fix(gateguard): ignore heredoc prose for tee and path-qualified sinks (#2886)

Expand proven-passive heredoc recognition beyond bare `cat` so documentation
writes via `tee`, `/bin/cat`, and `command cat` no longer trip the destructive
command detector on body text, while still failing closed for shells and pipes.

scripts/hooks/gateguard-heredoc.js

@@ -3,16 +3,23 @@
 const { extractCommandSubstitutions } = require('../lib/shell-substitution');
 
 /**
- * Recognize the deliberately narrow passive sink supported by this parser.
- * Shell operators and substitutions make the payload's destination ambiguous,
- * so every other form retains the original input for fail-closed checks.
+ * Recognize proven-passive sinks whose heredoc payload is data, not a command
+ * stream. `cat` and `tee` (optionally path-qualified, or wrapped in
+ * `command`/`builtin`/`env`) only write stdin; they do not execute the body.
+ * Shell operators or substitution markers make the destination ambiguous, so
+ * every other form retains the original input for fail-closed checks.
  *
  * @param {string} line
  * @returns {boolean}
  */
 function isProvenPassiveHeredocLine(line) {
   const trimmed = line.trim();
-  return /^cat(?=\s|[<>])/.test(trimmed) && !/[;&|()`]/.test(trimmed);
+  // Fail closed on control operators / grouping / command substitutions.
+  if (/[;&|()`]/.test(trimmed)) return false;
+  // Optional wrapper + optional path prefix + cat|tee, then args or redirect.
+  return /^(?:(?:command|builtin|env)\s+)?(?:(?:\.\/|\/(?:[\w.+-]+\/)*)?(?:cat|tee))(?=\s|[<>])/.test(
+    trimmed
+  );
 }
 
 /**

tests/hooks/gateguard-fact-force.test.js

@@ -1858,6 +1858,87 @@ function runTests() {
     passed++;
   else failed++;
 
+  if (
+    test('allows #2886 migration-doc heredoc repro with DROP TABLE prose', () => {
+      expectAllow(
+        [
+          "cat > migration-notes.md <<'EOF'",
+          "This migration will DROP TABLE old_sessions once we've verified nothing reads from it anymore.",
+          'EOF'
+        ].join('\n'),
+        'issue #2886 cat heredoc repro'
+      );
+    })
+  )
+    passed++;
+  else failed++;
+
+  if (
+    test('allows destructive SQL prose inside a tee heredoc', () => {
+      expectAllow(
+        [
+          "tee migration-notes.md <<'EOF'",
+          'This migration will DROP TABLE old_sessions after verification.',
+          'EOF'
+        ].join('\n'),
+        'tee heredoc SQL prose'
+      );
+    })
+  )
+    passed++;
+  else failed++;
+
+  if (
+    test('allows destructive rm prose inside a path-qualified cat heredoc', () => {
+      expectAllow(
+        [
+          "/bin/cat > notes.md <<'EOF'",
+          'Cleanup steps mention rm -rf old-cache; do not run yet.',
+          'EOF'
+        ].join('\n'),
+        'path-qualified cat heredoc prose'
+      );
+    })
+  )
+    passed++;
+  else failed++;
+
+  if (
+    test('allows destructive prose inside a command-wrapped cat heredoc', () => {
+      expectAllow(
+        [
+          "command cat > notes.md <<'EOF'",
+          'Notes: DELETE FROM sessions; truncate staging.',
+          'EOF'
+        ].join('\n'),
+        'command-wrapped cat heredoc prose'
+      );
+    })
+  )
+    passed++;
+  else failed++;
+
+  if (
+    test('still denies real destructive commands (not heredoc prose)', () => {
+      expectDestructiveDeny('rm -rf /tmp/real-destructive-target', 'real rm -rf');
+      expectDestructiveDeny('git reset --hard', 'real git reset --hard');
+      expectDestructiveDeny('drop table old_sessions', 'real drop table command text');
+    })
+  )
+    passed++;
+  else failed++;
+
+  if (
+    test('fails closed when tee pipes heredoc payload into a shell', () => {
+      expectDestructiveDeny(
+        ['tee notes.md <<EOF | bash', 'rm -rf /tmp/tee-piped-shell-target', 'EOF'].join('\n'),
+        'tee piped to shell'
+      );
+    })
+  )
+    passed++;
+  else failed++;
+
   if (
     test('denies substitutions inside literal quote characters in an unquoted heredoc', () => {
       for (const payload of [