Establishes the patterns every later backend issue copies: the actor
parameter, centralized role checks, and the version-guard/409 sync
protocol. The service layer is the seam both REST handlers and future
agent tools call, so permissions live here, not in handlers.

- service/gardens.go: Service methods take (ctx, actorID, args).
  requireGardenRole(ctx, actor, gardenID, min) is THE authorization point
  — owner is implicit via owner_id now; #16 extends it to consult
  garden_shares. A user with no role gets ErrNotFound (existence masked),
  not ErrForbidden. Create/Get/List/Update/Delete with input validation
  (name required, 0 dims default to 10 m on create / rejected on update,
  negatives always rejected, unit metric|imperial, 100 m cap).
- store/gardens.go: version-guarded UPDATE ... WHERE id=? AND version=?
  RETURNING; a no-match re-reads to return (current row,
  ErrVersionConflict) vs ErrNotFound. ListGardensForOwner returns a
  non-nil slice.
- api/gardens.go: GET,POST /gardens and GET,PATCH,DELETE /gardens/:id
  behind requireAuth. writeVersionConflict documents the 409 envelope
  ({error:{code,message}, current:{...}}) — the contract for every
  mutable resource. writeResourceError maps ErrNotFound/Forbidden/
  InvalidInput/VersionConflict; parseIDParam guards path ids.

Tests: service (defaults, validation, owned-only list, version
conflict returns current + retry, cross-user ErrNotFound, delete) and
api (full CRUD flow, 409 envelope shape, cross-user 404, auth required,
create validation). Verified against the running binary: create stores
imperial 122x244 cm and list returns it.

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

@@ -0,0 +16,4 @@
+// endpoints. Dimensions are centimeters (the API is metric-only; imperial is a
+// display concern). On create, omitted dimensions default server-side; on
+// update, version is required and every field is replaced.
+type gardenCreateRequest struct {

@@ -0,0 +30,4 @@
+	HeightCM float64 `json:"heightCm"`
+	UnitPref string  `json:"unitPref"`
+	Notes    string  `json:"notes"`
+	Version  int64   `json:"version" binding:"required"`

@@ -0,0 +116,4 @@
+
+// parseIDParam reads a positive int64 path parameter, writing a 400 and
+// returning ok=false on a malformed value.
+func parseIDParam(c *gin.Context, name string) (int64, bool) {

@@ -0,0 +136,4 @@
+	})
+}
+
+// writeResourceError maps the service-layer sentinel errors shared by every

@@ -0,0 +145,4 @@
+		writeAPIError(c, http.StatusNotFound, "NOT_FOUND", "not found")
+	case errors.Is(err, domain.ErrForbidden):
+		writeAPIError(c, http.StatusForbidden, "FORBIDDEN", "you don't have access")
+	case errors.Is(err, domain.ErrInvalidInput):

@@ -0,0 +150,4 @@
+	case errors.Is(err, domain.ErrVersionConflict):
+		// Reached only if a caller forgot to special-case the conflict (which
+		// needs the current row); still return a coherent 409.
+		writeAPIError(c, http.StatusConflict, "VERSION_CONFLICT", "the resource was modified; refetch and retry")

@@ -0,0 +12,4 @@
+// absurd or overflow-y values.
+const (
+	defaultGardenCM = 1000
+	maxGardenCM     = 100_000

@@ -0,0 +116,4 @@
+// gardenFromInput validates and normalizes input into a domain.Garden (without
+// identity/ownership fields). With applyDefaults, absent dimensions/unit are
+// filled in (create); without it, every field must be supplied (update).
+func gardenFromInput(in GardenInput, applyDefaults bool) (*domain.Garden, error) {

@@ -0,0 +133,4 @@
+			height = defaultGardenCM
+		}
+	}
+	if width <= 0 || height <= 0 || width > maxGardenCM || height > maxGardenCM {

@@ -0,0 +25,4 @@
+
+// CreateGarden inserts a garden (owner_id, name, dimensions, unit, notes already
+// set and validated by the service) and returns the stored row.
+func (d *DB) CreateGarden(ctx context.Context, g *domain.Garden) (*domain.Garden, error) {

@@ -0,0 +57,4 @@
+// ListGardensForOwner returns the gardens owned by ownerID, newest first. The
+// slice is always non-nil (an empty list, not null). Shared-with-me gardens are
+// added in #16.
+func (d *DB) ListGardensForOwner(ctx context.Context, ownerID int64) ([]domain.Garden, error) {