feat(sp7): migration 0006 — service_line_payments + line_reconciliations + FKs

Migration renumbered from 0005 to 0006 because 0005_create_ta1_acks.sql
(another agent's WIP, unmerged) already claims version 5. Bumping our
migration to version 6 avoids stepping on it; user_version will land
at 6 once both migrations run.

backend/src/cyclone/db.py

@@ -260,6 +260,9 @@ class Remittance(Base):
     total_paid: Mapped[Decimal] = mapped_column(Numeric(12, 2), nullable=False, default=Decimal("0"))
     patient_responsibility: Mapped[Optional[Decimal]] = mapped_column(Numeric(12, 2), nullable=True)
     adjustment_amount: Mapped[Decimal] = mapped_column(Numeric(12, 2), nullable=False, default=Decimal("0"))
+    claim_level_adjustment_amount: Mapped[Decimal] = mapped_column(
+        Numeric(12, 2), nullable=False, default=Decimal("0"), server_default=text("0")
+    )
     received_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
     service_date: Mapped[Optional[date]] = mapped_column(Date, nullable=True)
     is_reversal: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
@@ -292,11 +295,17 @@ class CasAdjustment(Base):
     reason_code: Mapped[str] = mapped_column(String(8), nullable=False)
     amount: Mapped[Decimal] = mapped_column(Numeric(12, 2), nullable=False)
     quantity: Mapped[Optional[Decimal]] = mapped_column(Numeric(10, 2), nullable=True)
+    service_line_payment_id: Mapped[Optional[int]] = mapped_column(
+        Integer,
+        ForeignKey("service_line_payments.id", ondelete="SET NULL"),
+        nullable=True,
+    )
 
     remittance: Mapped["Remittance"] = relationship(back_populates="cas_adjustments")
 
     __table_args__ = (
         Index("ix_cas_adjustments_remittance_id", "remittance_id"),
+        Index("ix_cas_adjustments_service_line_payment_id", "service_line_payment_id"),
     )
 
 
@@ -346,10 +355,15 @@ class LineReconciliation(Base):
     """One row per matched (or explicitly unmatched) 837 service line within a claim.
 
     SP7. Created during ``reconcile.run()`` after the claim↔remit match.
-    At least one of ``claim_service_line_id`` / ``service_line_payment_id``
+    At least one of ``claim_service_line_number`` / ``service_line_payment_id``
     must be non-null; the application enforces this.
 
-    See spec §3.2.
+    Implementation note: 837 service lines live in ``Claim.raw_json.service_lines[]``
+    keyed by ``line_number`` (1-based). They are NOT a separate ORM table, so the
+    claim-side FK is the line number itself; lookups join via the parent ``claim_id``
+    + this column to read the line from the JSON blob.
+
+    See spec §3.2 (with this implementation note appended during T3).
     """
     __tablename__ = "line_reconciliations"
 
@@ -357,10 +371,8 @@ class LineReconciliation(Base):
     claim_id: Mapped[str] = mapped_column(
         String(64), ForeignKey("claims.id", ondelete="CASCADE"), nullable=False
     )
-    claim_service_line_id: Mapped[Optional[int]] = mapped_column(
-        Integer,
-        ForeignKey("service_lines.id", ondelete="SET NULL"),
-        nullable=True,
+    claim_service_line_number: Mapped[Optional[int]] = mapped_column(
+        Integer, nullable=True
     )
     service_line_payment_id: Mapped[Optional[int]] = mapped_column(
         Integer,
@@ -376,7 +388,8 @@ class LineReconciliation(Base):
     __table_args__ = (
         Index("ix_line_reconciliations_claim_id", "claim_id"),
         Index(
-            "ix_line_reconciliations_claim_service_line_id", "claim_service_line_id"
+            "ix_line_reconciliations_claim_service_line_number",
+            "claim_service_line_number",
         ),
         Index(
             "ix_line_reconciliations_service_line_payment_id",

backend/src/cyclone/migrations/0006_line_reconciliation.sql

@@ -1,4 +1,4 @@
--- version: 5
+-- version: 6
 -- SP7: per-service-line adjustment audit
 -- See spec: docs/superpowers/specs/2026-06-20-cyclone-line-reconciliation-design.md
 
@@ -24,7 +24,7 @@ CREATE INDEX ix_service_line_payments_procedure_code_date ON service_line_paymen
 CREATE TABLE line_reconciliations (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
     claim_id VARCHAR(64) NOT NULL REFERENCES claims(id) ON DELETE CASCADE,
-    claim_service_line_id INTEGER REFERENCES service_lines(id) ON DELETE SET NULL,
+    claim_service_line_number INTEGER,
     service_line_payment_id INTEGER REFERENCES service_line_payments(id) ON DELETE SET NULL,
     status VARCHAR(16) NOT NULL,
     match_score INTEGER,
@@ -32,7 +32,7 @@ CREATE TABLE line_reconciliations (
 );
 
 CREATE INDEX ix_line_reconciliations_claim_id ON line_reconciliations(claim_id);
-CREATE INDEX ix_line_reconciliations_claim_service_line_id ON line_reconciliations(claim_service_line_id);
+CREATE INDEX ix_line_reconciliations_claim_service_line_number ON line_reconciliations(claim_service_line_number);
 CREATE INDEX ix_line_reconciliations_service_line_payment_id ON line_reconciliations(service_line_payment_id);
 
 ALTER TABLE cas_adjustments ADD COLUMN service_line_payment_id INTEGER REFERENCES service_line_payments(id) ON DELETE SET NULL;