fix: resolve bwrap from trusted PATH entry (#15791)

## Summary
- resolve system bwrap from PATH instead of hardcoding /usr/bin/bwrap
- skip PATH entries that resolve inside the current workspace before
launching the sandbox helper
- keep the vendored bubblewrap fallback when no trusted system bwrap is
found

## Validation
- cargo test -p codex-core bwrap --lib
- cargo test -p codex-linux-sandbox
- just fix -p codex-core
- just fix -p codex-linux-sandbox
- just fmt
- just argument-comment-lint
- cargo clean

codex-rs/core/src/config/mod.rs

@@ -145,7 +145,7 @@ pub(crate) const DEFAULT_AGENT_JOB_MAX_RUNTIME_SECONDS: Option<u64> = None;
 pub const CONFIG_TOML_FILE: &str = "config.toml";
 const OPENAI_BASE_URL_ENV_VAR: &str = "OPENAI_BASE_URL";
 #[cfg(target_os = "linux")]
-const SYSTEM_BWRAP_PATH: &str = "/usr/bin/bwrap";
+const SYSTEM_BWRAP_PROGRAM: &str = "bwrap";
 const RESERVED_MODEL_PROVIDER_IDS: [&str; 3] = [
     OPENAI_PROVIDER_ID,
     OLLAMA_OSS_PROVIDER_ID,
@@ -154,7 +154,7 @@ const RESERVED_MODEL_PROVIDER_IDS: [&str; 3] = [
 
 #[cfg(target_os = "linux")]
 pub fn system_bwrap_warning() -> Option<String> {
-    system_bwrap_warning_for_path(Path::new(SYSTEM_BWRAP_PATH))
+    system_bwrap_warning_for_lookup(find_system_bwrap_in_path())
 }
 
 #[cfg(not(target_os = "linux"))]
@@ -163,15 +163,40 @@ pub fn system_bwrap_warning() -> Option<String> {
 }
 
 #[cfg(target_os = "linux")]
-fn system_bwrap_warning_for_path(system_bwrap_path: &Path) -> Option<String> {
-    if !system_bwrap_path.is_file() {
-        return Some(format!(
-            "Codex could not find system bubblewrap at {}. Please install bubblewrap with your package manager. Codex will use the vendored bubblewrap in the meantime.",
-            system_bwrap_path.display()
-        ));
+fn system_bwrap_warning_for_lookup(system_bwrap_path: Option<PathBuf>) -> Option<String> {
+    match system_bwrap_path {
+        Some(_) => None,
+        None => Some(
+            "Codex could not find system bubblewrap on PATH. Please install bubblewrap with your package manager. Codex will use the vendored bubblewrap in the meantime."
+                .to_string(),
+        ),
     }
+}
 
-    None
+#[cfg(target_os = "linux")]
+pub fn find_system_bwrap_in_path() -> Option<PathBuf> {
+    let search_path = std::env::var_os("PATH")?;
+    let cwd = std::env::current_dir().ok()?;
+    find_system_bwrap_in_search_paths(std::iter::once(PathBuf::from(search_path)), &cwd)
+}
+
+#[cfg(target_os = "linux")]
+fn find_system_bwrap_in_search_paths(
+    search_paths: impl IntoIterator<Item = PathBuf>,
+    cwd: &Path,
+) -> Option<PathBuf> {
+    let search_path = std::env::join_paths(search_paths).ok()?;
+    let cwd = std::fs::canonicalize(cwd).unwrap_or_else(|_| cwd.to_path_buf());
+    which::which_in_all(SYSTEM_BWRAP_PROGRAM, Some(search_path), &cwd)
+        .ok()?
+        .find_map(|path| {
+            let path = std::fs::canonicalize(path).ok()?;
+            if path.starts_with(&cwd) {
+                None
+            } else {
+                Some(path)
+            }
+        })
 }
 
 fn resolve_sqlite_home_env(resolved_cwd: &Path) -> Option<PathBuf> {