diff --git a/packages/ui/desktop/src/app.ts b/packages/ui/desktop/src/app.ts
index fc855d951f..9641645088 100644
--- a/packages/ui/desktop/src/app.ts
+++ b/packages/ui/desktop/src/app.ts
@@ -211,7 +211,7 @@ function buildShell(): void {
       <aside class="source-list">
         <header class="app-brand">
           <button class="brand-title" data-module="sessions">DeepSeek Harness</button>
-          <span class="runtime-dot starting" id="runtimeDot"></span>
+          <span class="runtime-dot starting" id="runtimeDot" aria-hidden="true"></span>
         </header>
         <section class="primary-actions">
           <button class="primary-action" data-action="new-session"><span data-text="app.newChat"></span><kbd>⌘N</kbd></button>
@@ -233,7 +233,7 @@ function buildShell(): void {
           <strong id="footerRuntime"></strong>
         </footer>
       </aside>
-      <div class="pane-divider" id="dividerLeft" role="separator" aria-orientation="vertical"></div>
+      <div class="pane-divider" id="dividerLeft" role="separator" aria-orientation="vertical" data-label="app.resizeSidebar"></div>
       <main class="harness-main">
         <header class="topbar">
           <div class="title-area"><h1 id="topbarTitle"></h1></div>
@@ -283,7 +283,7 @@ function buildShell(): void {
           </div>
         </form>
       </main>
-      <div class="pane-divider" id="dividerInspector" role="separator" aria-orientation="vertical" hidden></div>
+      <div class="pane-divider" id="dividerInspector" role="separator" aria-orientation="vertical" hidden data-label="app.resizeInspector"></div>
       <aside class="inspector" id="inspector" hidden>
         <header class="inspector-head">
           <div>
@@ -348,11 +348,16 @@ function applyStaticText(): void {
   for (const node of appEl.querySelectorAll<HTMLElement>('[data-title]')) {
     node.title = t(node.dataset.title as I18nKey)
   }
+  for (const node of appEl.querySelectorAll<HTMLElement>('[data-label]')) {
+    node.setAttribute('aria-label', t(node.dataset.label as I18nKey))
+  }
+  document.documentElement.lang = state.locale
   el.searchInput.placeholder = t('app.searchPlaceholder')
   el.composerInput.placeholder = state.selectedSessionId === undefined
     ? t('composer.placeholderDraft')
     : t('composer.placeholderSession')
   el.sendButton.setAttribute('aria-label', t('composer.send'))
+  el.composerInput.setAttribute('aria-label', t('composer.send'))
   updateComposerState()
 }
 
@@ -652,7 +657,7 @@ function ensureLiveSkeleton(live: LiveTurn): void {
             <div data-live="tools"></div>
           </div>
           <div class="assistant-prose" data-live="answer" hidden></div>
-          <div class="live-status" data-live="status">${escapeHtml(t('chat.sending'))}</div>
+          <div class="live-status" role="status" data-live="status">${escapeHtml(t('chat.sending'))}</div>
         </div>
       </article>
     `
@@ -670,11 +675,26 @@ function ensureLiveSkeleton(live: LiveTurn): void {
   }
 }
 
+let scrollToBottomQueued = false
+
+/** Direct user actions scroll immediately; streaming updates coalesce per frame. */
 function scrollChatToBottom(force = false): void {
-  if (!force && !state.stickToBottom) return
-  el.chatView.scrollTop = el.chatView.scrollHeight
-  state.stickToBottom = true
-  updateLiveJump()
+  if (force) {
+    scrollToBottomQueued = false
+    el.chatView.scrollTop = el.chatView.scrollHeight
+    state.stickToBottom = true
+    updateLiveJump()
+    return
+  }
+  if (!state.stickToBottom || scrollToBottomQueued) return
+  scrollToBottomQueued = true
+  window.requestAnimationFrame(() => {
+    if (!scrollToBottomQueued) return
+    scrollToBottomQueued = false
+    el.chatView.scrollTop = el.chatView.scrollHeight
+    state.stickToBottom = true
+    updateLiveJump()
+  })
 }
 
 function updateLiveJump(): void {
@@ -690,11 +710,7 @@ function updateComposerState(): void {
   el.cancelButton.hidden = !busy
   el.composerHint.textContent = busy ? t('chat.working') : t('composer.hint')
   el.composerForm.classList.toggle('busy', busy)
-}
-
-function autosizeComposer(): void {
-  el.composerInput.style.height = '0px'
-  el.composerInput.style.height = `${Math.min(132, Math.max(42, el.composerInput.scrollHeight))}px`
+  el.composerForm.setAttribute('aria-busy', String(busy))
 }
 
