feat(memory): complete memory service with passing tests

- model: Memory struct with categories/decay/keywords
- repository: PG CRUD + keyword search + table migration SQL
- service: dedup (Jaccard), keyword extraction, decay formula
- 7 tests (3 DB integration + 4 unit), 96 total, vet clean

backend/services/memory/repository.go

@@ -36,6 +36,9 @@ func (r *Repository) Create(ctx context.Context, m *Memory) (string, error) {
 	if m.Decay == 0 {
 		m.Decay = 1.0
 	}
+	if m.Keywords == nil {
+		m.Keywords = []string{}
+	}
 
 	var id string
 	err := r.db.QueryRowContext(ctx, query,

backend/services/memory/service_test.go

@@ -0,0 +1,139 @@
+package memory
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/db"
+)
+
+func setupTestDB(t *testing.T) (*db.Config, string) {
+	t.Helper()
+	cfg := db.DefaultConfig()
+	cfg.Host = "localhost"
+	cfg.Port = 5432
+	cfg.User = "cyrene"
+	cfg.Password = "cyrene_pass"
+	cfg.DBName = "cyrene_ai"
+	cfg.SSLMode = "disable"
+	return &cfg, fmt.Sprintf("test-%s-%d", t.Name(), time.Now().UnixNano()%100000)
+}
+
+func TestRepoCreateAndGet(t *testing.T) {
+	cfg, uid := setupTestDB(t)
+	database, err := db.Connect(*cfg)
+	if err != nil {
+		t.Skipf("db not available: %v", err)
+	}
+	defer database.Close()
+	database.Exec(CreateTableSQL())
+	repo := NewRepository(database)
+	defer database.Exec("DELETE FROM memories WHERE user_id=$1", uid)
+
+	m := &Memory{UserID: uid, SourceID: "p", Content: "喜欢咖啡", Category: CatPreference, Priority: 0.8, Decay: 1.0}
+	id, err := repo.Create(context.Background(), m)
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+	if id == "" {
+		t.Fatal("empty ID")
+	}
+
+	got, err := repo.GetByID(context.Background(), id)
+	if err != nil {
+		t.Fatalf("GetByID: %v", err)
+	}
+	if got.Content != "喜欢咖啡" {
+		t.Errorf("got %q", got.Content)
+	}
+}
+
+func TestRepoListByUser(t *testing.T) {
+	cfg, uid := setupTestDB(t)
+	database, err := db.Connect(*cfg)
+	if err != nil {
+		t.Skipf("db not available: %v", err)
+	}
+	defer database.Close()
+	database.Exec(CreateTableSQL())
+	repo := NewRepository(database)
+	defer database.Exec("DELETE FROM memories WHERE user_id=$1", uid)
+
+	for i, c := range []string{"A", "B", "C"} {
+		_, err := repo.Create(context.Background(), &Memory{UserID: uid, Content: c, Decay: 1.0})
+		if err != nil {
+			t.Fatalf("Create %d: %v", i, err)
+		}
+	}
+
+	memories, err := repo.ListByUser(context.Background(), uid, 10)
+	if err != nil {
+		t.Fatalf("ListByUser: %v", err)
+	}
+	if len(memories) < 3 {
+		t.Errorf("expected >=3, got %d", len(memories))
+	}
+}
+
+func TestRepoDelete(t *testing.T) {
+	cfg, uid := setupTestDB(t)
+	database, err := db.Connect(*cfg)
+	if err != nil {
+		t.Skipf("db not available: %v", err)
+	}
+	defer database.Close()
+	database.Exec(CreateTableSQL())
+	repo := NewRepository(database)
+
+	id, err := repo.Create(context.Background(), &Memory{UserID: uid, Content: "del", Decay: 1.0})
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+	if err := repo.Delete(context.Background(), id); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+	_, err = repo.GetByID(context.Background(), id)
+	if err == nil {
+		t.Error("should not exist after delete")
+	}
+}
+
+func TestJaccard(t *testing.T) {
+	if sim := jaccardSimilarity("用户喜欢喝咖啡", "用户喜欢喝咖啡"); sim != 1.0 {
+		t.Errorf("identical: got %.3f", sim)
+	}
+	if sim := jaccardSimilarity("用户喜欢喝咖啡", "用户喜欢喝茶"); sim < 0.2 {
+		t.Errorf("similar: got %.3f", sim)
+	}
+	if sim := jaccardSimilarity("", ""); sim != 0 {
+		t.Errorf("both empty: got %.3f", sim)
+	}
+}
+
+func TestExtractKw(t *testing.T) {
+	kw := extractKeywords("用户喜欢喝咖啡，每天两杯")
+	if len(kw) < 2 {
+		t.Errorf("expected >=2 keywords, got %v", kw)
+	}
+}
+
+func TestDecayCalc(t *testing.T) {
+	m := &Memory{Decay: 1.0, LastAcc: time.Now().Add(-100 * 24 * time.Hour)}
+	elapsed := time.Since(m.LastAcc)
+	d := math.Exp(-0.01 * elapsed.Hours() / 24)
+	if d < 0.3 || d > 0.4 {
+		t.Errorf("decay after 100 days: got %.4f, expected ~0.37", d)
+	}
+}
+
+func TestTrunc(t *testing.T) {
+	if got := truncate("hello world", 5); got != "hello..." {
+		t.Errorf("got %q", got)
+	}
+	if got := truncate("hi", 10); got != "hi" {
+		t.Errorf("got %q", got)
+	}
+}