fix: harden skill linking to avoid canonical path corruption

bin/mosaic-sync-skills

@@ -91,13 +91,21 @@ link_targets=(
   "$HOME/.config/opencode/skills"
 )
 
+canonical_real="$(readlink -f "$MOSAIC_SKILLS_DIR")"
+
 link_skill_into_target() {
   local skill_path="$1"
   local target_dir="$2"
 
-  local name
+  local name link_path
   name="$(basename "$skill_path")"
-  local link_path="$target_dir/$name"
+
+  # Do not distribute hidden/system skill directories globally.
+  if [[ "$name" == .* ]]; then
+    return
+  fi
+
+  link_path="$target_dir/$name"
 
   if [[ -L "$link_path" ]]; then
     ln -sfn "$skill_path" "$link_path"
@@ -105,9 +113,8 @@ link_skill_into_target() {
   fi
 
   if [[ -e "$link_path" ]]; then
-    local backup="$link_path.mosaic-backup.$(date +%Y%m%d%H%M%S)"
-    mv "$link_path" "$backup"
-    echo "[mosaic-skills] Backed up existing entry: $link_path -> $backup"
+    echo "[mosaic-skills] Preserve existing runtime-specific entry: $link_path"
+    return
   fi
 
   ln -s "$skill_path" "$link_path"
@@ -116,6 +123,13 @@ link_skill_into_target() {
 for target in "${link_targets[@]}"; do
   mkdir -p "$target"
 
+  # If target already resolves to canonical dir, skip to avoid self-link recursion/corruption.
+  target_real="$(readlink -f "$target" 2>/dev/null || true)"
+  if [[ -n "$target_real" && "$target_real" == "$canonical_real" ]]; then
+    echo "[mosaic-skills] Skip target (already canonical): $target"
+    continue
+  fi
+
   while IFS= read -r -d '' skill; do
     link_skill_into_target "$skill" "$target"
   done < <(find "$MOSAIC_SKILLS_DIR" -mindepth 1 -maxdepth 1 -type d -print0)