diff --git a/frontend/src/features/reasoning/ui/AskRunner.vue b/frontend/src/features/reasoning/ui/AskRunner.vue
new file mode 100644
index 0000000..e36b151
--- /dev/null
+++ b/frontend/src/features/reasoning/ui/AskRunner.vue
@@ -0,0 +1,359 @@
+<template>
+  <div class="ask-runner" data-e2e="ask-runner">
+    <!-- Form -->
+    <form class="ask-form" @submit.prevent="run">
+      <label class="ask-label">{{ t('ask.questionLabel') }}</label>
+      <textarea
+        v-model="query"
+        class="ask-textarea"
+        :placeholder="t('ask.questionPlaceholder')"
+        :disabled="running"
+        rows="3"
+      />
+      <details class="ask-model-details">
+        <summary class="ask-model-summary">{{ t('ask.modelConfig') }}</summary>
+        <input
+          v-model="modelId"
+          class="ask-model-input"
+          :placeholder="t('ask.modelPlaceholder')"
+          :disabled="running"
+        />
+        <p class="ask-model-hint">{{ t('ask.modelHint') }}</p>
+      </details>
+      <button class="ask-submit" type="submit" :disabled="!query.trim() || running">
+        <span v-if="running" class="ask-spinner" />
+        <span>{{ running ? t('ask.running') : t('ask.run') }}</span>
+      </button>
+    </form>
+
+    <!-- Error -->
+    <div v-if="error" class="ask-error" data-e2e="ask-error">{{ error }}</div>
+
+    <!-- Result -->
+    <div v-if="result" class="ask-result" data-e2e="ask-result">
+      <!-- Answer -->
+      <div class="ask-answer">
+        <div class="ask-answer-header">
+          <span class="ask-answer-label">{{ t('ask.answerLabel') }}</span>
+          <span class="ask-converged" :class="{ yes: result.converged, no: !result.converged }">
+            {{ result.converged ? t('reasoning.converged') : t('reasoning.notConverged') }}
+          </span>
+        </div>
+        <!-- eslint-disable-next-line vue/no-v-html -- sanitized by DOMPurify -->
+        <div class="ask-answer-body" v-html="renderedAnswer" />
+      </div>
+
+      <!-- Iterations -->
+      <div class="ask-iterations">
+        <h4 class="ask-section-title">{{ t('reasoning.iterationsTitle') }}</h4>
+        <IterationCard
+          v-for="it in resolvedIterations"
+          :key="it.iteration"
+          :iteration="it"
+          :active="activeIteration === it.iteration"
+          @focus="onIterationFocus"
+        />
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed } from 'vue'
+import DOMPurify from 'dompurify'
+import { marked } from 'marked'
+import { runReasoning } from '../api'
+import type { ReasoningResult, ReasoningIteration, ResolvedIteration } from '../types'
+import IterationCard from './IterationCard.vue'
+import { useI18n } from '../../../shared/i18n'
+
+const props = defineProps<{ docId: string }>()
+
+const emit = defineEmits<{ sectionFocus: [sectionRef: string] }>()
+
+const { t } = useI18n()
+
+const query = ref('')
+const modelId = ref('')
+const running = ref(false)
+const error = ref<string | null>(null)
+const result = ref<ReasoningResult | null>(null)
+const activeIteration = ref<number | null>(null)
+
+const renderedAnswer = computed(() => {
+  const raw = result.value?.answer ?? ''
+  if (!raw.trim()) return ''
+  return DOMPurify.sanitize(marked.parse(raw, { async: false }) as string)
+})
+
+function toResolved(it: ReasoningIteration): ResolvedIteration {
+  return {
+    iteration: it.iteration,
+    sectionRef: it.section_ref,
+    nodeId: it.section_ref,
+    present: true,
+    reason: it.reason,
+    canAnswer: it.can_answer,
+    response: it.response,
+    sectionTextLength: it.section_text_length,
+  }
+}
+
+const resolvedIterations = computed<ResolvedIteration[]>(() =>
+  (result.value?.iterations ?? []).map(toResolved),
+)
+
+async function run(): Promise<void> {
+  if (!query.value.trim()) return
+  running.value = true
+  error.value = null
+  result.value = null
+  activeIteration.value = null
+  try {
+    result.value = await runReasoning(props.docId, query.value, modelId.value || undefined)
+  } catch (e) {
+    error.value = (e as Error).message || t('reasoning.runErrUnknown')
+  } finally {
+    running.value = false
+  }
+}
+
+function onIterationFocus(n: number): void {
+  activeIteration.value = n
+  const it = resolvedIterations.value.find((r) => r.iteration === n)
+  if (it?.sectionRef) emit('sectionFocus', it.sectionRef)
+}
+</script>
+
+<style scoped>
+.ask-runner {
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+  padding: 16px;
+  overflow-y: auto;
+  height: 100%;
+}
+
+.ask-form {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.ask-label {
+  font-size: 11px;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  color: var(--text-muted);
+}
+
+.ask-textarea {
+  font-family: inherit;
+  font-size: 13px;
+  color: var(--text);
+  background: var(--bg-elevated);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  padding: 10px 12px;
+  resize: vertical;
+  transition: border-color var(--transition);
+}
+
+.ask-textarea:focus {
