telepathy-haze currently ships a .manager file that may or may not contain an accurate list of protocols supported by telepathy-haze on the machine in question under the current phase of the moon.  Only at runtime, when libpurple probes for plugins, is the list known.

There needs to be some way to tell clients to just start up the CM and ask it what it supports rather than relying on the .manager.  One way would be to add a may-be-full-of-lies flag to the .manager.  Rob suggested that a cleaner technique would be for clients to use ListActivatableNames to figure out which CMs are installed, and start and probe those which do not have .manager files.