diff --git a/internal/api/seed_lots_test.go b/internal/api/seed_lots_test.go
new file mode 100644
index 0000000..55735a6
--- /dev/null
+++ b/internal/api/seed_lots_test.go
@@ -0,0 +1,264 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+)
+
+func seedLotPath(id int64) string {
+	return "/api/v1/seed-lots/" + strconv.FormatInt(id, 10)
+}
+
+// decodeList decodes a bare JSON array body. Seed lot listing returns the array
+// directly rather than wrapping it (unlike /journal's {"entries": …}), so a
+// helper that assumed an object would quietly read nothing.
+func decodeList(t *testing.T, body []byte) []any {
+	t.Helper()
+	var out []any
+	if err := json.Unmarshal(body, &out); err != nil {
+		t.Fatalf("decode list: %v (%s)", err, body)
+	}
+	return out
+}
+
+// createPlantAPI makes a custom plant and returns its id.
+func createPlantAPI(t *testing.T, r *gin.Engine, cookie *http.Cookie, name string, spacing float64) int64 {
+	t.Helper()
+	w := doJSON(t, r, http.MethodPost, "/api/v1/plants", map[string]any{
+		"name": name, "category": "vegetable", "spacingCm": spacing, "color": "#4a7c3f", "icon": "🌱",
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("create plant %q: status %d, body %s", name, w.Code, w.Body.String())
+	}
+	return int64(decodeMap(t, w.Body.Bytes())["id"].(float64))
+}
+
+// TestSeedLotCrudAPI walks the whole seed lot lifecycle over HTTP.
+//
+// It exists for the reason CLAUDE.md gives: service tests cannot see a route
+// that was never registered, or one registered with the wrong :param name. Every
+// other handler file had a sibling API test; this group did not, which is the
+// state PATCH/DELETE /journal/:id shipped in — implemented, unit-tested, and
+// completely unreachable.
+func TestSeedLotCrudAPI(t *testing.T) {
+	r := authEngine(t, localCfg())
+	cookie := registerAndCookie(t, r, "lots@example.com")
+	plantID := createPlantAPI(t, r, cookie, "Music Garlic", 15)
+
+	// Create.
+	w := doJSON(t, r, http.MethodPost, "/api/v1/seed-lots", map[string]any{
+		"plantId": plantID, "vendor": "Johnny's", "sku": "2761",
+		"quantity": 100, "unit": "seeds", "packedForYear": 2026, "costCents": 495,
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("create: status %d, body %s", w.Code, w.Body.String())
+	}
+	lot := decodeMap(t, w.Body.Bytes())
+	id := int64(lot["id"].(float64))
+	if lot["vendor"] != "Johnny's" || lot["unit"] != "seeds" {
+		t.Errorf("unexpected lot: %+v", lot)
+	}
+
+	// GET by id — the route most likely to be missing or mis-registered.
+	w = doJSON(t, r, http.MethodGet, seedLotPath(id), nil, cookie)
+	if w.Code != http.StatusOK {
+		t.Fatalf("get: status %d, body %s", w.Code, w.Body.String())
+	}
+	if got := decodeMap(t, w.Body.Bytes()); int64(got["id"].(float64)) != id {
+		t.Errorf("get returned id %v, want %d", got["id"], id)
+	}
+
+	// List, and the ?plantId= filter.
+	w = doJSON(t, r, http.MethodGet, "/api/v1/seed-lots", nil, cookie)
+	if w.Code != http.StatusOK {
+		t.Fatalf("list: status %d, body %s", w.Code, w.Body.String())
+	}
+	if n := len(decodeList(t, w.Body.Bytes())); n != 1 {
+		t.Fatalf("list returned %d lots, want 1: %s", n, w.Body.String())
+	}
+
+	other := createPlantAPI(t, r, cookie, "Cherokee Purple", 45)
+	w = doJSON(t, r, http.MethodGet, "/api/v1/seed-lots?plantId="+strconv.FormatInt(other, 10), nil, cookie)
+	if w.Code != http.StatusOK {
+		t.Fatalf("filtered list: status %d, body %s", w.Code, w.Body.String())
+	}
+	if n := len(decodeList(t, w.Body.Bytes())); n != 0 {
+		t.Errorf("filter by a plant with no lots returned %d, want 0", n)
+	}
+	// A bad plantId filter is 400, whether non-numeric or out of range — the
+	// handler rejects id < 1, not just unparseable strings.
