feat: detect duplicate CREATE in mxcli check (MDL-DUPDEF)

Phase 1 (mxcli check): CheckScriptDuplicates walks the AST in order,
tracking live names per document type. Flags a second plain CREATE of
the same qualified name as MDL-DUPDEF. CREATE OR MODIFY/REPLACE is
never flagged. DROP clears the name so CREATE/DROP/CREATE is clean.
RENAME removes the old name and registers the new one; module renames
cascade across all tracked names. RENAME DRY RUN leaves the registry
unchanged.

Phase 2 (mxcli check --references): CheckProjectConflicts loads the
project's existing documents once and errors on any plain CREATE that
targets a name already present in the project. Names created earlier
in the same script are excluded (Phase 1 owns those conflicts).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

cmd/mxcli/cmd_check.go

@@ -118,6 +118,9 @@ Examples:
 			}
 		}
 
+		// Check for intra-script duplicate definitions (CREATE X … CREATE X without DROP)
+		violations = append(violations, executor.CheckScriptDuplicates(prog)...)
+
 		if isStructured {
 			// Always emit structured output (even when clean)
 			formatter.Format(violations, os.Stderr)
@@ -159,6 +162,10 @@ Examples:
 
 			// Validate the program (considers objects defined within the script)
 			validationErrors := exec.ValidateProgram(prog)
+
+			// Check for project conflicts: plain CREATE where the document already exists
+			validationErrors = append(validationErrors, exec.CheckProjectConflicts(prog)...)
+
 			if len(validationErrors) > 0 {
 				if isStructured {
 					var refViolations []linter.Violation

mdl/executor/validate.go

@@ -191,6 +191,14 @@ func (e *Executor) ValidateProgram(prog *ast.Program) []error {
 	return validateProgram(e.newExecContext(context.Background()), prog)
 }
 
+// CheckProjectConflicts walks prog in statement order and returns errors for
+// any plain CREATE (non-OR-MODIFY) that targets a document name that already
+// exists in the connected project. Names created earlier in the same script are
+// excluded — those will be caught by CheckScriptDuplicates.
+func (e *Executor) CheckProjectConflicts(prog *ast.Program) []error {
+	return CheckProjectConflicts(e.newExecContext(context.Background()), prog)
+}
+
 // validateWithContext validates a statement, considering objects defined in the script.
 func validateWithContext(ctx *ExecContext, stmt ast.Statement, sc *scriptContext) error {
 	switch s := stmt.(type) {