+  outline: none;
+  border-color: var(--accent);
+}
+
+.ask-textarea:disabled {
+  opacity: 0.6;
+}
+
+.ask-model-details {
+  font-size: 12px;
+}
+
+.ask-model-summary {
+  cursor: pointer;
+  color: var(--text-secondary);
+  padding: 2px 0;
+  user-select: none;
+}
+
+.ask-model-input {
+  width: 100%;
+  margin-top: 6px;
+  font-family: 'IBM Plex Mono', monospace;
+  font-size: 12px;
+  color: var(--text);
+  background: var(--bg-elevated);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  padding: 6px 10px;
+  box-sizing: border-box;
+}
+
+.ask-model-input:focus {
+  outline: none;
+  border-color: var(--accent);
+}
+
+.ask-model-hint {
+  margin: 4px 0 0;
+  font-size: 11px;
+  color: var(--text-muted);
+}
+
+.ask-submit {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+  padding: 8px 16px;
+  font-size: 13px;
+  font-weight: 500;
+  background: var(--accent);
+  color: #fff;
+  border: none;
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  transition: opacity var(--transition);
+}
+
+.ask-submit:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.ask-submit:hover:not(:disabled) {
+  opacity: 0.9;
+}
+
+.ask-spinner {
+  width: 14px;
+  height: 14px;
+  border: 2px solid rgba(255, 255, 255, 0.4);
+  border-top-color: #fff;
+  border-radius: 50%;
+  animation: spin 0.6s linear infinite;
+  flex-shrink: 0;
+}
+
+@keyframes spin {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+.ask-error {
+  padding: 10px 12px;
+  background: rgba(239, 68, 68, 0.1);
+  border: 1px solid var(--error);
+  border-radius: var(--radius-sm);
+  color: var(--error);
+  font-size: 12px;
+}
+
+.ask-result {
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+}
+
+.ask-answer {
+  background: var(--bg);
+  border: 1px solid #ea580c;
+  border-radius: var(--radius);
+  padding: 14px 16px;
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  box-shadow: 0 1px 3px rgba(234, 88, 12, 0.08);
+}
+
+.ask-answer-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  gap: 8px;
+}
+
+.ask-answer-label {
+  font-size: 10px;
+  font-weight: 700;
+  letter-spacing: 0.8px;
+  text-transform: uppercase;
+  color: #ea580c;
+}
+
+.ask-converged {
+  font-size: 10px;
+  font-weight: 600;
+  padding: 2px 8px;
+  border-radius: 10px;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.ask-converged.yes {
+  background: rgba(22, 163, 74, 0.15);
+  color: #15803d;
+}
+
+.ask-converged.no {
+  background: rgba(234, 179, 8, 0.15);
+  color: #a16207;
+}
+
+.ask-answer-body {
+  font-size: 13.5px;
+  line-height: 1.6;
+  color: var(--text);
+}
+
+.ask-answer-body :deep(p) {
+  margin: 0 0 8px;
+}
+
+.ask-answer-body :deep(p:last-child) {
+  margin-bottom: 0;
+}
+
+.ask-answer-body :deep(ol),
+.ask-answer-body :deep(ul) {
+  margin: 4px 0 8px;
+  padding-left: 22px;
+}
+
+.ask-answer-body :deep(li) {
+  margin: 2px 0;
+}
+
+.ask-answer-body :deep(strong) {
+  font-weight: 600;
+}
+
+.ask-answer-body :deep(code) {
+  font-family: 'IBM Plex Mono', monospace;
+  font-size: 12px;
+  background: var(--border-light);
+  padding: 1px 5px;
+  border-radius: 3px;
+}
+
+.ask-section-title {
+  margin: 0 0 8px;
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  color: var(--text-muted);
+  font-weight: 600;
+}
+
+.ask-iterations {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+</style>
diff --git a/frontend/src/pages/DocAskTab.vue b/frontend/src/pages/DocAskTab.vue
index 3247339..ac2140c 100644
--- a/frontend/src/pages/DocAskTab.vue
+++ b/frontend/src/pages/DocAskTab.vue
@@ -1,44 +1,191 @@
 <template>
   <div class="ask-tab" data-e2e="ask-tab">
-    <div class="coming-soon">
-      <p class="coming-soon-title">{{ t('workspace.askComingSoon') }}</p>
-      <p class="coming-soon-sub">{{ t('workspace.askComingSoonHint') }}</p>
+    <!-- Loading analysis -->
+    <div v-if="loading" class="ask-state">
+      <span class="spinner" />
     </div>
+
+    <!-- Error -->
+    <div v-else-if="error" class="ask-state ask-state--error">
+      <p>{{ error }}</p>
+      <button class="retry-btn" @click="loadAnalysis">{{ t('inspect.retry') }}</button>
+    </div>
+
+    <!-- No analysis -->
+    <div v-else-if="pages.length === 0" class="ask-state">
+      <p class="ask-empty-title">{{ t('ask.noAnalysis') }}</p>
+      <p class="ask-empty-sub">{{ t('ask.noAnalysisSub') }}</p>
+      <RouterLink :to="{ name: ROUTES.STUDIO }" class="ask-cta">
+        {{ t('inspect.goToStudio') }}
+      </RouterLink>
+    </div>
+
+    <!-- Split layout: document left + ask panel right -->
+    <template v-else>
+      <div class="ask-doc-pane">
+        <StructureViewer
+          ref="structureViewerRef"
+          :pages="pages"
+          :document-id="docId"
+          :visited-by-self-ref="visitedBySelfRef"
+          :focused-self-ref="focusedSelfRef"
+          selectable
+        />
+      </div>
+      <div class="ask-panel-pane">
+        <AskRunner :doc-id="docId" @section-focus="onSectionFocus" />
+      </div>
+    </template>
   </div>
 </template>
 
