fix(ai-serving): route provider-aware normalization through root seams

Move Antigravity schema-preservation policy into the format crate and expose provider-aware Chat and Responses builders through the existing gateway root seam. Preserve legacy conversion and scoped Responses history behavior without weakening architecture tests.

Validated: 61 standalone architecture tests, 947 format tests, 527 transport tests, 2 actual-source planner tests, and gateway cargo check.

apps/aether-gateway/src/ai_serving/planner/standard/normalize/chat.rs

@@ -4,7 +4,7 @@ use crate::ai_serving::transport::apply_standard_provider_request_body_rules_wit
 use crate::ai_serving::{
     apply_codex_openai_responses_chat_body_edits,
     apply_openai_responses_compact_special_body_edits,
-    build_cross_format_openai_chat_request_body_with_model_directives as surface_build_cross_format_openai_chat_request_body,
+    build_cross_format_openai_chat_request_body_with_provider_context as surface_build_cross_format_openai_chat_request_body,
     build_local_openai_chat_request_body_with_model_directives as surface_build_local_openai_chat_request_body,
     GatewayProviderTransportSnapshot,
 };
@@ -70,23 +70,15 @@ pub(crate) fn build_cross_format_openai_chat_request_body(
     request_headers: &http::HeaderMap,
     enable_model_directives: bool,
 ) -> Option<Value> {
-    let provider_request_body = if provider_type.trim().eq_ignore_ascii_case("antigravity")
-        && aether_ai_formats::normalize_api_format_alias(provider_api_format)
-            == "gemini:generate_content"
-    {
-        aether_ai_formats::formats::shared::standard_matrix::build_standard_request_body_with_model_directives(
-            body_json, "openai:chat", mapped_model, provider_type, provider_api_format,
-            "", upstream_is_stream, None, user_api_key_id, enable_model_directives,
-        )?
-    } else {
-        surface_build_cross_format_openai_chat_request_body(
-            body_json,
-            mapped_model,
-            provider_api_format,
-            upstream_is_stream,
-            enable_model_directives,
-        )?
-    };
+    let provider_request_body = surface_build_cross_format_openai_chat_request_body(
+        body_json,
+        mapped_model,
+        provider_type,
+        provider_api_format,
+        upstream_is_stream,
+        enable_model_directives,
+        user_api_key_id,
+    )?;
     let mut provider_request_body =
         apply_standard_provider_request_body_rules_with_request_headers(
             provider_request_body,

apps/aether-gateway/src/ai_serving/planner/standard/normalize/responses.rs

@@ -3,7 +3,7 @@ use serde_json::Value;
 use crate::ai_serving::transport::apply_standard_provider_request_body_rules_with_request_headers;
 use crate::ai_serving::{
     apply_openai_responses_compact_special_body_edits,
-    build_cross_format_openai_responses_request_body_with_model_directives_and_history_scope as surface_build_cross_format_openai_responses_request_body,
+    build_cross_format_openai_responses_request_body_with_provider_context as surface_build_cross_format_openai_responses_request_body,
     build_local_openai_responses_request_body_with_model_directives as surface_build_local_openai_responses_request_body,
     GatewayProviderTransportSnapshot,
 };
@@ -214,25 +214,16 @@ pub(crate) fn build_cross_format_openai_responses_request_body_with_codex_model_
     model_capabilities: Option<&crate::ai_serving::CodexResponsesModelCapabilities>,
     enable_model_directives: bool,
 ) -> Option<Value> {
-    let provider_request_body = if provider_type.trim().eq_ignore_ascii_case("antigravity")
-        && aether_ai_formats::normalize_api_format_alias(provider_api_format)
-            == "gemini:generate_content"
-    {
-        aether_ai_formats::formats::shared::standard_matrix::build_standard_request_body_with_model_directives(
-            body_json, client_api_format, mapped_model, provider_type, provider_api_format,
-            "", upstream_is_stream, None, history_scope, enable_model_directives,
-        )?
-    } else {
-        surface_build_cross_format_openai_responses_request_body(
-            body_json,
-            mapped_model,
-            client_api_format,
-            provider_api_format,
-            upstream_is_stream,
-            enable_model_directives,
-            history_scope,
-        )?
-    };
+    let provider_request_body = surface_build_cross_format_openai_responses_request_body(
+        body_json,
+        mapped_model,
+        client_api_format,
+        provider_type,
+        provider_api_format,
+        upstream_is_stream,
+        enable_model_directives,
+        history_scope,
+    )?;
     let mut provider_request_body =
         apply_standard_provider_request_body_rules_with_request_headers(
             provider_request_body,

apps/aether-gateway/src/ai_serving/pure/mod.rs

@@ -17,9 +17,11 @@ pub(crate) use aether_ai_formats::api::{
     build_codex_model_catalog_metadata, build_codex_openai_image_api_provider_request_body,
     build_core_error_body_for_client_format, build_cross_format_openai_chat_request_body,
     build_cross_format_openai_chat_request_body_with_model_directives,
+    build_cross_format_openai_chat_request_body_with_provider_context,
     build_cross_format_openai_responses_request_body,
     build_cross_format_openai_responses_request_body_with_model_directives,
     build_cross_format_openai_responses_request_body_with_model_directives_and_history_scope,
+    build_cross_format_openai_responses_request_body_with_provider_context,
     build_gemini_image_request_body_from_openai_image_request,
     build_gemini_image_response_from_openai_image_response,
     build_gemini_image_response_from_openai_responses_image_response, build_generated_tool_call_id,