When context compression fires during run_conversation() in the gateway,
the compressed messages were silently lost on the next turn. Two bugs:
1. Agent-side: _flush_messages_to_session_db() calculated
flush_from = max(len(conversation_history), _last_flushed_db_idx).
After compression, _last_flushed_db_idx was correctly reset to 0,
but conversation_history still had its original pre-compression
length (e.g. 200). Since compressed messages are shorter (~30),
messages[200:] was empty — nothing written to the new session's
SQLite.
Fix: Set conversation_history = None after each _compress_context()
call so start_idx = 0 and all compressed messages are flushed.
2. Gateway-side: history_offset was always len(agent_history) — the
original pre-compression length. After compression shortened the
message list, agent_messages[200:] was empty, causing the gateway
to fall back to writing only a user/assistant pair, losing the
compressed summary and tail context.
Fix: Detect session splits (agent.session_id != original) and set
history_offset = 0 so all compressed messages are written to JSONL.
