feat: add case + party CRUD with case events (Phase 1B)

- CaseService: list (paginated, filterable), get detail (with parties,
  events, deadline count), create, update, soft-delete (archive)
- PartyService: list by case, create, update, delete
- Auto-create case_events on case creation, status change, party add,
  and case archive
- Auth middleware now resolves tenant_id from user_tenants table
- All operations scoped to tenant_id from auth context

backend/cmd/server/main.go

@@ -22,7 +22,7 @@ func main() {
 	}
 	defer database.Close()
 
-	authMW := auth.NewMiddleware(cfg.SupabaseJWTSecret)
+	authMW := auth.NewMiddleware(cfg.SupabaseJWTSecret, database)
 	handler := router.New(database, authMW)
 
 	log.Printf("Starting KanzlAI API server on :%s", cfg.Port)

backend/internal/auth/middleware.go

@@ -8,14 +8,16 @@ import (
 
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
 )
 
 type Middleware struct {
 	jwtSecret []byte
+	db        *sqlx.DB
 }
 
-func NewMiddleware(jwtSecret string) *Middleware {
-	return &Middleware{jwtSecret: []byte(jwtSecret)}
+func NewMiddleware(jwtSecret string, db *sqlx.DB) *Middleware {
+	return &Middleware{jwtSecret: []byte(jwtSecret), db: db}
 }
 
 func (m *Middleware) RequireAuth(next http.Handler) http.Handler {
@@ -33,6 +35,17 @@ func (m *Middleware) RequireAuth(next http.Handler) http.Handler {
 		}
 
 		ctx := ContextWithUserID(r.Context(), userID)
+
+		// Resolve tenant from user_tenants
+		var tenantID uuid.UUID
+		err = m.db.GetContext(r.Context(), &tenantID,
+			"SELECT tenant_id FROM user_tenants WHERE user_id = $1 LIMIT 1", userID)
+		if err != nil {
+			http.Error(w, "no tenant found for user", http.StatusForbidden)
+			return
+		}
+		ctx = ContextWithTenantID(ctx, tenantID)
+
 		next.ServeHTTP(w, r.WithContext(ctx))
 	})
 }

backend/internal/handlers/cases.go

@@ -0,0 +1,158 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+
+	"github.com/google/uuid"
+)
+
+type CaseHandler struct {
+	svc *services.CaseService
+}
+
+func NewCaseHandler(svc *services.CaseService) *CaseHandler {
+	return &CaseHandler{svc: svc}
+}
+
+func (h *CaseHandler) List(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
+	offset, _ := strconv.Atoi(r.URL.Query().Get("offset"))
+
+	filter := services.CaseFilter{
+		Status: r.URL.Query().Get("status"),
+		Type:   r.URL.Query().Get("type"),
+		Search: r.URL.Query().Get("search"),
+		Limit:  limit,
+		Offset: offset,
+	}
+
+	cases, total, err := h.svc.List(r.Context(), tenantID, filter)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"cases": cases,
+		"total": total,
+	})
+}
+
+func (h *CaseHandler) Create(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+	userID, _ := auth.UserFromContext(r.Context())
+
+	var input services.CreateCaseInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON body")
+		return
+	}
+	if input.CaseNumber == "" || input.Title == "" {
+		writeError(w, http.StatusBadRequest, "case_number and title are required")
+		return
+	}
+
+	c, err := h.svc.Create(r.Context(), tenantID, userID, input)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, c)
+}
+
+func (h *CaseHandler) Get(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	caseID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	detail, err := h.svc.GetByID(r.Context(), tenantID, caseID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	if detail == nil {
+		writeError(w, http.StatusNotFound, "case not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, detail)
+}
+
+func (h *CaseHandler) Update(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+	userID, _ := auth.UserFromContext(r.Context())
+
+	caseID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	var input services.UpdateCaseInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON body")
+		return
+	}
+
+	updated, err := h.svc.Update(r.Context(), tenantID, caseID, userID, input)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	if updated == nil {
+		writeError(w, http.StatusNotFound, "case not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, updated)
+}
+
+func (h *CaseHandler) Delete(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+	userID, _ := auth.UserFromContext(r.Context())
+
+	caseID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	if err := h.svc.Delete(r.Context(), tenantID, caseID, userID); err != nil {
+		writeError(w, http.StatusNotFound, "case not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"status": "archived"})
+}

