chore: import upstream snapshot with attribution

tests/grammar_cases.h

@@ -0,0 +1,31 @@
+/*
+ * grammar_cases.h — Shared per-language fixture table.
+ *
+ * One minimal source fixture per supported grammar. Shared by:
+ *   - test_grammar_regression.c : EXTRACTION-level breadth (cbm_extract_file with
+ *     an explicit language → defs/labels). Bypasses discover, so it covers every
+ *     grammar including those whose file extension collides with another's.
+ *   - test_lang_contract.c      : GRAPH-level breadth (full pipeline index → the
+ *     fixture's defs must reach the graph as nodes).
+ *
+ * Keep this the single source of truth for per-grammar fixtures.
+ */
+#ifndef CBM_TEST_GRAMMAR_CASES_H
+#define CBM_TEST_GRAMMAR_CASES_H
+
+#include "cbm.h"
+#include <stddef.h>
+
+typedef struct {
+    const char *name;       /* short grammar label (unique) */
+    CBMLanguage lang;       /* explicit language for extraction-level tests */
+    const char *path;       /* representative filename (drives discover by ext/name) */
+    const char *src;        /* fixture source */
+    int min_defs;           /* catastrophic-break floor (0 for data/config/markup) */
+    const char *expect[4];  /* expected def names (NULL-terminated), optional */
+} GrammarCase;
+
+extern const GrammarCase CBM_GRAMMAR_CASES[];
+extern const size_t CBM_GRAMMAR_CASES_COUNT;
+
+#endif /* CBM_TEST_GRAMMAR_CASES_H */