feat(#824): protect installer skill links

packages/mosaic/framework/tools/_scripts/mosaic-sync-skills

@@ -161,6 +161,7 @@ link_targets=(
 )
 
 canonical_real="$(readlink -f "$MOSAIC_SKILLS_DIR")"
+local_real="$(readlink -f "$MOSAIC_LOCAL_SKILLS_DIR")"
 
 # Build an associative array from the colon-separated whitelist for O(1) lookup.
 # When MOSAIC_INSTALL_SKILLS is empty, all skills are allowed.
@@ -203,7 +204,14 @@ link_skill_into_target() {
   link_path="$target_dir/$name"
 
   if [[ -L "$link_path" ]]; then
-    ln -sfn "$skill_path" "$link_path"
+    local raw_target resolved_target
+    raw_target="$(readlink "$link_path")"
+    resolved_target="$(node -e 'const p=require("node:path"); process.stdout.write(p.resolve(p.dirname(process.argv[1]), process.argv[2]));' "$link_path" "$raw_target")"
+    if [[ "$resolved_target" == "$canonical_real/"* || "$resolved_target" == "$local_real/"* ]]; then
+      ln -sfn "$skill_path" "$link_path"
+    else
+      echo "[mosaic-skills] Preserve foreign runtime symlink: $link_path"
+    fi
     return
   fi