0409 — There is no unversioned GetTopic(name); every topic read is version-addressed

Context. With multiple schema versions registered under one name, an unversioned lookup raises the question of what it should mean — an error, or “latest.”

Decision. The overload does not exist. Every read through pkg/admin and pkg/topic is explicitly version-addressed.

Consequences. The “error or latest?” question is resolved by never having to answer it — no default that could silently resolve to the wrong physical topic. Callers that genuinely want to enumerate a family go through the family-level reads (FamilyHealth) rather than an implicit resolution rule.

Superseded by [0618]: the schema version is a message_log column declared by the Message type; the topic catalog is keyed by name alone.