docs(memory-bank): record relay hardening policy baseline and operating knobs

memory-bank/patterns.md

@@ -64,3 +64,28 @@ Example paths:
 
 - `locales/en/**`, `locales/cy/**`
 - `next.config.js`, `i18n.js`
+
+### P-003: Shared Relay Policy via Middleware (No Endpoint Drift)
+
+date: 2026-03-24  
+author: Cline  
+scope: `pages/api/middleware/relayForwarding.js`, `pages/api/endpoint/*_api.js` relay GET handlers  
+type: pattern  
+rationale: Keep reliability and logging policy centralized so endpoint handlers remain thin and behavior stays consistent as relay surface evolves.  
+impact: Reduces duplication/drift in timeout/retry/error behavior and supports safer incremental endpoint migration/hardening.  
+status: accepted
+
+Pattern:
+Implement retry/timeout/redacted structured logging in shared relay middleware and keep endpoint handlers focused on validation, transform, and route-level response contracts.
+
+When to use:
+
+- Any new or migrated relay-backed endpoint
+- Any relay reliability/logging policy update
+
+Example paths:
+
+- `pages/api/middleware/relayForwarding.js`
+- `pages/api/endpoint/getadvancedsearch_api.js`
+- `pages/api/endpoint/getdnscoords_api.js`
+- `tests/phase21/relay-forwarding-hardening.test.cjs`