 async function sendPrompt(prompt: string): Promise<void> {
@@ -714,7 +730,6 @@ async function sendPrompt(prompt: string): Promise<void> {
   })
   state.busySessionId = draftKey
   el.composerInput.value = ''
-  autosizeComposer()
   updateComposerState()
   showError('')
   renderLiveTurn()
@@ -762,7 +777,6 @@ async function sendPrompt(prompt: string): Promise<void> {
     showError(String(error))
     if ((state.selectedSessionId === sessionId || (sessionId === undefined && state.draftChat)) && el.composerInput.value.trim().length === 0) {
       el.composerInput.value = prompt
-      autosizeComposer()
     }
     updateComposerState()
   } finally {
@@ -907,7 +921,7 @@ function renderConversation(): void {
 function renderConversationTurn(turn: ChatTurn): string {
   const userTarget = turn.userTargetId === undefined ? undefined : state.graph.targets.get(turn.userTargetId)
   const user = userTarget === undefined ? '' : `
-    <article class="message user ${selectedTargetClass(userTarget.id)}" data-target-id="${escapeHtml(userTarget.id)}">
+    <article class="message user ${selectedTargetClass(userTarget.id)}" role="button" tabindex="0" data-target-id="${escapeHtml(userTarget.id)}">
       <div class="message-card"><div class="user-bubble">${escapeHtml(contentText(userTarget.output))}</div></div>
     </article>
   `
@@ -932,9 +946,9 @@ function renderConversationActivity(activity: ChatActivity): string {
     <section class="chat-activity thinking ${selectedTargetClass(target.id)}">
       <div class="activity-row">
         <button class="activity-select" type="button" data-target-id="${escapeHtml(target.id)}"><span>${escapeHtml(t('chat.thinking'))}</span><strong>${escapeHtml(truncate(contentText(target.output), 112))}</strong></button>
-        <button class="activity-toggle" type="button" data-toggle-activity="${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '⌃' : '⌄'}</button>
+        <button class="activity-toggle" type="button" data-toggle-activity="${escapeHtml(target.id)}" aria-expanded="${expanded}" aria-controls="act-${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '⌃' : '⌄'}</button>
       </div>
-      <div class="activity-body" ${expanded ? '' : 'hidden'} data-target-id="${escapeHtml(target.id)}"><div>${escapeHtml(contentText(target.output))}</div></div>
+      <div class="activity-body" id="act-${escapeHtml(target.id)}" ${expanded ? '' : 'hidden'} data-target-id="${escapeHtml(target.id)}"><div>${escapeHtml(contentText(target.output))}</div></div>
     </section>
   `
 }
@@ -951,9 +965,9 @@ function renderChatToolActivity(target: TraceTarget): string {
     <section class="chat-activity tool-use ${failed ? 'failed' : ''} ${selectedTargetClass(target.id)}">
       <div class="activity-row">
         <button class="activity-select" type="button" data-target-id="${escapeHtml(target.id)}"><span>${escapeHtml(failed ? t('chat.toolFailed') : t('chat.toolUse'))}</span><strong>${escapeHtml(target.title)}${preview.length > 0 ? `<span class="activity-preview"> · ${escapeHtml(preview)}</span>` : ''}</strong></button>
-        <button class="activity-toggle" type="button" data-toggle-activity="${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '⌃' : '⌄'}</button>
+        <button class="activity-toggle" type="button" data-toggle-activity="${escapeHtml(target.id)}" aria-expanded="${expanded}" aria-controls="act-${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '⌃' : '⌄'}</button>
       </div>
-      <div class="activity-body" ${expanded ? '' : 'hidden'} data-target-id="${escapeHtml(target.id)}">${inputHtml}${outputHtml}${spawnedHtml}</div>
+      <div class="activity-body" id="act-${escapeHtml(target.id)}" ${expanded ? '' : 'hidden'} data-target-id="${escapeHtml(target.id)}">${inputHtml}${outputHtml}${spawnedHtml}</div>
     </section>
   `
 }
@@ -1055,7 +1069,7 @@ function renderGraphTrajectoryRow(targetId: string): string {
         <span class="token-cell">${escapeHtml(usage.output)}</span>
         <span class="token-cell">${escapeHtml(usage.think)}</span>
         <span class="token-cell offset">+${escapeHtml(formatMs(target.startTime - state.graph.startTime))}</span>
-        <button class="chevron traj-expand" type="button" data-toggle-traj="${escapeHtml(target.id)}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '▾' : '▸'}</button>
+        <button class="chevron traj-expand" type="button" data-toggle-traj="${escapeHtml(target.id)}" aria-expanded="${expanded}" aria-label="${escapeHtml(t(expanded ? 'trace.collapseRow' : 'trace.expandRow'))}">${expanded ? '▾' : '▸'}</button>
       </div>
       ${expanded ? renderGraphTrajectoryBody(target) : ''}
     </article>
@@ -1463,10 +1477,19 @@ async function submitFeedback(form: HTMLFormElement, sessionId: string, targetId
       state.trace.feedback = [...(state.trace.feedback ?? []), record]
     }
     state.feedbackDrafts.delete(feedbackDraftKey(sessionId, targetId))
+    form.querySelector('.form-error')?.remove()
     toast(t('feedback.saved'))
     return true
   } catch (error) {
-    toast(`${t('feedback.failed')}: ${String(error)}`)
+    // The error belongs next to the form, not only in a transient toast.
+    let errorLine = form.querySelector<HTMLElement>('.form-error')
+    if (errorLine === null) {
+      errorLine = document.createElement('p')
+      errorLine.className = 'form-error'
+      errorLine.setAttribute('role', 'alert')
+      form.appendChild(errorLine)
+    }
+    errorLine.textContent = `${t('feedback.failed')}: ${String(error)}`
     return false
   }
 }
@@ -1490,7 +1513,6 @@ function wireStaticEvents(): void {
   })
 
