diff --git a/document-parser/api/schemas.py b/document-parser/api/schemas.py
index 7d3d329..2cc9252 100644
--- a/document-parser/api/schemas.py
+++ b/document-parser/api/schemas.py
@@ -46,11 +46,14 @@ class HealthResponse(_CamelModel):
     # available: REASONING_ENABLED=true AND deps importable. Doesn't imply
     # Ollama itself is reachable — that's checked per-call.
     reasoning_available: bool = False
-    # 0.6.0 — Doc workspace mode flags (#210). Default true so existing
-    # frontends without the new keys (legacy backend image rolling forward)
-    # see the same behaviour they had.
+    # 0.6.1 — Surface flags (#257). Master flags select which surface(s)
+    # the frontend exposes. Defaults match the production target (RAG only).
+    studio_mode_enabled: bool = False
+    rag_pipeline_enabled: bool = True
+    # 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257). Default true
+    # so frontends pointed at an older backend keep every mode visible.
     inspect_mode_enabled: bool = True
-    chunks_mode_enabled: bool = True
+    linked_mode_enabled: bool = True
     ask_mode_enabled: bool = True
 
 
diff --git a/document-parser/infra/settings.py b/document-parser/infra/settings.py
index 6186168..ced0a07 100644
--- a/document-parser/infra/settings.py
+++ b/document-parser/infra/settings.py
@@ -55,11 +55,17 @@ class Settings:
     cors_origins: list[str] = field(
         default_factory=lambda: ["http://localhost:3000", "http://localhost:5173"]
     )
-    # 0.6.0 — Doc workspace mode flags (#210). All on by default to preserve
-    # existing behaviour; operators flip a flag off to hide a mode tab + redirect
-    # deep links. Per-tenant gating is out of scope for 0.6.0.
+    # 0.6.1 — Surface flags (#257). Two master flags select which UI surface
+    # is exposed: STUDIO_MODE_ENABLED (legacy OCR-debug) and
+    # RAG_PIPELINE_ENABLED (new doc-centric ingestion + visualization).
+    # At least one must be enabled. Sub-flags below gate individual modes
+    # inside the RAG pipeline surface.
+    studio_mode_enabled: bool = False
+    rag_pipeline_enabled: bool = True
+    # 0.6.0 — Doc workspace mode flags (#210, renamed in #257).
+    # Sub-flags effective only when rag_pipeline_enabled is true.
     inspect_mode_enabled: bool = True
-    chunks_mode_enabled: bool = True
+    linked_mode_enabled: bool = True
     ask_mode_enabled: bool = True
 
