diff --git a/packages/mosaic/framework/tools/_scripts/mosaic-sync-skills b/packages/mosaic/framework/tools/_scripts/mosaic-sync-skills
index 0a9d02f9..e57aad17 100755
--- a/packages/mosaic/framework/tools/_scripts/mosaic-sync-skills
+++ b/packages/mosaic/framework/tools/_scripts/mosaic-sync-skills
@@ -262,7 +262,12 @@ prune_stale_links_in_target() {
     # -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
+    # $canonical_real must be length-checked BEFORE use as a prefix: if it were
+    # ever empty, "$resolved" == "$canonical_real/"* collapses to == "/"* and
+    # matches every absolute path. Combined with the is_mosaic_skill_name skip
+    # above, that inverts the function precisely — it would delete exactly the
+    # FOREIGN symlinks and keep the mosaic ones. (#1087, reported by mos-claude.)
+    if [[ -n "$resolved" && -n "$canonical_real" && "$resolved" == "$canonical_real/"* ]]; then
       rm -f "$link_path"
       echo "[mosaic-skills] Removed stale retired skill link: $link_path"
     fi