feat: Add pluggable channel system for remote messaging via Telegram

[edenreich]

Summary

• Add a transport-agnostic channel abstraction that lets external messaging platforms (Telegram, WhatsApp, etc.) remote-control the agent
• The infer channels-manager command runs as a standalone long-running daemon, completely decoupled from the agent
• Each incoming message triggers infer agent --session-id <id> as a subprocess — the agent has no knowledge of channels

Architecture

Telegram Bot API  <-->  infer channels-manager (daemon)
                              |
                              v  (per message)
                        1. Check allowlist
                        2. Derive session ID (channel-telegram-<chatID>)
                        3. exec: infer agent --session-id <id> "<message>"
                        4. Parse JSON stdout
                        5. Send response via channel

What's included

• Channel interface (domain.Channel) with Start/Send/Stop lifecycle
• ChannelManager service — subprocess-based routing, per-sender mutex serialization, allowlist auth
• Telegram channel using go-telegram/bot SDK (long-polling, no webhook needed)
• infer channels-manager command — standalone daemon with signal handling
• Session ID bug fix — --session-id now persists the provided ID even when the session doesn't exist yet
• Per-channel allowlist security (secure-by-default: empty list rejects all)
• Full documentation (docs/channels.md), Docker Compose example, and test coverage

Key design decisions

• Decoupled: Channel manager is a standalone process, not embedded in the agent. The agent remains simple with no channel-related logic
• Subprocess per message: Each message spawns infer agent --session-id <id>, giving crash isolation and clean lifecycle
• Deterministic sessions: Session ID is channel-{name}-{senderID}, so conversations persist across messages using the existing ConversationRepository and auto-compact
• No new dependencies on agent internals: Removed MessageQueue/EventBridge coupling from the channel manager

TODOs

• Test the example to ensure the functionality works as expected with telegram
• Ensure there are not many processes running and exhausting the system - that the semaphore limit works as expected
• Test the agents tasks delegation - for example setup a browser agent and make sure it can use it when sending a message on telegram for example to get an article from the internet etc..
• Test with vision LLMs like Anthropic Opus that it can understand images I'm sending over telegram
• Implement approval flow for tools in telegram
• Refactor session rollover manager session groups - I'm not happy about the complexity, I need to refactor this

Closes #380

[edenreich]

Here are some tests with tools...