backend/internal/handlers/helpers.go

@@ -0,0 +1,16 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+func writeJSON(w http.ResponseWriter, status int, v interface{}) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(v)
+}
+
+func writeError(w http.ResponseWriter, status int, message string) {
+	writeJSON(w, status, map[string]string{"error": message})
+}

backend/internal/handlers/parties.go

@@ -0,0 +1,134 @@
+package handlers
+
+import (
+	"database/sql"
+	"encoding/json"
+	"net/http"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
+
+	"github.com/google/uuid"
+)
+
+type PartyHandler struct {
+	svc *services.PartyService
+}
+
+func NewPartyHandler(svc *services.PartyService) *PartyHandler {
+	return &PartyHandler{svc: svc}
+}
+
+func (h *PartyHandler) List(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	caseID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	parties, err := h.svc.ListByCase(r.Context(), tenantID, caseID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"parties": parties,
+	})
+}
+
+func (h *PartyHandler) Create(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+	userID, _ := auth.UserFromContext(r.Context())
+
+	caseID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid case ID")
+		return
+	}
+
+	var input services.CreatePartyInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON body")
+		return
+	}
+	if input.Name == "" {
+		writeError(w, http.StatusBadRequest, "name is required")
+		return
+	}
+
+	party, err := h.svc.Create(r.Context(), tenantID, caseID, userID, input)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			writeError(w, http.StatusNotFound, "case not found")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, party)
+}
+
+func (h *PartyHandler) Update(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	partyID, err := uuid.Parse(r.PathValue("partyId"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid party ID")
+		return
+	}
+
+	var input services.UpdatePartyInput
+	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON body")
+		return
+	}
+
+	updated, err := h.svc.Update(r.Context(), tenantID, partyID, input)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	if updated == nil {
+		writeError(w, http.StatusNotFound, "party not found")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, updated)
+}
+
+func (h *PartyHandler) Delete(w http.ResponseWriter, r *http.Request) {
+	tenantID, ok := auth.TenantFromContext(r.Context())
+	if !ok {
+		writeError(w, http.StatusForbidden, "missing tenant")
+		return
+	}
+
+	partyID, err := uuid.Parse(r.PathValue("partyId"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid party ID")
+		return
+	}
+
+	if err := h.svc.Delete(r.Context(), tenantID, partyID); err != nil {
+		writeError(w, http.StatusNotFound, "party not found")
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}

backend/internal/router/router.go

@@ -5,6 +5,8 @@ import (
 	"net/http"
 
 	"mgit.msbls.de/m/KanzlAI-mGMT/internal/auth"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/handlers"
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/services"
 
 	"github.com/jmoiron/sqlx"
 )
@@ -12,12 +14,34 @@ import (
 func New(db *sqlx.DB, authMW *auth.Middleware) http.Handler {
 	mux := http.NewServeMux()
 
+	// Services
+	caseSvc := services.NewCaseService(db)
+	partySvc := services.NewPartyService(db)
+
+	// Handlers
+	caseH := handlers.NewCaseHandler(caseSvc)
+	partyH := handlers.NewPartyHandler(partySvc)
+
 	// Public routes
 	mux.HandleFunc("GET /health", handleHealth(db))
 
