provider: 音频多模态序列化为 OpenAI「input_audio」格式

HomeAgent 的 ContentBlock.AudioURL 原本输出 audio_url（非 OpenAI 标准块）；
现通过 MarshalJSON 在 base64 数据时自动转为 OpenAI input_audio
（{data,format}），供支持音频的模型识别。非 base64(url)保留原样透传。
- parseAudioDataURL: data:mime;base64,data → （data,format）
- audioFormatFromMIME: wav/mp3/mp4/ogg/flac
- 新增单测：base64 转 input_audio、url 保留 audio_url

验证: go test ./... 27 包 0 失败；Windows 交叉编译通过；部署后服务健康

internal/agent/api/provider.go

@@ -3,6 +3,7 @@ package api
 import (
 	"bufio"
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -32,6 +33,67 @@ type AudioURL struct {
 	URL string `json:"url"`
 }
 
+// MarshalJSON 把音频块序列化成 OpenAI「input_audio」多模态格式（base64 内嵌），
+// 供支持音频的模型识别。audio_url 非 OpenAI 标准块；含 base64 数据时转
+// input_audio，否则回落到原生 audio_url（透传）。
+func (b ContentBlock) MarshalJSON() ([]byte, error) {
+	if b.Type == "audio_url" && b.AudioURL != nil && b.AudioURL.URL != "" {
+		if data, format, ok := parseAudioDataURL(b.AudioURL.URL); ok {
+			return json.Marshal(map[string]interface{}{
+				"type": "input_audio",
+				"input_audio": map[string]string{
+					"data":   data,
+					"format": format,
+				},
+			})
+		}
+	}
+	type alias ContentBlock
+	return json.Marshal(alias(b))
+}
+
+// parseAudioDataURL 从 data:<mime>;base64,<data> 提取 base64 与 format。
+// 非 base64（如 http url）返回 ok=false。
+func parseAudioDataURL(url string) (data, format string, ok bool) {
+	const prefix = "data:"
+	if !strings.HasPrefix(url, prefix) {
+		return "", "", false
+	}
+	rest := url[len(prefix):]
+	comma := strings.IndexByte(rest, ',')
+	if comma < 0 {
+		return "", "", false
+	}
+	mime := rest[:comma]
+	data = rest[comma+1:]
+	if mime == "" || data == "" {
+		return "", "", false
+	}
+	if _, err := base64.StdEncoding.DecodeString(data); err != nil {
+		return "", "", false
+	}
+	format = audioFormatFromMIME(mime)
+	return data, format, true
+}
+
+func audioFormatFromMIME(mime string) string {
+	m := strings.ToLower(strings.TrimSpace(mime))
+	switch {
+	case strings.Contains(m, "wav"):
+		return "wav"
+	case strings.Contains(m, "mp3"), strings.Contains(m, "mpeg"):
+		return "mp3"
+	case strings.Contains(m, "mp4"), strings.Contains(m, "m4a"):
+		return "mp4"
+	case strings.Contains(m, "ogg"), strings.Contains(m, "opus"):
+		return "ogg"
+	case strings.Contains(m, "flac"):
+		return "flac"
+	default:
+		return "wav"
+	}
+}
+
 // Message 表示对话消息。当 Blocks 不为空时 content 在 JSON 中序列化为数组（多模态格式）。
 type Message struct {
 	Role             string         `json:"role"`

internal/agent/api/router_test.go

@@ -2,14 +2,16 @@ package api
 
 import (
 	"context"
+	"encoding/json"
+	"strings"
 	"testing"
 )
 
 // stubRoutableProvider implements both Provider and RoutableProvider.
 type stubRoutableProvider struct {
-	name    string
-	model   string
-	prio    int
+	name  string
+	model string
+	prio  int
 }
 
 func (s *stubRoutableProvider) Name() string          { return s.name }
@@ -64,3 +66,40 @@ func names(ps []Provider) []string {
 	}
 	return out
 }
+func TestMessageAudioBlockToInputAudio(t *testing.T) {
+	const b64 = "QUJDREVG" // base64 of "ABCDEF"
+	m := Message{
+		Role: "user",
+		Blocks: []ContentBlock{
+			{Type: "text", Text: "what is this"},
+			{Type: "audio_url", AudioURL: &AudioURL{URL: "data:audio/wav;base64," + b64}},
+		},
+	}
+	data, err := json.Marshal(m)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	s := string(data)
+	if !strings.Contains(s, `"type":"input_audio"`) {
+		t.Fatalf("expected input_audio, got: %s", s)
+	}
+	if !strings.Contains(s, `"format":"wav"`) || !strings.Contains(s, b64) {
+		t.Fatalf("missing data/format: %s", s)
+	}
+	if strings.Contains(s, `"type":"audio_url"`) {
+		t.Fatalf("audio_url should be converted: %s", s)
+	}
+}
+
+func TestMessageAudioURLPassthroughWhenNotBase64(t *testing.T) {
+	m := Message{
+		Role: "user",
+		Blocks: []ContentBlock{
+			{Type: "audio_url", AudioURL: &AudioURL{URL: "https://cdn.example/a.wav"}},
+		},
+	}
+	data, _ := json.Marshal(m)
+	if !strings.Contains(string(data), `"type":"audio_url"`) {
+		t.Fatalf("non-base64 audio_url should stay: %s", data)
+	}
+}