Two independent grids, each with a size and a snap toggle:

- Garden grid (owner-set, in the garden settings form): drives the
  editor's visual grid and, when snapping is on, snaps objects on
  place/move and snaps their dimensions to whole grid steps on resize.
- Bed grid (per plantable object, in the bed Inspector): when snapping
  is on, plants snap to the bed's grid on place/move, and the grid is
  drawn inside the focused bed. Plant radius stays free.

Snapping defaults off on both, so existing gardens keep free placement.
Grid spacing shares the [1cm, 100m] range and defaults to 1m (garden) /
30cm (bed); 0 is treated as unset and re-defaulted.

Backend: migration 0005 adds grid_size_cm/snap_to_grid to gardens and
garden_objects, threaded through domain/store/service/api with service +
api round-trip tests. Frontend: new geometry snap helpers (unit-tested),
schema/type plumbing, canvas + overlay snapping, and the two forms.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01JdQpdYYsTgtkJBxbcpAszi

@@ -15,2 +15,3 @@
 func scanGarden(s scanner) (*domain.Garden, error) {
-	var g domain.Garden
+	var (
+		g    domain.Garden

@@ -0,0 +2,4 @@
+--
+-- Two independent grids:
+--   * gardens.grid_size_cm / snap_to_grid — the garden-scale grid the visual grid
+--     is drawn from and (when snap is on) objects snap to when placed/moved/resized.

@@ -54,1 +62,4 @@
     }
+    // The grid is entered at spacing scale (cm/in), so it converts with the
+    // spacing helpers, not the dimension ones.
+    const convertGrid = (s: string) => {

@@ -25,0 +29,4 @@
+function bedGridLines(half: number, step: number): number[] {
+  if (!(step > 0) || (2 * half) / step > BED_GRID_MAX_LINES) return []
+  const lines: number[] = []
+  for (let v = -half; v <= half + 1e-6; v += step) lines.push(v)

@@ -148,0 +161,4 @@
+    const halfH = focusedObject.heightCm / 2
+    // Snap the plant to the bed's grid when the bed opts in; snapLocalToBedGrid
+    // also clamps, so the plain clamp covers the non-snapping case.
+    const placed = focusedObject.snapToGrid

@@ -157,0 +179,4 @@
+  // so the user sees exactly where plants will land. Lines are in the bed's local
+  // frame (origin at center), anchored to the corner to match snapLocalToBedGrid.
+  const showBedGrid = !!focusedObject && focusedObject.plantable && focusedObject.snapToGrid
+  const bedVLines = showBedGrid ? bedGridLines(halfFW, focusedObject.gridSizeCm) : []

@@ -106,1 +112,3 @@
-        const next = clampLocal({ x: base.xCm + (p.x - start.x), y: base.yCm + (p.y - start.y) })
+        const moved: Point = { x: base.xCm + (p.x - start.x), y: base.yCm + (p.y - start.y) }
+        // snapLocalToBedGrid clamps too, so the plain clamp covers the non-snap case.
+        const next = snap ? snapLocalToBedGrid(moved, gridCm, halfW, halfH) : clampLocal(moved)

@@ -71,0 +90,4 @@
+ * clamped to the bed bounds so a plant never snaps outside it. step<=0 → only
+ * clamped, not snapped.
+ */
+export function snapLocalToBedGrid(p: Point, step: number, halfW: number, halfH: number): Point {