feat(gateway): harden provider request execution

Preserve exact request payloads and model client surface and API operation explicitly.

Add Anthropic compatibility profiles, bounded stream commitment, and scoped OAuth retry behavior across provider transports.

apps/aether-gateway/src/ai_serving/planner/standard/gemini/plan_builders.rs

@@ -1,12 +1,10 @@
 use std::collections::BTreeMap;
 
-use aether_contracts::RequestBody;
-
 use super::{
     augment_sync_report_context, build_ai_execution_plan_from_decision,
-    generic_decision_missing_exact_provider_request, take_ai_decision_plan_core,
-    take_ai_upstream_auth_pair, take_non_empty_string, AiExecutionPlanFromDecisionParts,
-    AiStreamAttempt, AiSyncAttempt,
+    generic_decision_missing_exact_provider_request, resolve_ai_passthrough_sync_request_body,
+    take_ai_decision_plan_core, take_ai_upstream_auth_pair, take_non_empty_string,
+    AiExecutionPlanFromDecisionParts, AiStreamAttempt, AiSyncAttempt,
 };
 use crate::ai_serving::transport::{
     build_standard_plan_fallback_headers, StandardPlanFallbackAcceptPolicy,
@@ -61,6 +59,10 @@ pub(crate) fn build_gemini_sync_plan_from_decision(
         &provider_request_headers,
         &provider_request_body_value,
     )?;
+    let request_body = resolve_ai_passthrough_sync_request_body(
+        Some(provider_request_body_value),
+        payload.provider_request_body_base64.take(),
+    );
     let stream = payload.upstream_is_stream;
     let plan = build_ai_execution_plan_from_decision(
         &mut payload,
@@ -70,7 +72,7 @@ pub(crate) fn build_gemini_sync_plan_from_decision(
             url,
             headers: std::mem::take(&mut provider_request_headers),
             content_type,
-            body: RequestBody::from_json(provider_request_body_value),
+            body: request_body,
             stream,
         },
     );
@@ -129,6 +131,10 @@ pub(crate) fn build_gemini_stream_plan_from_decision(
         &provider_request_headers,
         &provider_request_body_value,
     )?;
+    let request_body = resolve_ai_passthrough_sync_request_body(
+        Some(provider_request_body_value),
+        payload.provider_request_body_base64.take(),
+    );
     let plan = build_ai_execution_plan_from_decision(
         &mut payload,
         AiExecutionPlanFromDecisionParts {
@@ -137,7 +143,7 @@ pub(crate) fn build_gemini_stream_plan_from_decision(
             url,
             headers: std::mem::take(&mut provider_request_headers),
             content_type,
-            body: RequestBody::from_json(provider_request_body_value),
+            body: request_body,
             stream: true,
         },
     );