feat(memory): M4 记忆完善（三类作用域访问规则+项目索引分层+LLM异步提取+衰减溯源+向量接入，兼容既有57用例）

internal/runtime/memory/decay_test.go

@@ -0,0 +1,79 @@
+package memory
+
+import (
+	"context"
+	"math"
+	"testing"
+	"time"
+)
+
+func TestRetriever_DecayFactor_久未使用降权(t *testing.T) {
+	t.Parallel()
+	r := NewRetriever(newTestStore(t))
+	now := time.Now().UTC()
+
+	tests := []struct {
+		name        string
+		updatedAt   time.Time
+		decayWeight float64
+		want        float64
+	}{
+		{name: "fresh keeps full weight", updatedAt: now, decayWeight: 1.0, want: 1.0},
+		// Default half-life is 30 days: 60 days ago = 2 half-lives = 2^-2.
+		{name: "two half-lives halves twice", updatedAt: now.Add(-60 * 24 * time.Hour), decayWeight: 1.0, want: 0.25},
+		// Lower base decay_weight scales the whole curve down.
+		{name: "low decay_weight scales down", updatedAt: now, decayWeight: 0.5, want: 0.5},
+		{name: "low weight plus age compounds", updatedAt: now.Add(-60 * 24 * time.Hour), decayWeight: 0.5, want: 0.125},
+		// A future timestamp must not boost above the base weight.
+		{name: "future timestamp clamps to zero", updatedAt: now.Add(time.Hour), decayWeight: 1.0, want: 1.0},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got := r.decayFactor(MemoryItem{
+				DecayWeight: tt.decayWeight,
+				UpdatedAt:   tt.updatedAt,
+			}, now)
+			if math.Abs(got-tt.want) > 1e-9 {
+				t.Fatalf("decayFactor = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestRetriever_Retrieve_DecayWeight_降权(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	now := time.Now().UTC()
+	// A fresh item but with a near-zero decay_weight (design: 用户可削弱某记忆).
+	addItem(t, s, MemoryItem{
+		PersonaID: "persona.a", Content: "低权重但新鲜", UpdatedAt: now,
+		DecayWeight: 0.1, Scope: ScopePersona, Kind: KindWorldEvent,
+	})
+	// A slightly older item with a full decay_weight.
+	addItem(t, s, MemoryItem{
+		PersonaID: "persona.a", Content: "权重高稍旧", UpdatedAt: now.Add(-time.Hour),
+		DecayWeight: 1.0, Scope: ScopePersona, Kind: KindWorldEvent,
+	})
+
+	r := NewRetriever(s)
+	// A blank query matches nothing, so ordering is driven by the decay factor
+	// (decay_weight × time decay) alone: the low-weight fresh item must fall
+	// below the full-weight slightly-older item.
+	results, err := r.Retrieve(ctx, "persona.a", "", 10)
+	if err != nil {
+		t.Fatalf("Retrieve: %v", err)
+	}
+	if len(results) != 2 {
+		t.Fatalf("got %d results, want 2", len(results))
+	}
+	if got := results[0].Item.Content; got != "权重高稍旧" {
+		t.Fatalf("top result = %q, want the full-decay-weight item", got)
+	}
+	if got := results[1].Item.Content; got != "低权重但新鲜" {
+		t.Fatalf("second result = %q, want the low-decay-weight item", got)
+	}
+}