Backend Phase C: Sync-Kern + Caddy behind-proxy

Sync-Kern:
- internal/sync/hlc.go: Hybrid Logical Clock (wall_ms<<16|counter)
  Tick/Now/After, global mutex, strikt monoton + kausal korrekt
- internal/sync/hlc_test.go: Unit-Tests (monoton, kausal, keine Duplikate)

Store-Schicht:
- internal/store/opstore.go: AppendOps idempotent via UNIQUE(client_id,
  client_seq) ON CONFLICT DO NOTHING; LWW-Projektion (list_create/
  rename/delete, item_add/update/remove) in derselben Transaktion;
  PullOps mit Cursor (seq > since, 500er Pages)
- internal/store/liststore.go: CreateList / GetLists / GetList
- internal/store/itemstore.go: GetItems (nicht-gelöschte Items)
- internal/store/suggeststore.go: Search (pg_trgm + LIKE-fallback, 10)

HTTP-Handler:
- internal/httpapi/lists.go: GET/POST /api/lists, GET /api/lists/{id}
- internal/httpapi/ops.go: POST /api/lists/{id}/ops (Push),
  GET /api/lists/{id}/ops (Pull ?since=)
- internal/httpapi/suggest.go: GET /api/suggestions?q=
- internal/httpapi/api.go: alle Routen verdrahtet (RequireAuth)

Deployment:
- deploy/Caddyfile.behind-proxy: auto_https off, trusted_proxies
- deploy/Caddyfile: X-Forwarded-Proto hinzugefügt, Kommentar aktualisiert
- deploy/docker-compose.yml: CADDY_HTTP_PORT + CADDY_HTTPS_PORT
- deploy/.env.example: Caddy-Port-Variablen dokumentiert

go build ./... && go vet ./... && go test ./... ✅
HLC-Tests: monoton, kausal, keine Duplikate ✅
AGENTS.md: Phase C vollständig ✅

backend/internal/httpapi/lists.go

@@ -0,0 +1,162 @@
+package httpapi
+
+import (
+	"log/slog"
+	"net/http"
+	"strings"
+
+	"github.com/google/uuid"
+
+	"github.com/mitbringsl/backend/internal/store"
+)
+
+// ListHandler handles the /api/lists endpoints.
+type ListHandler struct {
+	lists *store.ListStore
+	items *store.ItemStore
+}
+
+// NewListHandler creates a ListHandler with the given stores.
+func NewListHandler(lists *store.ListStore, items *store.ItemStore) *ListHandler {
+	return &ListHandler{lists: lists, items: items}
+}
+
+// --- request / response types -----------------------------------------------
+
+type createListRequest struct {
+	Name string `json:"name"`
+}
+
+type listDTO struct {
+	ID        string `json:"id"`
+	Name      string `json:"name"`
+	UpdatedAt string `json:"updated_at"`
+	HLCTS     int64  `json:"hlc_ts"`
+}
+
+type listDetailDTO struct {
+	listDTO
+	Items []store.Item `json:"items"`
+}
+
+type listListResponse struct {
+	Lists []listDTO `json:"lists"`
+}
+
+// --- handlers ---------------------------------------------------------------
+
+// List returns all non-deleted lists for the authenticated user.
+// GET /api/lists
+func (h *ListHandler) List(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFromCtx(r)
+	if !ok {
+		renderError(w, http.StatusUnauthorized, "Unauthorized", "Missing user context.")
+		return
+	}
+
+	ls, err := h.lists.GetLists(r.Context(), userID)
+	if err != nil {
+		slog.Error("list lists failed", "error", err, "user_id", userID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not load lists.")
+		return
+	}
+
+	dtos := make([]listDTO, len(ls))
+	for i, l := range ls {
+		dtos[i] = listDTO{
+			ID:        l.ID.String(),
+			Name:      l.Name,
+			UpdatedAt: l.UpdatedAt.Format("2006-01-02T15:04:05Z07:00"),
+			HLCTS:     l.HLCTS,
+		}
+	}
+	renderJSON(w, http.StatusOK, listListResponse{Lists: dtos})
+}
+
+// Create creates a new list for the authenticated user.
+// POST /api/lists
+func (h *ListHandler) Create(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFromCtx(r)
+	if !ok {
+		renderError(w, http.StatusUnauthorized, "Unauthorized", "Missing user context.")
+		return
+	}
+
+	var req createListRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+	name := strings.TrimSpace(req.Name)
+	if name == "" {
+		renderError(w, http.StatusBadRequest, "Bad request", "List name must not be empty.")
+		return
+	}
+
+	l, err := h.lists.CreateList(r.Context(), userID, name)
+	if err != nil {
+		slog.Error("create list failed", "error", err, "user_id", userID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not create list.")
+		return
+	}
+	renderJSON(w, http.StatusCreated, listDTO{
+		ID:        l.ID.String(),
+		Name:      l.Name,
+		UpdatedAt: l.UpdatedAt.Format("2006-01-02T15:04:05Z07:00"),
+		HLCTS:     l.HLCTS,
+	})
+}
+
+// Get returns a single list with its items.
+// GET /api/lists/{id}
+func (h *ListHandler) Get(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFromCtx(r)
+	if !ok {
+		renderError(w, http.StatusUnauthorized, "Unauthorized", "Missing user context.")
+		return
+	}
+
+	listID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		renderError(w, http.StatusBadRequest, "Bad request", "Invalid list ID.")
+		return
+	}
+
+	l, err := h.lists.GetList(r.Context(), listID, userID)
+	if err != nil {
+		if !apiError(w, err) {
+			slog.Error("get list failed", "error", err, "list_id", listID)
+			renderError(w, http.StatusInternalServerError, "Internal error", "Could not load list.")
+		}
+		return
+	}
+
+	its, err := h.items.GetItems(r.Context(), listID)
+	if err != nil {
+		slog.Error("get items failed", "error", err, "list_id", listID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not load items.")
+		return
+	}
+	if its == nil {
+		its = []store.Item{}
+	}
+
+	renderJSON(w, http.StatusOK, listDetailDTO{
+		listDTO: listDTO{
+			ID:        l.ID.String(),
+			Name:      l.Name,
+			UpdatedAt: l.UpdatedAt.Format("2006-01-02T15:04:05Z07:00"),
+			HLCTS:     l.HLCTS,
+		},
+		Items: its,
+	})
+}
+
+// userIDFromCtx extracts the user UUID from the request context (set by RequireAuth).
+func userIDFromCtx(r *http.Request) (uuid.UUID, bool) {
+	v := r.Context().Value(ctxKeyUserID)
+	if v == nil {
+		return uuid.Nil, false
+	}
+	id, ok := v.(uuid.UUID)
+	return id, ok
+}