Address the remaining review findings on the wire-mirror layer:
- Export PROTOCOL_FD from protocol.ts as the TS-side source of truth the host
wires, and assert the Python constant against it in the mirror e2e instead of
a bare literal 3, so an fd drift on either side is caught.
- Correct the FrameFieldRoles JSDoc to point at the actual assertion site
(WIRE_FRAME_FIELD_ROLES's satisfies clause, not WIRE_FRAME_FIELDS).
- Drop the redundant explicit type annotation on WIRE_FRAME_FIELDS (the trailing
`as` cast already types it; Object.fromEntries returns an index signature).
- Refresh the mirror-test comment to describe the roles-map binding (a TS-side
add/remove/rename/optionality-flip fails typecheck; a Python-side change fails
the comparison).
4de8c914c9