BRIDGE-4: Shield ← CSMS Alert Pipeline (CBP GovDelivery → alerts)

Connect River Pipeline Stage 2 (CSMS) output to Shield /alerts endpoint. River already ingests: - csms_ace: ACE system changes - csms_adcvd: antidumping/countervailing duty orders - csms_duty_rates: tariff rate changes - csms_forced_labor: UFLPA enforcement actions - csms_govdelivery: general CBP bulletins All stored with watermarks in river_watermarks table. Currently these go nowhere after ingest. Bridge: 1. When River CSMS stage completes, publish Pub/Sub message: screening.csms_update 2. Shield subscribes to this topic 3. On new CSMS data: match against customer product portfolios (by HTS chapter) 4. Generate alerts: "AD/CVD order affects HTS 7304.29 — 3 of your products impacted" 5. Store in Shield alerts table, push to /alerts endpoint This IS Stream 17 ($99-499/month compliance alert subscription). Output: River → Pub/Sub adapter + Shield alert matching logic Blocked by: Shield service (0a6794bd)