diff --git a/canvas/src/components/canvas/__tests__/dragUtils.test.ts b/canvas/src/components/canvas/__tests__/dragUtils.test.ts
new file mode 100644
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+++ b/canvas/src/components/canvas/__tests__/dragUtils.test.ts
@@ -0,0 +1,299 @@
+/**
+ * Tests for dragUtils — the pure-ish geometry helpers the
+ * useDragHandlers hook delegates to for nest/un-nest decisions.
+ *
+ * Why test these in isolation: useDragHandlers is 296 LOC of React
+ * Flow + Zustand orchestration; the *decisions* live here. Pinning
+ * shouldDetach + clampChildIntoParent locks the hot path the user
+ * feels — drag-out hysteresis (does my drag count as un-nest?) and
+ * drift-back-in clamping (did my child snap back into the parent?).
+ *
+ * Issue: #2071 (Canvas test gaps follow-up). The full useDragHandlers
+ * orchestration test is left as a separate follow-up — it'd need
+ * heavyweight React Flow / Zustand mocking that wouldn't change
+ * these geometry contracts.
+ */
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+} from "vitest";
+
+// ── Hoisted mocks ────────────────────────────────────────────────────────────
+
+// useCanvasStore is the only external touchpoint dragUtils has —
+// clampChildIntoParent reads getState().nodes and writes setState().
+// vi.hoisted gives us a referentially-stable state object so tests
+// can mutate it between cases without losing the mock wiring.
+const { mockState } = vi.hoisted(() => ({
+  mockState: {
+    nodes: [] as Array<{
+      id: string;
+      position: { x: number; y: number };
+    }>,
+  },
+}));
+
+vi.mock("@/store/canvas", () => ({
+  useCanvasStore: Object.assign(
+    (selector: (s: typeof mockState) => unknown) => selector(mockState),
+    {
+      getState: () => mockState,
+      setState: (
+        patcher:
+          | Partial<typeof mockState>
+          | ((s: typeof mockState) => Partial<typeof mockState>),
+      ) => {
+        const patch = typeof patcher === "function" ? patcher(mockState) : patcher;
+        Object.assign(mockState, patch);
+      },
+    },
+  ),
+}));
+
+// Import the SUT after the mocks are declared.
+import {
+  DETACH_FRACTION,
+  shouldDetach,
+  clampChildIntoParent,
+} from "../dragUtils";
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+/**
+ * Build a fake InternalNode that mirrors the shape useReactFlow returns:
+ *   - measured.width/height (the live measured size React Flow tracks)
+ *   - width/height fallbacks (used when measured isn't populated yet)
+ *   - internals.positionAbsolute (canvas-coordinate top-left)
+ */
+function makeNode(
+  id: string,
+  x: number,
+  y: number,
+  w: number,
+  h: number,
+): unknown {
+  return {
+    id,
+    measured: { width: w, height: h },
+    width: w,
+    height: h,
+    internals: { positionAbsolute: { x, y } },
+  };
+}
+
+/**
+ * Make a getInternalNode resolver from a list of node fixtures.
+ * Returns undefined for any unknown id — matches useReactFlow's
+ * real shape so the missing-node fallback in shouldDetach can be
+ * exercised cleanly.
+ */
+function makeGetInternalNode(
+  fixtures: Record<string, unknown>,
+): (id: string) => unknown {
+  return (id: string) => fixtures[id];
+}
+
+beforeEach(() => {
+  mockState.nodes = [];
+});
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+// ── shouldDetach ─────────────────────────────────────────────────────────────
+
+describe("shouldDetach", () => {
+  it("returns false when child sits fully inside parent (no overlap loss)", () => {
+    // Parent at (0,0) 400x300; child at (50,50) 100x80 — fully inside.
+    const get = makeGetInternalNode({
+      child: makeNode("child", 50, 50, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("child", "parent", get as never)).toBe(false);
+  });
+
+  it("returns false when child has drifted just past the edge but stays under DETACH_FRACTION", () => {
+    // Child width=100; DETACH_FRACTION=0.2 → must lose >20% (>20px)
+    // outside on at least one axis. Drift the child 15px left of
+    // the parent edge (loses 15/100 = 15% on X) — still nested.
+    const get = makeGetInternalNode({
+      child: makeNode("child", -15, 50, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("child", "parent", get as never)).toBe(false);
+  });
+
+  it("returns true when child is dragged past the X-axis hysteresis threshold", () => {
+    // 25% of child outside on X (DETACH_FRACTION=0.2) — un-nest.
+    const get = makeGetInternalNode({
+      child: makeNode("child", -25, 50, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("child", "parent", get as never)).toBe(true);
+  });
+
+  it("returns true when child is dragged past the Y-axis hysteresis threshold", () => {
+    // 25% of child outside on Y. Either axis crossing the threshold
+    // triggers detach (matches the OR logic in the source).
+    const get = makeGetInternalNode({
+      child: makeNode("child", 50, -25, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("child", "parent", get as never)).toBe(true);
+  });
+
+  it("returns true (conservative) when child node is missing", () => {
+    // Source comment: \"Returns true when we can't measure either node\"
+    // — the conservative fallback so a missing measurement doesn't
+    // accidentally pin a child to a parent during a real un-nest.