+	for _, bad := range []string{"nope", "0", "-1"} {
+		if w := doJSON(t, r, http.MethodGet, "/api/v1/seed-lots?plantId="+bad, nil, cookie); w.Code != http.StatusBadRequest {
+			t.Errorf("plantId=%q filter = %d, want 400", bad, w.Code)
+		}
+	}
+
+	// PATCH with the current version.
+	w = doJSON(t, r, http.MethodPatch, seedLotPath(id), map[string]any{
+		"vendor": "Fedco", "version": lot["version"],
+	}, cookie)
+	if w.Code != http.StatusOK {
+		t.Fatalf("patch: status %d, body %s", w.Code, w.Body.String())
+	}
+	updated := decodeMap(t, w.Body.Bytes())
+	if updated["vendor"] != "Fedco" {
+		t.Errorf("vendor = %v, want Fedco", updated["vendor"])
+	}
+	if updated["version"].(float64) != lot["version"].(float64)+1 {
+		t.Errorf("patch didn't bump version: %v -> %v", lot["version"], updated["version"])
+	}
+
+	// A stale version conflicts and carries the current row back, so the client
+	// can rebase without a second request.
+	w = doJSON(t, r, http.MethodPatch, seedLotPath(id), map[string]any{
+		"vendor": "stale", "version": lot["version"],
+	}, cookie)
+	if w.Code != http.StatusConflict {
+		t.Fatalf("stale patch: status %d, want 409", w.Code)
+	}
+	if cur, ok := decodeMap(t, w.Body.Bytes())["current"].(map[string]any); !ok || cur["vendor"] != "Fedco" {
+		t.Errorf("409 body missing the current row: %s", w.Body.String())
+	}
+
+	// DELETE.
+	if w := doJSON(t, r, http.MethodDelete, seedLotPath(id), nil, cookie); w.Code != http.StatusNoContent {
+		t.Fatalf("delete: status %d, body %s", w.Code, w.Body.String())
+	}
+	if w := doJSON(t, r, http.MethodGet, seedLotPath(id), nil, cookie); w.Code != http.StatusNotFound {
+		t.Errorf("get after delete = %d, want 404", w.Code)
+	}
+}
+
+// TestSeedLotRemainingIsDerivedAPI checks that `remaining` reflects plantings
+// through the HTTP surface, not just in the service.
+//
+// DESIGN.md makes derivation load-bearing — "a decremented column drifts the
+// moment a planting is edited behind its back" — so a route that returned a
+// stored or stale figure would break the invariant silently, and the number is
+// the whole reason anyone opens the seed shelf.
+func TestSeedLotRemainingIsDerivedAPI(t *testing.T) {
+	r := authEngine(t, localCfg())
+	cookie := registerAndCookie(t, r, "remaining@example.com")
+	plantID := createPlantAPI(t, r, cookie, "Beans", 10)
+
+	w := doJSON(t, r, http.MethodPost, "/api/v1/seed-lots", map[string]any{
+		"plantId": plantID, "quantity": 50, "unit": "seeds",
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("create lot: status %d, body %s", w.Code, w.Body.String())
+	}
+	lotID := int64(decodeMap(t, w.Body.Bytes())["id"].(float64))
+
+	gid := createGardenAPI(t, r, cookie, "G")
+	w = doJSON(t, r, http.MethodPost, objectsPath(gid), map[string]any{
+		"kind": "bed", "widthCm": 100, "heightCm": 100, "plantable": true,
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("create object: status %d, body %s", w.Code, w.Body.String())
+	}
+	oid := int64(decodeMap(t, w.Body.Bytes())["id"].(float64))
+
+	// Plant 12 of them against the lot.
+	w = doJSON(t, r, http.MethodPost, objectPlantingsPath(oid), map[string]any{
+		"plantId": plantID, "xCm": 0, "yCm": 0, "radiusCm": 20, "count": 12, "seedLotId": lotID,
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("create planting: status %d, body %s", w.Code, w.Body.String())
+	}
+
+	w = doJSON(t, r, http.MethodGet, seedLotPath(lotID), nil, cookie)
+	if w.Code != http.StatusOK {
+		t.Fatalf("get lot: status %d, body %s", w.Code, w.Body.String())
+	}
+	got := decodeMap(t, w.Body.Bytes())
+	if rem, ok := got["remaining"].(float64); !ok || rem != 38 {
+		t.Errorf("remaining = %v, want 38 (50 bought - 12 planted): %s", got["remaining"], w.Body.String())
+	}
+
+	// Over-plant it: 45 more (57 total against 50 bought) drives remaining
+	// NEGATIVE. That's deliberate — the number is a derived truth about what
+	// you've committed, not a floor clamped at zero, and "you've planted more than
+	// you bought" is exactly the signal a gardener wants rather than a hidden -7.
