config_loader._dm_behavior_choice still normalized against {"pair","ignore"},
so `unauthorized_dm_behavior: decline` in config.yaml (top level or a
platform block) was coerced back to "pair" on the real startup path
(load_gateway_config), and `unauthorized_dm_decline_message` was never
bridged into gw_data. Both now go through gateway.config.UNAUTHORIZED_DM_BEHAVIORS
(single source) and the presence bridge. The round-trip test exercises
load_gateway_config with a real config.yaml (top-level decline, telegram
override, custom message) instead of GatewayConfig.from_dict.
Telegram's intake prefilter only forwarded unauthorized DMs when the
behavior was exactly "pair", so with an allowlist configured a decline was
never sent. Anything that needs an outbound reply (!= "ignore") passes.
`hermes gateway setup` gains a "Politely decline unknown senders" choice
that writes platforms.<platform>.unauthorized_dm_behavior: decline; docs
mention it. Upstream-source references dropped from docstrings.
fd303c0137