diff --git a/packages/core/src/services/index.ts b/packages/core/src/services/index.ts
index efcc79aa..670abe9b 100644
--- a/packages/core/src/services/index.ts
+++ b/packages/core/src/services/index.ts
@@ -9,3 +9,14 @@ export {
   pickHost,
   type Vec3,
 } from './hosting'
+export {
+  DEFAULT_ANGLE_STEP,
+  DEFAULT_GRID_STEP,
+  type SnapServices,
+  snapAngleToList,
+  snapPointToAngle,
+  snapPointToGrid,
+  snapScalar,
+  snapServices,
+  snapVec3ToGrid,
+} from './snap'
diff --git a/packages/core/src/services/snap.test.ts b/packages/core/src/services/snap.test.ts
new file mode 100644
index 00000000..1a4ddb38
--- /dev/null
+++ b/packages/core/src/services/snap.test.ts
@@ -0,0 +1,124 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  DEFAULT_ANGLE_STEP,
+  DEFAULT_GRID_STEP,
+  snapAngleToList,
+  snapPointToAngle,
+  snapPointToGrid,
+  snapScalar,
+  snapServices,
+  snapVec3ToGrid,
+  type Vec2,
+} from './snap'
+
+describe('snapScalar', () => {
+  test('rounds to multiples of step', () => {
+    expect(snapScalar(0.27, 0.25)).toBe(0.25)
+    expect(snapScalar(0.13, 0.25)).toBe(0.25)
+    expect(snapScalar(0.12, 0.25)).toBe(0)
+    expect(snapScalar(1.7, 0.25)).toBeCloseTo(1.75)
+  })
+
+  test('returns input unchanged when step is non-positive', () => {
+    expect(snapScalar(0.42, 0)).toBe(0.42)
+    expect(snapScalar(0.42, -1)).toBe(0.42)
+  })
+
+  test('default step is 0.25m', () => {
+    expect(snapScalar(0.3)).toBe(0.25)
+    expect(snapScalar(0.4)).toBe(0.5)
+    expect(DEFAULT_GRID_STEP).toBe(0.25)
+  })
+})
+
+describe('snapPointToGrid', () => {
+  test('snaps both components independently', () => {
+    expect(snapPointToGrid([0.3, 0.6], 0.25)).toEqual([0.25, 0.5])
+  })
+
+  test('preserves exact-grid points', () => {
+    expect(snapPointToGrid([1, 2], 0.5)).toEqual([1, 2])
+  })
+})
+
+describe('snapVec3ToGrid', () => {
+  test('snaps X and Z, leaves Y untouched', () => {
+    expect(snapVec3ToGrid([0.3, 1.7, 0.6], 0.25)).toEqual([0.25, 1.7, 0.5])
+  })
+})
+
+describe('snapPointToAngle', () => {
+  test('snaps to axis (0°) when cursor is near horizontal', () => {
+    const from: Vec2 = [0, 0]
+    const cursor: Vec2 = [1, 0.05] // near 0°
+    const snapped = snapPointToAngle(from, cursor, Math.PI / 4)
+    expect(snapped[0]).toBeCloseTo(1, 1)
+    expect(snapped[1]).toBeCloseTo(0, 5)
+  })
+
+  test('snaps to 45° at π/4 step', () => {
+    const from: Vec2 = [0, 0]
+    const cursor: Vec2 = [1, 0.9] // near 45°
+    const snapped = snapPointToAngle(from, cursor, Math.PI / 4)
+    // distance preserved (≈ √(1² + 0.9²) ≈ 1.345), angle locked to 45°
+    const expectedDist = Math.hypot(1, 0.9)
+    expect(snapped[0]).toBeCloseTo(expectedDist * Math.cos(Math.PI / 4))
+    expect(snapped[1]).toBeCloseTo(expectedDist * Math.sin(Math.PI / 4))
+  })
+
+  test('default angle step is π/12 (15°)', () => {
+    expect(DEFAULT_ANGLE_STEP).toBeCloseTo(Math.PI / 12)
+  })
+
+  test('grid-snaps the projected point when gridStep is provided', () => {
+    const from: Vec2 = [0, 0]
+    const cursor: Vec2 = [1.05, 0.02] // ~horizontal, slightly off grid
+    const snapped = snapPointToAngle(from, cursor, Math.PI / 4, 0.25)
+    // After 0° lock + 0.25m grid, X must be a 0.25 multiple.