+	w = doJSON(t, r, http.MethodPost, objectPlantingsPath(oid), map[string]any{
+		"plantId": plantID, "xCm": 40, "yCm": 40, "radiusCm": 20, "count": 45, "seedLotId": lotID,
+	}, cookie)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("over-plant: status %d, body %s", w.Code, w.Body.String())
+	}
+	w = doJSON(t, r, http.MethodGet, seedLotPath(lotID), nil, cookie)
+	if rem, ok := decodeMap(t, w.Body.Bytes())["remaining"].(float64); !ok || rem != -7 {
+		t.Errorf("remaining after over-planting = %v, want -7 (50 - 57)", rem)
+	}
+}
+
+// TestSeedLotsArePrivateAPI checks the ACL through the router.
+//
+// Lots are private to the buyer and deliberately never travel with a shared
+// garden, so another user must not be able to read or edit one. Per the
+// project's convention, no-access is ErrNotFound rather than ErrForbidden —
+// existence is masked — so every one of these is a 404, not a 403.
+func TestSeedLotsArePrivateAPI(t *testing.T) {
+	r := authEngine(t, localCfg())
+	alice := registerAndCookie(t, r, "alice-lots@example.com")
+	bob := registerAndCookie(t, r, "bob-lots@example.com")
+
+	plantID := createPlantAPI(t, r, alice, "Alice's garlic", 15)
+	w := doJSON(t, r, http.MethodPost, "/api/v1/seed-lots", map[string]any{
+		"plantId": plantID, "vendor": "Secret Vendor", "quantity": 10, "unit": "bulbs",
+	}, alice)
+	if w.Code != http.StatusCreated {
+		t.Fatalf("alice create: status %d, body %s", w.Code, w.Body.String())
+	}
+	lotID := int64(decodeMap(t, w.Body.Bytes())["id"].(float64))
+
+	for _, tc := range []struct {
+		name   string
+		method string
+		body   any
+	}{
+		{"get", http.MethodGet, nil},
+		{"patch", http.MethodPatch, map[string]any{"vendor": "hijacked", "version": 1}},
+		{"delete", http.MethodDelete, nil},
+	} {
+		if w := doJSON(t, r, tc.method, seedLotPath(lotID), tc.body, bob); w.Code != http.StatusNotFound {
+			t.Errorf("bob %s = %d, want 404 (existence is masked)", tc.name, w.Code)
+		}
+	}
+
+	// Bob's own listing must not include it either.
+	w = doJSON(t, r, http.MethodGet, "/api/v1/seed-lots", nil, bob)
+	if w.Code != http.StatusOK {
+		t.Fatalf("bob list: status %d", w.Code)
+	}
+	if n := len(decodeList(t, w.Body.Bytes())); n != 0 {
+		t.Errorf("bob sees %d of alice's lots, want 0: %s", n, w.Body.String())
+	}
+
+	// And it's still intact for alice.
+	if w := doJSON(t, r, http.MethodGet, seedLotPath(lotID), nil, alice); w.Code != http.StatusOK {
+		t.Errorf("alice lost access to her own lot: %d", w.Code)
+	}
+}
+
+// TestSeedLotsRequireAuthAPI: the group is behind requireAuth, and an
+// unauthenticated caller gets 401 rather than an empty list.
+func TestSeedLotsRequireAuthAPI(t *testing.T) {
+	r := authEngine(t, localCfg())
+	for _, tc := range []struct {
+		method, path string
+	}{
+		{http.MethodGet, "/api/v1/seed-lots"},
+		{http.MethodPost, "/api/v1/seed-lots"},
+		{http.MethodGet, seedLotPath(1)},
+		{http.MethodPatch, seedLotPath(1)},
+		{http.MethodDelete, seedLotPath(1)},
+	} {
+		if w := doJSON(t, r, tc.method, tc.path, nil, nil); w.Code != http.StatusUnauthorized {
+			t.Errorf("%s %s = %d, want 401", tc.method, tc.path, w.Code)
+		}
+	}
+}