+    const get = makeGetInternalNode({
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("missing-child", "parent", get as never)).toBe(true);
+  });
+
+  it("returns true (conservative) when parent node is missing", () => {
+    const get = makeGetInternalNode({
+      child: makeNode("child", 50, 50, 100, 80),
+    });
+    expect(shouldDetach("child", "missing-parent", get as never)).toBe(true);
+  });
+
+  it("falls back to default 220x120 dimensions when measured is absent", () => {
+    // Mirror real react-flow during initial mount: width/height come
+    // from React Flow's defaults until measurement runs. shouldDetach
+    // explicitly defaults to 220x120 in that case.
+    const noMeasure = (id: string, x: number, y: number) => ({
+      id,
+      width: undefined,
+      height: undefined,
+      measured: undefined,
+      internals: { positionAbsolute: { x, y } },
+    });
+    // Default child 220x120; parent 400x300; child at (-50, 0). 50/220
+    // ≈ 22.7% off on X — JUST past 20% threshold → detach.
+    const get = makeGetInternalNode({
+      child: noMeasure("child", -50, 0),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    expect(shouldDetach("child", "parent", get as never)).toBe(true);
+  });
+
+  it("DETACH_FRACTION is exported as 0.2 (Miro/tldraw convention)", () => {
+    // Pin the constant so a future refactor that bumps it to 0.3 has
+    // to update this test deliberately — sudden behavior change
+    // would otherwise just feel unresponsive on twitchy releases.
+    expect(DETACH_FRACTION).toBe(0.2);
+  });
+});
+
+// ── clampChildIntoParent ─────────────────────────────────────────────────────
+
+describe("clampChildIntoParent", () => {
+  it("no-op when child is already inside parent bounds (no setState write)", () => {
+    // Parent 400x300; child at relative (50, 50) 100x80 — fully inside.
+    // Source bails before setState when clamped position == current.
+    mockState.nodes = [
+      { id: "child", position: { x: 50, y: 50 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80), // absolute pos doesn't matter for clamp; only `cur.position` matters
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    const before = mockState.nodes;
+    clampChildIntoParent("child", "parent", get as never);
+    // Same array reference — proves no setState was called.
+    expect(mockState.nodes).toBe(before);
+    expect(mockState.nodes[0].position).toEqual({ x: 50, y: 50 });
+  });
+
+  it("clamps to (0, 0) when child has drifted past the top-left corner", () => {
+    // Negative relative position = past the parent's top-left edge.
+    mockState.nodes = [
+      { id: "child", position: { x: -10, y: -20 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    clampChildIntoParent("child", "parent", get as never);
+    expect(mockState.nodes[0].position).toEqual({ x: 0, y: 0 });
+  });
+
+  it("clamps to (parentW - childW, parentH - childH) at the bottom-right", () => {
+    // Child sticks out past the parent's bottom-right corner.
+    // Parent 400x300, child 100x80 → max valid relative pos is (300, 220).
+    mockState.nodes = [
+      { id: "child", position: { x: 500, y: 400 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    clampChildIntoParent("child", "parent", get as never);
+    expect(mockState.nodes[0].position).toEqual({ x: 300, y: 220 });
+  });
+
+  it("clamps independently on each axis (X clamps, Y stays)", () => {
+    // Child past edge on X but inside on Y — only X position is updated.
+    mockState.nodes = [
+      { id: "child", position: { x: -50, y: 100 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    clampChildIntoParent("child", "parent", get as never);
+    expect(mockState.nodes[0].position).toEqual({ x: 0, y: 100 });
+  });
+
+  it("returns early when child node not in store (no setState)", () => {
+    mockState.nodes = [
+      { id: "different", position: { x: 0, y: 0 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    const before = mockState.nodes;
+    clampChildIntoParent("child", "parent", get as never);
+    expect(mockState.nodes).toBe(before);
+  });
+
+  it("returns early when child internalNode is missing", () => {
+    mockState.nodes = [
+      { id: "child", position: { x: -10, y: -20 } },
+    ];
+    // Only parent is registered — getInternalNode returns undefined for child.
+    const get = makeGetInternalNode({
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    const before = mockState.nodes[0].position;
+    clampChildIntoParent("child", "parent", get as never);
+    // Position untouched — the early-return short-circuited.
+    expect(mockState.nodes[0].position).toEqual(before);
+  });
+
+  it("preserves other nodes in the store (only mutates the target)", () => {
+    // Multiple children; clamping one must NOT touch the others.
+    mockState.nodes = [
+      { id: "child", position: { x: -10, y: -10 } },
+      { id: "sibling", position: { x: 200, y: 200 } },
+      { id: "stranger", position: { x: 999, y: 999 } },
+    ];
+    const get = makeGetInternalNode({
+      child: makeNode("child", 0, 0, 100, 80),
+      parent: makeNode("parent", 0, 0, 400, 300),
+    });
+    clampChildIntoParent("child", "parent", get as never);
+    const byId = Object.fromEntries(mockState.nodes.map((n) => [n.id, n]));
+    expect(byId.child.position).toEqual({ x: 0, y: 0 });
+    expect(byId.sibling.position).toEqual({ x: 200, y: 200 });
+    expect(byId.stranger.position).toEqual({ x: 999, y: 999 });
+  });
+});