diff --git a/webui/src/features/board/harness/agent/arrange-created-nodes.ts b/webui/src/features/board/harness/agent/arrange-created-nodes.ts
index 7794e794..58899021 100644
--- a/webui/src/features/board/harness/agent/arrange-created-nodes.ts
+++ b/webui/src/features/board/harness/agent/arrange-created-nodes.ts
@@ -2,7 +2,7 @@ import { asNodeId, type CanvasStore, type Edge } from "@canvas-harness/core"
 import type { LinkEdge, NoteNode } from "@/features/board/types/flow"
 import { autoLayout } from "@/features/board/lib/graph/auto-layout"
 import { defaultLayoutOptions, type Direction } from "@/features/board/lib/graph/settings"
-import { NOTE_TAIL_GAP } from "./beneath-border"
+import { offsetToOrigin, originBeneath } from "./beneath-border"
 
 
 type XY = { x: number; y: number }
@@ -201,14 +201,10 @@ export const arrangeCreatedNodes = async (store: CanvasStore, createdIds: string
     (await layoutBidirectional(present, edges, sizeOf)) ?? (await runDagre(present, edges, sizeOf, "LR"))
   if (positions.size === 0) return
 
-  // Translate the laid-out cluster below existing (non-created) content.
+  // Translate the laid-out cluster below existing (non-created) content — the
+  // same placement rule the mindmap-apply drain uses (originBeneath).
   const others = store.getAllNodes().filter((n) => !ids.has(String(n.id)))
-  const originX = others.length ? Math.min(...others.map((n) => n.x)) : 0
-  const originY = others.length ? Math.max(...others.map((n) => n.y + n.h)) + NOTE_TAIL_GAP : 0
-  const xs = [...positions.values()].map((p) => p.x)
-  const ys = [...positions.values()].map((p) => p.y)
-  const dx = originX - Math.min(...xs)
-  const dy = originY - Math.min(...ys)
+  const { x: dx, y: dy } = offsetToOrigin([...positions.values()], originBeneath(others))
 
   store.batch(() => {
     for (const [id, p] of positions) {
diff --git a/webui/src/features/board/harness/agent/beneath-border.test.ts b/webui/src/features/board/harness/agent/beneath-border.test.ts
index a0dc22c1..ab0845e4 100644
--- a/webui/src/features/board/harness/agent/beneath-border.test.ts
+++ b/webui/src/features/board/harness/agent/beneath-border.test.ts
@@ -1,7 +1,7 @@
 import { beforeEach, describe, expect, it } from "vitest"
 import { asNodeId } from "@canvas-harness/core"
 import { addNode, freshStore, resetIdb } from "@/test/canvas"
-import { NOTE_TAIL_GAP, beneathBorderOrigin } from "./beneath-border"
+import { NOTE_TAIL_GAP, beneathBorderOrigin, offsetToOrigin, originBeneath } from "./beneath-border"
 