   el.composerInput.addEventListener('input', () => {
-    autosizeComposer()
     updateComposerState()
   })
   el.composerInput.addEventListener('keydown', (event) => {
diff --git a/packages/ui/desktop/src/i18n.ts b/packages/ui/desktop/src/i18n.ts
index fb46ffb97c..1dd2f24af9 100644
--- a/packages/ui/desktop/src/i18n.ts
+++ b/packages/ui/desktop/src/i18n.ts
@@ -75,6 +75,8 @@ const messages = {
     'toast.copied': '已复制',
     'feedback.saved': '标注已保存',
     'feedback.failed': '标注保存失败',
+    'app.resizeSidebar': '调整侧栏宽度',
+    'app.resizeInspector': '调整检查器宽度',
     'kind.user': '用户',
     'kind.reasoning': '思考',
     'kind.assistant': '回复',
@@ -346,6 +348,8 @@ const messages = {
     'toast.copied': 'Copied',
     'feedback.saved': 'Feedback saved',
     'feedback.failed': 'Failed to save feedback',
+    'app.resizeSidebar': 'Resize sidebar',
+    'app.resizeInspector': 'Resize inspector',
     'kind.user': 'User',
     'kind.reasoning': 'Thinking',
     'kind.assistant': 'Response',
diff --git a/packages/ui/desktop/src/styles.css b/packages/ui/desktop/src/styles.css
index 50e882e12d..c80f07daf7 100644
--- a/packages/ui/desktop/src/styles.css
+++ b/packages/ui/desktop/src/styles.css
@@ -15,8 +15,8 @@
   --fg: #20201f;
   --ink: var(--fg);
   --ink-soft: color-mix(in oklab, var(--fg) 72%, transparent);
-  --muted: color-mix(in oklab, var(--fg) 52%, transparent);
-  --faint: color-mix(in oklab, var(--fg) 36%, transparent);
+  --muted: color-mix(in oklab, var(--fg) 58%, transparent);
+  --faint: color-mix(in oklab, var(--fg) 44%, transparent);
 
   /* Borders derive from the same foreground. */
   --line: color-mix(in oklab, var(--fg) 11%, transparent);
@@ -49,11 +49,18 @@
   --control-xl: 36px;
   --row-table: 30px;
   --row-list: 42px;
+  --radius-xs: 6px;
   --radius-sm: 8px;
   --radius-md: 10px;
   --radius-lg: 12px;
   --radius-xl: 16px;
 
+  /* Z-index scale: sticky headers, floating controls, overlays, toast. */
+  --z-sticky: 2;
+  --z-floating: 3;
+  --z-overlay: 10;
+  --z-toast: 40;
+
   /* Motion: one curve, three duration tiers. */
   --ease-out: cubic-bezier(0.23, 1, 0.32, 1);
   --duration-fast: 80ms;
@@ -567,7 +574,7 @@ kbd {
   margin: 0 auto 18px;
   padding: 10px;
   border: 1px solid var(--line);
-  border-radius: 15px;
+  border-radius: var(--radius-xl);
   background: rgba(255, 255, 255, 0.82);
 }
 
@@ -699,7 +706,7 @@ kbd {
   max-width: min(680px, 76%);
   padding: 10px 13px;
   border: 1px solid var(--line);
-  border-radius: 17px;
+  border-radius: var(--radius-xl);
   background: #f2f2f0;
   color: var(--ink);
 }
@@ -785,7 +792,7 @@ kbd {
   height: var(--control-md);
   place-items: center;
   padding: 0;
-  border-radius: 6px;
+  border-radius: var(--radius-xs);
   color: var(--muted);
 }
 
