ref: vendor harec checker sources (#20)

ref/hare/ ships only ast/lex/parse/module/unparse — no checker. Every
bail-fix landing in A.6.2.1 (helper bail audit, N_IDENT bail audit,
enum fold) needs a `ref/harec/...` cite anchor so divergence rationale
isn't claimed against memory. PLAN.md L16, L35.

Snapshot of upstream commit ee640c6b2c17f57e8014d277a3028b262ffb7952
(`rt/+openbsd/start.ha: remove outdated comment about crt0`). 20 files:
5 src (check.c, eval.c, scope.c, types.c, type_store.c), 14 transitive
include/ headers (no parser/codegen surface), and COPYING.

License GPLv3 (COPYING included). Vendored as read-only reference per
CLAUDE.md rule 6 — no redistribution as binary, no edits.

ref/harec/include/identifier.h

@@ -0,0 +1,53 @@
+#ifndef HARE_IDENTIFIER_H
+#define HARE_IDENTIFIER_H
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+// Maximum length of an identifier, as the sum of the lengths (excluding NUL
+// terminators) of its parts plus one for each namespace deliniation.
+//
+// In other words, the length of "a::b::c" is 5.
+#define IDENT_MAX 255
+
+// Minimum buffer size needed to store an unparsed identifier, including the
+// terminating NUL byte.
+#define IDENT_BUFSIZ (IDENT_MAX / 2 + IDENT_MAX + 1)
+
+struct ident {
+	const char *name;
+	struct ident *ns;
+};
+
+struct identifiers {
+	struct ident *ident;
+	struct identifiers *next;
+};
+
+struct bucket {
+	void **ids;
+	size_t sz;
+	size_t cap;
+};
+
+struct intern_table {
+	struct bucket *sbuckets;
+	struct bucket *ibuckets;
+};
+
+bool ident_equal(const struct ident *a, const struct ident *b);
+uint32_t ident_hash(uint32_t init, const struct ident *ident);
+char *ident_unparse(const struct ident *ident);
+int ident_unparse_static(const struct ident *ident, char *buf);
+const char *ident_to_sym(struct intern_table *itbl, const struct ident *ident);
+
+void intern_init(struct intern_table *itbl);
+
+const char *intern_copy(struct intern_table *itbl, const char *s);
+const char *intern_owned(struct intern_table *itbl, char *s);
+
+struct ident *intern_ident(struct intern_table *itbl,
+		const char *name, struct ident *ns);
+struct ident *intern_name(struct intern_table *itbl, const char *name);
+
+#endif