When context compression rotates the agent's session_id to a new
child session, the API server was still returning the stale parent
session_id in the X-Hermes-Session-Id response header.
This caused external clients to keep sending the old session_id,
loading uncompressed parent history instead of the compressed
continuation.
Fix: _run_agent() now includes the effective session_id in its
result dict, and the response header uses it instead of the
original provided session_id.
7f735b4db2