, /getSkillMd\(msg\)/);
+  assert.match(toggleDisclosure, /disclosureRegistry\.remember\(element\)/);
+  assert.ok(
+    (source.match(/:data-message-uuid="msg\.uuid"/g) || []).length >= 6,
+    'every timeline root identifies its owning message for targeted disclosure restore',
+  );
   assert.match(dataSource, /messages:\s*markRaw\(assembledMessages\)/);
 });
 
 test('live totals and scroll position remain isolated across interleaved updates', () => {
   const source = readFileSync(new URL('../app/src/renderer/src/views/SessionDetail.vue', import.meta.url), 'utf8');
   const loadMessages = functionSource(source, 'loadMessages');
-  const syncTotalMessages = functionSource(source, 'syncTotalMessages');
+  const syncTimelineDom = functionSource(source, 'syncTimelineDom');
   const updateScrollProgress = functionSource(source, 'updateScrollProgress');
+  const navTo = functionSource(source, 'navTo');
 
-  assert.match(loadMessages, /await nextTick\(\);[\s\S]*syncTotalMessages\(\)/);
+  assert.match(loadMessages, /await nextTick\(\);[\s\S]*syncTimelineDom\(\)/);
-  assert.match(syncTotalMessages, /totalMsgs\.value\s*=/);
+  assert.match(syncTimelineDom, /createSessionDomIndex\(detailRef\.value\)/);
-  assert.doesNotMatch(syncTotalMessages, /currentMsgIdx\.value\s*=/);
+  assert.match(syncTimelineDom, /totalMsgs\.value\s*=/);
+  assert.doesNotMatch(syncTimelineDom, /currentMsgIdx\.value\s*=/);
   assert.match(updateScrollProgress, /currentMsgIdx\.value\s*=/);
   assert.doesNotMatch(updateScrollProgress, /totalMsgs\.value\s*=/);
+  assert.doesNotMatch(updateScrollProgress, /querySelectorAll/);
+  assert.doesNotMatch(navTo, /querySelectorAll/);
 });
 
 test('message navigation keeps the top progress bar aligned with the current position', () => {