fix(web): 会话列表合同跟着外壳搬家，无活跃会话不再静默吞发送

四条源码合同改到 (app)/layout 与注册载荷两端对断。列表只剩校正会话时普通输入框锁定，发送会打开校正或给出提示。

frontend/src/lib/rectification-session-composer-guard.ts

@@ -23,6 +23,24 @@ export function consultSendBlockedByRectificationSession(
   return isRectificationChatSession(session);
 }
 
+/** Empty active session with only rectification rows still occupies the ordinary composer. */
+export function composerLocksAsRectification(
+  activeSession: { sessionType?: string } | null | undefined,
+  sessions: readonly { sessionType: string }[],
+): boolean {
+  if (isRectificationChatSession(activeSession)) return true;
+  if (activeSession) return false;
+  return sessions.some((session) => session.sessionType === "birth_time_rectification");
+}
+
+export function missingActiveSessionSendAction(
+  sessions: readonly { id: string; sessionType: string }[],
+): { openSessionId: string } | { notice: string } {
+  const rectification = sessions.find((session) => session.sessionType === "birth_time_rectification");
+  if (rectification) return { openSessionId: rectification.id };
+  return { notice: "请先选一条对话，或点上方「新建对话」。" };
+}
+
 export function dropRectificationStoredPending<
   S extends { sessionId: string },
   T extends { id: string; sessionType: string },
@@ -63,5 +81,6 @@ export function rectificationOrdinaryComposerReopen(input: {
   if (!input.activeRectificationSession || !input.error || input.error === "profile_incomplete") {
     return false;
   }
+  if (!input.sessionId) return true;
   return !input.errorSessionId || input.errorSessionId === input.sessionId;
 }