feat(telegram): Voice pipeline refactor with STT integration and configurable routing

[maemreyo]

🎯 Overview

This PR introduces a comprehensive refactor of the Telegram voice pipeline, improving code organization, testability, and adding robust voice agent routing capabilities with STT (Speech-to-Text) integration.

✨ Key Features

1. Nested Voice Configuration Structure

• Introduced TelegramVoiceConfig to group all voice-related settings under a single voice JSON key
• Clear separation between base channel settings and voice pipeline configuration
• Backward compatible with legacy flat config layout via automatic promotion

2. Voice Agent Routing System

• Configurable voice agent routing with priority-based decision chain:
  1. Audio/Voice Media → Always routes to voice agent (highest priority)
  2. /start Command → Bootstraps voice session with customizable message
  3. Intent Keywords → Text-based routing via configurable keyword matching
  4. Session Affinity → Sticky routing with TTL-based expiration
  5. Affinity Clear Keywords → User-initiated switch back to default agent
• DM-only routing logic (groups excluded except for audio media)
• Case-insensitive keyword matching with defensive normalization

3. STT (Speech-to-Text) Integration

• Multipart form-data contract with /transcribe_audio endpoint
• Bearer token authentication support
• Tenant ID forwarding for multi-tenant deployments
• Configurable timeout (default: 30s)
• Concurrency control via buffered-channel semaphore (max 4 concurrent calls per channel)
• Shared HTTP client with connection pooling for performance

4. Audio Guard System

• Extracted into dedicated voiceguard package for better separation of concerns
• Zero dependencies on Telegram SDK or message bus
• Pure string→string transformation for easy unit testing
• Intercepts technical error language in voice agent replies
• User-friendly fallback messages with transcript support
• Customizable error markers (replaces built-in defaults when set)
• Supports both English and Vietnamese error detection

5. Enhanced Testability

• resolveTargetAgent() extracted as pure function (no I/O side effects)
• 14 table-driven test cases covering all routing scenarios
• Race condition testing with -race flag support
• 13 unit tests for audio guard logic
• Comprehensive STT test coverage

6. Agent Loop Improvements

• Rate limit model fallback support
• ForwardMedia field for delegation artifact forwarding
• Improved error handling and tracing

📊 Changes Summary

18 files changed
+2020 insertions
-247 deletions

New Files

• internal/channels/telegram/voiceguard/guard.go - Audio guard logic
• internal/channels/telegram/voiceguard/guard_test.go - Audio guard tests (13 tests)
• internal/channels/telegram/handlers_voice_routing_test.go - Voice routing tests (14 tests)
• internal/config/config_load_voice_test.go - Voice config tests
• internal/agent/loop_fallback_test.go - Model fallback tests
• cmd/gateway_consumer_audio_sanitize_test.go - Audio sanitization tests

Modified Files

• internal/config/config_channels.go - New TelegramVoiceConfig struct
• internal/channels/telegram/factory.go - Legacy config promotion logic
• internal/channels/telegram/handlers.go - Voice routing implementation
• internal/channels/telegram/stt.go - STT concurrency control & HTTP client pooling
• internal/agent/loop.go - ForwardMedia support & improved structure
• cmd/gateway_consumer.go - Integration with voiceguard package

🔄 Migration Path

For Existing Deployments

No immediate action required! The refactor is fully backward compatible:

• Existing DB rows with flat config layout continue to work
• Legacy fields are automatically promoted to nested structure on load
• No database migration needed

For New Deployments

Use the nested structure for cleaner configuration:

{
  "voice": {
    "agent_id": "speaking-agent",
    "stt_proxy_url": "https://stt.example.com",
    "stt_api_key": "secret-key",
    "intent_keywords": ["speaking", "pronunciation"],
    "affinity_clear_keywords": ["homework", "payment"],
    "affinity_ttl_minutes": 360,
    "dm_context_template": "Context:\n- tenant: {tenant_id}\n- user_id: {user_id}",
    "audio_guard_fallback_transcript": "🎙️ Got your voice: \"%s\". Please try again!",
    "audio_guard_error_markers": ["system error", "rate limit"]
  }
}

🧪 Testing

All tests pass:

✅ internal/channels/telegram - 14 routing tests
✅ internal/channels/telegram/voiceguard - 13 audio guard tests  
✅ internal/channels/telegram - STT tests updated
✅ cmd - audio sanitization tests

Run with race detector:

go test ./internal/channels/telegram/... -race -v

🔧 Environment Variables

New environment variable support:

• GOCLAW_VOICE_AGENT_ID - Override voice agent ID
• GOCLAW_STT_TENANT_ID - Override STT tenant ID
• GOCLAW_VOICE_DM_CONTEXT_TEMPLATE - Override DM context template
• GOCLAW_AUDIO_GUARD_FALLBACK_TRANSCRIPT - Override transcript fallback
• GOCLAW_AUDIO_GUARD_FALLBACK_NO_TRANSCRIPT - Override no-transcript fallback

📝 Documentation

Voice Routing Priority Chain

1. Audio/voice media present → voice agent (applies to groups too)
2. /start or start text (DM only) → voice agent + rewrite content
3. Text matches intent keywords (DM only) → voice agent + set affinity
4. Existing non-expired affinity (DM only) → continue routing to affinity agent
5. Text matches clear keywords (DM only) → evict affinity, route to default
6. Fallback → default agent

Audio Guard Behavior

• Only triggers for voice agent on Telegram DMs with audio/voice media
• Checks reply for technical error language
• Replaces with user-friendly fallback when error detected
• Supports custom error markers (replaces defaults when set)
• Extracts and includes transcript in fallback when available

🐛 Bug Fixes

• Fixed group affinity leak (affinity no longer stored for group chats)
• Fixed variable assignment in resolveTargetAgent call
• Normalized voice routing keywords to lowercase for case-insensitive matching
• Fixed STT contract to use audio field (not legacy file field)

🔍 Code Quality

• Zero breaking changes for existing deployments
• Comprehensive test coverage (27 new tests)
• Clear separation of concerns (voiceguard package)
• Improved code organization and maintainability
• Detailed inline documentation
• Performance optimizations (HTTP client pooling, concurrency control)

📚 Related Issues

Closes: (if any issue numbers)

🙏 Acknowledgments

This refactor builds upon the existing voice pipeline foundation and improves it with better structure, testability, and configurability for production deployments.