Function stream_reset_code_defined 

const fn stream_reset_code_defined(draft: DraftVersion) -> bool

Whether the draft defines a stream-reset error code vocabulary.

Drafts 07-10 do not, so the reset still executes with the code the action named and Effect::StreamReset / Effect::Truncated report code_defined: false — the code is a choice there, not a claim.

Exhaustive rather than !matches!(..). The negated form leans the other way from the rest of these predicates — a draft nobody listed would be granted a vocabulary rather than refused one, and the proxy would then publish code_defined: true about a draft no one has read. Either default is a guess; this one has to be written down.