INHERIT_RUBRIC_MODEL = '__dcode_inherit_rubric__'Checkpoint value meaning the rubric grader follows the active main model.
None cannot carry this: checkpoint reads go through state_values.get(),
which cannot tell an absent key from a key holding None. Absence has to keep
meaning "this thread never chose", because that is what falls back to the
startup grader model. /rubric model clear needs the stronger statement that
grading follows the active model, which this sentinel carries.
It cannot collide with a real spec: create_model resolves provider:model
(or a bare model name) and has no provider or model named __dcode_.... The
value stays plain ASCII for the same reason as INHERIT_CLASSIFIER_MODEL in
_cli_context — it is serialized to JSON and persisted, and Postgres
text/jsonb rejects NUL outright.