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/handlers/admin/provider/write/normalize.rs

@@ -195,11 +195,7 @@ pub(crate) fn validate_vertex_api_formats(
 
     let allowed = match auth_type {
         "api_key" => &["gemini:generate_content", "gemini:embedding"][..],
-        "service_account" | "vertex_ai" => &[
-            "claude:messages",
-            "gemini:generate_content",
-            "gemini:embedding",
-        ][..],
+        "service_account" | "vertex_ai" => &["gemini:generate_content", "gemini:embedding"][..],
         _ => return Ok(()),
     };
     let invalid = api_formats
@@ -410,20 +406,11 @@ mod tests {
     }
 
     #[test]
-    fn validate_vertex_api_formats_uses_canonical_message_formats() {
+    fn validate_vertex_api_formats_rejects_unimplemented_anthropic_transport() {
         assert!(validate_vertex_api_formats(
             "vertex_ai",
             "service_account",
-            &[
-                "claude:messages".to_string(),
-                "gemini:generate_content".to_string()
-            ],
-        )
-        .is_ok());
-        assert!(validate_vertex_api_formats(
-            "vertex_ai",
-            "service_account",
-            &["claude:chat".to_string()],
+            &["claude:messages".to_string()],
         )
         .is_err());
     }
@@ -443,7 +430,6 @@ mod tests {
             "vertex_ai",
             "service_account",
             &[
-                "claude:messages".to_string(),
                 "gemini:generate_content".to_string(),
                 "gemini:embedding".to_string()
             ],