Implement shared knowledge retrieval, card mirror switch, and SSE project gate

Why: The three pinned reds define EXT-8 slice 2 - adapter-granted cross-owner knowledge must be retrievable, conversation cards must stay out of public project streams when the host opts out, and project-stream subscription must honor the authorizer.
Evidence: TestConvCardMirrorSwitch, TestSharedKnowledgeRetrieval, TestProjectSSEScopeGate green; go test ./... 32/32 packages ok; rows follow on the task card.
Impact: store gains predicate-based SearchKnowledgeShared (FTS/LIKE shared variants + PG); searchKnowledge appends adapter-authorized hits; cardsvc emit gate (no publish = no persistence = clean replay); events project scope consults authorizeSharedProject. Default behavior unchanged everywhere.
Refs: EXT-8/EXT-12 proposals; red run at surface commit.

internal/store/content.go

@@ -353,7 +353,72 @@ func (s *Store) SearchKnowledge(owner string, q core.RetrievalQuery) ([]core.Ret
 	return s.searchKnowledgeSQLite(owner, q)
 }
 
+// knowledgePred 命中可见性谓词（owner 作用域或共享作用域由调用方决定）。
+type knowledgePred func(d core.KnowledgeDoc) bool
+
+func ownerVisible(owner string, q core.RetrievalQuery) knowledgePred {
+	return func(d core.KnowledgeDoc) bool { return knowledgeVisible(owner, q, d) }
+}
+
+// sharedVisible EXT-8 切片 2：他人 owner 且其 ProjectID 经授权回调放行的行可见；
+// 无 ProjectID 的行无法授权（拒绝）；项目/来源过滤沿用查询口径。
+func sharedVisible(requester string, q core.RetrievalQuery, allow func(docOwner, projectID core.ID) bool) knowledgePred {
+	return func(d core.KnowledgeDoc) bool {
+		if d.Owner == "" || d.Owner == requester || d.ProjectID == "" {
+			return false
+		}
+		if q.ProjectID != "" && d.ProjectID != q.ProjectID {
+			return false
+		}
+		if len(q.Sources) > 0 && !containsStr(q.Sources, d.Source) {
+			return false
+		}
+		return allow(d.Owner, d.ProjectID)
+	}
+}
+
+// SearchKnowledgeShared 共享检索（EXT-8 切片 2）：返回他人 owner 的项目知识中，
+// 经 allow(docOwner, projectID) 放行的命中（全文通道；向量通道共享仍留后续切片）。
+// allow 出错由调用方前置处理——本层只见布尔。
+func (s *Store) SearchKnowledgeShared(requester string, q core.RetrievalQuery, allow func(docOwner, projectID core.ID) bool) ([]core.RetrievalHit, error) {
+	pred := sharedVisible(requester, q, allow)
+	if s.dialect.name() == "postgres" {
+		return s.searchKnowledgePGShared(requester, q, pred)
+	}
+	return s.searchKnowledgeSQLiteShared(requester, q, pred)
+}
+
 func (s *Store) searchKnowledgeSQLite(owner string, q core.RetrievalQuery) ([]core.RetrievalHit, error) {
+	out, err := s.searchKnowledgeFTS(ownerVisible(owner, q), q)
+	if err != nil {
+		return nil, err
+	}
+	// CJK 兜底：unicode61 分词把中文整句当单 token，FTS 前缀匹配失效时用 LIKE 子串。
+	if len(out) == 0 && q.Text != "" {
+		topK := q.TopK
+		if topK <= 0 {
+			topK = 5
+		}
+		return s.searchKnowledgeLike(owner, q, topK)
+	}
+	return out, nil
+}
+
+// searchKnowledgeSQLiteShared 共享版：FTS SQL 本身无 owner 预过滤（可见性原为
+// 后置判定），直接换谓词即可；LIKE 兜底换“他人行”预过滤。
+func (s *Store) searchKnowledgeSQLiteShared(requester string, q core.RetrievalQuery, pred knowledgePred) ([]core.RetrievalHit, error) {
+	out, err := s.searchKnowledgeFTS(pred, q)
+	if err != nil {
+		return nil, err
+	}
+	if len(out) == 0 && q.Text != "" {
+		return s.searchKnowledgeLikeShared(requester, q, pred)
+	}
+	return out, nil
+}
+
+// searchKnowledgeFTS FTS 通道（owner 作用域与共享作用域共用：可见性谓词由调用方注入）。
+func (s *Store) searchKnowledgeFTS(pred knowledgePred, q core.RetrievalQuery) ([]core.RetrievalHit, error) {
 	topK := q.TopK
 	if topK <= 0 {
 		topK = 5
@@ -372,7 +437,7 @@ func (s *Store) searchKnowledgeSQLite(owner string, q core.RetrievalQuery) ([]co
 		if err != nil {
 			return nil, err
 		}
-		if !knowledgeVisible(owner, q, h.Doc) {
+		if !pred(h.Doc) {
 			continue
 		}
 		out = append(out, h)
@@ -380,14 +445,38 @@ func (s *Store) searchKnowledgeSQLite(owner string, q core.RetrievalQuery) ([]co
 			break
 		}
 	}
-	if err := rows.Err(); err != nil {
+	return out, rows.Err()
+}
+
+func (s *Store) searchKnowledgeLikeShared(requester string, q core.RetrievalQuery, pred knowledgePred) ([]core.RetrievalHit, error) {
+	topK := q.TopK
+	if topK <= 0 {
+		topK = 5
+	}
+	rows, err := s.db.Query(s.q(`SELECT id,owner,project_id,source,title,ref,chunk,created_at FROM knowledge WHERE owner<>? AND owner<>'' AND (chunk LIKE ? OR title LIKE ?) LIMIT ?`),
+		requester, "%"+q.Text+"%", "%"+q.Text+"%", topK)
+	if err != nil {
 		return nil, err
 	}
-	// CJK 兜底：unicode61 分词把中文整句当单 token，FTS 前缀匹配失效时用 LIKE 子串。
-	if len(out) == 0 && q.Text != "" {
-		return s.searchKnowledgeLike(owner, q, topK)
+	defer rows.Close()
+	out := []core.RetrievalHit{}
+	for rows.Next() {
+		var d core.KnowledgeDoc
+		var own, ca string
+		if err := rows.Scan(&d.ID, &own, &d.ProjectID, &d.Source, &d.Title, &d.Ref, &d.Chunk, &ca); err != nil {
+			return nil, err
+		}
+		d.Owner = own
+		d.CreatedAt, _ = parseTime(ca)
+		if !pred(d) {
+			continue
+		}
+		out = append(out, core.RetrievalHit{Doc: d, Score: 1.0, Kind: "fulltext"})
+		if len(out) >= topK {
+			break
+		}
 	}
-	return out, nil
+	return out, rows.Err()
 }
 
 func (s *Store) searchKnowledgeLike(owner string, q core.RetrievalQuery, topK int) ([]core.RetrievalHit, error) {