 	// Authenticated API routes
 	api := http.NewServeMux()
-	api.HandleFunc("GET /api/cases", placeholder("cases"))
+
+	// Cases
+	api.HandleFunc("GET /api/cases", caseH.List)
+	api.HandleFunc("POST /api/cases", caseH.Create)
+	api.HandleFunc("GET /api/cases/{id}", caseH.Get)
+	api.HandleFunc("PUT /api/cases/{id}", caseH.Update)
+	api.HandleFunc("DELETE /api/cases/{id}", caseH.Delete)
+
+	// Parties (nested under cases for creation/listing, top-level for update/delete)
+	api.HandleFunc("GET /api/cases/{id}/parties", partyH.List)
+	api.HandleFunc("POST /api/cases/{id}/parties", partyH.Create)
+	api.HandleFunc("PUT /api/parties/{partyId}", partyH.Update)
+	api.HandleFunc("DELETE /api/parties/{partyId}", partyH.Delete)
+
+	// Placeholder routes for future phases
 	api.HandleFunc("GET /api/deadlines", placeholder("deadlines"))
 	api.HandleFunc("GET /api/appointments", placeholder("appointments"))
 	api.HandleFunc("GET /api/documents", placeholder("documents"))

backend/internal/services/case_service.go

@@ -0,0 +1,277 @@
+package services
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+)
+
+type CaseService struct {
+	db *sqlx.DB
+}
+
+func NewCaseService(db *sqlx.DB) *CaseService {
+	return &CaseService{db: db}
+}
+
+type CaseFilter struct {
+	Status string
+	Type   string
+	Search string
+	Limit  int
+	Offset int
+}
+
+type CaseDetail struct {
+	models.Case
+	Parties        []models.Party     `json:"parties"`
+	RecentEvents   []models.CaseEvent `json:"recent_events"`
+	DeadlinesCount int                `json:"deadlines_count"`
+}
+
+type CreateCaseInput struct {
+	CaseNumber string  `json:"case_number"`
+	Title      string  `json:"title"`
+	CaseType   *string `json:"case_type,omitempty"`
+	Court      *string `json:"court,omitempty"`
+	CourtRef   *string `json:"court_ref,omitempty"`
+	Status     string  `json:"status"`
+}
+
+type UpdateCaseInput struct {
+	CaseNumber *string `json:"case_number,omitempty"`
+	Title      *string `json:"title,omitempty"`
+	CaseType   *string `json:"case_type,omitempty"`
+	Court      *string `json:"court,omitempty"`
+	CourtRef   *string `json:"court_ref,omitempty"`
+	Status     *string `json:"status,omitempty"`
+}
+
+func (s *CaseService) List(ctx context.Context, tenantID uuid.UUID, filter CaseFilter) ([]models.Case, int, error) {
+	if filter.Limit <= 0 {
+		filter.Limit = 20
+	}
+	if filter.Limit > 100 {
+		filter.Limit = 100
+	}
+
+	// Build WHERE clause
+	where := "WHERE tenant_id = $1"
+	args := []interface{}{tenantID}
+	argIdx := 2
+
+	if filter.Status != "" {
+		where += fmt.Sprintf(" AND status = $%d", argIdx)
+		args = append(args, filter.Status)
+		argIdx++
+	}
+	if filter.Type != "" {
+		where += fmt.Sprintf(" AND case_type = $%d", argIdx)
+		args = append(args, filter.Type)
+		argIdx++
+	}
+	if filter.Search != "" {
+		where += fmt.Sprintf(" AND (title ILIKE $%d OR case_number ILIKE $%d)", argIdx, argIdx)
+		args = append(args, "%"+filter.Search+"%")
+		argIdx++
+	}
+
+	// Count total
+	var total int
+	countQuery := "SELECT COUNT(*) FROM cases " + where
