feat(channelbridge): 出站语音结论落 voice 列并挂出站 Media（M58）

- voice.Ref 增 SourceTTS 与 FallbackReason，Validate/IsZero/validSource 同步
- 出站成功：INSERT -> 补写 voice 列 -> notify（首帧即带 voice）
- 出站降级：source=tts + status=failed + fallbackReason，正文原样
- 首条气泡挂出站 Media（新开条目，不复制 target.Media）
- gateway historyVoice 投影 fallbackReason
- 新增 outbound_voice.go 与整链 e2e 测试（含变异打红验证时序）

internal/runtime/voice/voice_test.go

@@ -31,6 +31,14 @@ func TestEncodeDecodeRoundTrip(t *testing.T) {
 			Source: SourceASR, Status: StatusEmpty, Name: "0123456789abcdef0123456789abcdef.mp3",
 			MIME: "audio/mpeg", Size: 4321,
 		}},
+		{"出站合成成功 + 可播副本", Ref{
+			Source: SourceTTS, Status: StatusTranscribed,
+			Name: "fedcba9876543210fedcba9876543210.ogg", MIME: "audio/ogg",
+			Size: 8192, DurationMs: 1500,
+		}},
+		{"出站合成降级（正文照发文本）", Ref{
+			Source: SourceTTS, Status: StatusFailed, FallbackReason: "budget_exceeded",
+		}},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -119,6 +127,11 @@ func TestEncodeRejectsBrokenRef(t *testing.T) {
 		{"有 name 无 mime", Ref{Source: SourceASR, Status: StatusTranscribed, Name: "x.ogg", Size: 12}},
 		{"有 name 无 size", Ref{Source: SourceASR, Status: StatusTranscribed, Name: "x.ogg", MIME: "audio/ogg"}},
 		{"时长为负", Ref{Source: SourceASR, Status: StatusTranscribed, DurationMs: -1}},
+		{"降级原因挂在成功态", Ref{
+			Source: SourceTTS, Status: StatusTranscribed,
+			Name: "x.ogg", MIME: "audio/ogg", Size: 12, FallbackReason: "budget_exceeded",
+		}},
+		{"只有降级原因", Ref{FallbackReason: "budget_exceeded"}},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -149,6 +162,7 @@ func TestDecodeRejectsGarbage(t *testing.T) {
 		{"闭集外的来源", `{"source":"cloud","status":"transcribed"}`},
 		{"闭集外的状态", `{"source":"asr","status":"done"}`},
 		{"副本字段不同生共死", `{"source":"asr","status":"transcribed","size":9}`},
+		{"降级原因挂在成功态", `{"source":"tts","status":"transcribed","fallbackReason":"x"}`},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -164,6 +178,33 @@ func TestDecodeRejectsGarbage(t *testing.T) {
 	}
 }
 
+// TestOutboundTTSJSONShape 把**出站**两种落库形状钉死（design/25 §7.1）：
+// 成功 = source/status/name/mime/size（+ 可选 durationMs）；降级 = source/status +
+// fallbackReason，**没有 name/url**（正文照发文本，客户端据此只挂一个小标）。
+func TestOutboundTTSJSONShape(t *testing.T) {
+	t.Parallel()
+	raw, err := Encode(Ref{
+		Source: SourceTTS, Status: StatusTranscribed,
+		Name: "fedcba9876543210fedcba9876543210.ogg", MIME: "audio/ogg", Size: 8192,
+	})
+	if err != nil {
+		t.Fatalf("Encode(成功): %v", err)
+	}
+	want := `{"source":"tts","status":"transcribed","name":"fedcba9876543210fedcba9876543210.ogg",` +
+		`"mime":"audio/ogg","size":8192}`
+	if raw != want {
+		t.Fatalf("出站成功 JSON = %s\n           want %s", raw, want)
+	}
+
+	raw, err = Encode(Ref{Source: SourceTTS, Status: StatusFailed, FallbackReason: "budget_exceeded"})
+	if err != nil {
+		t.Fatalf("Encode(降级): %v", err)
+	}
+	if want := `{"source":"tts","status":"failed","fallbackReason":"budget_exceeded"}`; raw != want {
+		t.Fatalf("出站降级 JSON = %s\n           want %s", raw, want)
+	}
+}
+
 // TestRefIsVoiceAndHasCopy 钉住两个判据的边界：
 // IsVoice = 来源与状态都在闭集内（= 这条消息来自一条语音）；
 // HasCopy  = 有 name（name/mime/size 同生共死，因此 name 是代表）。
@@ -178,6 +219,8 @@ func TestRefIsVoiceAndHasCopy(t *testing.T) {
 		{"零值（不是语音消息）", Ref{}, false, false},
 		{"平台转写无副本", Ref{Source: SourcePlatform, Status: StatusTranscribed}, true, false},
 		{"有副本", Ref{Source: SourceASR, Status: StatusFailed, Name: "n.wav", MIME: "audio/wav", Size: 4}, true, true},
+		{"出站合成成功", Ref{Source: SourceTTS, Status: StatusTranscribed, Name: "n.ogg", MIME: "audio/ogg", Size: 4}, true, true},
+		{"出站降级（算语音消息，但无可播副本）", Ref{Source: SourceTTS, Status: StatusFailed, FallbackReason: "no_capability"}, true, false},
 		{"只有来源（半截，不算语音）", Ref{Source: SourceASR}, false, false},
 	}
 	for _, tc := range cases {