feat(routing): add modality-aware target selection

crates/libsy-llm-client/src/backend.rs

@@ -52,6 +52,14 @@ pub struct HttpBackendConfig {
     pub extra_headers: BTreeMap<String, String>,
     /// Default top-level request fields, applied only when the request omits the key.
     pub extra_body: BTreeMap<String, Value>,
+    /// Reasoning effort forced onto every outbound request for this target.
+    pub reasoning_effort_override: Option<String>,
+    /// Whether Responses custom tools are bridged through upstream function tools.
+    pub bridge_custom_tools: bool,
+    /// Whether Responses deferred tools are made eagerly available upstream.
+    pub eager_load_tool_search: bool,
+    /// Whether cross-provider Responses fields are normalized for xAI.
+    pub xai_responses_compatibility: bool,
     /// Additional attempts after the initial upstream request.
     pub max_retries: u32,
 }
@@ -64,6 +72,13 @@ impl fmt::Debug for HttpBackendConfig {
             .field("forward_auth", &self.forward_auth)
             .field("extra_header_names", &self.extra_headers.keys())
             .field("extra_body_keys", &self.extra_body.keys())
+            .field("reasoning_effort_override", &self.reasoning_effort_override)
+            .field("bridge_custom_tools", &self.bridge_custom_tools)
+            .field("eager_load_tool_search", &self.eager_load_tool_search)
+            .field(
+                "xai_responses_compatibility",
+                &self.xai_responses_compatibility,
+            )
             .field("max_retries", &self.max_retries)
             .finish()
     }
@@ -248,6 +263,26 @@ impl Backend {
         &self.config().extra_body
     }
 
+    /// Target-specific reasoning effort that replaces a caller-supplied value.
+    pub fn reasoning_effort_override(&self) -> Option<&str> {
+        self.config().reasoning_effort_override.as_deref()
+    }
+
+    /// Whether Responses custom tools must be represented as function tools upstream.
+    pub fn bridge_custom_tools(&self) -> bool {
+        self.config().bridge_custom_tools
+    }
+
+    /// Whether Responses tool discovery must be converted to eager definitions upstream.
+    pub fn eager_load_tool_search(&self) -> bool {
+        self.config().eager_load_tool_search
+    }
+
+    /// Whether Responses requests need xAI cross-provider compatibility normalization.
+    pub fn xai_responses_compatibility(&self) -> bool {
+        self.config().xai_responses_compatibility
+    }
+
     /// Additional attempts allowed after the initial request.
     pub fn max_retries(&self) -> u32 {
         self.config().max_retries
@@ -343,6 +378,10 @@ mod tests {
             forward_auth: false,
             extra_headers: BTreeMap::new(),
             extra_body: BTreeMap::new(),
+            reasoning_effort_override: None,
+            bridge_custom_tools: false,
+            eager_load_tool_search: false,
+            xai_responses_compatibility: false,
             max_retries: 0,
         }
     }