Module extensions 

Extension namespace registry and unknown-message classification (RFC §21).

Two responsibilities live here:

1. Namespace validation via is_extension_name. Extension names follow one of two forms: arcpx.<vendor-or-domain>.<name>.v<n> (recommended) or a reverse-DNS prefix such as com.acme.workflow.v2.
2. Type classification. Given a wire-level type string, what should a receiver do? classify_type returns a TypeClassification that drives the dispatch decision per §21.3.

The bare x- prefix is reserved for transport-internal experimental fields and MUST NOT appear on long-lived deployments. We accept it for parsing but classify it as TypeClassification::ReservedExperimental.

Structs

ExtensionRegistry

Per-session/runtime registry of advertised extension names (§7, §21.2).

Enums

TypeClassification

What a receiver should do with a wire-level message type string.

Functions

classify_type

Classify a wire-level type string against the empty registry.

is_core_type

True if type_name is one of the core protocol types from RFC §6.2.

is_extension_name

True if name follows the §21.1 extension naming rules.