Address Gadfly review on #14: bounds trap, date order, count cap

- UpdatePlanting: only re-check the object-bounds when the position is actually
  being moved. A plop orphaned outside its object by a later resize stays
  editable/removable instead of becoming a row you can't fix or delete.
- finalizePlanting: reject removed_at before planted_at.
- derivedCount: guard Inf (not just NaN) and cap the result at maxExplicitCount
  (1e6) — the same ceiling a manual override honors — so a huge radius / tiny
  spacing can't overflow a 32-bit int or return an absurd value.
- Refresh stale docs that referenced #14 as not-yet-landed (FullGarden,
  ListActivePlantingsForGarden, ListReferencedPlants) and note the date-only
  layout beside timeLayout.

Deliberately did NOT add a plantable re-check to Update/Delete: existing plops
must stay editable/removable even if their object was later marked non-plantable
(same trap as the bounds case).

Tests: derived-count cap, removed-before-planted rejection, and edit/move of a
plop orphaned by an object shrink.

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

internal/service/plantings.go

@@ -21,10 +21,12 @@ const (
 
 // derivedCount is the plant count implied by a plop's area and the plant's
 // 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.
+// formula (also feeds #15's display and #19's FillRegion). A non-positive or
+// non-finite radius/spacing collapses to the floor of 1; the result is capped at
+// maxExplicitCount so a huge radius / tiny spacing can't yield an absurd (or, on
+// a 32-bit int, overflowing) value — the same ceiling a manual override honors.
 func derivedCount(radiusCM, spacingCM float64) int {
-	if radiusCM <= 0 || spacingCM <= 0 || math.IsNaN(radiusCM) || math.IsNaN(spacingCM) {
+	if radiusCM <= 0 || spacingCM <= 0 || !isFinite(radiusCM) || !isFinite(spacingCM) {
 		return 1
 	}
 	area := math.Pi * radiusCM * radiusCM
@@ -32,6 +34,9 @@ func derivedCount(radiusCM, spacingCM float64) int {
 	if n < 1 {
 		return 1
 	}
+	if n > maxExplicitCount {
+		return maxExplicitCount
+	}
 	return n
 }
 
@@ -93,7 +98,7 @@ func (s *Service) CreatePlanting(ctx context.Context, actorID, objectID int64, i
 		today := s.now().UTC().Format(dateLayout)
 		p.PlantedAt = &today
 	}
-	if err := finalizePlanting(p, o); err != nil {
+	if err := finalizePlanting(p, o, true); err != nil {
 		return nil, err
 	}
 	created, err := s.store.CreatePlanting(ctx, p)
@@ -122,7 +127,12 @@ func (s *Service) UpdatePlanting(ctx context.Context, actorID, plantingID int64,
 	if err != nil {
 		return nil, err
 	}
-	if err := finalizePlanting(pl, o); err != nil {
+	// Only re-check the object bounds when the position is actually being moved.
+	// A plop left outside its object's bounds by a later object resize must still
+	// be editable (radius, dates, soft-remove) — otherwise it becomes a row you
+	// can neither fix nor remove.
+	checkBounds := patch.XCM != nil || patch.YCM != nil
+	if err := finalizePlanting(pl, o, checkBounds); err != nil {
 		return nil, err
 	}
 	pl.Version = version
@@ -207,8 +217,11 @@ func applyPlantingPatch(pl *domain.Planting, p PlantingPatch) {
 }
 
 // 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 {
+// Shared by create and update so both enforce the same invariants. checkBounds
+// gates the center-in-object-bounds test: create always checks it, update only
+// when the position is being moved (so a resize that orphans a plop outside the
+// shrunken object doesn't block editing/removing it).
+func finalizePlanting(p *domain.Planting, o *domain.GardenObject, checkBounds bool) error {
 	if !isFinite(p.RadiusCM) || p.RadiusCM <= 0 || p.RadiusCM > maxRadiusCM {
 		return domain.ErrInvalidInput
 	}
@@ -217,7 +230,7 @@ func finalizePlanting(p *domain.Planting, o *domain.GardenObject) error {
 	}
 	// Loose bounds: the plop's CENTER must sit within the object's unrotated
 	// local bounds (origin at object center); the radius may overhang.
-	if math.Abs(p.XCM) > o.WidthCM/2 || math.Abs(p.YCM) > o.HeightCM/2 {
+	if checkBounds && (math.Abs(p.XCM) > o.WidthCM/2 || math.Abs(p.YCM) > o.HeightCM/2) {
 		return domain.ErrInvalidInput
 	}
 	if p.Count != nil && (*p.Count < 1 || *p.Count > maxExplicitCount) {
@@ -229,6 +242,14 @@ func finalizePlanting(p *domain.Planting, o *domain.GardenObject) error {
 	if !validDatePtr(p.PlantedAt) || !validDatePtr(p.RemovedAt) {
 		return domain.ErrInvalidInput
 	}
+	// A plop can't be removed before it was planted (nonsensical interval).
+	if p.PlantedAt != nil && p.RemovedAt != nil {
+		planted, _ := time.Parse(dateLayout, *p.PlantedAt)
+		removed, _ := time.Parse(dateLayout, *p.RemovedAt)
+		if removed.Before(planted) {
+			return domain.ErrInvalidInput
+		}
+	}
 	return nil
 }