Forwards frames between MAVLink2.Links, by MAVLink's routing rules:

• Each frame received teaches the router that its sender, {sysid, compid}, is reachable through the link it arrived on.
• A broadcast goes out on every other link: a frame with no target, or a target system of 0. A frame whose id the dialect lacks (a link with unknown: :keep) is a broadcast.
• A frame for another system goes out on the other links where that system has been seen, any component of it.
• A frame for the router's own system (:sysid) and a component other than 0 goes out on the other links where that component has been seen; for component 0, where any component of the system has been seen.
• A target not seen on any other link goes nowhere, and nothing goes back out on the link it came in on.
• SETUP_SIGNING is never forwarded: it carries a signing key.
• A frame a link's signing refuses is forwarded by the same rules, but teaches the router nothing, so a forged sender cannot take a route.
• A SYSTEM_TIME whose time_boot_ms goes back means its sender has rebooted: that system's routes are forgotten.

The target is the header's target_sysid when present, else the payload's target_system and target_component, found through the dialect's target_offsets/1 (MAVLink2.Dialect).

Frames go out with MAVLink2.Link.forward/2, unchanged. The router is a subscriber like any other: an application on the same links sees every frame too, and decides for itself what is addressed to it.

Options:

The router stops when one of its links does, so a supervisor restarting both resubscribes it.