- domain: Planting gains a computed (non-persisted) DerivedCount field.
- store/plantings.go: Get/Create/Update (version-guarded)/Delete alongside the
  existing /full read helper.
- service/plantings.go: place/move/resize/soft-remove a plop; editor role on the
  object's garden; object must be plantable; plant_id must be visible to the
  actor (built-in or own) else ErrInvalidInput; center must sit within the
  object's unrotated local bounds (radius may overhang); planted_at defaults to
  today. derivedCount = max(1, round(π·r²/spacing²)) — one unit-tested helper,
  reused by /full (via a spacing map, no N+1) and single responses.
- api: POST /objects/:id/plantings, PATCH/DELETE /plantings/:id; nullable
  count/label/plantedAt/removedAt use RawMessage so null (clear) is distinct
  from absent (unchanged). removedAt is the soft-remove / "clear bed" seam.
- /full now enriches each active plop with its derivedCount.

Service tests: formula edge cases (tiny radius → 1), defaults + derived, count
override, move/resize + clear override, non-plantable rejection, foreign/unknown
plant rejection, bounds, soft-remove leaves /full, version conflict, cross-user
masking, delete. Plus an API-level create/patch/full/delete flow.

GOWORK=off go build/vet/test ./internal/... green.

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

@@ -0,0 +80,4 @@
+		return
+	}
+	var req plantingCreateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {

@@ -0,0 +98,4 @@
+		return
+	}
+	var req plantingUpdateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {

@@ -0,0 +23,4 @@
+// mature spacing: max(1, round(π·r² / spacing²)). It is the single source of the
+// formula (also feeds #15's display and #19's FillRegion). A non-positive radius
+// or spacing collapses to the floor of 1.
+func derivedCount(radiusCM, spacingCM float64) int {

@@ -0,0 +28,4 @@
+		return 1
+	}
+	area := math.Pi * radiusCM * radiusCM
+	n := int(math.Round(area / (spacingCM * spacingCM)))

@@ -0,0 +104,4 @@
+	return created, nil
+}
+
+// UpdatePlanting applies a partial, version-guarded patch to a plop in an object

@@ -0,0 +110,4 @@
+	pl, err := s.store.GetPlanting(ctx, plantingID)
+	if err != nil {
+		return nil, err // ErrNotFound
+	}

@@ -0,0 +116,4 @@
+		return nil, err
+	}
+
+	applyPlantingPatch(pl, patch)

@@ -0,0 +145,4 @@
+	pl, err := s.store.GetPlanting(ctx, plantingID)
+	if err != nil {
+		return err
+	}

@@ -0,0 +171,4 @@
+
+// enrichDerived best-effort sets p.DerivedCount from its plant's spacing (used
+// when we don't already hold the plant, e.g. a conflict's current row).
+func (s *Service) enrichDerived(ctx context.Context, p *domain.Planting) {

@@ -0,0 +208,4 @@
+
+// finalizePlanting validates a built/merged plop against its parent object.
+// Shared by create and update so both enforce the same invariants.
+func finalizePlanting(p *domain.Planting, o *domain.GardenObject) error {

@@ -0,0 +226,4 @@
+	if p.Label != nil && len(*p.Label) > maxPlantingLabelLen {
+		return domain.ErrInvalidInput
+	}
+	if !validDatePtr(p.PlantedAt) || !validDatePtr(p.RemovedAt) {

@@ -0,0 +242,4 @@
+}
+
+// trimStringPtr trims a *string, preserving nil (distinct from empty).
+func trimStringPtr(s *string) *string {