     def __post_init__(self) -> None:
@@ -96,6 +102,8 @@ class Settings:
             )
         if self.embedding_dimension < 1:
             errors.append(f"embedding_dimension must be >= 1 (got {self.embedding_dimension})")
+        if not (self.studio_mode_enabled or self.rag_pipeline_enabled):
+            errors.append("at least one of STUDIO_MODE_ENABLED / RAG_PIPELINE_ENABLED must be true")
         if self.default_table_mode not in ("accurate", "fast"):
             errors.append(
                 f"default_table_mode must be 'accurate' or 'fast' (got '{self.default_table_mode}')"
@@ -159,10 +167,15 @@ class Settings:
             max_paste_image_size_mb=int(os.environ.get("MAX_PASTE_IMAGE_SIZE_MB", "10")),
             paste_allowed_image_types=[t.strip() for t in paste_types_raw.split(",") if t.strip()],
             cors_origins=[o.strip() for o in cors_raw.split(",")],
-            # 0.6.0 — Doc workspace mode flags (#210). Defaults: enabled.
+            # 0.6.1 — Surface flags (#257).
+            studio_mode_enabled=os.environ.get("STUDIO_MODE_ENABLED", "false").lower()
+            in ("1", "true", "yes", "on"),
+            rag_pipeline_enabled=os.environ.get("RAG_PIPELINE_ENABLED", "true").lower()
+            in ("1", "true", "yes", "on"),
+            # 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257).
             inspect_mode_enabled=os.environ.get("INSPECT_MODE_ENABLED", "true").lower()
             in ("1", "true", "yes", "on"),
-            chunks_mode_enabled=os.environ.get("CHUNKS_MODE_ENABLED", "true").lower()
+            linked_mode_enabled=os.environ.get("LINKED_MODE_ENABLED", "true").lower()
             in ("1", "true", "yes", "on"),
             ask_mode_enabled=os.environ.get("ASK_MODE_ENABLED", "true").lower()
             in ("1", "true", "yes", "on"),
diff --git a/document-parser/main.py b/document-parser/main.py
index ce00bdd..0008dea 100644
--- a/document-parser/main.py
+++ b/document-parser/main.py
@@ -343,8 +343,11 @@ async def health() -> HealthResponse:
         # actual Ollama reachability is checked lazily at call-time to avoid
         # blocking health checks on the LLM host.
         reasoning_available=runner is not None and runner.is_available,
-        # 0.6.0 — Doc workspace mode flags (#210).
+        # 0.6.1 — Surface flags (#257).
+        studio_mode_enabled=settings.studio_mode_enabled,
+        rag_pipeline_enabled=settings.rag_pipeline_enabled,
+        # 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257).
         inspect_mode_enabled=settings.inspect_mode_enabled,
-        chunks_mode_enabled=settings.chunks_mode_enabled,
+        linked_mode_enabled=settings.linked_mode_enabled,
         ask_mode_enabled=settings.ask_mode_enabled,
     )
diff --git a/document-parser/tests/test_api_endpoints.py b/document-parser/tests/test_api_endpoints.py
index 1b43cf4..46851ed 100644
--- a/document-parser/tests/test_api_endpoints.py
+++ b/document-parser/tests/test_api_endpoints.py
@@ -68,16 +68,26 @@ class TestHealthEndpoint:
         data = resp.json()
         assert data["ingestionAvailable"] is True
 
+    def test_health_exposes_surface_flags(self, client):
+        """0.6.1 (#257): /api/health surfaces studio + rag_pipeline master flags."""
+        resp = client.get("/api/health")
+        data = resp.json()
+        assert "studioModeEnabled" in data
+        assert "ragPipelineEnabled" in data
+        # Defaults: studio off, rag pipeline on (production target).
+        assert data["studioModeEnabled"] is False
+        assert data["ragPipelineEnabled"] is True
+
     def test_health_exposes_doc_mode_flags(self, client):
-        """0.6.0 (#210): /api/health surfaces inspect/chunks/ask mode flags."""
+        """0.6.0 (#210, renamed in #257): /api/health surfaces inspect/linked/ask sub-flags."""
         resp = client.get("/api/health")
         data = resp.json()
         assert "inspectModeEnabled" in data
-        assert "chunksModeEnabled" in data
+        assert "linkedModeEnabled" in data
         assert "askModeEnabled" in data
-        # Defaults preserve current behaviour (all enabled).
+        # Sub-flag defaults preserve current behaviour (all enabled).
         assert data["inspectModeEnabled"] is True
-        assert data["chunksModeEnabled"] is True
+        assert data["linkedModeEnabled"] is True
         assert data["askModeEnabled"] is True
 
 
diff --git a/frontend/src/app/router/index.ts b/frontend/src/app/router/index.ts
index d63c0fe..16ea104 100644
--- a/frontend/src/app/router/index.ts
+++ b/frontend/src/app/router/index.ts
@@ -4,6 +4,7 @@ import { useFeatureFlagStore } from '../../features/feature-flags/store'
 import { isDocMode } from '../../shared/routing/modes'
 import { ROUTES } from '../../shared/routing/names'
 import { resolveMode } from '../../shared/routing/resolveMode'
+import { resolveSurface } from '../../shared/routing/resolveSurface'
 import { routes } from './routes'
 
 export { routes }
@@ -14,20 +15,29 @@ export const router = createRouter({
 })
 