+    expect(snapped[0] / 0.25).toBeCloseTo(Math.round(snapped[0] / 0.25))
+  })
+
+  test('preserves distance from `from`', () => {
+    const from: Vec2 = [2, 3]
+    const cursor: Vec2 = [3, 4]
+    const distance = Math.hypot(1, 1)
+    const snapped = snapPointToAngle(from, cursor, Math.PI / 4)
+    expect(Math.hypot(snapped[0] - 2, snapped[1] - 3)).toBeCloseTo(distance)
+  })
+})
+
+describe('snapAngleToList', () => {
+  test('snaps to the nearest entry within tolerance', () => {
+    const targets = [0, Math.PI / 2, Math.PI, (3 * Math.PI) / 2]
+    expect(snapAngleToList(0.05, targets, Math.PI / 36)).toBe(0)
+    expect(snapAngleToList(Math.PI / 2 + 0.02, targets, Math.PI / 36)).toBe(Math.PI / 2)
+  })
+
+  test('returns original angle when no target is within tolerance', () => {
+    const targets = [0, Math.PI / 2]
+    expect(snapAngleToList(0.5, targets, Math.PI / 36)).toBe(0.5)
+  })
+
+  test('handles wrap-around near ±π', () => {
+    const targets = [Math.PI]
+    expect(snapAngleToList(-Math.PI + 0.01, targets, Math.PI / 36)).toBe(Math.PI)
+  })
+})
+
+describe('snapServices facade', () => {
+  test('grid.snap matches snapPointToGrid', () => {
+    expect(snapServices.grid.snap([0.3, 0.6], 0.25)).toEqual(snapPointToGrid([0.3, 0.6], 0.25))
+  })
+
+  test('grid.snapScalar matches snapScalar', () => {
+    expect(snapServices.grid.snapScalar(0.3, 0.25)).toBe(snapScalar(0.3, 0.25))
+  })
+
+  test('angle.snapTo matches snapPointToAngle', () => {
+    const from: Vec2 = [0, 0]
+    const cursor: Vec2 = [1, 0.9]
+    expect(snapServices.angle.snapTo(from, cursor, Math.PI / 4)).toEqual(
+      snapPointToAngle(from, cursor, Math.PI / 4),
+    )
+  })
+})
diff --git a/packages/core/src/services/snap.ts b/packages/core/src/services/snap.ts
new file mode 100644
index 00000000..74aa9cd8
--- /dev/null
+++ b/packages/core/src/services/snap.ts
@@ -0,0 +1,122 @@
+/**
+ * Pure snap math — no React, no R3F, no scene access.
+ *
+ * Phase 1 ships the kind-agnostic snappers (grid + angle). Wall-specific
+ * snapping (snap-to-endpoint, snap-along-T) currently lives in
+ * `editor/src/components/tools/wall/wall-drafting.ts` and stays there until
+ * Phase 3, when the wall migration ports it here behind a `wallSnap` namespace.
+ *
+ * The functions here are stable contract — Phase 3 only adds, never removes.
