fix(audit): dedupe repeated backend CLI selections

Normalize repeated --backend values in phase0 capture/drift scripts so backend lists are unique and deterministic. Architecture/protocol diagrams reviewed; no updates needed for this parsing-only change.

scripts/capture-phase0-live-baseline.ts

@@ -146,9 +146,14 @@ function parseBackendTargets(raw: string | undefined): Phase0BackendTarget[] | u
     return undefined;
   }
   const parsed: Phase0BackendTarget[] = [];
+  const seen = new Set<Phase0BackendTarget>();
   for (const value of values) {
     if (BACKEND_TARGETS.includes(value as Phase0BackendTarget)) {
-      parsed.push(value as Phase0BackendTarget);
+      const backend = value as Phase0BackendTarget;
+      if (!seen.has(backend)) {
+        parsed.push(backend);
+        seen.add(backend);
+      }
       continue;
     }
     throw new Error(`Invalid backend "${value}".`);

scripts/check-phase0-baseline-backend-drift.ts

@@ -126,9 +126,14 @@ function parseOptionalInteger(raw: string | undefined, flag: string): number | u
 function parseBackends(raw: string | undefined): Phase0BackendTarget[] {
   const values = parseCsv(raw) ?? ['pi_embedded', 'native'];
   const parsed: Phase0BackendTarget[] = [];
+  const seen = new Set<Phase0BackendTarget>();
   for (const value of values) {
     if (BACKEND_TARGETS.includes(value as Phase0BackendTarget)) {
-      parsed.push(value as Phase0BackendTarget);
+      const backend = value as Phase0BackendTarget;
+      if (!seen.has(backend)) {
+        parsed.push(backend);
+        seen.add(backend);
+      }
       continue;
     }
     throw new Error(`Invalid backend "${value}".`);