 
 beforeEach(() => resetIdb())
@@ -21,3 +21,45 @@ describe("beneathBorderOrigin", () => {
     expect(beneathBorderOrigin(store)).toEqual({ x: 40, y: 240 + NOTE_TAIL_GAP })
   })
 })
+
+
+describe("originBeneath", () => {
+  it("returns (0,0) for no nodes", () => {
+    expect(originBeneath([])).toEqual({ x: 0, y: 0 })
+  })
+
+  it("takes min x and max bottom + gap across the given nodes", () => {
+    const nodes = [
+      { x: 40, y: 0, h: 100 }, // bottom 100, leftmost
+      { x: 300, y: 60, h: 180 }, // bottom 240
+    ]
+    expect(originBeneath(nodes)).toEqual({ x: 40, y: 240 + NOTE_TAIL_GAP })
+  })
+})
+
+
+describe("offsetToOrigin", () => {
+  it("no move for an empty cluster", () => {
+    expect(offsetToOrigin([], { x: 100, y: 500 })).toEqual({ x: 0, y: 0 })
+  })
+
+  it("shifts the cluster's top-left corner onto the origin", () => {
+    // Cluster min corner is (10, 20); moving it to (100, 500) is (+90, +480).
+    const cluster = [
+      { x: 10, y: 40 },
+      { x: 60, y: 20 },
+    ]
+    expect(offsetToOrigin(cluster, { x: 100, y: 500 })).toEqual({ x: 90, y: 480 })
+  })
+
+  it("places a cluster beneath existing content when composed with originBeneath", () => {
+    // Existing content bottoms out at y=240; a new cluster anchored near the
+    // origin must shift below it, not overlap.
+    const existing = [{ x: 40, y: 0, h: 100 }, { x: 300, y: 60, h: 180 }]
+    const cluster = [{ x: 0, y: 0 }, { x: 0, y: 120 }]
+    const shift = offsetToOrigin(cluster, originBeneath(existing))
+    expect(shift).toEqual({ x: 40, y: 240 + NOTE_TAIL_GAP })
+    // Applied: the cluster's top now sits one gap below the lowest existing bottom.
+    expect(Math.min(...cluster.map((n) => n.y + shift.y))).toBe(240 + NOTE_TAIL_GAP)
+  })
+})
diff --git a/webui/src/features/board/harness/agent/beneath-border.ts b/webui/src/features/board/harness/agent/beneath-border.ts
index 38514240..b9ab1a3c 100644
--- a/webui/src/features/board/harness/agent/beneath-border.ts
+++ b/webui/src/features/board/harness/agent/beneath-border.ts
@@ -8,18 +8,45 @@ export const NOTE_TAIL_GAP = 80
 
 
 type XY = { x: number; y: number }
+type Box = { x: number; y: number; h: number }
 
 
 /**
- * Top-left origin just beneath the current graph's border: left-aligned to the
- * leftmost node, one gap below the lowest bottom edge. `(0, 0)` on an empty
- * board. Frontend analog of the backend's `compute_note_position`
- * (min existing x, max existing bottom + gap).
+ * Top-left origin just beneath a set of nodes' border: left-aligned to the
+ * leftmost node, one gap below the lowest bottom edge. `(0, 0)` when empty.
+ * The shared placement rule for freshly-added content (min x, max bottom + gap).
  */
-export const beneathBorderOrigin = (store: CanvasStore): XY => {
-  const nodes = store.getAllNodes()
+export const originBeneath = (nodes: ReadonlyArray<Box>): XY => {
   if (nodes.length === 0) return { x: 0, y: 0 }
-  const x = Math.min(...nodes.map((n) => n.x))
-  const y = Math.max(...nodes.map((n) => n.y + n.h)) + NOTE_TAIL_GAP
-  return { x, y }
+  // Reduce (not Math.min/max spread) — this runs over the whole board, which can
+  // be large enough to exceed the engine's call-argument limit when spread.
+  let minX = Infinity
+  let maxBottom = -Infinity
+  for (const n of nodes) {
+    if (n.x < minX) minX = n.x
+    const bottom = n.y + n.h
+    if (bottom > maxBottom) maxBottom = bottom
+  }
+  return { x: minX, y: maxBottom + NOTE_TAIL_GAP }
 }
+
+
+/**
+ * The (dx, dy) that moves a freshly-laid-out cluster so its top-left corner
+ * lands on `origin` (left edge → origin.x, top → origin.y). No move for an
+ * empty cluster. Apply the result to every node in the cluster.
+ */
+export const offsetToOrigin = (cluster: ReadonlyArray<XY>, origin: XY): XY => {
+  if (cluster.length === 0) return { x: 0, y: 0 }
+  const minX = Math.min(...cluster.map((n) => n.x))
+  const minY = Math.min(...cluster.map((n) => n.y))
+  return { x: origin.x - minX, y: origin.y - minY }
+}
+
+
+/**
+ * Top-left origin just beneath the current graph's border. Frontend analog of
+ * the backend's `compute_note_position` (min existing x, max existing bottom +
+ * gap). `(0, 0)` on an empty board.
+ */
+export const beneathBorderOrigin = (store: CanvasStore): XY => originBeneath(store.getAllNodes())
diff --git a/webui/src/features/board/harness/agent/use-harness-apply-mindmap.ts b/webui/src/features/board/harness/agent/use-harness-apply-mindmap.ts
index 3e12ccc5..da7baa54 100644
--- a/webui/src/features/board/harness/agent/use-harness-apply-mindmap.ts
+++ b/webui/src/features/board/harness/agent/use-harness-apply-mindmap.ts
@@ -7,6 +7,7 @@ import type { Link } from "@/features/board/types/link"
 import type { Note } from "@/features/board/types/note"
 import { linkToEdge } from "../convert/link-to-edge"
 import { noteToNode } from "../convert/note-to-node"
+import { NOTE_TAIL_GAP, offsetToOrigin, originBeneath } from "./beneath-border"
 