 /**
- * Doc workspace mode guard (#210).
+ * Surface gating (#257) + mode gating (#210).
  *
- * - `/docs/:id?mode=<disabled>` → redirect with the same id but the
- *   first enabled mode (ask > chunks > inspect priority).
- * - All three modes off → redirect to `/docs?reason=no-mode-enabled`.
- * - Any other route is left untouched.
+ * Surface: two master flags select which UI surface is exposed. When a
+ * route from a disabled surface is requested, redirect to the other
+ * surface's landing page — or to `/` if both are off (defensive net;
+ * backend refuses to start in that state).
  *
- * Pure resolution lives in `resolveMode`; the guard is just the
- * router-level wiring.
+ * Mode: inside the doc workspace, the requested mode falls back to the
+ * first enabled mode when the deep-linked one is off.
  */
 router.beforeEach((to) => {
+  const flagStore = useFeatureFlagStore()
+  const name = String(to.name ?? '')
+
+  const surfaceRedirect = resolveSurface(name, {
+    studio: flagStore.studioModeEnabled,
+    rag: flagStore.ragPipelineEnabled,
+  })
+  if (surfaceRedirect !== null) return { name: surfaceRedirect }
+
   if (to.name !== ROUTES.DOC_WORKSPACE) return true
 
-  const flags = useFeatureFlagStore().modeFlags()
+  const flags = flagStore.modeFlags()
   const requestedRaw = Array.isArray(to.query.mode) ? to.query.mode[0] : to.query.mode
   const requested = isDocMode(requestedRaw) ? requestedRaw : undefined
   const resolved = resolveMode(requested, flags)
diff --git a/frontend/src/features/feature-flags/store.test.ts b/frontend/src/features/feature-flags/store.test.ts
index 33193cc..f2bee9f 100644
--- a/frontend/src/features/feature-flags/store.test.ts
+++ b/frontend/src/features/feature-flags/store.test.ts
@@ -156,19 +156,58 @@ describe('useFeatureFlagStore', () => {
     expect(store.isEnabled('disclaimer')).toBe(false)
   })
 
-  // 0.6.0 — Doc workspace mode flags (#210).
-  it('exposes inspectMode / chunksMode / askMode flags from /api/health', async () => {
+  // 0.6.1 — Surface master flags (#257).
+  it('exposes studioMode / ragPipeline master flags from /api/health', async () => {
     mockApiFetch.mockResolvedValue({
       status: 'ok',
       engine: 'local',
-      inspectModeEnabled: false,
-      chunksModeEnabled: true,
+      studioModeEnabled: true,
+      ragPipelineEnabled: false,
+    })
+    const store = useFeatureFlagStore()
+    await store.load()
+    expect(store.isEnabled('studioMode')).toBe(true)
+    expect(store.isEnabled('ragPipeline')).toBe(false)
+  })
+
+  it('defaults studio off, rag pipeline on when /api/health omits the fields', async () => {
+    mockApiFetch.mockResolvedValue({ status: 'ok', engine: 'local' })
+    const store = useFeatureFlagStore()
+    await store.load()
+    expect(store.isEnabled('studioMode')).toBe(false)
+    expect(store.isEnabled('ragPipeline')).toBe(true)
+  })
+
+  it('sub-flags require ragPipeline enabled', async () => {
+    mockApiFetch.mockResolvedValue({
+      status: 'ok',
+      engine: 'local',
+      ragPipelineEnabled: false,
+      inspectModeEnabled: true,
+      linkedModeEnabled: true,
       askModeEnabled: true,
     })
     const store = useFeatureFlagStore()
     await store.load()
     expect(store.isEnabled('inspectMode')).toBe(false)
-    expect(store.isEnabled('chunksMode')).toBe(true)
+    expect(store.isEnabled('linkedMode')).toBe(false)
+    expect(store.isEnabled('askMode')).toBe(false)
+  })
+
+  // 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257).
+  it('exposes inspectMode / linkedMode / askMode flags from /api/health', async () => {
+    mockApiFetch.mockResolvedValue({
+      status: 'ok',
+      engine: 'local',
+      ragPipelineEnabled: true,
+      inspectModeEnabled: false,
+      linkedModeEnabled: true,
+      askModeEnabled: true,
+    })
+    const store = useFeatureFlagStore()
+    await store.load()
+    expect(store.isEnabled('inspectMode')).toBe(false)
+    expect(store.isEnabled('linkedMode')).toBe(true)
     expect(store.isEnabled('askMode')).toBe(true)
   })
 