+	if err := s.db.GetContext(ctx, &total, countQuery, args...); err != nil {
+		return nil, 0, fmt.Errorf("counting cases: %w", err)
+	}
+
+	// Fetch page
+	query := fmt.Sprintf("SELECT * FROM cases %s ORDER BY updated_at DESC LIMIT $%d OFFSET $%d",
+		where, argIdx, argIdx+1)
+	args = append(args, filter.Limit, filter.Offset)
+
+	var cases []models.Case
+	if err := s.db.SelectContext(ctx, &cases, query, args...); err != nil {
+		return nil, 0, fmt.Errorf("listing cases: %w", err)
+	}
+
+	return cases, total, nil
+}
+
+func (s *CaseService) GetByID(ctx context.Context, tenantID, caseID uuid.UUID) (*CaseDetail, error) {
+	var c models.Case
+	err := s.db.GetContext(ctx, &c,
+		"SELECT * FROM cases WHERE id = $1 AND tenant_id = $2", caseID, tenantID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("getting case: %w", err)
+	}
+
+	detail := &CaseDetail{Case: c}
+
+	// Parties
+	if err := s.db.SelectContext(ctx, &detail.Parties,
+		"SELECT * FROM parties WHERE case_id = $1 AND tenant_id = $2 ORDER BY name",
+		caseID, tenantID); err != nil {
+		return nil, fmt.Errorf("getting parties: %w", err)
+	}
+
+	// Recent events (last 20)
+	if err := s.db.SelectContext(ctx, &detail.RecentEvents,
+		"SELECT * FROM case_events WHERE case_id = $1 AND tenant_id = $2 ORDER BY created_at DESC LIMIT 20",
+		caseID, tenantID); err != nil {
+		return nil, fmt.Errorf("getting events: %w", err)
+	}
+
+	// Deadlines count
+	if err := s.db.GetContext(ctx, &detail.DeadlinesCount,
+		"SELECT COUNT(*) FROM deadlines WHERE case_id = $1 AND tenant_id = $2",
+		caseID, tenantID); err != nil {
+		return nil, fmt.Errorf("counting deadlines: %w", err)
+	}
+
+	return detail, nil
+}
+
+func (s *CaseService) Create(ctx context.Context, tenantID uuid.UUID, userID uuid.UUID, input CreateCaseInput) (*models.Case, error) {
+	if input.Status == "" {
+		input.Status = "active"
+	}
+
+	id := uuid.New()
+	now := time.Now()
+
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO cases (id, tenant_id, case_number, title, case_type, court, court_ref, status, metadata, created_at, updated_at)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8, '{}', $9, $9)`,
+		id, tenantID, input.CaseNumber, input.Title, input.CaseType, input.Court, input.CourtRef, input.Status, now)
+	if err != nil {
+		return nil, fmt.Errorf("creating case: %w", err)
+	}
+
+	// Create case_created event
+	createEvent(ctx, s.db, tenantID, id, userID, "case_created", "Case created", nil)
+
+	var c models.Case
+	if err := s.db.GetContext(ctx, &c, "SELECT * FROM cases WHERE id = $1", id); err != nil {
+		return nil, fmt.Errorf("fetching created case: %w", err)
+	}
+	return &c, nil
+}
+
+func (s *CaseService) Update(ctx context.Context, tenantID, caseID uuid.UUID, userID uuid.UUID, input UpdateCaseInput) (*models.Case, error) {
+	// Fetch current to detect status change
+	var current models.Case
+	err := s.db.GetContext(ctx, &current,
+		"SELECT * FROM cases WHERE id = $1 AND tenant_id = $2", caseID, tenantID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("fetching case for update: %w", err)
+	}
+
