Pull Worldtree main's role/model-cutover doc correction (worldtree commit
b4a278c) into the pinned conversation-api-spec: the Echo ephemeral-template
section now documents allowed_roles/default_role, config.role (omitted ->
default_role "echo"), the repurposed model_not_allowed (any non-empty
config.model hard-rejects), and the new role_required error. Frozen OpenAPI
untouched. affect-egress-consumer-reference re-synced in the same pass;
re-pin hashes in .corviduo-canonicals.toml.
Resolves the role<->model drift ratatoskr-dev raised on althing (thread
01KXT976NN91DRBZBPXNZ2BVZR); worldtree-dev cleared the re-sync.
No version bump (vendored-canonical docs sync).
vh
5d06a274bf