Allow listeners to mix named pools in a single chain using pool:name
syntax. Bare "pool" continues to use the listener's default pool.
Replaces pool_hops field with pool_seq list; pool_hops is now a
backward-compatible property. Each hop draws from its own pool and
failure reporting targets the correct source pool.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
ef0d8f347b