+	// Build SET clause dynamically
+	sets := []string{}
+	args := []interface{}{}
+	argIdx := 1
+
+	if input.CaseNumber != nil {
+		sets = append(sets, fmt.Sprintf("case_number = $%d", argIdx))
+		args = append(args, *input.CaseNumber)
+		argIdx++
+	}
+	if input.Title != nil {
+		sets = append(sets, fmt.Sprintf("title = $%d", argIdx))
+		args = append(args, *input.Title)
+		argIdx++
+	}
+	if input.CaseType != nil {
+		sets = append(sets, fmt.Sprintf("case_type = $%d", argIdx))
+		args = append(args, *input.CaseType)
+		argIdx++
+	}
+	if input.Court != nil {
+		sets = append(sets, fmt.Sprintf("court = $%d", argIdx))
+		args = append(args, *input.Court)
+		argIdx++
+	}
+	if input.CourtRef != nil {
+		sets = append(sets, fmt.Sprintf("court_ref = $%d", argIdx))
+		args = append(args, *input.CourtRef)
+		argIdx++
+	}
+	if input.Status != nil {
+		sets = append(sets, fmt.Sprintf("status = $%d", argIdx))
+		args = append(args, *input.Status)
+		argIdx++
+	}
+
+	if len(sets) == 0 {
+		return &current, nil
+	}
+
+	sets = append(sets, fmt.Sprintf("updated_at = $%d", argIdx))
+	args = append(args, time.Now())
+	argIdx++
+
+	query := fmt.Sprintf("UPDATE cases SET %s WHERE id = $%d AND tenant_id = $%d",
+		joinStrings(sets, ", "), argIdx, argIdx+1)
+	args = append(args, caseID, tenantID)
+
+	if _, err := s.db.ExecContext(ctx, query, args...); err != nil {
+		return nil, fmt.Errorf("updating case: %w", err)
+	}
+
+	// Log status change event
+	if input.Status != nil && *input.Status != current.Status {
+		desc := fmt.Sprintf("Status changed from %s to %s", current.Status, *input.Status)
+		createEvent(ctx, s.db, tenantID, caseID, userID, "status_changed", desc, nil)
+	}
+
+	var updated models.Case
+	if err := s.db.GetContext(ctx, &updated, "SELECT * FROM cases WHERE id = $1", caseID); err != nil {
+		return nil, fmt.Errorf("fetching updated case: %w", err)
+	}
+	return &updated, nil
+}
+
+func (s *CaseService) Delete(ctx context.Context, tenantID, caseID uuid.UUID, userID uuid.UUID) error {
+	result, err := s.db.ExecContext(ctx,
+		"UPDATE cases SET status = 'archived', updated_at = $1 WHERE id = $2 AND tenant_id = $3 AND status != 'archived'",
+		time.Now(), caseID, tenantID)
+	if err != nil {
+		return fmt.Errorf("archiving case: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	createEvent(ctx, s.db, tenantID, caseID, userID, "case_archived", "Case archived", nil)
+	return nil
+}
+
+func createEvent(ctx context.Context, db *sqlx.DB, tenantID, caseID uuid.UUID, userID uuid.UUID, eventType, title string, description *string) {
+	now := time.Now()
+	db.ExecContext(ctx,
+		`INSERT INTO case_events (id, tenant_id, case_id, event_type, title, description, event_date, created_by, metadata, created_at, updated_at)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8, '{}', $7, $7)`,
+		uuid.New(), tenantID, caseID, eventType, title, description, now, userID)
+}
+
+func joinStrings(strs []string, sep string) string {
+	result := ""
+	for i, s := range strs {
+		if i > 0 {
+			result += sep
+		}
+		result += s
+	}
+	return result
+}

