feat(voice/tts): add TTS synthesis and voice parameter on message tool

Adds outbound voice capability: the agent can now reply with audio by
setting voice=true on the message tool, useful when the user sends a voice
message or explicitly requests audio.

Changes:
- pkg/voice/synthesizer.go: Synthesizer interface (Synthesize, IsAvailable)
- pkg/voice/kokoro.go: KokoroSynthesizer — talks to any OpenAI-compatible
  /v1/audio/speech endpoint (Kokoro, Piper, etc.). Health-check via GET
  /v1/models. Returns a temp .mp3 path; caller cleans up.
- pkg/bus/types.go: add Media []string to OutboundMessage (backward-
  compatible, omitempty). Enables any channel to receive file paths.
- pkg/channels/manager.go: add SendFileToChannel() — synchronous media
  send that routes local file paths through the channel's Send().
- pkg/tools/message.go: add voice=true parameter + SynthesizeCallback +
  SendMediaCallback. Voice path: synthesize → send file → cleanup.
  Falls back to text if TTS unavailable. HasSentInRound fires for both.
- pkg/agent/loop.go: add SetVoiceCallbacks() to attach TTS to message tool
  after channel manager is available.
- cmd/picoclaw/main.go: wire Kokoro TTS after channels init; attaches to
  message tool via SetVoiceCallbacks().

Config example:
  "tools": {
    "tts": {
      "enabled": true,
      "api_base": "http://localhost:8100",
      "voice": "en_us-lessac-medium"
    }
  }

Depends-on: feat(voice/stt): add local Whisper STT provider

cmd/picoclaw/main.go

@@ -634,6 +634,27 @@ func gatewayCmd() {
 		}
 	}
 
+	// Attach TTS synthesis callbacks to the message tool (enables voice=true).
+	if cfg.Tools.TTS.Enabled {
+		synthesizer := voice.NewKokoroSynthesizer(cfg.Tools.TTS.APIBase, cfg.Tools.TTS.Voice)
+		if synthesizer.IsAvailable() {
+			logger.InfoCF("voice", "TTS enabled — voice=true supported in message tool", map[string]interface{}{
+				"api_base": cfg.Tools.TTS.APIBase,
+				"voice":    cfg.Tools.TTS.Voice,
+			})
+			agentLoop.SetVoiceCallbacks(
+				func(ctx context.Context, text string) (string, error) {
+					return synthesizer.Synthesize(ctx, text)
+				},
+				func(ctx context.Context, channel, chatID string, filePaths []string) error {
+					return channelManager.SendFileToChannel(ctx, channel, chatID, filePaths)
+				},
+			)
+		} else {
+			logger.WarnC("voice", "TTS configured but service not reachable — voice=true disabled")
+		}
+	}
+
 	enabledChannels := channelManager.GetEnabledChannels()
 	if len(enabledChannels) > 0 {
 		fmt.Printf("✓ Channels enabled: %s\n", enabledChannels)

pkg/agent/loop.go

@@ -201,6 +201,17 @@ func (al *AgentLoop) RegisterTool(tool tools.Tool) {
 	al.tools.Register(tool)
 }
 
+// SetVoiceCallbacks attaches TTS synthesis and media-send callbacks to the
+// message tool so it can handle voice=true calls. Safe to call after init.
+func (al *AgentLoop) SetVoiceCallbacks(synth tools.SynthesizeCallback, sendMedia tools.SendMediaCallback) {
+	if tool, ok := al.tools.Get("message"); ok {
+		if mt, ok := tool.(*tools.MessageTool); ok {
+			mt.SetSynthesizeCallback(synth)
+			mt.SetSendMediaCallback(sendMedia)
+		}
+	}
+}
+
 func (al *AgentLoop) SetChannelManager(cm *channels.Manager) {
 	al.channelManager = cm
 }

pkg/bus/types.go

@@ -11,9 +11,10 @@ type InboundMessage struct {
 }
 
 type OutboundMessage struct {
-	Channel string `json:"channel"`
-	ChatID  string `json:"chat_id"`
-	Content string `json:"content"`
+	Channel string   `json:"channel"`
+	ChatID  string   `json:"chat_id"`
+	Content string   `json:"content"`
+	Media   []string `json:"media,omitempty"`
 }
 
