diff --git a/lib/tests/toggle-external-repo-resolution.test.sh b/lib/tests/toggle-external-repo-resolution.test.sh
new file mode 100644
index 0000000..8c54109
--- /dev/null
+++ b/lib/tests/toggle-external-repo-resolution.test.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# lib/tests/toggle-external-repo-resolution.test.sh
+#
+# Regression test for J4-20 (BLK-006 class): toggle-external.sh:34 resolved
+# REPO with a LOGICAL `cd` (no -P). Direct invocation via a symlinked path —
+# exactly the real ~/.claude/lib -> <repo>/lib layout — resolves REPO to the
+# SYMLINK's logical parent instead of the physical repo root, so every path
+# derived from it (SKILLS_DIR, DISABLED_DIR) points at the wrong tree.
+set -u
+HELPER_SRC="$(cd "$(dirname "$0")/../.." && pwd)/lib/toggle-external.sh"
+pass=0; fail=0
+check() { if [ "$2" = "$3" ]; then pass=$((pass+1)); else fail=$((fail+1));
+  printf 'FAIL %s: got[%s] want[%s]\n' "$1" "$2" "$3"; fi; }
+
+SANDBOX="$(mktemp -d)"
+mkdir -p "$SANDBOX/repo/lib" "$SANDBOX/repo/skills-external/emil-design-eng" \
+  "$SANDBOX/repo/skills" "$SANDBOX/home/.claude"
+cp "$HELPER_SRC" "$SANDBOX/repo/lib/toggle-external.sh"
+# mark emil-design-eng ENABLED in the real (physical) repo tree
+ln -s "$SANDBOX/repo/skills-external/emil-design-eng" "$SANDBOX/repo/skills/emil-design-eng"
+# replicate the real ~/.claude/lib -> <repo>/lib symlink
+ln -s "$SANDBOX/repo/lib" "$SANDBOX/home/.claude/lib"
+
+out="$(bash "$SANDBOX/home/.claude/lib/toggle-external.sh" status emil-design-eng)"
+check T1-repo-resolves-through-symlink "$out" enabled
+
+rm -rf "$SANDBOX"
+printf 'PASS=%s FAIL=%s\n' "$pass" "$fail"; [ "$fail" -eq 0 ]