@@ -177,7 +216,7 @@ describe('useFeatureFlagStore', () => {
     const store = useFeatureFlagStore()
     await store.load()
     expect(store.isEnabled('inspectMode')).toBe(true)
-    expect(store.isEnabled('chunksMode')).toBe(true)
+    expect(store.isEnabled('linkedMode')).toBe(true)
     expect(store.isEnabled('askMode')).toBe(true)
   })
 
@@ -186,7 +225,7 @@ describe('useFeatureFlagStore', () => {
       status: 'ok',
       engine: 'local',
       inspectModeEnabled: true,
-      chunksModeEnabled: false,
+      linkedModeEnabled: false,
       askModeEnabled: true,
     })
     const store = useFeatureFlagStore()
diff --git a/frontend/src/features/feature-flags/store.ts b/frontend/src/features/feature-flags/store.ts
index 653270b..fa83c05 100644
--- a/frontend/src/features/feature-flags/store.ts
+++ b/frontend/src/features/feature-flags/store.ts
@@ -15,10 +15,14 @@ interface HealthResponse {
   maxFileSizeMb?: number
   ingestionAvailable?: boolean
   reasoningAvailable?: boolean
-  // 0.6.0 — Doc workspace mode flags (#210). Optional so an older backend
-  // image without these fields keeps working: missing → fall back to true.
+  // 0.6.1 — Surface master flags (#257). Optional for backward compat:
+  // studio defaults to false (production target), rag pipeline to true.
+  studioModeEnabled?: boolean
+  ragPipelineEnabled?: boolean
+  // 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257). Optional so an
+  // older backend image without these fields keeps working: missing → true.
   inspectModeEnabled?: boolean
-  chunksModeEnabled?: boolean
+  linkedModeEnabled?: boolean
   askModeEnabled?: boolean
 }
 
@@ -27,8 +31,10 @@ export type FeatureFlag =
   | 'disclaimer'
   | 'ingestion'
   | 'reasoning'
+  | 'studioMode'
+  | 'ragPipeline'
   | 'inspectMode'
-  | 'chunksMode'
+  | 'linkedMode'
   | 'askMode'
 
 interface FeatureFlagDef {
@@ -41,8 +47,10 @@ interface FeatureFlagContext {
   deploymentMode: DeploymentMode | null
   ingestionAvailable: boolean
   reasoningAvailable: boolean
+  studioModeEnabled: boolean
+  ragPipelineEnabled: boolean
   inspectModeEnabled: boolean
-  chunksModeEnabled: boolean
+  linkedModeEnabled: boolean
   askModeEnabled: boolean
 }
 