 <script setup lang="ts">
+import { ref, computed, onMounted } from 'vue'
+import { RouterLink } from 'vue-router'
+import type { Analysis, Page } from '../shared/types'
+import { fetchDocumentAnalyses } from '../features/analysis/api'
+import StructureViewer from '../features/analysis/ui/StructureViewer.vue'
+import AskRunner from '../features/reasoning/ui/AskRunner.vue'
 import { useI18n } from '../shared/i18n'
+import { ROUTES } from '../shared/routing/names'
 
-defineProps<{ docId: string }>()
+const props = defineProps<{ docId: string }>()
 
 const { t } = useI18n()
+
+const loading = ref(false)
+const error = ref<string | null>(null)
+const analysis = ref<Analysis | null>(null)
+const focusedSelfRef = ref<string | null>(null)
+const structureViewerRef = ref<InstanceType<typeof StructureViewer> | null>(null)
+
+const pages = computed<Page[]>(() => {
+  if (!analysis.value?.pagesJson) return []
+  try {
+    return JSON.parse(analysis.value.pagesJson) as Page[]
+  } catch {
+    return []
+  }
+})
+
+const visitedBySelfRef = computed<Map<string, number>>(() => new Map())
+
+async function loadAnalysis(): Promise<void> {
+  loading.value = true
+  error.value = null
+  try {
+    const analyses = await fetchDocumentAnalyses(props.docId)
+    analysis.value = analyses.find((a) => a.status === 'COMPLETED') ?? null
+  } catch (e) {
+    error.value = (e as Error).message || 'Failed to load analysis'
+  } finally {
+    loading.value = false
+  }
+}
+
+function onSectionFocus(sectionRef: string): void {
+  if (focusedSelfRef.value === sectionRef) {
+    structureViewerRef.value?.scrollToFocused(sectionRef)
+  } else {
+    focusedSelfRef.value = sectionRef
+  }
+}
+
+onMounted(loadAnalysis)
 </script>
 
 <style scoped>
 .ask-tab {
   display: flex;
-  align-items: center;
-  justify-content: center;
   height: 100%;
-  color: var(--text-muted);
+  overflow: hidden;
 }
 
