diff --git a/src/server/subagent.rs b/src/server/subagent.rs
index eb2f09f..8ef1b8a 100644
--- a/src/server/subagent.rs
+++ b/src/server/subagent.rs
@@ -64,8 +64,8 @@ impl SubagentRunner for ServerSubagentRunner {
             "You are a threaded fork of agent {}. You share their tools, their \
              memory boundaries, their dual-state architecture. After you respond, \
              your N+1 pass will surface observations back to them.\n\n\
-             Your final message will be returned to the caller.\n\n{}",
-            params.parent_agent_id, params.prompt
+             Your final message will be returned to the caller.",
+            params.parent_agent_id
         );
 
         // Build tool definitions
@@ -93,8 +93,14 @@ impl SubagentRunner for ServerSubagentRunner {
             ),
         );
 
-        // Initial messages: system prompt + user prompt
-        let mut messages = vec![BifrostMessage::text("system", system_prompt)];
+        // Initial messages: system prompt + user prompt.
+        // The task must be a *user* message: providers that hoist system
+        // messages into a separate field are left with an empty messages
+        // array otherwise, and reject the request.
+        let mut messages = vec![
+            BifrostMessage::text("system", system_prompt),
+            BifrostMessage::text("user", params.prompt.clone()),
+        ];
 
         let mut final_content = String::new();
         let mut tool_round = 0u32;