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.

crates/aether-contracts/src/lib.rs

@@ -9,9 +9,10 @@ mod usage;
 pub use error::{ExecutionError, ExecutionErrorKind, ExecutionPhase};
 pub use frame::{StreamFrame, StreamFramePayload, StreamFrameType};
 pub use plan::{
-    ExecutionPlan, ExecutionTimeouts, ProxySnapshot, RequestBody, ResolvedTransportProfile,
-    EXECUTION_REQUEST_ACCEPT_INVALID_CERTS_HEADER, EXECUTION_REQUEST_FOLLOW_REDIRECTS_HEADER,
-    EXECUTION_REQUEST_HTTP1_ONLY_HEADER, MAX_EXECUTION_REQUEST_TIMEOUT_MS,
+    ExecutionPlan, ExecutionResponseBodyMode, ExecutionTimeouts, ProxySnapshot, RequestBody,
+    ResolvedTransportProfile, EXECUTION_REQUEST_ACCEPT_INVALID_CERTS_HEADER,
+    EXECUTION_REQUEST_FOLLOW_REDIRECTS_HEADER, EXECUTION_REQUEST_HTTP1_ONLY_HEADER,
+    EXECUTION_RESPONSE_BODY_MODE_HEADER, MAX_EXECUTION_REQUEST_TIMEOUT_MS,
     MAX_EXECUTION_REQUEST_TIMEOUT_SECS, MAX_EXECUTION_STREAM_FIRST_BYTE_TIMEOUT_MS,
     MAX_EXECUTION_STREAM_FIRST_BYTE_TIMEOUT_SECS, TRANSPORT_BACKEND_BROWSER_WREQ,
     TRANSPORT_BACKEND_HYPER_RUSTLS, TRANSPORT_BACKEND_REQWEST_RUSTLS, TRANSPORT_HTTP_MODE_AUTO,

crates/aether-contracts/src/plan.rs

@@ -7,12 +7,39 @@ pub const EXECUTION_REQUEST_FOLLOW_REDIRECTS_HEADER: &str = "x-aether-execution-
 pub const EXECUTION_REQUEST_HTTP1_ONLY_HEADER: &str = "x-aether-execution-http1-only";
 pub const EXECUTION_REQUEST_ACCEPT_INVALID_CERTS_HEADER: &str =
     "x-aether-execution-accept-invalid-certs";
+pub const EXECUTION_RESPONSE_BODY_MODE_HEADER: &str = "x-aether-execution-response-body-mode";
 pub const MAX_EXECUTION_REQUEST_TIMEOUT_SECS: u64 = 1_200;
 pub const MAX_EXECUTION_REQUEST_TIMEOUT_MS: u64 = MAX_EXECUTION_REQUEST_TIMEOUT_SECS * 1_000;
 pub const MAX_EXECUTION_STREAM_FIRST_BYTE_TIMEOUT_SECS: u64 = 300;
 pub const MAX_EXECUTION_STREAM_FIRST_BYTE_TIMEOUT_MS: u64 =
     MAX_EXECUTION_STREAM_FIRST_BYTE_TIMEOUT_SECS * 1_000;
 
+#[derive(Debug, Clone, Copy, Default, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+pub enum ExecutionResponseBodyMode {
+    #[default]
+    StructuredJson,
+    PreserveBytes,
+}
+
+impl ExecutionResponseBodyMode {
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::StructuredJson => "structured_json",
+            Self::PreserveBytes => "preserve_bytes",
+        }
+    }
+
+    pub fn from_header_value(value: Option<&str>) -> Self {
+        match value.map(str::trim) {
+            Some(value) if value.eq_ignore_ascii_case(Self::PreserveBytes.as_str()) => {
+                Self::PreserveBytes
+            }
+            _ => Self::StructuredJson,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(default)]
 pub struct ExecutionTimeouts {
@@ -139,6 +166,22 @@ pub struct ExecutionPlan {
 mod tests {
     use super::*;
 
+    #[test]
+    fn response_body_mode_is_fail_closed_to_structured_json() {
+        assert_eq!(
+            ExecutionResponseBodyMode::from_header_value(Some(" preserve_bytes ")),
+            ExecutionResponseBodyMode::PreserveBytes
+        );
+        assert_eq!(
+            ExecutionResponseBodyMode::from_header_value(Some("unexpected")),
+            ExecutionResponseBodyMode::StructuredJson
+        );
+        assert_eq!(
+            ExecutionResponseBodyMode::from_header_value(None),
+            ExecutionResponseBodyMode::StructuredJson
+        );
+    }
+
     #[test]
     fn serializes_plan_with_json_body() {
         let plan = ExecutionPlan {