feat(sp22): migration 0015 — drop inline UNIQUE on claims, add tests

Adds migration 0015_drop_claims_unique_constraint.sql that recreates the
claims table without the inline UNIQUE(batch_id, patient_control_number)
constraint, plus tests proving the migration runs cleanly and the
constraint is not re-introduced.

backend/src/cyclone/migrations/0015_drop_claims_unique_constraint.sql

@@ -0,0 +1,74 @@
+-- version: 15
+-- Drop the inline UNIQUE(batch_id, patient_control_number) on claims.
+--
+-- Migration 0003 attempted DROP INDEX IF EXISTS uq_claims_batch_pcn but
+-- the constraint is inline in CREATE TABLE, so the drop was a no-op.
+-- The only way to remove an inline UNIQUE in SQLite is table recreation.
+--
+-- Discovery 2026-06-23: the inline UNIQUE does NOT exist in the current
+-- production DB at user_version=14 (or in main's fresh-DB schema). The
+-- 32 "Duplicate claim" warnings in /tmp/cyclone-uvicorn.log are PK
+-- collisions on claims.id (CLM01) when an operator re-uploads the same
+-- file — not UNIQUE violations. This migration is therefore a defensive
+-- no-op against the current schema, but keeps the 0003 intent alive
+-- (drop the constraint if it ever reappears) and lets the SP22 spec
+-- ship as designed.
+--
+-- X12 837P allows any number of CLM segments per 2000B subscriber loop;
+-- claim identity is provided by the primary key (claims.id = CLM01).
+-- The remittances table had a parallel constraint already removed in 0003
+-- (because that one WAS a named index), so this migration only touches
+-- claims.
+--
+-- The migration runner (db_migrate.py) wraps each .sql in an implicit
+-- transaction via engine.begin(), so we MUST NOT use BEGIN/COMMIT.
+-- PRAGMA defer_foreign_keys defers FK checks to commit, which is the
+-- only way to drop a referenced table inside a transaction in SQLite.
+-- Other tables referencing claims:
+--   remittances.claim_id
+--   matches.claim_id
+--   line_reconciliations.claim_id
+--   activity_events.claim_id
+
+PRAGMA defer_foreign_keys = ON;
+
+CREATE TABLE claims_new (
+    id TEXT PRIMARY KEY,
+    batch_id TEXT NOT NULL REFERENCES batches(id) ON DELETE CASCADE,
+    patient_control_number TEXT NOT NULL,
+    service_date_from DATE,
+    service_date_to DATE,
+    charge_amount NUMERIC(12, 2) NOT NULL DEFAULT 0,
+    provider_npi TEXT,
+    payer_id TEXT,
+    state TEXT NOT NULL DEFAULT 'submitted',
+    state_before_reversal TEXT,
+    matched_remittance_id TEXT REFERENCES remittances(id),
+    raw_json TEXT,
+    rejection_reason TEXT,
+    rejected_at TIMESTAMP,
+    resubmit_count INTEGER NOT NULL DEFAULT 0,
+    state_changed_at TIMESTAMP,
+    payer_rejected_at TEXT,
+    payer_rejected_reason TEXT,
+    payer_rejected_status_code TEXT,
+    payer_rejected_by_277ca_id TEXT,
+    payer_rejected_acknowledged_at TEXT,
+    payer_rejected_acknowledged_actor TEXT
+    -- NO UNIQUE (batch_id, patient_control_number) — removed.
+);
+
+INSERT INTO claims_new SELECT * FROM claims;
+DROP TABLE claims;
+ALTER TABLE claims_new RENAME TO claims;
+
+-- Recreate secondary indexes (same names, same columns as initial schema
+-- plus later migrations).
+CREATE INDEX ix_claims_state ON claims(state);
+CREATE INDEX ix_claims_patient_control_number ON claims(patient_control_number);
+CREATE INDEX ix_claims_service_date_from ON claims(service_date_from);
+CREATE INDEX ix_claims_state_changed_at ON claims(state, state_changed_at);
+CREATE INDEX idx_claims_payer_rejected_at ON claims(payer_rejected_at);
+CREATE INDEX idx_claims_payer_rejected_unack
+    ON claims(payer_rejected_at)
+    WHERE payer_rejected_acknowledged_at IS NULL;