@@ -67,20 +75,31 @@ const featureRegistry: Record<FeatureFlag, FeatureFlagDef> = {
     description: 'Reasoning trace tunnel (docling-agent ReasoningResult viewer)',
     isEnabled: (ctx) => ctx.reasoningAvailable,
   },
-  // 0.6.0 — Doc workspace mode flags (#210). Each one gates a tab in the
-  // doc workspace (#216 / E4) and triggers a router-level redirect when a
-  // disabled mode is requested via deep link. Defaults: enabled.
+  // 0.6.1 — Surface master flags (#257). Select which UI surface(s) are
+  // exposed; at least one must be on (validated server-side too).
+  studioMode: {
+    description: 'Legacy Studio surface (OCR debug, original 0.5.x UI)',
+    isEnabled: (ctx) => ctx.studioModeEnabled,
+  },
+  ragPipeline: {
+    description: 'New doc-centric RAG ingestion + visualization pipeline',
+    isEnabled: (ctx) => ctx.ragPipelineEnabled,
+  },
+  // 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257). Each gates a
+  // mode inside the doc workspace and triggers a router-level redirect
+  // when a disabled mode is requested via deep link. Effective only when
+  // ragPipeline is enabled.
   inspectMode: {
     description: 'Doc workspace Inspect mode (tree + bbox debug view)',
-    isEnabled: (ctx) => ctx.inspectModeEnabled,
+    isEnabled: (ctx) => ctx.ragPipelineEnabled && ctx.inspectModeEnabled,
   },
-  chunksMode: {
-    description: 'Doc workspace Chunks mode (editable chunkset + push to store)',
-    isEnabled: (ctx) => ctx.chunksModeEnabled,
+  linkedMode: {
+    description: 'Doc workspace Linked mode (preview + aligned chunks panel)',
+    isEnabled: (ctx) => ctx.ragPipelineEnabled && ctx.linkedModeEnabled,
   },
   askMode: {
     description: 'Doc workspace Ask mode (agentic reasoning over the doc)',
-    isEnabled: (ctx) => ctx.askModeEnabled,
+    isEnabled: (ctx) => ctx.ragPipelineEnabled && ctx.askModeEnabled,
   },
 }
 
@@ -91,10 +110,14 @@ export const useFeatureFlagStore = defineStore('feature-flags', () => {
   const maxFileSizeMb = ref<number>(0)
   const ingestionAvailable = ref(false)
   const reasoningAvailable = ref(false)
-  // 0.6.0 — Doc workspace mode flags (#210). Default true so a backend
-  // that hasn't shipped the new fields yet behaves like the legacy one.
+  // 0.6.1 — Surface master flags (#257). Defaults match production target:
+  // legacy Studio off, new RAG pipeline on.
+  const studioModeEnabled = ref(false)
+  const ragPipelineEnabled = ref(true)
+  // 0.6.0 — RAG-pipeline sub-flags (#210, renamed in #257). Default true
+  // so a backend without these fields behaves like the legacy one.
   const inspectModeEnabled = ref(true)
-  const chunksModeEnabled = ref(true)
+  const linkedModeEnabled = ref(true)
   const askModeEnabled = ref(true)
   const appVersion = ref<string>(__APP_VERSION__)
   const loaded = ref(false)
@@ -105,8 +128,10 @@ export const useFeatureFlagStore = defineStore('feature-flags', () => {
     deploymentMode: deploymentMode.value,
     ingestionAvailable: ingestionAvailable.value,
     reasoningAvailable: reasoningAvailable.value,
+    studioModeEnabled: studioModeEnabled.value,
+    ragPipelineEnabled: ragPipelineEnabled.value,
     inspectModeEnabled: inspectModeEnabled.value,
-    chunksModeEnabled: chunksModeEnabled.value,
+    linkedModeEnabled: linkedModeEnabled.value,
     askModeEnabled: askModeEnabled.value,
   }))
 