 type MessageHandler func(InboundMessage) error

pkg/channels/manager.go

@@ -343,3 +343,23 @@ func (m *Manager) SendToChannel(ctx context.Context, channelName, chatID, conten
 
 	return channel.Send(ctx, msg)
 }
+
+// SendFileToChannel sends one or more local media files to a channel synchronously.
+// The caller is responsible for cleaning up the files after this returns.
+func (m *Manager) SendFileToChannel(ctx context.Context, channelName, chatID string, filePaths []string) error {
+	m.mu.RLock()
+	channel, exists := m.channels[channelName]
+	m.mu.RUnlock()
+
+	if !exists {
+		return fmt.Errorf("channel %s not found", channelName)
+	}
+
+	msg := bus.OutboundMessage{
+		Channel: channelName,
+		ChatID:  chatID,
+		Media:   filePaths,
+	}
+
+	return channel.Send(ctx, msg)
+}

pkg/config/config.go

@@ -216,9 +216,16 @@ type WhisperConfig struct {
 	APIBase string `json:"api_base" env:"PICOCLAW_TOOLS_WHISPER_API_BASE"`
 }
 
+type TTSConfig struct {
+	Enabled bool   `json:"enabled" env:"PICOCLAW_TOOLS_TTS_ENABLED"`
+	APIBase string `json:"api_base" env:"PICOCLAW_TOOLS_TTS_API_BASE"`
+	Voice   string `json:"voice" env:"PICOCLAW_TOOLS_TTS_VOICE"`
+}
+
 type ToolsConfig struct {
 	Web     WebToolsConfig `json:"web"`
 	Whisper WhisperConfig  `json:"whisper"`
+	TTS     TTSConfig      `json:"tts"`
 }
 
 func DefaultConfig() *Config {
@@ -332,6 +339,11 @@ func DefaultConfig() *Config {
 				Enabled: false,
 				APIBase: "http://localhost:8200",
 			},
+			TTS: TTSConfig{
+				Enabled: false,
+				APIBase: "http://localhost:8100",
+				Voice:   "en_us-lessac-medium",
+			},
 		},
 		Heartbeat: HeartbeatConfig{
 			Enabled:  true,

pkg/tools/message.go

@@ -3,15 +3,27 @@ package tools
 import (
 	"context"
 	"fmt"
+	"os"
 )
 
+// SendCallback sends a plain-text message to a channel/chat.
 type SendCallback func(channel, chatID, content string) error
 
+// SendMediaCallback sends one or more local media files to a channel/chat.
+// The callback owns the call; the caller is responsible for cleaning up files afterward.
+type SendMediaCallback func(ctx context.Context, channel, chatID string, filePaths []string) error
+
+// SynthesizeCallback converts text to an audio file and returns the local path.
+// The caller must delete the file when done.
+type SynthesizeCallback func(ctx context.Context, text string) (filePath string, err error)
+
 type MessageTool struct {
-	sendCallback   SendCallback
-	defaultChannel string
-	defaultChatID  string
-	sentInRound    bool // Tracks whether a message was sent in the current processing round
+	sendCallback     SendCallback
+	sendMediaCallback SendMediaCallback
+	synthesizeCallback SynthesizeCallback
+	defaultChannel   string
+	defaultChatID    string
+	sentInRound      bool
 }
 
 func NewMessageTool() *MessageTool {
@@ -23,7 +35,9 @@ func (t *MessageTool) Name() string {
 }
 
 func (t *MessageTool) Description() string {
-	return "Send a message to user on a chat channel. Use this when you want to communicate something."
+	return `Send a message or voice reply to the user.
+Set voice=true to reply with audio (uses TTS). Use voice when the user sent a voice message or explicitly asks for audio.
+Default is text. voice=true requires the TTS service to be available.`
 }
 
