feat(openai): align GPT-5.6 and Codex request contracts

apps/aether-gateway/src/ai_serving/planner/standard/codex.rs

@@ -3,5 +3,29 @@
 mod tests;
 
 pub(crate) use crate::ai_serving::{
-    apply_codex_openai_responses_special_body_edits, apply_codex_openai_responses_special_headers,
+    apply_codex_openai_responses_special_body_edits, apply_codex_openai_special_headers,
 };
+
+pub(crate) fn codex_model_capabilities_for_transport(
+    transport: &crate::ai_serving::GatewayProviderTransportSnapshot,
+    provider_api_format: &str,
+    provider_model: &str,
+    source_model: &str,
+) -> Option<crate::ai_serving::CodexResponsesModelCapabilities> {
+    if !transport
+        .provider
+        .provider_type
+        .trim()
+        .eq_ignore_ascii_case("codex")
+        || !crate::ai_serving::is_openai_responses_family_format(provider_api_format)
+    {
+        return None;
+    }
+    Some(
+        crate::ai_serving::resolve_codex_responses_model_capabilities(
+            provider_model,
+            source_model,
+            transport.key.upstream_metadata.as_ref(),
+        ),
+    )
+}