test(hooks): fence against heredocs in the hook chain (red; #571)

tests/hooks/test-no-heredocs-in-hooks.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Heredocs are banned from the hook delivery chain: bash >= 5.1 delivers
+# them through a pre-fork pipe write that deadlocks on macOS under pipe
+# pressure (issue #571; the #571 class). This fence fails the moment one
+# returns. The operator is spelled out of a variable so this file does not
+# trip its own check.
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
+
+OP='<''<'
+FAILURES=0
+for f in "$REPO_ROOT"/hooks/*; do
+    case "$f" in *.json) continue;; esac
+    [ -f "$f" ] || continue
+    if hits="$(grep -nE "$OP" "$f")"; then
+        echo "  [FAIL] heredoc operator in ${f#"$REPO_ROOT"/}:"
+        printf '%s\n' "$hits" | sed 's/^/    /'
+        FAILURES=$((FAILURES + 1))
+    else
+        echo "  [PASS] ${f#"$REPO_ROOT"/} is heredoc-free"
+    fi
+done
+
+if [ "$FAILURES" -gt 0 ]; then
+    echo "STATUS: FAILED ($FAILURES file(s))"
+    exit 1
+fi
+echo "STATUS: PASSED"