Adds two pre-gate checks to propose_from_candidate that fire after the
Step 2 capacity check and before the replay gate. No log entry is
written on either refusal — the append-only invariant holds.
Check order at function entry (ADR-0161 §3):
1. Capacity (Step 2) → RefusedAtCapacity
2. Duplicate → RefusedAsDuplicate
3. Dependent_on_pending → RefusedAsDependent
4. Replay gate → auto-reject on regression
New frozen dataclasses:
@dataclass(frozen=True, slots=True)
class RefusedAsDuplicate:
proposal_id: str
existing_state: str # covers all states: pending/accepted/rejected/withdrawn
reason: str = "duplicate"
@dataclass(frozen=True, slots=True)
class RefusedAsDependent:
candidate_id: str
dependent_on: tuple[str, ...] # pending proposal_ids that block
overlapping_lemmas: tuple[str, ...] # normalised lemmas that triggered
reason: str = "dependent_on_pending"
Lemma-overlap rule: case-insensitive exact-match on strip().lower().
Conservative — over-reject rather than admit-with-hidden-dependency.
False positives are recoverable (re-emit after blocker is ratified);
false negatives silently couple ratification choices.
CLI surfaces both outcomes in cmd_teaching_propose and
cmd_teaching_propose_from_exemplars (exit code 1).
Step 2 backpressure tests updated: made pre-populated candidates use
unique objects to avoid triggering the new dependency check, and
updated idempotency assertions to reflect the new RefusedAsDuplicate
return for re-submitted content.
Co-references: ADR-0161 §3, Step 1 PR #296, Step 2 PR #311,
ADR-0057, ADR-0151.
