feat(sp33): apply_999_rejections uses batch_envelope_index

The 999 handler's rejection pass was looking up claims by patient
control number, but Gainwell rejects at the SET level (ST envelope)
when the whole batch fails the NM109=CO_TXIX rule. That meant a SET
rejection was treated as a no-op even though every claim in the SET
was actually rejected by the payer.

Add a batch_envelope_index param (mirrors apply_999_acceptances from
SP28) so SET-level rejections cascade to every claim in the SET.
Falls back to the legacy PCN lookup when the index has no entry.

Also tightens test_payer.py: PayerConfig.co_medicaid() now returns
payer_id='CO_TXIX' and payer_name='CO_TXIX' per HCPF 837P Companion
Guide (June 2025 - Version 2.5).

backend/tests/test_apply_999_rejections.py

@@ -0,0 +1,120 @@
+"""SP33: apply_999_rejections must use batch_envelope_index (mirrors
+SP28's apply_999_acceptances fix) so SET-level 999 rejections cascade
+to claim state transitions.
+
+The pre-SP33 bug: ``claim_lookup(sr.set_control_number)`` passed the
+SET control_number to a PCN-based lookup, so no claim was ever matched
+and rejections silently died. SP33 threads the same
+``batch_envelope_index`` that ``apply_999_acceptances`` already has.
+"""
+from __future__ import annotations
+
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+from cyclone.db import ClaimState
+from cyclone.inbox_state import apply_999_rejections
+
+
+def _mk_set_response(code: str = "R", scn: str = "991102994"):
+    """Build a stand-in for ``ParseResult999.set_responses[0]``."""
+    return SimpleNamespace(
+        set_accept_reject=SimpleNamespace(code=code),
+        set_control_number=scn,
+        segment_errors=[],
+    )
+
+
+def _mk_claim(cid: str = "claim-x", state=ClaimState.SUBMITTED):
+    c = MagicMock()
+    c.id = cid
+    c.state = state
+    return c
+
+
+def test_set_level_rejection_cascades_via_envelope_index():
+    """When the SET-level 999 has set_control_number=991102994 and the
+    batch_envelope_index maps it to a list of 3 claim_ids, all 3 should
+    transition to REJECTED.
+    """
+    session = MagicMock()
+    claims = [_mk_claim(f"c-{i}") for i in range(3)]
+    session.query.return_value.filter.return_value.all.return_value = claims
+
+    parsed = SimpleNamespace(set_responses=[_mk_set_response(code="R", scn="991102994")])
+    index = {"991102994": [c.id for c in claims]}
+
+    result = apply_999_rejections(
+        session, parsed,
+        claim_lookup=lambda _pcn: None,
+        batch_envelope_index=index,
+    )
+
+    assert sorted(result.matched) == sorted(c.id for c in claims)
+    assert result.orphans == []
+    session.commit.assert_called_once()
+    for c in claims:
+        # ClaimState.REJECTED is the lowercase 'rejected' string (the enum
+        # value stored in the DB column via SQLAlchemy Enum type).
+        assert c.state == ClaimState.REJECTED
+
+
+def test_set_level_rejection_without_index_still_uses_legacy_lookup():
+    """Backwards compat: when batch_envelope_index is None, the function
+    must fall back to claim_lookup (existing behavior preserved).
+    """
+    session = MagicMock()
+    parsed = SimpleNamespace(set_responses=[_mk_set_response(code="R", scn="991102994")])
+    legacy_claim = _mk_claim("legacy-claim")
+
+    result = apply_999_rejections(
+        session, parsed,
+        claim_lookup=lambda scn: legacy_claim if scn == "991102994" else None,
+    )
+
+    assert result.matched == ["legacy-claim"]
+
+
+def test_no_envelope_index_no_match_becomes_orphan():
+    """Empty index + empty legacy lookup => the SET becomes an orphan."""
+    session = MagicMock()
+    parsed = SimpleNamespace(set_responses=[_mk_set_response(code="R", scn="991102999")])
+
+    result = apply_999_rejections(
+        session, parsed,
+        claim_lookup=lambda _pcn: None,
+        batch_envelope_index={},  # empty index
+    )
+    assert result.matched == []
+    assert "991102999" in result.orphans
+
+
+def test_accepted_999_does_not_reject():
+    """An 'A' code must not transition any claim to REJECTED."""
+    session = MagicMock()
+    parsed = SimpleNamespace(set_responses=[_mk_set_response(code="A", scn="991102994")])
+
+    result = apply_999_rejections(
+        session, parsed,
+        claim_lookup=lambda _pcn: None,
+        batch_envelope_index={"991102994": ["claim-x"]},
+    )
+    assert result.matched == []
+    session.query.assert_not_called()
+    session.commit.assert_not_called()
+
+
+def test_already_rejected_is_idempotent():
+    """Pre-REJECTED claims in the index are left alone (no second commit)."""
+    session = MagicMock()
+    already = _mk_claim("already-rejected", state=ClaimState.REJECTED)
+    session.query.return_value.filter.return_value.all.return_value = [already]
+
+    parsed = SimpleNamespace(set_responses=[_mk_set_response(code="R", scn="991102994")])
+    result = apply_999_rejections(
+        session, parsed,
+        claim_lookup=lambda _pcn: None,
+        batch_envelope_index={"991102994": ["already-rejected"]},
+    )
+    assert result.matched == []
+    assert already.state == ClaimState.REJECTED  # untouched

backend/tests/test_payer.py

@@ -8,8 +8,8 @@ def test_co_medicaid_defaults():
     assert cfg.allowed_claim_frequencies == {1, 7, 8}
     assert cfg.require_ref_g1_for_adjustments is False  # lenient in v1
     assert cfg.allowed_bht06 == {"CH"}
-    assert cfg.payer_id == "SKCO0"
-    assert cfg.payer_name == "COHCPF"
+    assert cfg.payer_id == "CO_TXIX"
+    assert cfg.payer_name == "CO_TXIX"
     assert cfg.no_patient_loop is True
     assert cfg.encounter_claim_in_same_batch is False