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.

docs/plans/state.json

@@ -581,6 +581,18 @@
       ],
       "test_status": "pnpm test:run src/audit/phase0BaselineScriptWiring.test.ts + pnpm typecheck passing"
     },
+    "phase0-live-baseline-backend-list-dedup-in-cli": {
+      "status": "completed",
+      "date": "2026-02-27",
+      "updated": "2026-02-27",
+      "summary": "Deduplicated repeated backend names in phase-0 capture/drift CLI parsing so repeated `--backend` values do not duplicate drift evaluation rows or alter backend-scoped artifact suffix selection.",
+      "files_modified": [
+        "scripts/capture-phase0-live-baseline.ts",
+        "scripts/check-phase0-baseline-backend-drift.ts",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm typecheck + node --import tsx/esm scripts/check-phase0-baseline-backend-drift.ts --artifacts-dir docs/plans/artifacts --backend native,native --format json + synthetic-audit capture smoke check passing"
+    },
     "phase0-instrumentation-ticket-checklist": {
       "status": "completed",
       "date": "2026-02-25",