Add configurable grid + snap to the layout system

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

internal/service/gardens.go

@@ -13,11 +13,12 @@ import (
 // sanity range that also rejects NaN/Inf and absurd values. Name/notes are
 // length-capped so untrusted input can't balloon storage.
 const (
-	defaultGardenCM   = 1000   // 10 m
-	minGardenCM       = 1      // 1 cm
-	maxGardenCM       = 10_000 // 100 m
-	maxGardenNameLen  = 200
-	maxGardenNotesLen = 10_000
+	defaultGardenCM     = 1000   // 10 m
+	minGardenCM         = 1      // 1 cm
+	maxGardenCM         = 10_000 // 100 m
+	defaultGardenGridCM = 100    // 1 m, matching the editor's previous fixed grid
+	maxGardenNameLen    = 200
+	maxGardenNotesLen   = 10_000
 )
 
 // gardenRole ranks a user's access to a garden. Higher includes lower
@@ -48,11 +49,13 @@ func (r gardenRole) String() string {
 
 // GardenInput is the mutable field set for creating or updating a garden.
 type GardenInput struct {
-	Name     string
-	WidthCM  float64
-	HeightCM float64
-	UnitPref string
-	Notes    string
+	Name       string
+	WidthCM    float64
+	HeightCM   float64
+	UnitPref   string
+	Notes      string
+	GridSizeCM float64
+	SnapToGrid bool
 }
 
 // requireGardenRole loads a garden and enforces that the actor holds at least
@@ -198,12 +201,26 @@ func gardenFromInput(in GardenInput, applyDefaults bool) (*domain.Garden, error)
 		return nil, domain.ErrInvalidInput
 	}
 
+	// Grid spacing shares the garden dimension range [1 cm, 100 m]. 0 means
+	// "unset" — defaulted (not just on create: an older client that omits it must
+	// not wipe the column to an invalid 0), so a saved garden always has a usable
+	// grid even if snapping is off.
+	grid := in.GridSizeCM
+	if grid == 0 {
+		grid = defaultGardenGridCM
+	}
+	if !validDimensionCM(grid) {
+		return nil, domain.ErrInvalidInput
+	}
+
 	return &domain.Garden{
-		Name:     name,
-		WidthCM:  width,
-		HeightCM: height,
-		UnitPref: unit,
-		Notes:    notes,
+		Name:       name,
+		WidthCM:    width,
+		HeightCM:   height,
+		UnitPref:   unit,
+		Notes:      notes,
+		GridSizeCM: grid,
+		SnapToGrid: in.SnapToGrid,
 	}, nil
 }
 

internal/service/gardens_test.go

@@ -57,6 +57,7 @@ func TestCreateGardenValidation(t *testing.T) {
 		{Name: "X", WidthCM: math.NaN()},                             // NaN slips past naive < / >
 		{Name: "X", HeightCM: math.Inf(1)},                           // +Inf
 		{Name: "X", WidthCM: math.SmallestNonzeroFloat64},            // subnormal, > 0 but < 1 cm
+		{Name: "X", GridSizeCM: maxGardenCM + 1},                     // grid over the cap
 	}
 	for i, in := range cases {
 		if _, err := s.CreateGarden(context.Background(), owner, in); !errors.Is(err, domain.ErrInvalidInput) {
@@ -70,6 +71,51 @@ func TestCreateGardenValidation(t *testing.T) {
 	}
 }
 
+func TestGardenGridSettings(t *testing.T) {
+	s := newTestService(t, openConfig())
+	owner := seedUser(t, s, "[email protected]")
+	ctx := context.Background()
+
+	// An omitted grid size lands the default; snap defaults off.
+	g, err := s.CreateGarden(ctx, owner, GardenInput{Name: "G"})
+	if err != nil {
+		t.Fatalf("CreateGarden: %v", err)
+	}
+	if g.GridSizeCM != defaultGardenGridCM {
+		t.Errorf("grid = %v, want default %d", g.GridSizeCM, defaultGardenGridCM)
+	}
+	if g.SnapToGrid {
+		t.Error("snap should default off")
+	}
+
+	// An update sets an explicit grid and turns snap on; both persist.
+	up, err := s.UpdateGarden(ctx, owner, g.ID, GardenInput{
+		Name: "G", WidthCM: g.WidthCM, HeightCM: g.HeightCM, UnitPref: g.UnitPref,
+		GridSizeCM: 25, SnapToGrid: true,
+	}, g.Version)
+	if err != nil {
+		t.Fatalf("UpdateGarden: %v", err)
+	}
+	got, err := s.GetGarden(ctx, owner, g.ID)
+	if err != nil {
+		t.Fatalf("GetGarden: %v", err)
+	}
+	if got.GridSizeCM != 25 || !got.SnapToGrid {
+		t.Errorf("persisted grid=%v snap=%v, want 25/true", got.GridSizeCM, got.SnapToGrid)
+	}
+
+	// An update omitting the grid size (0) is re-defaulted, not stored as 0.
+	up2, err := s.UpdateGarden(ctx, owner, g.ID, GardenInput{
+		Name: "G", WidthCM: g.WidthCM, HeightCM: g.HeightCM, UnitPref: g.UnitPref,
+	}, up.Version)
+	if err != nil {
+		t.Fatalf("UpdateGarden(reset): %v", err)
+	}
+	if up2.GridSizeCM != defaultGardenGridCM || up2.SnapToGrid {
+		t.Errorf("after omit grid=%v snap=%v, want default/false", up2.GridSizeCM, up2.SnapToGrid)
+	}
+}
+
 func TestListGardensOwnedOnly(t *testing.T) {
 	s := newTestService(t, openConfig())
 	alice := seedUser(t, s, "[email protected]")

internal/service/objects.go

@@ -10,9 +10,10 @@ import (
 )
 
 const (
-	maxObjectNameLen  = 200
-	maxObjectNotesLen = 10_000
-	maxObjectPropsLen = 20_000
+	maxObjectNameLen    = 200
+	maxObjectNotesLen   = 10_000
+	maxObjectPropsLen   = 20_000
+	defaultObjectGridCM = 30 // ~1 ft, a practical bed cell for plant snapping
 )
 
