feat(gateway): inject reply-to message context when quoted message is not in session history

[anpicasso]

Problem

When a user replies to a specific message on Telegram (or other platforms), the agent has no visibility into which message is being referenced. The MessageEvent dataclass has a reply_to_message_id field, but:

1. The Telegram adapter's _build_message_event() never populates it
2. There is no field for the replied-to message's text content
3. The gateway never injects the quoted text into the agent's context

This is especially problematic when replying to messages that are outside the current session context — cron job results, /background task outputs, messages from previous sessions, or messages that were compressed away. The agent receives the user's reply with zero context about what it refers to.

Proposed Solution

A token-efficient approach that only adds context when needed:

1. MessageEvent — add reply_to_text: Optional[str] field
2. Telegram adapter — populate reply_to_message_id and reply_to_text from message.reply_to_message (Telegram already sends the full quoted message in the update — no extra API call needed)
3. Gateway message handler — before running the agent, check if the replied-to text appears in the conversation history:
   • Found in history → do nothing (zero extra tokens)
   • Not found → prepend [Replying to: "<quoted text>"] to the message

This keeps token usage minimal for normal same-session replies while providing critical context for cross-session/cron/background replies.

Use Cases Solved

• Replying to cron job results (delivered via adapter.send(), not in session transcript)
• Replying to /background task outputs
• Replying to messages from previous sessions (after /new or context compression)
• Replying to old messages that were compressed away
• Future: replying to background delegation results

Files Changed

• gateway/platforms/base.py — add reply_to_text field to MessageEvent
• gateway/platforms/telegram.py — populate reply_to_message_id + reply_to_text in _build_message_event()
• gateway/run.py — conditional context injection before _run_agent()

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Submitted by Yuqi — Angello's Hermes Agent (@anpicasso)