diff --git a/frontend/src/components/canvas/DiagramCanvas.vue b/frontend/src/components/canvas/DiagramCanvas.vue
index c0655d7..67e0717 100644
--- a/frontend/src/components/canvas/DiagramCanvas.vue
+++ b/frontend/src/components/canvas/DiagramCanvas.vue
@@ -75,7 +75,10 @@ const isWhiteboard = computed(() => activeType.value === 'whiteboard')
 // strategy, so activeType would read 'block'. On a unified doc the shared block
 // substrate and the whiteboard layer compose over one canvas (the auto-layout
 // types become frames in a later phase); legacy single-type docs are unchanged.
-const isUnified = computed(() => isUnifiedDocument(store.state))
+// A unified doc renders the composed canvas — EXCEPT while a frame is focused for
+// editing, when the mode strategy is overridden to that sub-model's type and the
+// editor renders as its single-type editor (so isUnified goes false here).
+const isUnified = computed(() => isUnifiedDocument(store.state) && !editorUi.state.focusedFrame)
 const showBlockLayer = computed(() => !rendersOwnLayer.value || isUnified.value)
 
 const mindmapLayout = computed(() =>
@@ -379,6 +382,14 @@ function openAtActualSize() {
 
 let resizeObserver = null
 
+// Entering/leaving a frame's focus mode reframes the view: on enter, fit the now
+// single-type content (the frame); on exit, fit the unified canvas. Without this
+// the frame renders at its own coords, off-screen from where the frame sat.
+watch(
+  () => editorUi.state.focusedFrame,
+  () => nextTick(fitToView),
+)
+
 onMounted(() => {
   openAtActualSize()
   // Route editorUi.fit() (bottom-left control + ⇧1 shortcut) through fitToView so
@@ -835,6 +846,7 @@ const surfaceCursor = computed(() => {
             :stroke-width="selectedFrame === 'mindmap' ? 1.5 : 0"
             stroke-dasharray="6 4" style="cursor: move"
             @pointerdown.stop="startFrameDrag('mindmap', $event)"
+            @dblclick.stop="editorUi.setFocusedFrame('mindmap')"
           />
           <g class="unified-frame-content">
             <MindMapNodeLayer :mindmap="store.state.mindmap" :positions="mindmapLayout.positions" />
@@ -849,6 +861,7 @@ const surfaceCursor = computed(() => {
             :stroke-width="selectedFrame === 'flowchart' ? 1.5 : 0"
             stroke-dasharray="6 4" style="cursor: move"
             @pointerdown.stop="startFrameDrag('flowchart', $event)"
+            @dblclick.stop="editorUi.setFocusedFrame('flowchart')"
           />
           <g style="pointer-events: none">
             <FlowchartLayer :flowchart="store.state.flowchart" />
diff --git a/frontend/src/pages/EditorShell.vue b/frontend/src/pages/EditorShell.vue
index ccb9ff6..07c5bbd 100644
--- a/frontend/src/pages/EditorShell.vue
+++ b/frontend/src/pages/EditorShell.vue
@@ -19,6 +19,7 @@ import { useCollaboration } from '@/composables/useCollaboration.js'
 import { useAppSettings } from '@/composables/useAppSettings.js'
 import TopToolbar from '@/components/toolbar/TopToolbar.vue'
 import DiagramCanvas from '@/components/canvas/DiagramCanvas.vue'
+import LucideIcon from '@/icons/LucideIcon.vue'
 import Minimap from '@/components/canvas/Minimap.vue'
 import WhiteboardMinimap from '@/components/canvas/WhiteboardMinimap.vue'
 import MindMapOverlay from '@/components/canvas/MindMapOverlay.vue'
@@ -41,8 +42,13 @@ const editorUi = createEditorUi()
 provideDiagramStore(store)
 provideEditorUi(editorUi)
 
-// Active mode module for this diagram's type (spec diagram-types §0/G1).
-const modeStrategy = computed(() => getModeStrategy(store.state.diagramType))
+// Active mode module for this diagram's type (spec diagram-types §0/G1). On the
+// unified canvas, entering a frame (editorUi.state.focusedFrame) overrides the
+// strategy to that sub-model's type, so the whole editor becomes its single-type
+// editor (full node editing/keyboard/toolbar) until "Back to canvas".
+const modeStrategy = computed(() =>
+  getModeStrategy(editorUi.state.focusedFrame || store.state.diagramType),
+)
 provideModeStrategy(modeStrategy)
 
 // Surface-interaction delegation seam (spec diagram-types Part G1/G4). The active
@@ -128,6 +134,16 @@ onMounted(() => {
 
     <div class="flex min-h-0 flex-1">
       <main class="relative min-h-0 min-w-0 flex-1">
+        <!-- Focus-mode bar: shown while editing a frame on the unified canvas. -->
+        <button
+          v-if="editorUi.state.focusedFrame"
+          class="absolute left-1/2 top-3 z-20 flex -translate-x-1/2 items-center gap-1.5 rounded-full border border-outline-gray-2 bg-surface-base px-3 py-1.5 text-[13px] font-medium text-ink-gray-8 shadow-md hover:bg-surface-gray-2"
+          @click="editorUi.setFocusedFrame(null)"
+        >
+          <LucideIcon name="arrow-left" class="h-4 w-4" />
+          Back to canvas
+          <span class="text-ink-gray-5">· editing {{ editorUi.state.focusedFrame }}</span>
+        </button>
         <DiagramCanvas />
         <Minimap />
         <WhiteboardMinimap v-if="modeStrategy.type === 'whiteboard'" />
diff --git a/frontend/src/stores/useEditorUi.js b/frontend/src/stores/useEditorUi.js
index 773c4cc..05d9db4 100644
--- a/frontend/src/stores/useEditorUi.js
+++ b/frontend/src/stores/useEditorUi.js
@@ -20,6 +20,10 @@ export function createEditorUi() {
     infiniteCanvas: true,
     // The selected section id (chrome — sections aren't part of shape selection).
     selectedSectionId: null,
+    // Unified canvas: the frame being edited in focus mode ('mindmap'|'flowchart'
+    // |null). While set, the editor behaves as that sub-model's single-type editor
+    // (full node editing/keyboard/toolbar); "Back to canvas" clears it.
+    focusedFrame: null,
     // True for a short window after a layout op (tidy / flip) so node positions
     // tween instead of jumping (spec 17.1). Off during free drag → no lag.
     animateLayout: false,
@@ -48,6 +52,11 @@ function assembleUi(state, viewport) {
 // Switching to draw remembers the chosen shape so the tool can be re-armed.
 function attachTools(ui, state) {
   ui.setTool = (tool) => (state.tool = tool)
+  // Enter/leave a frame's focused single-type editing mode (unified canvas).
+  ui.setFocusedFrame = (kind) => {
+    state.focusedFrame = kind || null
+    state.tool = 'select'
+  }
   ui.setDrawShape = (type) => {
     state.drawShapeType = type
     state.lastShapeType = type