fix: validate builtin arity before argument access

docs/CURRENT_STATUS.md

@@ -9,6 +9,21 @@ This file is the beginner-safe status map for the current package. It separates
 - **Experimental/planned**: do not rely on it in beginner lessons yet.
 - **Historical**: kept for release history, not current instructions.
 
+## Security and correctness review progress
+
+The v1.18.26 review identified missing-argument reads in standard-library built-ins. The current runtime now validates required argument counts centrally before any builtin indexes `args[]`. Covered calls include `math.abs`, `math.clamp`, `random.seed`, `random.int`, text helpers, CSV helpers, path helpers, and collection helpers. Missing arguments produce a beginner-facing `needs N arguments` runtime error.
+
+Focused regression coverage: `tests/38_builtin_arity.claro`.
+
+Verified in this checkout on 2026-09-22:
+
+- `gcc -std=c99 -O0 -g -fsanitize=address,undefined src/claro.c -o /tmp/claro-asan -lm` plus `ASAN_OPTIONS=detect_leaks=0 /tmp/claro-asan tests/38_builtin_arity.claro`: no AddressSanitizer or UndefinedBehaviorSanitizer report; LeakSanitizer still reports the pre-existing interpreter-wide cleanup backlog when leak detection is enabled.
+- `./claro test`: `PASS: 0 failure(s)`.
+- `./claro doctor`: all checks `OK`.
+- `./claro validate`: validation passed.
+
+This slice does not yet fix inverted `random.int` ranges, recursion depth, memory cleanup, `LASTEXIT`, HTTP buffering/status handling, or other review findings. Claro remains a trusted-script interpreter, not a sandbox.
+
 ## Feature matrix
 
 ### Beginner scripting core