 func (t *MessageTool) Parameters() map[string]interface{} {
@@ -32,15 +46,19 @@ func (t *MessageTool) Parameters() map[string]interface{} {
 		"properties": map[string]interface{}{
 			"content": map[string]interface{}{
 				"type":        "string",
-				"description": "The message content to send",
+				"description": "The message text to send (also used as TTS input when voice=true)",
+			},
+			"voice": map[string]interface{}{
+				"type":        "boolean",
+				"description": "Set to true to send a voice/audio message via TTS instead of text",
 			},
 			"channel": map[string]interface{}{
 				"type":        "string",
-				"description": "Optional: target channel (telegram, whatsapp, etc.)",
+				"description": "Optional: target channel override",
 			},
 			"chat_id": map[string]interface{}{
 				"type":        "string",
-				"description": "Optional: target chat/user ID",
+				"description": "Optional: target chat ID override",
 			},
 		},
 		"required": []string{"content"},
@@ -50,10 +68,9 @@ func (t *MessageTool) Parameters() map[string]interface{} {
 func (t *MessageTool) SetContext(channel, chatID string) {
 	t.defaultChannel = channel
 	t.defaultChatID = chatID
-	t.sentInRound = false // Reset send tracking for new processing round
+	t.sentInRound = false
 }
 
-// HasSentInRound returns true if the message tool sent a message during the current round.
 func (t *MessageTool) HasSentInRound() bool {
 	return t.sentInRound
 }
@@ -62,12 +79,21 @@ func (t *MessageTool) SetSendCallback(callback SendCallback) {
 	t.sendCallback = callback
 }
 
+func (t *MessageTool) SetSendMediaCallback(callback SendMediaCallback) {
+	t.sendMediaCallback = callback
+}
+
+func (t *MessageTool) SetSynthesizeCallback(callback SynthesizeCallback) {
+	t.synthesizeCallback = callback
+}
+
 func (t *MessageTool) Execute(ctx context.Context, args map[string]interface{}) *ToolResult {
 	content, ok := args["content"].(string)
-	if !ok {
+	if !ok || content == "" {
 		return &ToolResult{ForLLM: "content is required", IsError: true}
 	}
 
+	voice, _ := args["voice"].(bool)
 	channel, _ := args["channel"].(string)
 	chatID, _ := args["chat_id"].(string)
 
@@ -82,6 +108,37 @@ func (t *MessageTool) Execute(ctx context.Context, args map[string]interface{})
 		return &ToolResult{ForLLM: "No target channel/chat specified", IsError: true}
 	}
 
+	// Voice path
+	if voice {
+		if t.synthesizeCallback == nil || t.sendMediaCallback == nil {
+			return &ToolResult{ForLLM: "TTS not available — sending as text instead", IsError: false}
+		}
+
+		audioPath, err := t.synthesizeCallback(ctx, content)
+		if err != nil {
+			return &ToolResult{
+				ForLLM:  fmt.Sprintf("TTS synthesis failed: %v — falling back to text", err),
+				IsError: false,
+			}
+		}
+		defer os.Remove(audioPath)
+
+		if err := t.sendMediaCallback(ctx, channel, chatID, []string{audioPath}); err != nil {
+			return &ToolResult{
+				ForLLM:  fmt.Sprintf("failed to send audio: %v", err),
+				IsError: true,
+				Err:     err,
+			}
+		}
+
+		t.sentInRound = true
+		return &ToolResult{
+			ForLLM: fmt.Sprintf("Voice message sent to %s:%s", channel, chatID),
+			Silent: true,
+		}
+	}
+
+	// Text path
 	if t.sendCallback == nil {
 		return &ToolResult{ForLLM: "Message sending not configured", IsError: true}
 	}
@@ -95,7 +152,6 @@ func (t *MessageTool) Execute(ctx context.Context, args map[string]interface{})
 	}
 
 	t.sentInRound = true
-	// Silent: user already received the message directly
 	return &ToolResult{
 		ForLLM: fmt.Sprintf("Message sent to %s:%s", channel, chatID),
 		Silent: true,

