Address Gadfly review on #19: batch fills + tighten Region

- FillRegion: insert the whole batch in one transaction (store.CreatePlantings)
  instead of one round-trip per plop, and refuse fills over maxFillPlops (5000)
  so a max-sized bed with tiny spacing can't generate ~10^5 sequential writes.
  Guards the computed radius is finite/positive and clamps the region to the
  object's bounds before packing (bounds hexCenters).
- FillNamedRegion + FillRegion share a fillLoaded body, so the object is loaded
  and authorized once (no double objectForRole).
- Region is now rect-only — dropped the speculative circle fields/branch that
  NamedRegion never produced and hexCenters didn't pack (circles are post-v1).
- NamedRegion guards a nil object and no longer maps a blank name to "all"
  (blank → ErrInvalidInput, matching the doc).
- ClearObject documents why it deliberately doesn't require plantable.

Tests: empty/nil region name → ErrInvalidInput; an oversized fill → ErrInvalidInput
(over the cap). Tagged demo tidied (checked errors, domain.RoleViewer, t.Helper).

GOWORK=off go build/vet/test ./internal/... green; tagged agent test green against
majordomo (go.mod stays majordomo-free).

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

internal/agent/tools_test.go

@@ -10,6 +10,7 @@ import (
 	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
 
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/config"
+	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/service"
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/store"
 )
@@ -51,9 +52,9 @@ func TestToolboxScenario(t *testing.T) {
 	if err != nil {
 		t.Fatalf("garden: %v", err)
 	}
-	garlic, _ := svc.CreatePlant(ctx, owner.ID, service.PlantInput{Name: "Garlic", Category: "vegetable", SpacingCM: 15, Color: "#d9d2c5", Icon: "🧄"})
-	basil, _ := svc.CreatePlant(ctx, owner.ID, service.PlantInput{Name: "Basil", Category: "herb", SpacingCM: 25, Color: "#4a7c3f", Icon: "🌿"})
-	beans, _ := svc.CreatePlant(ctx, owner.ID, service.PlantInput{Name: "Beans", Category: "vegetable", SpacingCM: 10, Color: "#6b8e23", Icon: "🫘"})
+	garlic := mustPlant(t, svc, owner.ID, "Garlic", 15, "🧄")
+	basil := mustPlant(t, svc, owner.ID, "Basil", 25, "🌿")
+	beans := mustPlant(t, svc, owner.ID, "Beans", 10, "🫘")
 
 	// create_object → a 400×400 bed.
 	res := call("create_object", map[string]any{
@@ -114,12 +115,15 @@ func TestToolboxScenario(t *testing.T) {
 	}
 
 	// ACL: a viewer's fill_region is refused (the toolbox runs as that actor).
-	viewerUser, _ := svc.Register(ctx, service.RegisterInput{Email: "[email protected]", DisplayName: "V", Password: "password123"})
-	if _, err := svc.AddShare(ctx, owner.ID, g.ID, "[email protected]", "viewer"); err != nil {
+	viewerUser, err := svc.Register(ctx, service.RegisterInput{Email: "[email protected]", DisplayName: "V", Password: "password123"})
+	if err != nil {
+		t.Fatalf("register viewer: %v", err)
+	}
+	if _, err := svc.AddShare(ctx, owner.ID, g.ID, "[email protected]", domain.RoleViewer); err != nil {
 		t.Fatalf("share: %v", err)
 	}
 	viewerBox := NewToolbox(svc, viewerUser.ID)
-	vr := viewerBox.Execute(ctx, llm.ToolCall{ID: "2", Name: "fill_region", Arguments: mustJSON(map[string]any{
+	vr := viewerBox.Execute(ctx, llm.ToolCall{ID: "2", Name: "fill_region", Arguments: mustJSON(t, map[string]any{
 		"objectId": bed.ID, "region": "all", "plantId": garlic.ID,
 	})})
 	if !vr.IsError {
@@ -127,7 +131,22 @@ func TestToolboxScenario(t *testing.T) {
 	}
 }
 
-func mustJSON(v any) json.RawMessage {
-	b, _ := json.Marshal(v)
+func mustJSON(t *testing.T, v any) json.RawMessage {
+	t.Helper()
+	b, err := json.Marshal(v)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
 	return b
 }
+
+func mustPlant(t *testing.T, svc *service.Service, owner int64, name string, spacing float64, icon string) *domain.Plant {
+	t.Helper()
+	p, err := svc.CreatePlant(context.Background(), owner, service.PlantInput{
+		Name: name, Category: domain.CategoryVegetable, SpacingCM: spacing, Color: "#4a7c3f", Icon: icon,
+	})
+	if err != nil {
+		t.Fatalf("create plant %s: %v", name, err)
+	}
+	return p
+}