Codex stop-time review flagged the new ab-v3 composite cookbook
recipes calling add_section_header_v0 with a `subtitle` arg the tool
doesn't accept (silently dropped at runtime today, but teaches live
models to emit invalid shapes). The same bug was in the dry-run stub
fixtures.
Split each header into add_section_header_v0(title) +
add_body_text_v0(content) — semantically what the ab-v3 briefs ask
for, and reinforces the multi-tool chaining the cookbook now teaches.
Also fills in the missing required `number` arg on the onboarding
recipe's final completed step card (schema requires it even when
completed=true renders a check instead of the number).
c2252f2172