backend/internal/services/party_service.go

@@ -0,0 +1,152 @@
+package services
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+
+	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+)
+
+type PartyService struct {
+	db *sqlx.DB
+}
+
+func NewPartyService(db *sqlx.DB) *PartyService {
+	return &PartyService{db: db}
+}
+
+type CreatePartyInput struct {
+	Name           string          `json:"name"`
+	Role           *string         `json:"role,omitempty"`
+	Representative *string         `json:"representative,omitempty"`
+	ContactInfo    json.RawMessage `json:"contact_info,omitempty"`
+}
+
+type UpdatePartyInput struct {
+	Name           *string         `json:"name,omitempty"`
+	Role           *string         `json:"role,omitempty"`
+	Representative *string         `json:"representative,omitempty"`
+	ContactInfo    json.RawMessage `json:"contact_info,omitempty"`
+}
+
+func (s *PartyService) ListByCase(ctx context.Context, tenantID, caseID uuid.UUID) ([]models.Party, error) {
+	var parties []models.Party
+	err := s.db.SelectContext(ctx, &parties,
+		"SELECT * FROM parties WHERE case_id = $1 AND tenant_id = $2 ORDER BY name",
+		caseID, tenantID)
+	if err != nil {
+		return nil, fmt.Errorf("listing parties: %w", err)
+	}
+	return parties, nil
+}
+
+func (s *PartyService) Create(ctx context.Context, tenantID, caseID uuid.UUID, userID uuid.UUID, input CreatePartyInput) (*models.Party, error) {
+	// Verify case exists and belongs to tenant
+	var exists bool
+	err := s.db.GetContext(ctx, &exists,
+		"SELECT EXISTS(SELECT 1 FROM cases WHERE id = $1 AND tenant_id = $2)", caseID, tenantID)
+	if err != nil {
+		return nil, fmt.Errorf("checking case: %w", err)
+	}
+	if !exists {
+		return nil, sql.ErrNoRows
+	}
+
+	id := uuid.New()
+	contactInfo := input.ContactInfo
+	if contactInfo == nil {
+		contactInfo = json.RawMessage("{}")
+	}
+
+	_, err = s.db.ExecContext(ctx,
+		`INSERT INTO parties (id, tenant_id, case_id, name, role, representative, contact_info)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7)`,
+		id, tenantID, caseID, input.Name, input.Role, input.Representative, contactInfo)
+	if err != nil {
+		return nil, fmt.Errorf("creating party: %w", err)
+	}
+
+	// Log event
+	desc := fmt.Sprintf("Party added: %s", input.Name)
+	createEvent(ctx, s.db, tenantID, caseID, userID, "party_added", desc, nil)
+
+	var party models.Party
+	if err := s.db.GetContext(ctx, &party, "SELECT * FROM parties WHERE id = $1", id); err != nil {
+		return nil, fmt.Errorf("fetching created party: %w", err)
+	}
+	return &party, nil
+}
+
+func (s *PartyService) Update(ctx context.Context, tenantID, partyID uuid.UUID, input UpdatePartyInput) (*models.Party, error) {
+	// Verify party exists and belongs to tenant
+	var current models.Party
+	err := s.db.GetContext(ctx, &current,
+		"SELECT * FROM parties WHERE id = $1 AND tenant_id = $2", partyID, tenantID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("fetching party: %w", err)
+	}
+
+	sets := []string{}
+	args := []interface{}{}
+	argIdx := 1
+
+	if input.Name != nil {
+		sets = append(sets, fmt.Sprintf("name = $%d", argIdx))
+		args = append(args, *input.Name)
+		argIdx++
+	}
+	if input.Role != nil {
+		sets = append(sets, fmt.Sprintf("role = $%d", argIdx))
+		args = append(args, *input.Role)
+		argIdx++
+	}
+	if input.Representative != nil {
+		sets = append(sets, fmt.Sprintf("representative = $%d", argIdx))
+		args = append(args, *input.Representative)
+		argIdx++
+	}
+	if input.ContactInfo != nil {
+		sets = append(sets, fmt.Sprintf("contact_info = $%d", argIdx))
+		args = append(args, input.ContactInfo)
+		argIdx++
+	}
+
+	if len(sets) == 0 {
+		return &current, nil
+	}
+
+	query := fmt.Sprintf("UPDATE parties SET %s WHERE id = $%d AND tenant_id = $%d",
+		joinStrings(sets, ", "), argIdx, argIdx+1)
+	args = append(args, partyID, tenantID)
+
+	if _, err := s.db.ExecContext(ctx, query, args...); err != nil {
+		return nil, fmt.Errorf("updating party: %w", err)
+	}
+
+	var updated models.Party
+	if err := s.db.GetContext(ctx, &updated, "SELECT * FROM parties WHERE id = $1", partyID); err != nil {
+		return nil, fmt.Errorf("fetching updated party: %w", err)
+	}
+	return &updated, nil
+}
+
+func (s *PartyService) Delete(ctx context.Context, tenantID, partyID uuid.UUID) error {
+	result, err := s.db.ExecContext(ctx,
+		"DELETE FROM parties WHERE id = $1 AND tenant_id = $2", partyID, tenantID)
+	if err != nil {
+		return fmt.Errorf("deleting party: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}