feat(linear-static-3d-euler-beam): step 8 - core-diagnostics

include/fesa/core/diagnostic.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include "fesa/core/source_identity.hpp"
+
+#include <string>
+#include <vector>
+
+namespace fesa {
+
+// Distinguishes recoverable warnings from errors that stop the current operation.
+enum class Severity {
+    warning,
+    error
+};
+
+// Carries a structured, backend-independent diagnostic record.
+struct Diagnostic {
+    Severity severity;
+    std::string code;
+    SourceLocation location;
+    std::string keyword;
+    std::string entityIdentity;
+    std::string message;
+};
+
+// Orders diagnostics by their externally visible source tuple while retaining
+// discovery order for records with identical keys.
+void sortDiagnostics(std::vector<Diagnostic>& diagnostics);
+
+} // namespace fesa