diff --git a/backend/src/cyclone/rebill/pipeline_a.py b/backend/src/cyclone/rebill/pipeline_a.py
new file mode 100644
index 0000000..a52ce14
--- /dev/null
+++ b/backend/src/cyclone/rebill/pipeline_a.py
@@ -0,0 +1,79 @@
+"""Pipeline A: denied/partial → frequency-7 replacement 837Ps.
+
+For each visit the previous adjudication said was DENIED or PARTIAL,
+emit a fresh 837P with CLM05-3 = '7' (replacement claim) and the
+original claim_submit_id preserved as CLM01. The 837P carries the
+original DOS and the same procedure / member.
+
+The CARC-aware filter is the gate — only REBILL / REVIEW decisions are
+emitted; EXCLUDED visits never make it to a file.
+"""
+from dataclasses import dataclass
+from datetime import date
+from decimal import Decimal
+from pathlib import Path
+
+from cyclone.rebill.carc_filter import CarcDecision
+from cyclone.rebill.reconcile import ReconcileOutcome, OutcomeCategory
+
+
+@dataclass(frozen=True)
+class RebillClaim:
+    claim_id: str           # reuses original claim_submit_id
+    member_id: str
+    procedure: str
+    svc_date: date
+    charge: Decimal
+    frequency_code: str     # always "7" for Pipeline A
+    needs_review: bool      # True for CARC REVIEW decisions
+    original_carc_reasons: tuple[str, ...]
+
+
+def build_pipeline_a_claims(
+    original_claim_id: str,
+    visit_outcomes: list[ReconcileOutcome],
+    carc_decisions: list[CarcDecision],
+    cas_reasons_per_visit: list[tuple[str, ...]],
+) -> list[RebillClaim]:
+    """One input list per visit; align by index."""
+    out: list[RebillClaim] = []
+    for vo, carc, reasons in zip(visit_outcomes, carc_decisions, cas_reasons_per_visit):
+        if vo.category not in (OutcomeCategory.DENIED, OutcomeCategory.PARTIAL):
+            continue
+        if carc == CarcDecision.EXCLUDED:
+            continue
+        out.append(RebillClaim(
+            claim_id=original_claim_id,
+            member_id=vo.visit.member_id,
+            procedure=vo.visit.procedure,
+            svc_date=vo.visit.date,
+            charge=vo.visit.billed,
+            frequency_code="7",
+            needs_review=(carc == CarcDecision.REVIEW),
+            original_carc_reasons=tuple(reasons),
+        ))
+    return out
+
+
+def write_pipeline_a_files(
+    claims: list[RebillClaim],
+    out_dir: Path,
+    serialize_837_fn,  # injected: cyclone.parsers.serialize_837.serialize_837
+    tpid: str,
+) -> list[Path]:
+    """Write one 837P per claim, using HCPF-spec filenames via build_outbound_filename.
+
+    `serialize_837_fn(claim)` returns the X12 byte string. The filename is
+    `cyclone.edi.filenames.build_outbound_filename(tpid, '837P')`.
+    """
+    from cyclone.edi.filenames import build_outbound_filename
+
+    out_dir.mkdir(parents=True, exist_ok=True)
+    paths: list[Path] = []
+    for c in claims:
+        body = serialize_837_fn(c)
+        fname = build_outbound_filename(tpid, "837P")
+        path = out_dir / fname
+        path.write_bytes(body)
+        paths.append(path)
+    return paths
diff --git a/backend/tests/test_rebill_pipeline_a.py b/backend/tests/test_rebill_pipeline_a.py
new file mode 100644
index 0000000..e4ebb1d
--- /dev/null
+++ b/backend/tests/test_rebill_pipeline_a.py
@@ -0,0 +1,60 @@
+"""Pipeline A: denied/partial visits become frequency-7 replacement claims."""
+from datetime import date
+from decimal import Decimal
+from pathlib import Path
+from cyclone.rebill.pipeline_a import (
+    RebillClaim,
+    build_pipeline_a_claims,
+    write_pipeline_a_files,
+)
+from cyclone.rebill.reconcile import VisitRow, ReconcileOutcome, OutcomeCategory
+from cyclone.rebill.carc_filter import CarcDecision
+
+
+def _outcome(date_, member, proc, billed, cat, unpaid=Decimal("0")):
+    visit = VisitRow(date=date_, member_id=member, procedure=proc, billed=Decimal(billed))
+    return ReconcileOutcome(visit, cat, unpaid, 0)
+
+
+def test_pipeline_a_emits_frequency_7():
+    """CLM05-3 must be 7 (replacement), preserving the original claim_submit_id."""
+    out = build_pipeline_a_claims(
+        original_claim_id="ORIG-001",
+        visit_outcomes=[
+            _outcome(date(2026, 6, 27), "J813715", "T1019", "2.32",
+                     OutcomeCategory.DENIED, unpaid=Decimal("2.32")),
+        ],
+        carc_decisions=[CarcDecision.REBILL],
+        cas_reasons_per_visit=[()],
+    )
+    assert len(out) == 1
+    assert out[0].claim_id == "ORIG-001"
+    assert out[0].frequency_code == "7"
+    assert out[0].svc_date == date(2026, 6, 27)
+
+
+def test_pipeline_a_excludes_carc_excluded_visits():
+    out = build_pipeline_a_claims(
+        original_claim_id="ORIG-002",
+        visit_outcomes=[
+            _outcome(date(2026, 6, 27), "J813715", "T1019", "2.32",
+                     OutcomeCategory.DENIED),
+        ],
+        carc_decisions=[CarcDecision.EXCLUDED],
+        cas_reasons_per_visit=[("CO-45",)],
+    )
+    assert out == []  # not emitted
+
+
+def test_pipeline_a_surfaces_review_visits_with_flag():
+    out = build_pipeline_a_claims(
+        original_claim_id="ORIG-003",
+        visit_outcomes=[
+            _outcome(date(2026, 6, 27), "J813715", "T1019", "2.32",
+                     OutcomeCategory.DENIED),
+        ],
+        carc_decisions=[CarcDecision.REVIEW],
+        cas_reasons_per_visit=[("PI-16",)],
+    )
+    assert len(out) == 1
+    assert out[0].needs_review is True