diff --git a/.github/workflows/check-tools.yml b/.github/workflows/check-tools.yml
index ec13b3ec..a11fa13f 100644
--- a/.github/workflows/check-tools.yml
+++ b/.github/workflows/check-tools.yml
@@ -32,3 +32,6 @@ jobs:
 
       - name: Validate agent selection (install.sh --agent / --agents-file)
         run: bash scripts/test-agent-selection.sh
+
+      - name: Protect unrelated Hermes destinations
+        run: bash scripts/test-install-hermes-destination.sh
diff --git a/scripts/install.sh b/scripts/install.sh
index 50f46893..f730f222 100755
--- a/scripts/install.sh
+++ b/scripts/install.sh
@@ -1295,6 +1295,16 @@ install_hermes() {
     err "Hermes: refusing to remove '$dest' — expected an agency-agents-router directory."
     return 1
   fi
+  # The basename alone does not establish ownership: --path or an existing
+  # Hermes setup may point here with unrelated user files. Replace only a
+  # previous copy of this plugin, identified by its generated manifest.
+  if [[ -e "$dest" || -L "$dest" ]]; then
+    if [[ ! -f "$dest/plugin.yaml" ]] || \
+       ! grep -Eq '^[[:space:]]*name:[[:space:]]*agency-agents-router[[:space:]]*$' "$dest/plugin.yaml"; then
+      err "Hermes: refusing to replace '$dest' because it is not an existing agency-agents-router plugin."
+      return 1
+    fi
+  fi
   rm -rf "$dest"
   if $USE_LINK; then
     ln -s "$src" "$dest"
diff --git a/scripts/test-install-hermes-destination.sh b/scripts/test-install-hermes-destination.sh
new file mode 100644
index 00000000..28bba326
--- /dev/null
+++ b/scripts/test-install-hermes-destination.sh
@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Hermes installation must replace only a directory owned by this plugin.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+tmp="$(mktemp -d "${TMPDIR:-/tmp}/agency-hermes-dest.XXXXXX")"
+trap 'rm -rf "$tmp"' EXIT
+repo="$tmp/repo"
+home="$tmp/home"
+plugin="$home/.hermes/plugins/agency-agents-router"
+mkdir -p "$repo/scripts" "$repo/engineering" \
+  "$repo/integrations/hermes/agency-agents-router/data" "$plugin"
+cp "$SCRIPT_DIR/install.sh" "$SCRIPT_DIR/lib.sh" "$repo/scripts/"
+cat > "$repo/divisions.json" <<'EOF'
+{
+  "divisions": {
+    "engineering": {}
+  }
+}
+EOF
+cat > "$repo/integrations/hermes/agency-agents-router/plugin.yaml" <<'EOF'
+name: agency-agents-router
+EOF
+printf '# Plugin\n' > "$repo/integrations/hermes/agency-agents-router/__init__.py"
+printf '[]\n' > "$repo/integrations/hermes/agency-agents-router/data/agents.json"
+printf 'personal content\n' > "$plugin/personal.txt"
+
+if HOME="$home" bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert > "$tmp/output" 2>&1; then
+  echo 'FAIL: Hermes replaced an unrelated directory with the plugin name' >&2
+  exit 1
+fi
+[[ -f "$plugin/personal.txt" ]] || {
+  echo 'FAIL: Hermes removed unrelated user content' >&2
+  exit 1
+}
+grep -q 'refusing to replace' "$tmp/output" || {
+  echo 'FAIL: Hermes rejection did not explain the destination conflict' >&2
+  exit 1
+}
+echo 'PASS: unrelated destination remains untouched'
+
+cat > "$plugin/plugin.yaml" <<'EOF'
+name: agency-agents-router
+EOF
+printf 'outdated\n' > "$plugin/old.txt"
+HOME="$home" bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert > "$tmp/upgrade-output" 2>&1
+[[ -f "$plugin/__init__.py" && -f "$plugin/data/agents.json" && ! -e "$plugin/old.txt" ]] || {
+  echo 'FAIL: a prior Agency plugin was not upgraded' >&2
+  exit 1
+}
+echo 'PASS: a prior Agency plugin upgrades normally'
+
+fresh_home="$tmp/fresh-home"
+HOME="$fresh_home" bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert > "$tmp/fresh-output" 2>&1
+[[ -f "$fresh_home/.hermes/plugins/agency-agents-router/plugin.yaml" ]] || {
+  echo 'FAIL: fresh Hermes installation did not create the plugin' >&2
+  exit 1
+}
+echo 'PASS: fresh Hermes installation works normally'