Routing is configured via $GLOBALS['TYPO3_CONF_VARS']['SYS']['messenger']['routing'], a map of message type to one or more transport identifiers. A routing value may be a single transport identifier (string) or an ordered list of transport identifiers (array) to route a single message to multiple transports.

The routing keys (the "types") are matched against the type chain of the dispatched message, which is derived from the message's PHP type - not from the order of the routing configuration. The chain, as produced by HandlersLocator::listTypes(), is, from most to least specific: the message class, its parent classes, its implemented interfaces, the namespace wildcards for every namespace level (My\Sub\Message*, My\Sub*, My*) and finally the global wildcard '*'.

Resolution rules:

1. An explicit TransportNamesStamp on the envelope always wins.
2. Otherwise senders are collected across every matching type in that type chain order, deduplicated (first occurrence wins).
3. A wildcard route - a namespace wildcard (My\Message*) or the global '*' - acts as a fallback: it is skipped as soon as a more specific type already matched, and only applies when no specific route matched. This mirrors the upstream Symfony SendersLocator and removes the need to unset a wildcard route to keep a message on its specific transport only.