feat(channels): 陌生人私聊正常聊天（跳概率门）+ 强制流控 6条/分与回合槽位 + 安静时段不再硬静默 + 受限车道边界行前置

- 陌生人私聊：不再走「值不值得回」的概率门，唯一闸门 = 每发送者 6 条/分滑窗 + 同会话 1 个在跑回合
- 被限流只登记不回，且留带 source 的可见告警（不静默）
- 安静时段在回复侧只作信号（规则层不再静默），群聊取消夜间静默
- 锁定流控常量：FlowDirectDefault 加字面量钉桩测试（放大它 = 静默关流控，且会让额度循环跑百万轮）

internal/services/channelbridge/transcript_test.go

@@ -249,27 +249,29 @@ func TestGroupTurnSeedsItsOwnSessionTranscript(t *testing.T) {
 
 	b.process(context.Background(), groupMessage("9", adapter.Actor{Role: adapter.RoleMember}))
 
-	// 形状：该群最近 3 条转录（最旧优先）+ 第三方边界/来源系统行 + 当次用户消息。
+	// 形状（frame 先行）：第三方边界/来源系统行**在最前**，该群最近 3 条转录居中
+	// （最旧优先），当次用户消息在最后。
 	if len(chat.msgs) != 5 {
-		t.Fatalf("loop messages = %d, want 5 (transcript 3 + boundary + user): %+v", len(chat.msgs), chat.msgs)
+		t.Fatalf("loop messages = %d, want 5 (boundary + transcript 3 + user): %+v", len(chat.msgs), chat.msgs)
+	}
+	// 边界行必须最先：历史里的陌生人发言绝不能在她还不知道「这是群、这些人是外人」
+	// 之前进入上下文（提示词注入面，主人 2026-10-05 裁定）。
+	if got := chat.msgs[0]; got.Role != model.RoleSystem || !strings.Contains(turnMessageText(got), thirdPartyBoundaryPrompt) ||
+		!strings.Contains(turnMessageText(got), "群「Gang」") {
+		t.Fatalf("messages[0] = %+v, want the origin + third-party boundary system row first", got)
 	}
 	// 说话人归属逐条正确：两个不同说话人各归各，且走结构化字段（不是织进正文的标签）。
-	if got := chat.msgs[0]; got.Role != model.RoleUser || turnMessageText(got) != "晚上要不要开黑" || got.SenderName != "张三" {
-		t.Fatalf("messages[0] = %+v, want 张三's earlier line attributed to 张三", got)
+	if got := chat.msgs[1]; got.Role != model.RoleUser || turnMessageText(got) != "晚上要不要开黑" || got.SenderName != "张三" {
+		t.Fatalf("messages[1] = %+v, want 张三's earlier line attributed to 张三", got)
 	}
-	if got := chat.msgs[1]; got.Role != model.RoleUser || turnMessageText(got) != "我还在加班" || got.SenderName != "李四" {
-		t.Fatalf("messages[1] = %+v, want 李四's silenced line attributed to 李四", got)
+	if got := chat.msgs[2]; got.Role != model.RoleUser || turnMessageText(got) != "我还在加班" || got.SenderName != "李四" {
+		t.Fatalf("messages[2] = %+v, want 李四's silenced line attributed to 李四", got)
 	}
-	if got := chat.msgs[2]; got.Role != model.RoleAssistant || turnMessageText(got) != "那你先忙" || got.SenderName != "cyrene" {
-		t.Fatalf("messages[2] = %+v, want her earlier reply attributed to cyrene", got)
-	}
-	// 第三方身份边界与来源行照旧（内容一个字没变，仍在每轮注入）。
-	if got := chat.msgs[3]; got.Role != model.RoleSystem || !strings.Contains(turnMessageText(got), thirdPartyBoundaryPrompt) ||
-		!strings.Contains(turnMessageText(got), "群「Gang」") {
-		t.Fatalf("messages[3] = %+v, want the origin + third-party boundary system row", got)
+	if got := chat.msgs[3]; got.Role != model.RoleAssistant || turnMessageText(got) != "那你先忙" || got.SenderName != "cyrene" {
+		t.Fatalf("messages[3] = %+v, want her earlier reply attributed to cyrene", got)
 	}
 	if got := chat.msgs[4]; got.Role != model.RoleUser || turnMessageText(got) != "hello all" || got.SenderName != "张三" {
-		t.Fatalf("messages[4] = %+v, want this turn's user message", got)
+		t.Fatalf("messages[4] = %+v, want this turn's user message last", got)
 	}
 	// 当次消息只出现一次：转录是在本回合消息落库**之前**读的。活夹具把已经落库的行也返回，
 	// 因此播种时刻一旦挪到落库之后，这里立刻数出两次。
@@ -430,10 +432,18 @@ func TestOwnerGroupTurnSeedsOnlyItsOwnIsolatedTranscript(t *testing.T) {
 		t.Fatalf("loop session id = %q, want the isolated sess-g", chat.sessionID)
 	}
 	if len(chat.msgs) != 3 {
-		t.Fatalf("loop messages = %d, want 3 (isolated transcript + origin/boundary + user): %+v", len(chat.msgs), chat.msgs)
+		t.Fatalf("loop messages = %d, want 3 (boundary + isolated transcript + user): %+v", len(chat.msgs), chat.msgs)
 	}
-	if got := chat.msgs[0]; turnMessageText(got) != "群里的上一句" || got.SenderName != "张三" {
-		t.Fatalf("messages[0] = %+v, want the group's own earlier line", got)
+	// frame 先行：主人本人在群里同样是受限（群聊）车道 —— 边界/来源行仍在最前，
+	// 转录居中，当次消息在最后。
+	if got := chat.msgs[0]; got.Role != model.RoleSystem || !strings.Contains(turnMessageText(got), thirdPartyBoundaryPrompt) {
+		t.Fatalf("messages[0] = %+v, want the boundary/origin system row first", got)
+	}
+	if got := chat.msgs[1]; turnMessageText(got) != "群里的上一句" || got.SenderName != "张三" {
+		t.Fatalf("messages[1] = %+v, want the group's own earlier line", got)
+	}
+	if got := chat.msgs[2]; got.Role != model.RoleUser {
+		t.Fatalf("messages[2] = %+v, want this turn's user message last", got)
 	}
 	for i, m := range chat.msgs {
 		if strings.Contains(turnMessageText(m), "主人的私事") {