fix(gateway): OpenAI 图像 finalize 统一返回 b64_json 并对齐 codex CLI 候选流式上游

- finalize 移除 response_format=url 的 data URL 分支，统一输出 b64_json
- image planner decision 依据请求体中的 stream 字段决定 upstream_is_stream
- openai chat sync plan 对 codex+openai:cli 候选强制上游流式
- 扩充 conversion registry 与 standard matrix 的全量 surface 对端测试

apps/aether-gateway/src/ai_pipeline/planner/specialized/image/decision.rs

@@ -57,6 +57,11 @@ pub(super) async fn maybe_build_local_openai_image_decision_payload_for_candidat
         extra_fields.insert("proxy".to_string(), proxy_value);
     }
     extra_fields.insert("image_request".to_string(), resolved.input_summary.clone());
+    let upstream_is_stream = resolved
+        .provider_request_body
+        .get("stream")
+        .and_then(serde_json::Value::as_bool)
+        .unwrap_or(spec_metadata.require_streaming);
     let report_context = build_local_execution_report_context(LocalExecutionReportContextParts {
         auth_context: &input.auth_context,
         request_id: trace_id,
@@ -82,7 +87,7 @@ pub(super) async fn maybe_build_local_openai_image_decision_payload_for_candidat
         original_request_body_json: Some(body_json),
         original_request_body_base64: body_base64,
         client_requested_stream: spec_metadata.require_streaming,
-        upstream_is_stream: spec_metadata.require_streaming,
+        upstream_is_stream,
         has_envelope: false,
         needs_conversion: false,
         extra_fields,
@@ -117,7 +122,7 @@ pub(super) async fn maybe_build_local_openai_image_decision_payload_for_candidat
             proxy,
             tls_profile,
             timeouts: resolve_transport_execution_timeouts(&transport),
-            upstream_is_stream: spec_metadata.require_streaming,
+            upstream_is_stream,
             report_kind: spec_metadata.report_kind.map(ToOwned::to_owned),
             report_context: Some(report_context),
             auth_context: input.auth_context.clone(),

apps/aether-gateway/src/ai_pipeline/planner/standard/openai/chat/plans/sync.rs

@@ -10,12 +10,21 @@ use super::diagnostic::{
     set_local_openai_chat_candidate_evaluation_diagnostic, set_local_openai_chat_miss_diagnostic,
 };
 use super::resolve::resolve_local_openai_chat_decision_input;
-use crate::ai_pipeline::planner::common::OPENAI_CHAT_SYNC_PLAN_KIND;
+use crate::ai_pipeline::planner::common::{
+    force_upstream_streaming_for_provider, OPENAI_CHAT_SYNC_PLAN_KIND,
+};
 use crate::ai_pipeline::planner::plan_builders::{
     build_openai_chat_sync_plan_from_decision, LocalSyncPlanAndReport,
 };
 use crate::ai_pipeline::planner::runtime_miss::apply_local_runtime_candidate_terminal_reason;
 
+fn openai_chat_sync_upstream_is_stream_for_candidate(
+    provider_type: &str,
+    provider_api_format: &str,
+) -> bool {
+    force_upstream_streaming_for_provider(provider_type, provider_api_format)
+}
+
 pub(crate) async fn build_local_openai_chat_sync_plan_and_reports(
     state: &AppState,
     parts: &http::request::Parts,
@@ -88,6 +97,10 @@ pub(crate) async fn build_local_openai_chat_sync_plan_and_reports(
 
     let mut plans = Vec::new();
     for attempt in attempts {
+        let upstream_is_stream = openai_chat_sync_upstream_is_stream_for_candidate(
+            attempt.eligible.transport.provider.provider_type.as_str(),
+            attempt.eligible.provider_api_format.as_str(),
+        );
         let Some(payload) = maybe_build_local_openai_chat_decision_payload_for_candidate(
             state,
             parts,
@@ -97,7 +110,7 @@ pub(crate) async fn build_local_openai_chat_sync_plan_and_reports(
             attempt,
             OPENAI_CHAT_SYNC_PLAN_KIND,
             "openai_chat_sync_success",
-            false,
+            upstream_is_stream,
         )
         .await
         else {
@@ -121,3 +134,24 @@ pub(crate) async fn build_local_openai_chat_sync_plan_and_reports(
 
     Ok(plans)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::openai_chat_sync_upstream_is_stream_for_candidate;
+
+    #[test]
+    fn openai_chat_sync_forces_streaming_for_codex_openai_cli_candidates() {
+        assert!(openai_chat_sync_upstream_is_stream_for_candidate(
+            "codex",
+            "openai:cli"
+        ));
+        assert!(!openai_chat_sync_upstream_is_stream_for_candidate(
+            "openai",
+            "openai:cli"
+        ));
+        assert!(!openai_chat_sync_upstream_is_stream_for_candidate(
+            "codex",
+            "openai:chat"
+        ));
+    }
+}