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/memory/store.go

@@ -234,9 +234,10 @@ func (s *Store) Get(ctx context.Context, id string) (MemoryItem, error) {
 // ListByPersona returns every item for personaID, newest first. rowid breaks
 // created_at ties so items written within the same clock tick keep a stable
 // newest-first order. It is the persona-isolation boundary: items belonging to
-// other personas are never returned, so personas never share memory (design
-// §4). Use ListScope when a caller needs to see shared user/project scopes or
-// another persona's read-only items.
+// other personas are never returned, so personas never share their own 角色日常
+// namespace (design §4). It is only the *own* half of the retrieval candidate
+// set — the retriever unions it with the shared user/project scopes before
+// ranking (design §3/§4, see Retriever.visibleCandidates).
 func (s *Store) ListByPersona(ctx context.Context, personaID string) ([]MemoryItem, error) {
 	if strings.TrimSpace(personaID) == "" {
 		return nil, ErrMissingPersona