fix(security): allow 2>/dev/null and 2>&1 in shell commands, add policy logging

The redirect blocker was rejecting safe stderr patterns like
2>/dev/null and 2>&1. Strip these before operator checks so they
don't trigger the generic > or & blockers.

Also adds debug/trace logging to all early rejection paths in
is_command_allowed for audit visibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/security/policy.rs

@@ -184,6 +184,19 @@ fn contains_single_ampersand(s: &str) -> bool {
     false
 }
 
+/// Strip safe stderr redirection patterns before policy checks.
+///
+/// Removes `2>/dev/null`, `2> /dev/null`, and `2>&1` so they don't
+/// trigger the generic `>` or `&` blockers.
+fn strip_safe_stderr(s: &str) -> String {
+    let mut result = s.to_string();
+    // Order matters: longest patterns first
+    for pat in ["2> /dev/null", "2>/dev/null", "2>&1"] {
+        result = result.replace(pat, "");
+    }
+    result
+}
+
 impl SecurityPolicy {
     /// Classify command risk. Any high-risk segment marks the whole command high.
     pub fn command_risk_level(&self, command: &str) -> CommandRiskLevel {
@@ -359,37 +372,46 @@ impl SecurityPolicy {
     /// - Blocks dangerous arguments (e.g. `find -exec`, `git config`)
     pub fn is_command_allowed(&self, command: &str) -> bool {
         if self.autonomy == AutonomyLevel::ReadOnly {
+            tracing::trace!(command, "Command blocked: read-only mode");
             return false;
         }
 
+        // Strip safe stderr redirections (2>/dev/null, 2>&1) before
+        // operator checks so they don't trigger the generic `>` or `&` blockers.
+        let sanitized = strip_safe_stderr(command);
+
         // Block subshell/expansion operators — these allow hiding arbitrary
         // commands inside an allowed command (e.g. `echo $(rm -rf /)`)
-        if command.contains('`')
-            || command.contains("$(")
-            || command.contains("${")
-            || command.contains("<(")
-            || command.contains(">(")
+        if sanitized.contains('`')
+            || sanitized.contains("$(")
+            || sanitized.contains("${")
+            || sanitized.contains("<(")
+            || sanitized.contains(">(")
         {
+            tracing::debug!(command, "Command blocked: subshell/expansion operator");
             return false;
         }
 
-        // Block output redirections — they can write to arbitrary paths
-        if command.contains('>') {
+        // Block output redirections that write to arbitrary paths.
+        if sanitized.contains('>') {
+            tracing::debug!(command, "Command blocked: output redirection");
             return false;
         }
 
         // Block `tee` — it can write to arbitrary files, bypassing the
         // redirect check above (e.g. `echo secret | tee /etc/crontab`)
-        if command
+        if sanitized
             .split_whitespace()
             .any(|w| w == "tee" || w.ends_with("/tee"))
         {
+            tracing::debug!(command, "Command blocked: tee can write arbitrary files");
             return false;
         }
 
         // Block background command chaining (`&`), which can hide extra
         // sub-commands and outlive timeout expectations. Keep `&&` allowed.
-        if contains_single_ampersand(command) {
+        if contains_single_ampersand(&sanitized) {
+            tracing::debug!(command, "Command blocked: background & operator");
             return false;
         }
 
@@ -1107,6 +1129,22 @@ mod tests {
         let p = default_policy();
         assert!(!p.is_command_allowed("echo secret > /etc/crontab"));
         assert!(!p.is_command_allowed("ls >> /tmp/exfil.txt"));
+        assert!(!p.is_command_allowed("cat file > /tmp/out"));
+    }
+
+    #[test]
+    fn stderr_to_devnull_allowed() {
+        let p = SecurityPolicy {
+            allowed_commands: vec!["*".into()],
+            ..SecurityPolicy::default()
+        };
+        assert!(p.is_command_allowed("ls -la /tmp/*.py 2>/dev/null"));
+        assert!(p.is_command_allowed("ls -la 2> /dev/null"));
+        assert!(p.is_command_allowed("grep pattern file 2>&1"));
+        assert!(p.is_command_allowed("cmd 2>/dev/null | grep foo"));
+        // Stdout redirect still blocked
+        assert!(!p.is_command_allowed("echo hello > /tmp/file"));
+        assert!(!p.is_command_allowed("echo hello 1> /tmp/file"));
     }
 
     #[test]