fix: validate workspace secret source paths

scripts/test-verify-workspace-install-docs.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Regression test for copyable installation examples and secret-file validation.
+# Regression test for copyable installation examples and secret-path validation.
 set -euo pipefail
 
 root="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -15,7 +15,8 @@ for fixture in \
   "copied SSH Git override fixture" \
   "copied connector binding/secret fixture" \
   "core process sees connector bindings and secret files" \
-  "non-path secret-file fixture rejected"; do
+  "non-path secret-file fixture rejected" \
+  "literal secret-source fixture rejected"; do
   grep -Fqx "$fixture passed" "$output" >/dev/null || {
     echo "missing fixture verification: $fixture" >&2
     cat "$output" >&2