 
 /**
@@ -29,11 +30,16 @@ export const useHarnessApplyMindMap = (
   store: CanvasStore,
   boardId: string | null,
   rootId: string | null,
+  ready: boolean,
 ): void => {
   const drainingRef = useRef(false)
 
   useEffect(() => {
-    if (!boardId) return
+    // Wait for hydration: draining into an empty (not-yet-loaded) store would
+    // place the cluster at {0,0} (originBeneath of nothing) and then be overlapped
+    // by the existing nodes that hydrate a moment later. When `ready` flips true
+    // this effect re-runs and drains anything staged in the meantime.
+    if (!boardId || !ready) return
 
     const drain = (): void => {
       if (drainingRef.current) return
@@ -44,9 +50,23 @@ export const useHarnessApplyMindMap = (
       drainingRef.current = true
       try {
         const ops: Op[] = []
+        // Place each staged cluster beneath existing board content (and beneath
+        // any cluster already placed in this drain), left-aligned — the same
+        // rule write_note + arrangeCreatedNodes follow. autoLayout anchors the
+        // staged nodes near the origin with no knowledge of what's on the board,
+        // so without this translate they land on top of existing nodes.
+        const start = originBeneath(store.getAllNodes())
+        const originX = start.x
+        let frontierY = start.y
         for (const mindmap of pending) {
           const { nodes, edges } = mindmap
-          const harnessNodes = convertStagedNodes(nodes, rootId, boardId)
+          const staged = convertStagedNodes(nodes, rootId, boardId)
+          const shift = offsetToOrigin(staged, { x: originX, y: frontierY })
+          const harnessNodes = staged.map((n) => ({ ...n, x: n.x + shift.x, y: n.y + shift.y }))
+          if (harnessNodes.length > 0) {
+            // Next cluster stacks below this one.
+            frontierY = Math.max(...harnessNodes.map((n) => n.y + n.h)) + NOTE_TAIL_GAP
+          }
           const nodeMap = new Map(
             harnessNodes.map((n) => [n.id as unknown as string, n]),
           )
@@ -77,7 +97,7 @@ export const useHarnessApplyMindMap = (
       const b = next.mindmaps.get(boardId)?.length ?? 0
       if (b > a) drain()
     })
-  }, [store, boardId, rootId])
+  }, [store, boardId, rootId, ready])
 }
 
 
diff --git a/webui/src/features/board/harness/canvas/harness-canvas.tsx b/webui/src/features/board/harness/canvas/harness-canvas.tsx
index 9da4b12d..1acb790b 100644
--- a/webui/src/features/board/harness/canvas/harness-canvas.tsx
+++ b/webui/src/features/board/harness/canvas/harness-canvas.tsx
@@ -183,7 +183,7 @@ export function HarnessCanvas({ local = false }: { local?: boolean } = {}) {
   useLocalDocIndex(boardId ?? "", agentLocalIndexes)
   useDocNodeCascade(store, boardId ?? "", agentLocalIndexes)
   useBlockFolderCopy(store)
-  useHarnessApplyMindMap(store, boardId, rootId)
+  useHarnessApplyMindMap(store, boardId, rootId, ready)
   useHydrateIconNodes(store, boardId, rootId, ready)
   useThemeColorProjection(store, ready)
   // Local boards store the thumbnail in IndexedDB; capture only at the root