@@ -125,10 +150,14 @@ export const useFeatureFlagStore = defineStore('feature-flags', () => {
       maxFileSizeMb.value = data.maxFileSizeMb ?? 0
       ingestionAvailable.value = data.ingestionAvailable ?? false
       reasoningAvailable.value = data.reasoningAvailable ?? false
-      // 0.6.0 — fall back to true when the field is missing so a frontend
-      // pointed at an older backend keeps every mode visible.
+      // 0.6.1 — surface flags. Backward compat: missing studio → false
+      // (production target), missing rag pipeline → true (legacy behaviour).
+      studioModeEnabled.value = data.studioModeEnabled ?? false
+      ragPipelineEnabled.value = data.ragPipelineEnabled ?? true
+      // Sub-flags: fall back to true so an older backend keeps every mode
+      // visible.
       inspectModeEnabled.value = data.inspectModeEnabled ?? true
-      chunksModeEnabled.value = data.chunksModeEnabled ?? true
+      linkedModeEnabled.value = data.linkedModeEnabled ?? true
       askModeEnabled.value = data.askModeEnabled ?? true
       appMaxFileSizeMb.value = maxFileSizeMb.value
       appMaxPageCount.value = maxPageCount.value
@@ -147,10 +176,12 @@ export const useFeatureFlagStore = defineStore('feature-flags', () => {
    * guard does not need to know about the FeatureFlag union.
    */
   function modeFlags(): { ask: boolean; inspect: boolean; chunks: boolean } {
+    // Mode key 'chunks' is kept until T3 (Linked view) renames the DocMode
+    // union and route segment. The flag is already linkedModeEnabled.
     return {
       ask: askModeEnabled.value,
       inspect: inspectModeEnabled.value,
-      chunks: chunksModeEnabled.value,
+      chunks: linkedModeEnabled.value,
     }
   }
 
@@ -161,8 +192,10 @@ export const useFeatureFlagStore = defineStore('feature-flags', () => {
     maxFileSizeMb,
     ingestionAvailable,
     reasoningAvailable,
+    studioModeEnabled,
+    ragPipelineEnabled,
     inspectModeEnabled,
-    chunksModeEnabled,
+    linkedModeEnabled,
     askModeEnabled,
     appVersion,
     loaded,
diff --git a/frontend/src/features/reasoning/ui/ReasoningPanel.vue b/frontend/src/features/reasoning/ui/ReasoningPanel.vue
index 64f4e5f..e502549 100644
--- a/frontend/src/features/reasoning/ui/ReasoningPanel.vue
+++ b/frontend/src/features/reasoning/ui/ReasoningPanel.vue
@@ -108,7 +108,7 @@ const props = defineProps<{
   /**
    * The live Cytoscape instance from the GraphView. May be `null` while the
    * graph is loading or if Maintain hasn't been run for this document.
-   * Passed down from StudioPage via `graphViewRef.cy`.
+   * Passed down by the host page via `graphViewRef.cy`.
    */
   cy: Core | null
 }>()
diff --git a/frontend/src/shared/i18n.test.ts b/frontend/src/shared/i18n.test.ts
index a96ce62..ac33012 100644
--- a/frontend/src/shared/i18n.test.ts
+++ b/frontend/src/shared/i18n.test.ts
@@ -50,7 +50,9 @@ describe('useI18n', () => {
     const { t } = useI18n()
     expect(t('history.tabAnalyses')).toBe('Analyses')
     expect(t('history.tabDocuments')).toBe('Documents')
-    expect(t('history.emptyDocs')).toBe('Aucun document. Importez un document depuis le Studio.')
+    expect(t('history.emptyDocs')).toBe(
+      'Aucun document. Importez un document depuis la bibliothèque.',
+    )
   })
 
   it('has history tab keys in English', () => {
@@ -59,7 +61,7 @@ describe('useI18n', () => {
     const { t } = useI18n()
     expect(t('history.tabAnalyses')).toBe('Analyses')
     expect(t('history.tabDocuments')).toBe('Documents')
-    expect(t('history.emptyDocs')).toBe('No documents yet. Upload a document from the Studio.')
+    expect(t('history.emptyDocs')).toBe('No documents yet. Upload a document from the library.')
   })
 
