feat(mosaic): add secure skill registration CLI (#826)

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
 
@@ -234,14 +242,10 @@ prune_stale_links_in_target() {
       continue
     fi
 
-    resolved="$(readlink -f "$link_path" 2>/dev/null || true)"
-    if [[ -z "$resolved" ]]; then
-      rm -f "$link_path"
-      echo "[mosaic-skills] Removed stale broken skill link: $link_path"
-      continue
-    fi
-
-    if [[ "$resolved" == "$MOSAIC_HOME/"* ]]; then
+    # -m resolves lexical dangling targets too. If resolution fails, ownership
+    # is unproven and the link must be preserved.
+    resolved="$(readlink -m "$link_path" 2>/dev/null || true)"
+    if [[ -n "$resolved" && "$resolved" == "$canonical_real/"* ]]; then
       rm -f "$link_path"
       echo "[mosaic-skills] Removed stale retired skill link: $link_path"
     fi