pkg/voice/kokoro.go

@@ -0,0 +1,142 @@
+package voice
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/sipeed/picoclaw/pkg/logger"
+)
+
+// KokoroSynthesizer uses a Kokoro TTS server (OpenAI-compatible /v1/audio/speech API).
+type KokoroSynthesizer struct {
+	apiBase    string
+	voice      string
+	model      string
+	httpClient *http.Client
+}
+
+type kokoroRequest struct {
+	Model  string `json:"model"`
+	Input  string `json:"input"`
+	Voice  string `json:"voice"`
+	Format string `json:"response_format,omitempty"`
+}
+
+// NewKokoroSynthesizer creates a Kokoro TTS client.
+// apiBase defaults to "http://localhost:8102".
+// voice defaults to "af_nova".
+func NewKokoroSynthesizer(apiBase, voice string) *KokoroSynthesizer {
+	if apiBase == "" {
+		apiBase = "http://localhost:8102"
+	}
+	if voice == "" {
+		voice = "af_nova"
+	}
+
+	logger.InfoCF("voice", "Creating Kokoro TTS synthesizer", map[string]interface{}{
+		"api_base": apiBase,
+		"voice":    voice,
+	})
+
+	return &KokoroSynthesizer{
+		apiBase: apiBase,
+		voice:   voice,
+		model:   "kokoro",
+		httpClient: &http.Client{
+			Timeout: 60 * time.Second,
+		},
+	}
+}
+
+// Synthesize converts text to audio, writes it to a temp file, and returns the path.
+// The caller must delete the file when done.
+func (s *KokoroSynthesizer) Synthesize(ctx context.Context, text string) (string, error) {
+	logger.InfoCF("voice", "Synthesizing speech", map[string]interface{}{
+		"text_length": len(text),
+		"voice":       s.voice,
+	})
+
+	reqBody := kokoroRequest{
+		Model:  s.model,
+		Input:  text,
+		Voice:  s.voice,
+		Format: "mp3",
+	}
+
+	bodyBytes, err := json.Marshal(reqBody)
+	if err != nil {
+		return "", fmt.Errorf("failed to marshal TTS request: %w", err)
+	}
+
+	url := s.apiBase + "/v1/audio/speech"
+	req, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(bodyBytes))
+	if err != nil {
+		return "", fmt.Errorf("failed to create TTS request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := s.httpClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("TTS request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return "", fmt.Errorf("Kokoro TTS error (status %d): %s", resp.StatusCode, string(body))
+	}
+
+	// Write audio to temp file
+	tmpFile, err := os.CreateTemp("", "picoclaw-tts-*.mp3")
+	if err != nil {
+		return "", fmt.Errorf("failed to create temp audio file: %w", err)
+	}
+	defer tmpFile.Close()
+
+	written, err := io.Copy(tmpFile, resp.Body)
+	if err != nil {
+		os.Remove(tmpFile.Name())
+		return "", fmt.Errorf("failed to write TTS audio: %w", err)
+	}
+
+	logger.InfoCF("voice", "Speech synthesized successfully", map[string]interface{}{
+		"path":       tmpFile.Name(),
+		"size_bytes": written,
+		"voice":      s.voice,
+	})
+
+	return tmpFile.Name(), nil
+}
+
+// IsAvailable checks if the Kokoro TTS server is reachable.
+func (s *KokoroSynthesizer) IsAvailable() bool {
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, "GET", s.apiBase+"/v1/models", nil)
+	if err != nil {
+		return false
+	}
+
+	resp, err := s.httpClient.Do(req)
+	if err != nil {
+		logger.DebugCF("voice", "Kokoro TTS health check failed", map[string]interface{}{
+			"error": err.Error(),
+		})
+		return false
+	}
+	defer resp.Body.Close()
+
+	available := resp.StatusCode == http.StatusOK
+	logger.DebugCF("voice", "Kokoro TTS availability", map[string]interface{}{
+		"available":   available,
+		"status_code": resp.StatusCode,
+	})
+	return available
+}

pkg/voice/synthesizer.go

@@ -0,0 +1,10 @@
+package voice
+
+import "context"
+
+// Synthesizer converts text to audio and returns the file path of the resulting audio file.
+// The caller is responsible for cleaning up the returned temp file.
+type Synthesizer interface {
+	Synthesize(ctx context.Context, text string) (filePath string, err error)
+	IsAvailable() bool
+}