   it('has detailed pipeline option hints in French', () => {
diff --git a/frontend/src/shared/i18n.ts b/frontend/src/shared/i18n.ts
index 2654e78..1566e54 100644
--- a/frontend/src/shared/i18n.ts
+++ b/frontend/src/shared/i18n.ts
@@ -207,8 +207,8 @@ const messages: Messages = {
     'history.title': 'Historique',
     'history.tabAnalyses': 'Analyses',
     'history.tabDocuments': 'Documents',
-    'history.empty': 'Aucune analyse. Allez dans Studio pour analyser votre premier document.',
-    'history.emptyDocs': 'Aucun document. Importez un document depuis le Studio.',
+    'history.empty': 'Aucune analyse. Analysez votre premier document pour commencer.',
+    'history.emptyDocs': 'Aucun document. Importez un document depuis la bibliothèque.',
     'history.open': 'Ouvrir',
 
     // Chunking
@@ -264,7 +264,7 @@ const messages: Messages = {
     'reasoning.uploading': 'Import du document...',
     'reasoning.existingDocs': 'Documents déjà analysés',
     'reasoning.noAnalyzedDocs':
-      'Aucun des documents existants n\u2019a encore été analysé — lance-en un depuis Studio, ou dépose un nouveau PDF ci-dessus.',
+      'Aucun des documents existants n\u2019a encore été analysé — lance-en un depuis la bibliothèque, ou dépose un nouveau PDF ci-dessus.',
     'reasoning.pagesCount': '{n} pages',
     'reasoning.changeDoc': 'Changer de document',
     'reasoning.modeSwitchLabel': 'Mode d\u2019affichage',
@@ -712,8 +712,8 @@ const messages: Messages = {
     'history.title': 'History',
     'history.tabAnalyses': 'Analyses',
     'history.tabDocuments': 'Documents',
-    'history.empty': 'No analyses yet. Go to Studio to analyze your first document.',
-    'history.emptyDocs': 'No documents yet. Upload a document from the Studio.',
+    'history.empty': 'No analyses yet. Analyze your first document to get started.',
+    'history.emptyDocs': 'No documents yet. Upload a document from the library.',
     'history.open': 'Open',
 
