PR #71 shipped the core-data-structures catalog and the verify-type-equiv
drift gate without an RFC (judged small at the time). Add the retroactive
implemented RFC so the sibling pair is documented symmetrically: the
spine-vs-seam scoping rule (discovered by testing candidate definitions against
borderline types like BashExecRequest and ToolDefinition), the
verbatim-match-over-assignability choice for the gate, and the process —
including the Codex-caught scan-gap bug fixed in 6da7a0f. Cross-link the two
catalog RFCs to each other and index the new one.
Tianyi Cui
d614f3aabf