fix: stabilize learning path, reliability and legacy Windows builds

Unify beginner syntax while preserving compatibility, repair ownership and parser guards, add verified distribution tooling and VC6 Windows 98 build inputs, and clarify documentation and release status. Preserve DOS build-input line endings and exclude generated binaries/caches.

tools/validate_nesting_guards.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+"""Deep control blocks must produce diagnostics, not checker/CPU stack overflows."""
+from pathlib import Path
+import os
+import subprocess
+import tempfile
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def main():
+    if os.name == 'nt':
+        print('SKIP: current nesting sanitizer build requires POSIX')
+        return
+    with tempfile.TemporaryDirectory(prefix='claro-nesting-', dir=os.environ.get('TMPDIR')) as tmp:
+        work = Path(tmp)
+        exe = work / 'claro-asan'
+        subprocess.run(['gcc', '-std=c89', '-pedantic-errors', '-Werror=implicit-function-declaration', '-O0', '-g', '-fsanitize=address,undefined', str(ROOT / 'src/claro.c'), '-o', str(exe), '-lm'], check=True)
+        env = dict(os.environ, ASAN_OPTIONS='detect_leaks=1:halt_on_error=1', UBSAN_OPTIONS='halt_on_error=1')
+        for depth, expected in [(64, 0), (600, 1)]:
+            script = work / 'nested.claro'
+            script.write_text('IF YES\n' * depth + 'SAY "OK"\n' + 'END\n' * depth)
+            for command in ['check', 'run']:
+                run = subprocess.run([str(exe), command, str(script)], cwd=work, env=env, capture_output=True, text=True, timeout=15)
+                combined = run.stdout + run.stderr
+                assert run.returncode == expected, (depth, command, run.returncode, combined[-2000:])
+                assert not any(s in combined for s in ['AddressSanitizer', 'LeakSanitizer', 'runtime error:']), combined
+                if expected:
+                    assert 'block nesting' in combined.lower(), (command, combined)
+                else:
+                    assert run.stdout == ('OK\n' if command == 'run' else 'OK\n'), (command, combined)
+                print('PASS:', command, 'block depth', depth)
+
+
+if __name__ == '__main__':
+    main()