@@ -984,7 +991,7 @@ pre {
   align-items: center;
   gap: 8px;
   width: 100%;
-  min-height: 38px;
+  min-height: var(--row-table);
   padding: 6px 8px;
   border-radius: var(--radius-md);
   text-align: left;
@@ -1243,7 +1250,7 @@ pre {
 .traj-group-head {
   position: sticky;
   top: 0;
-  z-index: 2;
+  z-index: var(--z-sticky);
   display: flex;
   align-items: baseline;
   gap: 10px;
@@ -1473,7 +1480,7 @@ pre {
 }
 
 .traj-inspect {
-  height: 24px;
+  height: var(--control-sm);
   padding: 0 7px;
   border: 1px solid var(--line);
   border-radius: var(--radius-sm);
@@ -1495,7 +1502,7 @@ pre {
   overflow: auto;
   padding: 12px 16px 16px;
   border: 1px solid var(--line);
-  border-radius: 14px;
+  border-radius: var(--radius-lg);
   background: #fff;
 }
 
@@ -1510,7 +1517,7 @@ pre {
 .wf-head-row {
   position: sticky;
   top: 0;
-  z-index: 1;
+  z-index: var(--z-sticky);
   margin-bottom: 6px;
   padding-bottom: 6px;
   border-bottom: 1px solid var(--line);
@@ -1547,7 +1554,7 @@ pre {
   width: 22px;
   height: 17px;
   place-items: center;
-  border-radius: 5px;
+  border-radius: var(--radius-xs);
   background: #eef1f6;
   color: #4b5565;
   font-family: "SF Mono", ui-monospace, Menlo, Monaco, Consolas, monospace;
@@ -1594,7 +1601,7 @@ pre {
 .wf-track {
   position: relative;
   height: 22px;
-  border-radius: 5px;
+  border-radius: var(--radius-xs);
   background-image: linear-gradient(90deg, rgba(135, 145, 160, 0.18) 1px, transparent 1px);
   background-repeat: repeat-x;
   background-size: 25% 100%;
@@ -1631,7 +1638,7 @@ pre {
 .module-card,
 .compare-column {
   border: 1px solid var(--line);
-  border-radius: 14px;
+  border-radius: var(--radius-lg);
   background: rgba(255, 255, 255, 0.78);
 }
 
@@ -1686,8 +1693,9 @@ pre {
 }
 
 .composer textarea {
+  field-sizing: content;
   min-height: var(--row-list);
-  max-height: 128px;
+  max-height: 132px;
   resize: none;
   overflow: auto;
   border: 0;
@@ -2270,7 +2278,7 @@ pre {
 .dev-loop-card {
   padding: 14px 16px;
   border: 1px solid var(--line);
-  border-radius: 14px;
+  border-radius: var(--radius-lg);
   background: rgba(255, 255, 255, 0.82);
   box-shadow: 0 1px 1px rgba(0, 0, 0, 0.025);
 }
@@ -2350,7 +2358,7 @@ dd {
     top: 58px;
     right: 0;
     bottom: 0;
-    z-index: 10;
+    z-index: var(--z-overlay);
     width: 360px;
     box-shadow: var(--shadow);
   }
@@ -2399,7 +2407,7 @@ dd {
 .chat-live-jump {
   position: sticky;
   bottom: 12px;
-  z-index: 3;
+  z-index: var(--z-floating);
   display: block;
   width: fit-content;
   margin: 0 auto;
@@ -2754,7 +2762,7 @@ dd {
 .assistant-prose code,
 .assistant-text code {
   padding: 1px 5px;
-  border-radius: 5px;
+  border-radius: var(--radius-xs);
   background: rgba(0, 0, 0, 0.055);
   font-family: "SF Mono", ui-monospace, Menlo, Monaco, Consolas, monospace;
   font-size: 0.88em;
@@ -2826,7 +2834,7 @@ dd {
   position: fixed;
   bottom: 26px;
   left: 50%;
-  z-index: 40;
+  z-index: var(--z-toast);
   padding: 8px 14px;
   border-radius: 999px;
   background: var(--ink);
@@ -2936,3 +2944,35 @@ dd {
 .inspector-open .traj-tree {
   display: none;
 }
+
+/* ── ui-skills pass: numerics, inline form errors ─────────────────────────── */
+
+/* Data columns and metrics read as columns of digits: keep them tabular. */
+.token-cell,
+.wf-dur,
+.g-dur,
+.t-dur,
+.wf-summary strong,
+.session-copy small,
+.run-metrics strong {
+  font-variant-numeric: tabular-nums;
+}
+
+/* Inline form errors live next to the action, not only in a toast. */
+.form-error {
+  margin: 6px 0 0;
+  color: var(--red);
+  font-size: 12px;
+}
+
+/* Headings balance; prose avoids awkward last lines. */
+.empty-thread h2,
+.empty-state h2 {
+  text-wrap: balance;
+}
+
+.assistant-prose p,
+.empty-thread p,
+.empty-state p {
+  text-wrap: pretty;
+}