-.coming-soon {
-  text-align: center;
+.ask-state {
   display: flex;
   flex-direction: column;
-  gap: 8px;
+  align-items: center;
+  justify-content: center;
+  width: 100%;
+  gap: 12px;
+  color: var(--text-muted);
+  font-size: 13px;
 }
 
-.coming-soon-title {
+.ask-state--error {
+  color: var(--error);
+}
+
+.ask-empty-title {
   font-size: 14px;
   font-weight: 500;
   color: var(--text-secondary);
+  margin: 0;
 }
 
-.coming-soon-sub {
+.ask-empty-sub {
   font-size: 12px;
   color: var(--text-muted);
+  margin: 0;
+}
+
+.ask-cta {
+  font-size: 13px;
+  color: var(--accent);
+  text-decoration: none;
+  border: 1px solid var(--accent);
+  padding: 6px 14px;
+  border-radius: var(--radius-sm);
+  transition: all var(--transition);
+}
+
+.ask-cta:hover {
+  background: var(--accent-muted);
+}
+
+.retry-btn {
+  font-size: 13px;
+  color: var(--text-secondary);
+  background: none;
+  border: 1px solid var(--border);
+  padding: 6px 14px;
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  transition: all var(--transition);
+}
+
+.retry-btn:hover {
+  border-color: var(--text-secondary);
+  color: var(--text);
+}
+
+.ask-doc-pane {
+  flex: 1;
+  min-width: 0;
+  overflow-y: auto;
+  border-right: 1px solid var(--border);
+  padding: 16px 20px;
+}
+
+.ask-panel-pane {
+  width: 360px;
+  flex-shrink: 0;
+  overflow-y: auto;
+  background: var(--bg-surface);
+}
+
+.spinner {
+  width: 28px;
+  height: 28px;
+  border: 2px solid var(--border-light);
+  border-top-color: var(--accent);
+  border-radius: 50%;
+  animation: spin 0.6s linear infinite;
+}
+
+@keyframes spin {
+  to {
+    transform: rotate(360deg);
+  }
 }
 </style>
diff --git a/frontend/src/shared/i18n.ts b/frontend/src/shared/i18n.ts
index fec9e06..c7ba395 100644
--- a/frontend/src/shared/i18n.ts
+++ b/frontend/src/shared/i18n.ts
@@ -372,6 +372,18 @@ const messages: Messages = {
     'inspect.noElements':
       'Aucun \u00e9l\u00e9ment \u2014 lancez une analyse pour g\u00e9n\u00e9rer la structure.',
 
+    // Ask tab (#242)
+    'ask.questionLabel': 'Question',
+    'ask.questionPlaceholder': 'Ex\u00a0: Quelles sont les obligations du fournisseur\u00a0?',
+    'ask.modelConfig': 'Mod\u00e8le (optionnel)',
+    'ask.modelPlaceholder': 'gpt-oss:20b',
+    'ask.modelHint': 'Mod\u00e8le Ollama. Laisser vide pour le d\u00e9faut serveur.',
+    'ask.run': 'Lancer',
+    'ask.running': 'Reasoning en cours\u2026',
+    'ask.answerLabel': 'R\u00e9ponse',
+    'ask.noAnalysis': 'Aucune analyse disponible',
+    'ask.noAnalysisSub': 'Analysez ce document dans le Studio avant de poser une question.',
+
     // Doc workspace (#216, #218)
     'workspace.tabs.ask': 'Ask',
     'workspace.tabs.inspect': 'Inspect',
@@ -779,6 +791,18 @@ const messages: Messages = {
     'inspect.retry': 'Retry',
     'inspect.noElements': 'No elements — run an analysis to generate structure.',
 
+    // Ask tab (#242)
+    'ask.questionLabel': 'Question',
+    'ask.questionPlaceholder': 'e.g. What are the supplier obligations?',
+    'ask.modelConfig': 'Model (optional)',
+    'ask.modelPlaceholder': 'gpt-oss:20b',
+    'ask.modelHint': 'Ollama model name. Leave empty to use the server default.',
+    'ask.run': 'Run',
+    'ask.running': 'Reasoning…',
+    'ask.answerLabel': 'Answer',
+    'ask.noAnalysis': 'No analysis available',
+    'ask.noAnalysisSub': 'Analyze this document in Studio before asking a question.',
+
     // Doc workspace (#216, #218)
     'workspace.tabs.ask': 'Ask',
     'workspace.tabs.inspect': 'Inspect',