test: selfhost multi-error recovery regression fixture

Makefile

@@ -140,6 +140,11 @@ test-errors: ensure-buxc
 	@chmod +x tests/error_golden/run.sh
 	@tests/error_golden/run.sh ./$(OUT)
 
+test-error-recovery: ensure-buxc selfhost
+	@echo "=== Selfhost multi-error recovery test ==="
+	@chmod +x _test_error_recovery/run.sh
+	@_test_error_recovery/run.sh
+
 test-stdlib: ensure-buxc
 	@echo "=== Stdlib golden tests ==="
 	@chmod +x tests/stdlib_golden/run.sh

_test_error_recovery/run.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Regression: buxc2 must report ALL independent semantic errors in one run.
+set -euo pipefail
+HERE="$(cd "$(dirname "$0")" && pwd)"
+ROOT="$(cd "$HERE/.." && pwd)"
+BUXC2="$ROOT/build/selfhost/build/buxc2"
+export BUX_STDLIB="$ROOT/lib"
+
+if [[ ! -x "$BUXC2" ]]; then
+  echo "=== building selfhost (buxc2) ==="
+  (cd "$ROOT" && make selfhost)
+fi
+if [[ ! -x "$BUXC2" ]]; then
+  echo "error: buxc2 not found at $BUXC2" >&2
+  exit 1
+fi
+
+out="$(cd "$HERE" && "$BUXC2" check src/Main.bux 2>&1 || true)"
+echo "$out"
+
+grep -q "cannot assign String to int" <<<"$out"
+grep -q "cannot assign int to bool" <<<"$out"
+grep -q "undeclared identifier 'undefined_variable'" <<<"$out"
+
+echo "PASS: all independent semantic errors reported in one run"