     'studio.prepare': 'Prepare',
@@ -767,7 +767,7 @@ const messages: Messages = {
     'reasoning.uploading': 'Uploading document...',
     'reasoning.existingDocs': 'Previously analyzed documents',
     'reasoning.noAnalyzedDocs':
-      'None of your existing documents have been analyzed yet — run one from Studio, or drop a new PDF above.',
+      'None of your existing documents have been analyzed yet — run one from the library, or drop a new PDF above.',
     'reasoning.pagesCount': '{n} pages',
     'reasoning.changeDoc': 'Change document',
     'reasoning.modeSwitchLabel': 'View mode',
diff --git a/frontend/src/shared/routing/resolveSurface.test.ts b/frontend/src/shared/routing/resolveSurface.test.ts
new file mode 100644
index 0000000..98b4fe4
--- /dev/null
+++ b/frontend/src/shared/routing/resolveSurface.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from 'vitest'
+
+import { ROUTES } from './names'
+import { resolveSurface } from './resolveSurface'
+
+describe('resolveSurface', () => {
+  it('allows studio routes when studio surface is enabled', () => {
+    expect(resolveSurface(ROUTES.STUDIO, { studio: true, rag: false })).toBeNull()
+    expect(resolveSurface(ROUTES.HISTORY, { studio: true, rag: true })).toBeNull()
+  })
+
+  it('allows rag routes when rag surface is enabled', () => {
+    expect(resolveSurface(ROUTES.DOCS_LIBRARY, { studio: false, rag: true })).toBeNull()
+    expect(resolveSurface(ROUTES.DOC_WORKSPACE, { studio: true, rag: true })).toBeNull()
+  })
+
+  it('redirects studio routes to docs library when studio off and rag on', () => {
+    expect(resolveSurface(ROUTES.STUDIO, { studio: false, rag: true })).toBe(ROUTES.DOCS_LIBRARY)
+    expect(resolveSurface(ROUTES.HISTORY, { studio: false, rag: true })).toBe(ROUTES.DOCS_LIBRARY)
+    expect(resolveSurface(ROUTES.DOCUMENTS, { studio: false, rag: true })).toBe(ROUTES.DOCS_LIBRARY)
+    expect(resolveSurface(ROUTES.SEARCH, { studio: false, rag: true })).toBe(ROUTES.DOCS_LIBRARY)
+  })
+
+  it('redirects rag routes to studio when rag off and studio on', () => {
+    expect(resolveSurface(ROUTES.DOCS_LIBRARY, { studio: true, rag: false })).toBe(ROUTES.STUDIO)
+    expect(resolveSurface(ROUTES.STORES_LIST, { studio: true, rag: false })).toBe(ROUTES.STUDIO)
+    expect(resolveSurface(ROUTES.RUNS, { studio: true, rag: false })).toBe(ROUTES.STUDIO)
+  })
+
+  it('falls back to home when both surfaces are off', () => {
+    // Defensive case — backend refuses to start in this state.
+    expect(resolveSurface(ROUTES.STUDIO, { studio: false, rag: false })).toBe(ROUTES.HOME)
+    expect(resolveSurface(ROUTES.DOCS_LIBRARY, { studio: false, rag: false })).toBe(ROUTES.HOME)
+  })
+
+  it('leaves surface-neutral routes untouched', () => {
+    expect(resolveSurface(ROUTES.HOME, { studio: false, rag: true })).toBeNull()
+    expect(resolveSurface(ROUTES.SETTINGS, { studio: false, rag: true })).toBeNull()
+    expect(resolveSurface(ROUTES.REASONING, { studio: false, rag: true })).toBeNull()
+  })
+})
diff --git a/frontend/src/shared/routing/resolveSurface.ts b/frontend/src/shared/routing/resolveSurface.ts
new file mode 100644
index 0000000..efec7f8
--- /dev/null
+++ b/frontend/src/shared/routing/resolveSurface.ts
@@ -0,0 +1,48 @@
+import { ROUTES } from './names'
+
+/**
+ * Surface gating (#257).
+ *
+ * Two master flags select which UI surface is exposed:
+ * - `studioMode` gates the legacy Studio surface
+ * - `ragPipeline` gates the new doc-centric RAG pipeline
+ *
+ * `resolveSurface` is a pure helper consumed by the router's `beforeEach`
+ * guard. Returns the target route name to redirect to, or `null` when
+ * the requested route is allowed.
+ */
+
+export const STUDIO_SURFACE_ROUTES: ReadonlySet<string> = new Set([
+  ROUTES.STUDIO,
+  ROUTES.HISTORY,
+  ROUTES.DOCUMENTS,
+  ROUTES.SEARCH,
+])
+
+export const RAG_SURFACE_ROUTES: ReadonlySet<string> = new Set([
+  ROUTES.DOCS_LIBRARY,
+  ROUTES.DOCS_NEW,
+  ROUTES.DOC_WORKSPACE,
+  ROUTES.STORES_LIST,
+  ROUTES.STORE_CREATE,
+  ROUTES.STORE_DETAIL,
+  ROUTES.STORE_EDIT,
+  ROUTES.STORE_QUERY,
+  ROUTES.RUNS,
+  ROUTES.RUN_DETAIL,
+])
+
+export interface SurfaceFlags {
+  studio: boolean
+  rag: boolean
+}
+
+export function resolveSurface(routeName: string, flags: SurfaceFlags): string | null {
+  if (STUDIO_SURFACE_ROUTES.has(routeName) && !flags.studio) {
+    return flags.rag ? ROUTES.DOCS_LIBRARY : ROUTES.HOME
+  }
+  if (RAG_SURFACE_ROUTES.has(routeName) && !flags.rag) {
+    return flags.studio ? ROUTES.STUDIO : ROUTES.HOME
+  }
+  return null
+}