[codex] Retry temporarily offline exec-server recovery (#30098)

## Summary

- retry ERS `409 environment_offline` responses inside the existing
exec-server recovery loop
- keep all other registry conflicts terminal
- add focused coverage for both cases

## Root cause

When an exec server disconnects and reconnects, the client already
starts recovery and calls ERS `/connect`. During the transient executor
presence gap, ERS can return `409 environment_offline`. The retry
classifier treated every 409 as terminal, so the first response aborted
the existing 25-second recovery window before the executor came back
online. That then caused active processes to be marked lost.

This change classifies only the structured `environment_offline`
conflict as retryable. Recovery continues with the existing bounded
deadline, exponential backoff, and jitter.

## Validation

- `just test -p codex-exec-server client::recovery::tests` — 4 passed
- `just fix -p codex-exec-server` — passed
- `just fmt` — passed
- Full `just test -p codex-exec-server` reached unrelated macOS
filesystem-sandbox integration failures because nested
`/usr/bin/sandbox-exec` is denied in this environment (`sandbox_apply:
Operation not permitted`).

codex-rs/exec-server/src/client_recovery.rs

@@ -530,10 +530,15 @@ fn is_retryable_registry_error(error: &ExecServerError) -> bool {
             if error.is_connect() || error.is_timeout()
     ) || matches!(
         error,
-        ExecServerError::EnvironmentRegistryHttp { status, .. }
+        ExecServerError::EnvironmentRegistryHttp { status, code, .. }
             if status.is_server_error()
                 || *status == reqwest::StatusCode::REQUEST_TIMEOUT
                 || *status == reqwest::StatusCode::TOO_MANY_REQUESTS
+                // TODO: Replace this coarse retry with an explicit registry/presence
+                // recovery FSM so `environment_offline` is retried only while the
+                // executor is expected to reconnect.
+                || (*status == reqwest::StatusCode::CONFLICT
+                    && code.as_deref() == Some("environment_offline"))
     )
 }
 

codex-rs/exec-server/src/client_recovery_tests.rs

@@ -2,10 +2,10 @@ use std::time::Duration;
 
 use super::*;
 
-fn registry_error() -> ExecServerError {
+fn registry_error(status: reqwest::StatusCode, code: Option<&str>) -> ExecServerError {
     ExecServerError::EnvironmentRegistryHttp {
-        status: reqwest::StatusCode::TOO_MANY_REQUESTS,
-        code: None,
+        status,
+        code: code.map(str::to_string),
         message: "registry unavailable".to_string(),
     }
 }
@@ -33,8 +33,24 @@ fn registry_recovery_retry_delay_exponentially_backs_off_and_caps() {
 
 #[test]
 fn recovery_retries_transient_registry_errors() {
-    let error = registry_error();
+    let error = registry_error(reqwest::StatusCode::TOO_MANY_REQUESTS, /*code*/ None);
 
     assert!(is_retryable_registry_error(&error));
     assert!(is_retryable_recovery_error(&error));
 }
+
+#[test]
+fn recovery_retries_environment_offline_conflicts() {
+    let error = registry_error(reqwest::StatusCode::CONFLICT, Some("environment_offline"));
+
+    assert!(is_retryable_registry_error(&error));
+    assert!(is_retryable_recovery_error(&error));
+}
+
+#[test]
+fn recovery_does_not_retry_other_registry_conflicts() {
+    let error = registry_error(reqwest::StatusCode::CONFLICT, Some("registration_conflict"));
+
+    assert!(!is_retryable_registry_error(&error));
+    assert!(!is_retryable_recovery_error(&error));
+}