fix(codex): support exec optimizer backend

skillopt/model/backend_config.py

@@ -49,10 +49,18 @@ CLAUDE_CODE_EXEC_MAX_THINKING_TOKENS = max(
 def set_optimizer_backend(backend: str) -> None:
     global OPTIMIZER_BACKEND
     OPTIMIZER_BACKEND = normalize_backend_name(backend or "openai_chat")
-    if OPTIMIZER_BACKEND not in {"openai_chat", "claude_chat", "qwen_chat", "minimax_chat", "openai_compatible"}:
+    if OPTIMIZER_BACKEND not in {
+        "openai_chat",
+        "claude_chat",
+        "qwen_chat",
+        "minimax_chat",
+        "openai_compatible",
+        "codex_exec",
+    }:
         raise ValueError(
             f"Unsupported optimizer backend: {OPTIMIZER_BACKEND!r}. "
-            "Supported values are 'openai_chat', 'claude_chat', 'qwen_chat', 'minimax_chat', and 'openai_compatible'."
+            "Supported values are 'openai_chat', 'claude_chat', 'qwen_chat', 'minimax_chat', "
+            "'openai_compatible', and 'codex_exec'."
         )
     os.environ["OPTIMIZER_BACKEND"] = OPTIMIZER_BACKEND
 
@@ -81,7 +89,14 @@ def is_target_exec_backend() -> bool:
 
 
 def is_optimizer_chat_backend() -> bool:
-    return OPTIMIZER_BACKEND in {"openai_chat", "claude_chat", "qwen_chat", "minimax_chat", "openai_compatible"}
+    return OPTIMIZER_BACKEND in {
+        "openai_chat",
+        "claude_chat",
+        "qwen_chat",
+        "minimax_chat",
+        "openai_compatible",
+        "codex_exec",
+    }
 
 
 def is_target_chat_backend() -> bool: