diff --git a/internal/ai/bailian_tts.go b/internal/ai/bailian_tts.go
index ddfa003..113e982 100644
--- a/internal/ai/bailian_tts.go
+++ b/internal/ai/bailian_tts.go
@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/url"
 	"os/exec"
+	"strconv"
 	"strings"
 )
 
@@ -109,6 +110,36 @@ func synthesizeBailianTTS(ctx context.Context, approved TTSConfig, text string)
 	return pcm.Bytes(), nil
 }
 
+// bailianFailureSummary emits only fixed categories and HTTP status codes;
+// provider responses, signed URLs, credentials and prompt text stay private.
+func bailianFailureSummary(err error) (string, int) {
+	if err == nil {
+		return "none", 0
+	}
+	message := err.Error()
+	for _, item := range []struct{ prefix, kind string }{
+		{"Bailian TTS rejected request: HTTP ", "generation_http"},
+		{"Bailian audio download rejected: HTTP ", "audio_http"},
+	} {
+		if status, err := strconv.Atoi(strings.TrimPrefix(message, item.prefix)); strings.HasPrefix(message, item.prefix) && err == nil && status >= 100 && status <= 599 {
+			return item.kind, status
+		}
+	}
+	for _, item := range []struct{ prefix, kind string }{
+		{"Bailian TTS response has no complete audio reference", "missing_audio"},
+		{"Bailian TTS request failed:", "generation_transport"},
+		{"Bailian audio download failed:", "audio_transport"},
+		{"Bailian audio conversion failed:", "audio_conversion"},
+		{"Bailian TTS deadline or cancellation:", "deadline"},
+		{"Bailian TTS returned incomplete PCM16 audio", "incomplete_audio"},
+	} {
+		if strings.HasPrefix(message, item.prefix) {
+			return item.kind, 0
+		}
+	}
+	return "unknown", 0
+}
+
 type boundedPCM struct{ bytes.Buffer }
 
 func (w *boundedPCM) Write(data []byte) (int, error) {
diff --git a/internal/ai/bailian_tts_test.go b/internal/ai/bailian_tts_test.go
index 1c66eee..5cae02c 100644
--- a/internal/ai/bailian_tts_test.go
+++ b/internal/ai/bailian_tts_test.go
@@ -3,6 +3,7 @@ package ai
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"os/exec"
@@ -50,6 +51,23 @@ func mockBailianTTS(t *testing.T, pcm []byte, observe func(string)) (string, *at
 	return server.URL + "/api/v1/services/aigc/multimodal-generation/generation", calls
 }
 
+func TestBailianFailureSummaryNeverLogsProviderPayload(t *testing.T) {
+	for _, tc := range []struct {
+		message, kind string
+		status        int
+	}{
+		{"Bailian TTS rejected request: HTTP 403", "generation_http", 403},
+		{"Bailian audio download rejected: HTTP 502", "audio_http", 502},
+		{"Bailian TTS response has no complete audio reference", "missing_audio", 0},
+		{"Authorization: Bearer private-signature and prompt", "unknown", 0},
+	} {
+		kind, status := bailianFailureSummary(errors.New(tc.message))
+		if kind != tc.kind || status != tc.status || strings.Contains(kind, "private") {
+			t.Fatalf("unsafe failure summary: kind=%q status=%d", kind, status)
+		}
+	}
+}
+
 func TestBailianTTSDownloadFailureDoesNotLeakSignedURLOrRetry(t *testing.T) {
 	if _, err := exec.LookPath("ffmpeg"); err != nil {
 		t.Skip("Bailian TTS conversion requires ffmpeg")
diff --git a/internal/ai/pipeline.go b/internal/ai/pipeline.go
index e0148c4..06e2019 100644
--- a/internal/ai/pipeline.go
+++ b/internal/ai/pipeline.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"log/slog"
 	"net/url"
 	"strings"
 	"sync"
@@ -55,6 +56,7 @@ func (c *Call) Open(ctx context.Context) ([]byte, error) {
 	}
 	audio, err := c.bound.Synthesize(ctx, c.bound.Opening)
 	if err != nil {
+		slog.Error("approved opening synthesis failed", "stage", "opening")
 		return nil, err
 	}
 	c.mu.Lock()
@@ -233,6 +235,8 @@ func (b Binding) synthesize(ctx context.Context, text string, alreadyPending int
 	// missing or failed response never counts as queued audio.
 	audio, err := synthesizeBailianTTS(ctx, *b.TTS, text)
 	if err != nil {
+		kind, status := bailianFailureSummary(err)
+		slog.Error("approved TTS synthesis failed", "category", kind, "http_status", status, "cause_type", fmt.Sprintf("%T", err))
 		return nil, 0, err
 	}
 	return audio, 1, nil