fix(install): never follow a symlink when replacing the Hermes plugin

`rm -rf "$dest/"` follows a symlink and empties its target. basename ignores a
trailing slash, so HERMES_PLUGIN_DIR=".../agency-agents-router/" passed every
check, and a symlinked destination (our own --link install, or a user's folder)
had its target's contents deleted. #903's ownership check didn't cover it: the
check reads through the link and the rm still follows it.

- Strip all trailing slashes from the destination before any check.
- A symlinked destination is removed with `rm -f` (the link itself), never
  `rm -rf`.
- test-install-hermes-destination.sh: two new cases (trailing slash on a
  symlink to a folder with a matching plugin.yaml; re-install over a --link
  install). Both fail before this commit and pass after.

Found by a destructive-path matrix (25 scenarios, throwaway container, fake HOME
with sentinel files): main fails 10 (deletes unrelated dirs, files and symlink
targets at the plugin path); the series without this commit fails 2 (H8/H9);
with it, 25/25.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

scripts/install.sh

@@ -1390,6 +1390,9 @@ install_hermes() {
   local src="$INTEGRATIONS/hermes/agency-agents-router"
   local hermes_home; hermes_home="$(hermes_home_dir)"
   local dest; dest="$(resolve_dest hermes "${hermes_home}/plugins/agency-agents-router")"
+  # Strip trailing slashes first: basename ignores them, but `rm -rf link/`
+  # follows a symlink and empties its target instead of removing the link.
+  while [[ "$dest" == */ && "$dest" != "/" ]]; do dest="${dest%/}"; done
   # HERMES_PLUGIN_DIR is ambiguous: its name invites setting it to the plugins
   # parent (~/.hermes/plugins) rather than the full plugin path. Always target
   # the agency-agents-router subdir so we never rm -rf a shared plugins dir that
@@ -1417,7 +1420,12 @@ install_hermes() {
       return 1
     fi
   fi
-  rm -rf "$dest"
+  # A symlink (e.g. from an earlier --link install) is replaced, never followed.
+  if [[ -L "$dest" ]]; then
+    rm -f -- "$dest"
+  else
+    rm -rf -- "$dest"
+  fi
   if $USE_LINK; then
     ln -s "$src" "$dest"
   else

scripts/test-install-hermes-destination.sh

@@ -57,3 +57,30 @@ HOME="$fresh_home" bash "$repo/scripts/install.sh" --no-interactive --tool herme
   exit 1
 }
 echo 'PASS: fresh Hermes installation works normally'
+
+# A trailing slash must not turn "replace the plugin" into "empty whatever a
+# symlink points at": `rm -rf link/` follows the link and deletes the target's
+# contents. Seen on real installs via HERMES_PLUGIN_DIR=".../agency-agents-router/".
+link_home="$tmp/link-home"
+link_plugin="$link_home/.hermes/plugins/agency-agents-router"
+personal="$tmp/personal"
+mkdir -p "$personal" "$(dirname "$link_plugin")"
+printf 'name: agency-agents-router\n' > "$personal/plugin.yaml"
+printf 'personal content\n' > "$personal/personal.txt"
+ln -s "$personal" "$link_plugin"
+HOME="$link_home" HERMES_PLUGIN_DIR="$link_plugin/" bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert > "$tmp/slash-output" 2>&1 || true
+[[ -f "$personal/personal.txt" ]] || {
+  echo 'FAIL: a trailing slash deleted the contents of a symlinked directory' >&2
+  exit 1
+}
+echo 'PASS: a trailing slash on a symlinked destination leaves its target intact'
+
+relink_home="$tmp/relink-home"
+HOME="$relink_home" bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert --link > "$tmp/link-output" 2>&1
+HOME="$relink_home" HERMES_PLUGIN_DIR="$relink_home/.hermes/plugins/agency-agents-router/" \
+  bash "$repo/scripts/install.sh" --no-interactive --tool hermes --no-convert > "$tmp/relink-output" 2>&1
+[[ -f "$repo/integrations/hermes/agency-agents-router/plugin.yaml" ]] || {
+  echo 'FAIL: re-installing over a --link install deleted the plugin source in the clone' >&2
+  exit 1
+}
+echo 'PASS: re-installing over a --link install keeps the clone intact'