feat(artifactvault): close same-tx staging, recover-apply, and GET zero-write gaps

Approve/commit now write FAV staging in the domain transaction, recover-apply materializes scratch collections, and unpublished or GET paths cannot mutate the registry.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/ctxmgr/chat_turns.go

@@ -332,3 +332,49 @@ func (m *ContextManager) GetChatTurn(ctx context.Context, sessionID, clientTurnI
 	cp := *rec
 	return &cp, nil
 }
+
+// GetChatTurnByAssistantMessageID 按会话 + 助手消息定位回合；用于 copy_only 显式 pin。
+func (m *ContextManager) GetChatTurnByAssistantMessageID(ctx context.Context, sessionID string, assistantMessageID int64) (*ChatTurnRecord, error) {
+	if sessionID == "" || assistantMessageID <= 0 {
+		return nil, ErrChatTurnNotFound
+	}
+	if m.pool != nil {
+		var rec ChatTurnRecord
+		var completedAt *time.Time
+		var leaseExpiresAt *time.Time
+		err := m.pool.QueryRow(ctx, `
+			SELECT id, session_id, client_turn_id,
+			       COALESCE(user_id, 0), COALESCE(project_id, 0),
+			       COALESCE(user_message_id, 0), COALESCE(assistant_message_id, 0),
+			       request_body_sha256, status,
+			       COALESCE(first_request_id, ''), COALESCE(last_request_id, ''),
+			       attempt_count, created_at, updated_at, completed_at, lease_expires_at
+			FROM chat_turns
+			WHERE session_id = $1 AND assistant_message_id = $2
+			ORDER BY id DESC
+			LIMIT 1
+		`, sessionID, assistantMessageID).Scan(
+			&rec.ID, &rec.SessionID, &rec.ClientTurnID,
+			&rec.UserID, &rec.ProjectID,
+			&rec.UserMessageID, &rec.AssistantMessageID,
+			&rec.RequestBodySHA256, &rec.Status,
+			&rec.FirstRequestID, &rec.LastRequestID,
+			&rec.AttemptCount, &rec.CreatedAt, &rec.UpdatedAt, &completedAt, &leaseExpiresAt,
+		)
+		if err != nil {
+			return nil, ErrChatTurnNotFound
+		}
+		rec.CompletedAt = completedAt
+		rec.LeaseExpiresAt = leaseExpiresAt
+		return &rec, nil
+	}
+	memTurnsMu.Lock()
+	defer memTurnsMu.Unlock()
+	for _, rec := range memTurns {
+		if rec != nil && rec.SessionID == sessionID && rec.AssistantMessageID == assistantMessageID {
+			cp := *rec
+			return &cp, nil
+		}
+	}
+	return nil, ErrChatTurnNotFound
+}