 // objectKinds maps each valid garden_objects.kind to its traits. plantable is
@@ -43,6 +44,8 @@ type ObjectInput struct {
 	Plantable   *bool
 	Color       *string
 	Props       *string
+	GridSizeCM  float64
+	SnapToGrid  bool
 	Notes       string
 }
 
@@ -65,6 +68,8 @@ type ObjectPatch struct {
 	Color       *string
 	SetProps    bool
 	Props       *string
+	GridSizeCM  *float64
+	SnapToGrid  *bool
 	Notes       *string
 }
 
@@ -110,6 +115,8 @@ func (s *Service) CreateObject(ctx context.Context, actorID, gardenID int64, in
 		Plantable:   plantable,
 		Color:       in.Color,
 		Props:       in.Props,
+		GridSizeCM:  in.GridSizeCM,
+		SnapToGrid:  in.SnapToGrid,
 		Notes:       strings.TrimSpace(in.Notes),
 	}
 	if err := finalizeObject(o, g); err != nil {
@@ -229,6 +236,12 @@ func applyObjectPatch(o *domain.GardenObject, p ObjectPatch) {
 	if p.SetProps {
 		o.Props = p.Props
 	}
+	if p.GridSizeCM != nil {
+		o.GridSizeCM = *p.GridSizeCM
+	}
+	if p.SnapToGrid != nil {
+		o.SnapToGrid = *p.SnapToGrid
+	}
 	if p.Notes != nil {
 		o.Notes = strings.TrimSpace(*p.Notes)
 	}
@@ -251,6 +264,15 @@ func finalizeObject(o *domain.GardenObject, g *domain.Garden) error {
 	if !validDimensionCM(o.WidthCM) || !validDimensionCM(o.HeightCM) {
 		return domain.ErrInvalidInput
 	}
+	// Grid spacing shares the dimension range [1 cm, 100 m]; 0 means "unset" and
+	// is defaulted so a create (or an older client omitting it) still lands a
+	// usable bed grid.
+	if o.GridSizeCM == 0 {
+		o.GridSizeCM = defaultObjectGridCM
+	}
+	if !validDimensionCM(o.GridSizeCM) {
+		return domain.ErrInvalidInput
+	}
 	if !isFinite(o.XCM) || !isFinite(o.YCM) || !isFinite(o.RotationDeg) {
 		return domain.ErrInvalidInput
 	}

internal/service/objects_test.go

@@ -48,6 +48,41 @@ func TestCreateObjectDefaults(t *testing.T) {
 	}
 }
 
+func TestObjectGridSettings(t *testing.T) {
+	s := newTestService(t, openConfig())
+	owner := seedUser(t, s, "[email protected]")
+	g := seedGarden(t, s, owner)
+	ctx := context.Background()
+
+	// An omitted grid size defaults; snap defaults off.
+	o, err := s.CreateObject(ctx, owner, g.ID, ObjectInput{
+		Kind: domain.KindBed, XCM: 500, YCM: 500, WidthCM: 200, HeightCM: 100,
+	})
+	if err != nil {
+		t.Fatalf("CreateObject: %v", err)
+	}
+	if o.GridSizeCM != defaultObjectGridCM {
+		t.Errorf("grid = %v, want default %d", o.GridSizeCM, defaultObjectGridCM)
+	}
+	if o.SnapToGrid {
+		t.Error("snap should default off")
+	}
+
+	// Patching grid + snap round-trips and leaves other fields untouched.
+	grid := 15.0
+	snap := true
+	up, err := s.UpdateObject(ctx, owner, o.ID, ObjectPatch{GridSizeCM: &grid, SnapToGrid: &snap}, o.Version)
+	if err != nil {
+		t.Fatalf("UpdateObject: %v", err)
+	}
+	if up.GridSizeCM != 15 || !up.SnapToGrid {
+		t.Errorf("after patch grid=%v snap=%v, want 15/true", up.GridSizeCM, up.SnapToGrid)
+	}
+	if up.WidthCM != 200 || up.HeightCM != 100 {
+		t.Errorf("a grid patch changed dimensions: %vx%v", up.WidthCM, up.HeightCM)
+	}
+}
+
 func TestCreateObjectPlantableByKind(t *testing.T) {
 	s := newTestService(t, openConfig())
 	owner := seedUser(t, s, "[email protected]")
@@ -105,6 +140,7 @@ func TestCreateObjectValidation(t *testing.T) {
 		{Kind: domain.KindBed, XCM: 500, YCM: 500, WidthCM: 100, HeightCM: 100, Color: strPtr("nope")},                         // bad color
 		{Kind: domain.KindBed, XCM: 500, YCM: 500, WidthCM: 100, HeightCM: 100, Props: strPtr("{not json")},                    // bad props
 		{Kind: domain.KindBed, XCM: 500, YCM: 500, WidthCM: 100, HeightCM: 100, Name: strings.Repeat("x", maxObjectNameLen+1)}, // name too long
+		{Kind: domain.KindBed, XCM: 500, YCM: 500, WidthCM: 100, HeightCM: 100, GridSizeCM: maxGardenCM + 1},                   // grid over the cap
 	}
 	for i, in := range bad {
 		if _, err := s.CreateObject(context.Background(), owner, g.ID, in); !errors.Is(err, domain.ErrInvalidInput) {