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/ops.go

@@ -0,0 +1,147 @@
+package httpapi
+
+import (
+	"fmt"
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/google/uuid"
+
+	"github.com/mitbringsl/backend/internal/store"
+)
+
+// OpsHandler handles push and pull of op_log entries.
+type OpsHandler struct {
+	ops   *store.OpStore
+	lists *store.ListStore
+}
+
+// NewOpsHandler creates an OpsHandler with the given stores.
+func NewOpsHandler(ops *store.OpStore, lists *store.ListStore) *OpsHandler {
+	return &OpsHandler{ops: ops, lists: lists}
+}
+
+// --- request / response types -----------------------------------------------
+
+type pushRequest struct {
+	ClientID uuid.UUID         `json:"client_id"`
+	Ops      []store.IncomingOp `json:"ops"`
+}
+
+type pushResponse struct {
+	Results []store.OpResult `json:"results"`
+}
+
+type pullResponse struct {
+	Ops     []store.Op `json:"ops"`
+	HasMore bool       `json:"has_more"`
+}
+
+// --- handlers ---------------------------------------------------------------
+
+// Push accepts a batch of ops from the client, inserts them idempotently into
+// op_log, applies the LWW projection, and returns the server-assigned seq+hlc
+// for each op.
+//
+// POST /api/lists/{id}/ops
+func (h *OpsHandler) Push(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
+	}
+
+	// Verify the user owns (or is a member of) the list.
+	if _, err := h.lists.GetList(r.Context(), listID, userID); err != nil {
+		if !apiError(w, err) {
+			renderError(w, http.StatusNotFound, "Not found", "List not found.")
+		}
+		return
+	}
+
+	var req pushRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+
+	if req.ClientID == uuid.Nil {
+		renderError(w, http.StatusBadRequest, "Bad request", "client_id must be a non-nil UUID.")
+		return
+	}
+	if len(req.Ops) == 0 {
+		renderJSON(w, http.StatusOK, pushResponse{Results: []store.OpResult{}})
+		return
+	}
+	maxBatch := store.MaxPushBatch()
+	if len(req.Ops) > maxBatch {
+		renderError(w, http.StatusBadRequest, "Bad request",
+			fmt.Sprintf("Too many ops in a single request (max %d).", maxBatch))
+		return
+	}
+
+	results, err := h.ops.AppendOps(r.Context(), listID, userID, req.ClientID, req.Ops)
+	if err != nil {
+		slog.Error("push ops failed", "error", err, "list_id", listID, "user_id", userID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not store ops.")
+		return
+	}
+	renderJSON(w, http.StatusOK, pushResponse{Results: results})
+}
+
+// Pull returns ops for a list since a given server seq cursor.
+//
+// GET /api/lists/{id}/ops?since=0
+func (h *OpsHandler) Pull(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
+	}
+
+	// Verify list access.
+	if _, err := h.lists.GetList(r.Context(), listID, userID); err != nil {
+		if !apiError(w, err) {
+			renderError(w, http.StatusNotFound, "Not found", "List not found.")
+		}
+		return
+	}
+
+	since := int64(0)
+	if s := r.URL.Query().Get("since"); s != "" {
+		v, err := strconv.ParseInt(s, 10, 64)
+		if err != nil || v < 0 {
+			renderError(w, http.StatusBadRequest, "Bad request", "since must be a non-negative integer.")
+			return
+		}
+		since = v
+	}
+
+	ops, err := h.ops.PullOps(r.Context(), listID, since)
+	if err != nil {
+		slog.Error("pull ops failed", "error", err, "list_id", listID, "since", since)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not load ops.")
+		return
+	}
+	if ops == nil {
+		ops = []store.Op{}
+	}
+
+	// has_more is true when we returned exactly the page-size limit.
+	// The client should pull again with the last returned seq.
+	hasMore := len(ops) == 500 // pullPageSize is 500 in opstore.go
+
+	renderJSON(w, http.StatusOK, pullResponse{Ops: ops, HasMore: hasMore})
+}