diff --git a/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/specs/NoModuleKeyRegressionSpecTest.java b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/specs/NoModuleKeyRegressionSpecTest.java
new file mode 100644
index 00000000..a61897ed
--- /dev/null
+++ b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/specs/NoModuleKeyRegressionSpecTest.java
@@ -0,0 +1,75 @@
+package p.studio.compiler.specs;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Pattern;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+class NoModuleKeyRegressionSpecTest {
+    private static final Pattern FORBIDDEN_IDENTIFIERS = Pattern.compile("\\bmoduleKey\\b|\\bcalleeModuleKey\\b");
+    private static final List<String> STRUCTURAL_SOURCE_ROOTS = List.of(
+            "prometeu-compiler/prometeu-frontend-api/src/main/java/p/studio/compiler/models",
+            "prometeu-compiler/prometeu-compiler-core/src/main/java/p/studio/compiler/source/tables",
+            "prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs",
+            "prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/services",
+            "prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/irvm");
+
+    @Test
+    void structuralContractsMustNotReintroduceLegacyModuleKeyIdentifiers() throws IOException {
+        final var repoRoot = locateRepoRoot();
+        final var violations = new ArrayList<String>();
+        for (final var rootRelativePath : STRUCTURAL_SOURCE_ROOTS) {
+            final var root = repoRoot.resolve(rootRelativePath);
+            if (!Files.isDirectory(root)) {
+                continue;
+            }
+            try (Stream<Path> files = Files.walk(root)) {
+                files.filter(path -> Files.isRegularFile(path) && path.toString().endsWith(".java"))
+                        .forEach(path -> recordViolation(path, repoRoot, violations));
+            }
+        }
+
+        assertTrue(
+                violations.isEmpty(),
+                "legacy moduleKey identifier is forbidden in structural FE/BE contracts:\n" + String.join("\n", violations));
+    }
+
+    private void recordViolation(
+            final Path path,
+            final Path repoRoot,
+            final ArrayList<String> violations) {
+        final String content;
+        try {
+            content = Files.readString(path);
+        } catch (IOException e) {
+            throw new IllegalStateException("failed to read source file: " + path, e);
+        }
+        final var matcher = FORBIDDEN_IDENTIFIERS.matcher(content);
+        if (matcher.find()) {
+            final var relativePath = repoRoot.relativize(path).toString().replace('\\', '/');
+            violations.add(relativePath + " (" + matcher.group() + ")");
+        }
+    }
+
+    private Path locateRepoRoot() {
+        var cursor = Path.of(System.getProperty("user.dir")).toAbsolutePath().normalize();
+        while (cursor != null) {
+            final var hasDocs = Files.isDirectory(cursor.resolve("docs/general/specs"));
+            final var hasCompiler = Files.isDirectory(cursor.resolve("prometeu-compiler"));
+            if (hasDocs && hasCompiler) {
+                return cursor;
+            }
+            cursor = cursor.getParent();
+        }
+        fail("could not locate repository root from working directory");
+        throw new IllegalStateException("unreachable");
+    }
+}