fix(memory,loop): 记忆作用域读写成对 + source_conversation 结构化（裁决 1.9/04.4.2/04.4.3）

- 04.4.2/1.9 读侧：Retrieve 候选集并集 = 本人 persona 域 ∪ user 共享域 ∪ project 共享域（他角色 persona 域仍排除），群聊/陌生人取受限收窄
- 写侧：群聊/陌生人整段跳过记忆提取（可查不可写），persona 域仅属主可写
- 04.4.3：source_conversation 不再由 LLM 自由生成（prompt 不索要、候选结构不含该键），落库时无条件盖真实 {session_id,message_id}，编解码集中在 memory/source.go
- 新增跨角色种子用例（原用例即使关掉并集也会通过）+ 成对用例「同群聊上下文：读得到共享域、写不进 store」
- 同步 store.go/retrieve.go 文档注释，与 design/03 §3/§4 口径一致

internal/runtime/loop/memory_source_test.go

@@ -0,0 +1,67 @@
+package loop
+
+import (
+	"context"
+	"testing"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/memory"
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/model"
+)
+
+// TestPersistMemories_StampsRealSource 证明裁决 04.4.3 的落库值：
+// 提取调用点（persistMemories）从运行上下文盖真实 session/message id，
+// extractor 产出的自由文本来源被无条件覆盖。
+func TestPersistMemories_StampsRealSource(t *testing.T) {
+	t.Parallel()
+	store := newTestMemoryStore(t)
+	l := New(Options{Memory: store, Extractor: memory.NewManualExtractor("persona-a", "owner"), PersonaID: "persona-a"})
+
+	// extractor 刻意夹带一条伪造来源，证明持久化层会盖掉它。
+	bogus := []memory.MemoryItem{{
+		PersonaID: "persona-a", Scope: memory.ScopeUser, Kind: memory.KindRelationship,
+		Content: "用户习惯：爱喝冰美式", SourceConversation: "模型瞎编的来源",
+	}}
+	ctx := withLoopSession(WithTurnID(WithSessionEnv(context.Background(), OwnerEnv()), "turn-1"), "web:abc")
+	l.persistMemories(ctx, bogus, 1)
+
+	items, err := store.ListByPersona(context.Background(), "persona-a")
+	if err != nil {
+		t.Fatalf("ListByPersona: %v", err)
+	}
+	if len(items) != 1 {
+		t.Fatalf("stored %d items, want 1", len(items))
+	}
+	ref, ok := memory.ParseSourceConversation(items[0].SourceConversation)
+	if !ok {
+		t.Fatalf("SourceConversation %q is not structured, want real ids", items[0].SourceConversation)
+	}
+	if ref.SessionID != "web:abc" || ref.MessageID != "turn-1" {
+		t.Fatalf("source ref = %+v, want session web:abc / message turn-1", ref)
+	}
+}
+
+// TestPersistMemories_SourceSessionOnly 证明未挂 turn id 的调用方
+// （渠道路径现状）溯源降级为仅会话粒度 —— 真实、可解析，不伪造。
+func TestPersistMemories_SourceSessionOnly(t *testing.T) {
+	t.Parallel()
+	store := newTestMemoryStore(t)
+	l := New(Options{Memory: store, Extractor: memory.NewManualExtractor("persona-a", "owner"), PersonaID: "persona-a"})
+
+	ctx := withLoopSession(WithSessionEnv(context.Background(), OwnerEnv()), "qq-obv11:group:42")
+	l.extractMemory(ctx, []model.Message{model.TextMessage(model.RoleUser, "记住 我爱喝冰美式")}, 1)
+
+	items, err := store.ListByPersona(context.Background(), "persona-a")
+	if err != nil {
+		t.Fatalf("ListByPersona: %v", err)
+	}
+	if len(items) != 1 {
+		t.Fatalf("stored %d items, want 1", len(items))
+	}
+	ref, ok := memory.ParseSourceConversation(items[0].SourceConversation)
+	if !ok {
+		t.Fatalf("SourceConversation %q is not structured", items[0].SourceConversation)
+	}
+	if ref.SessionID != "qq-obv11:group:42" || ref.MessageID != "" {
+		t.Fatalf("source ref = %+v, want session-only provenance", ref)
+	}
+}