+ */
+
+export type Vec2 = readonly [number, number]
+export type Vec3 = readonly [number, number, number]
+
+/** Default planar grid spacing in meters. Matches the editor's wall tool. */
+export const DEFAULT_GRID_STEP = 0.25
+
+/** Default angle-snap step — π/12 = 15°. Wall tools also use π/4 (45°). */
+export const DEFAULT_ANGLE_STEP = Math.PI / 12
+
+// ─── Grid snap ────────────────────────────────────────────────────────
+
+/** Snaps a single scalar to the nearest multiple of `step`. */
+export function snapScalar(value: number, step: number = DEFAULT_GRID_STEP): number {
+  if (step <= 0) return value
+  return Math.round(value / step) * step
+}
+
+/** Snaps a 2D point to a regular planar grid. */
+export function snapPointToGrid(point: Vec2, step: number = DEFAULT_GRID_STEP): Vec2 {
+  return [snapScalar(point[0], step), snapScalar(point[1], step)]
+}
+
+/** Snaps a 3D point to a regular grid in the X/Z plane, preserving Y. */
+export function snapVec3ToGrid(point: Vec3, step: number = DEFAULT_GRID_STEP): Vec3 {
+  return [snapScalar(point[0], step), point[1], snapScalar(point[2], step)]
+}
+
+// ─── Angle snap ───────────────────────────────────────────────────────
+
+/**
+ * Snaps a cursor point to the nearest angle multiple of `angleStep` (radians)
+ * measured from `from`, preserving distance. Useful for axis/diagonal-locked
+ * placement and wall draft endpoint locking.
+ *
+ * After the angle snap, the result is grid-snapped if `gridStep` is provided
+ * — keeps endpoints landing on grid intersections.
+ */
+export function snapPointToAngle(
+  from: Vec2,
+  cursor: Vec2,
+  angleStep: number = DEFAULT_ANGLE_STEP,
+  gridStep?: number,
+): Vec2 {
+  const dx = cursor[0] - from[0]
+  const dz = cursor[1] - from[1]
+  const angle = Math.atan2(dz, dx)
+  const snappedAngle = Math.round(angle / angleStep) * angleStep
+  const distance = Math.hypot(dx, dz)
+  const projected: Vec2 = [
+    from[0] + Math.cos(snappedAngle) * distance,
+    from[1] + Math.sin(snappedAngle) * distance,
+  ]
+  return gridStep == null ? projected : snapPointToGrid(projected, gridStep)
+}
+
+/**
+ * Snaps an angle (in radians) to the nearest entry in `snapAngles` (also in
+ * radians). Returns the original angle if no entry is within `toleranceRad`.
+ */
+export function snapAngleToList(
+  angle: number,
+  snapAngles: readonly number[],
+  toleranceRad: number = Math.PI / 36, // 5°
+): number {
+  let best: number | null = null
+  let bestDelta = Number.POSITIVE_INFINITY
+  for (const target of snapAngles) {
+    // wrap delta to [-π, π]
+    let delta = ((angle - target) % (Math.PI * 2)) + Math.PI * 3
+    delta = (delta % (Math.PI * 2)) - Math.PI
+    const abs = Math.abs(delta)
+    if (abs < bestDelta && abs <= toleranceRad) {
+      bestDelta = abs
+      best = target
+    }
+  }
+  return best ?? angle
+}
+
+// ─── Top-level SnapServices facade ────────────────────────────────────
+
+/**
+ * Stable surface that `DragAction.snap` callbacks receive. Phase 1 ships
+ * `grid` and `angle`. Phase 3 adds a `wall` namespace populated by wall
+ * migration. Plugin authors should target this facade rather than importing
+ * the individual functions, so future Phase contributions become visible
+ * without code changes.
+ */
+export type SnapServices = {
+  grid: {
+    snap: (point: Vec2, step?: number) => Vec2
+    snapVec3: (point: Vec3, step?: number) => Vec3
+    snapScalar: (value: number, step?: number) => number
+  }
+  angle: {
+    snapTo: (from: Vec2, cursor: Vec2, angleStep?: number, gridStep?: number) => Vec2
+    snapToList: (angle: number, list: readonly number[], toleranceRad?: number) => number
+  }
+}
+
+export const snapServices: SnapServices = {
+  grid: {
+    snap: snapPointToGrid,
+    snapVec3: snapVec3ToGrid,
+    snapScalar,
+  },
+  angle: {
+    snapTo: snapPointToAngle,
+    snapToList: snapAngleToList,
+  },
+}