From ded3b254a115067e3d0dbd3c69414fa5ee4eca71 Mon Sep 17 00:00:00 2001
From: Dylan Hurd <dylan.hurd@openai.com>
Date: Sat, 31 Jan 2026 14:55:49 -0700
Subject: [PATCH] Deduplicate execpolicy prefix append

---
 codex-rs/execpolicy/src/amend.rs   | 39 ++++++++++++------------------
 codex-rs/execpolicy/tests/basic.rs | 21 ++++++++++++++++
 2 files changed, 37 insertions(+), 23 deletions(-)

diff --git a/codex-rs/execpolicy/src/amend.rs b/codex-rs/execpolicy/src/amend.rs
index 9114d3a64f..9809a46fe2 100644
--- a/codex-rs/execpolicy/src/amend.rs
+++ b/codex-rs/execpolicy/src/amend.rs
@@ -105,35 +105,28 @@ fn append_locked_line(policy_path: &Path, line: &str) -> Result<(), AmendError>
         source,
     })?;
 
-    let len = file
-        .metadata()
-        .map_err(|source| AmendError::PolicyMetadata {
+    file.seek(SeekFrom::Start(0))
+        .map_err(|source| AmendError::SeekPolicyFile {
             path: policy_path.to_path_buf(),
             source,
-        })?
-        .len();
+        })?;
+    let mut contents = String::new();
+    file.read_to_string(&mut contents)
+        .map_err(|source| AmendError::ReadPolicyFile {
+            path: policy_path.to_path_buf(),
+            source,
+        })?;
 
-    // Ensure file ends in a newline before appending.
-    if len > 0 {
-        file.seek(SeekFrom::End(-1))
-            .map_err(|source| AmendError::SeekPolicyFile {
+    if contents.lines().any(|existing| existing == line) {
+        return Ok(());
+    }
+
+    if !contents.is_empty() && !contents.ends_with('\n') {
+        file.write_all(b"\n")
+            .map_err(|source| AmendError::WritePolicyFile {
                 path: policy_path.to_path_buf(),
                 source,
             })?;
-        let mut last = [0; 1];
-        file.read_exact(&mut last)
-            .map_err(|source| AmendError::ReadPolicyFile {
-                path: policy_path.to_path_buf(),
-                source,
-            })?;
-
-        if last[0] != b'\n' {
-            file.write_all(b"\n")
-                .map_err(|source| AmendError::WritePolicyFile {
-                    path: policy_path.to_path_buf(),
-                    source,
-                })?;
-        }
     }
 
     file.write_all(format!("{line}\n").as_bytes())
diff --git a/codex-rs/execpolicy/tests/basic.rs b/codex-rs/execpolicy/tests/basic.rs
index ed6cf3185e..040509f115 100644
--- a/codex-rs/execpolicy/tests/basic.rs
+++ b/codex-rs/execpolicy/tests/basic.rs
@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::fs;
 use std::sync::Arc;
 
 use anyhow::Context;
@@ -10,10 +11,12 @@ use codex_execpolicy::Policy;
 use codex_execpolicy::PolicyParser;
 use codex_execpolicy::RuleMatch;
 use codex_execpolicy::RuleRef;
+use codex_execpolicy::blocking_append_allow_prefix_rule;
 use codex_execpolicy::rule::PatternToken;
 use codex_execpolicy::rule::PrefixPattern;
 use codex_execpolicy::rule::PrefixRule;
 use pretty_assertions::assert_eq;
+use tempfile::tempdir;
 
 fn tokens(cmd: &[&str]) -> Vec<String> {
     cmd.iter().map(std::string::ToString::to_string).collect()
@@ -46,6 +49,24 @@ fn rule_snapshots(rules: &[RuleRef]) -> Vec<RuleSnapshot> {
         .collect()
 }
 
+#[test]
+fn append_allow_prefix_rule_dedupes_existing_rule() -> Result<()> {
+    let tmp = tempdir().context("create temp dir")?;
+    let policy_path = tmp.path().join("rules").join("default.rules");
+    let prefix = tokens(&["python3"]);
+
+    blocking_append_allow_prefix_rule(&policy_path, &prefix)?;
+    blocking_append_allow_prefix_rule(&policy_path, &prefix)?;
+
+    let contents = fs::read_to_string(&policy_path).context("read policy")?;
+    assert_eq!(
+        contents,
+        r#"prefix_rule(pattern=["python3"], decision="allow")
+"#
+    );
+    Ok(())
+}
+
 #[test]
 fn basic_match() -> Result<()> {
     let policy_src = r#"