diff --git a/.gitea/workflows/build-and-test.yml b/.gitea/workflows/build-and-test.yml
index 1fbd334e..fae13e8a 100644
--- a/.gitea/workflows/build-and-test.yml
+++ b/.gitea/workflows/build-and-test.yml
@@ -49,6 +49,13 @@ jobs:
         run: |
           bun install
 
+      # Tripwire for domain-taxonomy leaks into the presentation layer (a
+      # multi-type includeItemTypes query defining a category in the frontend).
+      # See scripts/check-frontend-boundary.sh and
+      # docs/specs/scoped-search-boundary.md.
+      - name: Check frontend/backend boundary
+        run: bash scripts/check-frontend-boundary.sh
+
       - name: Run frontend tests
         run: |
           bunx svelte-kit sync
diff --git a/package.json b/package.json
index 7ae171ab..e0f5ec95 100644
--- a/package.json
+++ b/package.json
@@ -17,6 +17,7 @@
     "test:e2e:dev": "wdio run ./wdio.conf.ts --watch",
     "test:all": "./scripts/test-all.sh",
     "test:rust": "./scripts/test-rust.sh",
+    "check:boundary": "bash scripts/check-frontend-boundary.sh",
     "android:build": "./scripts/build-android.sh",
     "android:build:release": "./scripts/build-android.sh release",
     "android:build:clean": "rm -rf node_modules/.vite dist .svelte-kit .next build target src-tauri/target && bun install && bun run build",
diff --git a/scripts/check-frontend-boundary.sh b/scripts/check-frontend-boundary.sh
new file mode 100755
index 00000000..e24e1817
--- /dev/null
+++ b/scripts/check-frontend-boundary.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# Boundary tripwire: flag domain-taxonomy leaks in the Svelte frontend.
+#
+# The project rule (CLAUDE.md, docs/architecture/02-svelte-frontend.md) is that
+# the frontend is presentation-only and the Rust backend owns domain logic —
+# including Jellyfin's item-type *taxonomy* (what the category "Music" means as a
+# set of item types). See docs/specs/scoped-search-boundary.md for the incident
+# that motivated this check.
+#
+# ⚠️ This is a TRIPWIRE, NOT A PROOF. A grep cannot distinguish taxonomy-as-policy
+# (a leak) from taxonomy-as-display (legitimate: "is this a music card?"). It
+# targets the one machine-detectable signature of the leak class — a *query* that
+# names a multi-type category — and defers everything subtler to the human
+# spec-review checklist (docs/specs/SPEC-REVIEW-CHECKLIST.md). A clean run here
+# does not mean the boundary is respected; it means the crudest violation isn't
+# present.
+#
+# What it flags: an `includeItemTypes: [ ... , ... ]` array literal with two or
+# more types — i.e. the frontend deciding that a *category* maps to a *set* of
+# Jellyfin types, which is domain knowledge the backend should own. Single-type
+# query arrays (`includeItemTypes: ["Movie"]`) are a page saying "I show movies"
+# and are allowed. Type *inspection* (`item.type === "Audio"`) is display logic
+# and is not matched.
+#
+# Escaping a genuine exception: add the file+reason to the ALLOWLIST below.
+
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+# Files permitted to contain a multi-type includeItemTypes query, with the reason.
+# Keep this SHORT. A growing allowlist means the boundary is eroding — that is a
+# signal to push taxonomy into Rust, not to keep appending here.
+ALLOWLIST=(
+  # "Things a person appeared in" is arguably taxonomy, but it is a fixed
+  # two-type filmography query with no category-configuration behind it. Tracked
+  # as acceptable pending any person-scope work; revisit if it grows.
+  "src/lib/components/library/PersonDetailView.svelte"
+)
+
+is_allowed() {
+  local file="$1"
+  for allowed in "${ALLOWLIST[@]}"; do
+    [[ "$file" == "$allowed" ]] && return 0
+  done
+  return 1
+}
+
+# Multi-element includeItemTypes array: `includeItemTypes: [ <x> , <y> ... ]`.
+# The comma inside the brackets is what makes it multi-type.
+PATTERN='includeItemTypes:[[:space:]]*\[[^]]*,[^]]*\]'
+
+echo "🔎 Checking frontend for domain-taxonomy leaks (multi-type query arrays)…"
+
+# Collect hits, excluding tests and the allowlist.
+violations=""
+while IFS= read -r line; do
+  [[ -z "$line" ]] && continue
+  file="${line%%:*}"
+  case "$file" in
+    *.test.*) continue ;;
+  esac
+  if is_allowed "$file"; then
+    echo "  ⏭️  allowlisted: $line"
+    continue
+  fi
+  violations+="$line"$'\n'
+done < <(grep -rInE "$PATTERN" src/ 2>/dev/null || true)
+
+if [[ -n "$violations" ]]; then
+  echo ""
+  echo "❌ Frontend boundary violation: a multi-type includeItemTypes query defines"
+  echo "   a category in the presentation layer. That taxonomy belongs in Rust —"
+  echo "   send an opaque scope and let the backend expand it to item types."
+  echo "   See docs/specs/scoped-search-boundary.md and CLAUDE.md."
+  echo ""
+  echo "$violations" | sed 's/^/   /'
+  echo "   If this is a genuine exception, add the file + reason to ALLOWLIST in"
+  echo "   scripts/check-frontend-boundary.sh — but prefer moving it to Rust."
+  exit 1
+fi
+
+echo "✅ No multi-type taxonomy queries in the frontend."
+echo "   (Reminder: this is a tripwire, not a proof — the spec-review checklist is"
+echo "    the real gate for subtler leaks.)"