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(`rt/+openbsd/start.ha: remove outdated comment about crt0`). 20 files: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/scope.h

@@ -0,0 +1,96 @@
+#ifndef HAREC_SCOPE_H
+#define HAREC_SCOPE_H
+#include "expr.h"
+#include "identifier.h"
+
+#define SCOPE_BUCKETS 4096
+
+enum object_type {
+	O_BIND,
+	O_CONST,
+	O_DECL,
+	O_SCAN,
+	O_TYPE,
+};
+
+enum scope_object_flags {
+	SO_THREADLOCAL = 1 << 0,
+	SO_FOR_EACH_SUBJECT = 1 << 1,
+};
+
+struct scope_object {
+	enum object_type otype;
+	// name is the name of the object within this scope (for lookups)
+	// ident is the global identifier (these may be different in some cases)
+	struct ident *name;
+	struct ident *ident;
+	enum scope_object_flags flags;
+
+	union {
+		const struct type *type;
+		struct expression *value; // For O_CONST
+	};
+	 // Cannot be in union because type and idecl are needed at the same time
+	struct incomplete_decl *idecl;
+
+	struct scope_object *lnext; // Linked list
+	struct scope_object *mnext; // Hash map
+};
+
+enum scope_class {
+	SCOPE_COMPOUND,
+	SCOPE_DEFER,
+	SCOPE_ENUM,
+	SCOPE_FUNC,
+	SCOPE_LOOP,
+	SCOPE_MATCH,
+	SCOPE_SUBUNIT,
+	SCOPE_UNIT,
+	SCOPE_DEFINES,
+};
+
+struct yield { // and break
+	struct expression **expression;
+	struct yield *next;
+};
+
+struct scope {
+	enum scope_class class;
+	const char *label;
+	struct scope *parent;
+
+	const struct type *hint;
+	struct type_tagged_union results;
+	struct yield *yields;
+
+	// Linked list in insertion order
+	// Used for function parameters and enum values, where order matters
+	struct scope_object *objects;
+	struct scope_object **next;
+
+	// Hash map in reverse insertion order
+	// Used for lookups, and accounts for shadowing
+	struct scope_object *buckets[SCOPE_BUCKETS];
+};
+
+struct scopes {
+	struct scope *scope;
+	struct scopes *next;
+};
+
+struct scope *scope_push(struct scope **stack, enum scope_class class);
+struct scope *scope_pop(struct scope **stack);
+
+struct scope *scope_lookup_class(struct scope *scope, enum scope_class class);
+struct scope *scope_lookup_label(struct scope *scope, const char *label);
+
+void scope_free(struct scope *scope);
+void scope_free_all(struct scopes *scopes);
+
+struct scope_object *scope_insert(struct scope *scope,
+	enum object_type otype, struct ident *ident, struct ident *name,
+	const struct type *type, struct expression *value);
+
+struct scope_object *scope_lookup(struct scope *scope, struct ident *ident);
+
+#endif