feat(protocols)!: accept the root chat message role

protocols/src/types/chat.rs

@@ -978,6 +978,9 @@ pub struct ChatCompletionRequestAssistantMessage {
 pub enum ChatCompletionRequestMessage {
     #[cfg_attr(feature = "protocol-schema", schema(value_type = crate::schema::ChatCompletionRequestDeveloperMessage))]
     Developer(ChatCompletionRequestDeveloperMessage),
+    /// MiniMax-M3's top-priority system prompt. Kept distinct from `System` so
+    /// chat templates see `role: "root"`; it cannot carry Kimi `tools`.
+    Root(ChatCompletionRequestSystemMessage),
     System(ChatCompletionRequestSystemMessage),
     User(ChatCompletionRequestUserMessage),
     Assistant(ChatCompletionRequestAssistantMessage),
@@ -1020,6 +1023,7 @@ impl<'de> Deserialize<'de> for ChatCompletionRequestMessage {
         #[serde(rename_all = "lowercase")]
         enum Wire {
             Developer(ForbidToolsAndPartial<ChatCompletionRequestDeveloperMessage>),
+            Root(ForbidToolsAndPartial<ChatCompletionRequestSystemMessage>),
             System(ForbidPartial<ChatCompletionRequestSystemMessage>),
             User(ForbidToolsAndPartial<ChatCompletionRequestUserMessage>),
             Assistant(ForbidTools<ChatCompletionRequestAssistantMessage>),
@@ -1052,6 +1056,15 @@ impl<'de> Deserialize<'de> for ChatCompletionRequestMessage {
                 reject_forbidden::<D::Error>(partial, "partial", "assistant", "developer")?;
                 ChatCompletionRequestMessage::Developer(message)
             }
+            Wire::Root(ForbidToolsAndPartial {
+                tools,
+                partial,
+                message,
+            }) => {
+                reject_forbidden::<D::Error>(tools, "tools", "system", "root")?;
+                reject_forbidden::<D::Error>(partial, "partial", "assistant", "root")?;
+                ChatCompletionRequestMessage::Root(message)
+            }
             Wire::System(ForbidPartial { partial, message }) => {
                 reject_forbidden::<D::Error>(partial, "partial", "assistant", "system")?;
                 ChatCompletionRequestMessage::System(message)
@@ -2483,6 +2496,37 @@ mod tests {
         }
     }
 
+    #[test]
+    fn root_message_round_trips_with_its_role() {
+        for wire in [
+            serde_json::json!({"role": "root", "content": "You are a helpful assistant."}),
+            serde_json::json!({
+                "role": "root",
+                "content": [{"type": "text", "text": "You are a helpful assistant."}],
+                "name": "policy",
+            }),
+        ] {
+            let parsed: ChatCompletionRequestMessage =
+                serde_json::from_value(wire.clone()).unwrap();
+            assert!(
+                matches!(parsed, ChatCompletionRequestMessage::Root(_)),
+                "{wire}"
+            );
+            assert_eq!(serde_json::to_value(&parsed).unwrap(), wire);
+        }
+    }
+
+    #[test]
+    fn message_rejects_unknown_role() {
+        let error = serde_json::from_value::<ChatCompletionRequestMessage>(
+            serde_json::json!({"role": "admin", "content": "hi"}),
+        )
+        .unwrap_err()
+        .to_string();
+        assert!(error.contains("unknown variant `admin`"), "{error}");
+        assert!(error.contains("root"), "{error}");
+    }
+
     #[test]
     fn message_rejects_tools_and_partial_on_wrong_roles() {
         let tools = serde_json::json!([{"name": "lookup"}]);
@@ -2503,6 +2547,16 @@ mod tests {
                 serde_json::json!({"role": "developer", "content": "hi", "tools": tools}),
                 "`tools` is only accepted on system messages, not on role developer",
             ),
+            (
+                "tools on root",
+                serde_json::json!({"role": "root", "content": "hi", "tools": tools}),
+                "`tools` is only accepted on system messages, not on role root",
+            ),
+            (
+                "partial on root",
+                serde_json::json!({"role": "root", "content": "hi", "partial": true}),
+                "`partial` is only accepted on assistant messages, not on role root",
+            ),
             (
                 "partial on user",
                 serde_json::json!({"role": "user", "content": "hi", "partial": true}),

protocols/tests/protocol_schema.rs

@@ -129,6 +129,7 @@ fn custom_deserializers_produce_schema_valid_canonical_messages() {
     canonical::<CreateChatCompletionRequest>(json!({
         "model":"test",
         "messages":[
+            {"role":"root","content":"policy"},
             {"role":"system","tools":[{"name":"lookup"}]},
             {"role":"assistant","reasoning":"thinking","content":null,
              "tool_calls":[{"id":"call1","function":{"name":"lookup","arguments":{"q":"hi"}}}]}

renderer/src/template/oai.rs

@@ -900,6 +900,33 @@ mod tests {
         assert!(out.contains("<|im_start|>system\nmid-conversation reminder<|im_end|>"));
     }
 
+    #[test]
+    fn root_role_reaches_the_template_verbatim() {
+        // MiniMax-M3's role mapping: root is the system prompt, a following
+        // system/developer turn becomes the developer prompt.
+        let f = formatter_for(concat!(
+            "{%- set ns = namespace(rest=messages, root=none, dev=none) -%}",
+            "{%- if ns.rest and ns.rest[0].role == 'root' -%}",
+            "{%- set ns.root = ns.rest[0].content -%}{%- set ns.rest = ns.rest[1:] -%}",
+            "{%- endif -%}",
+            "{%- if ns.rest and ns.rest[0].role in ['system', 'developer'] -%}",
+            "{%- set ns.dev = ns.rest[0].content -%}{%- set ns.rest = ns.rest[1:] -%}",
+            "{%- endif -%}",
+            "[system]{{ ns.root }}[developer]{{ ns.dev }}",
+            "{%- for m in ns.rest -%}[{{ m.role }}]{{ m.content }}{%- endfor -%}",
+        ));
+        let out = render_shape(
+            &f,
+            json!([
+                {"role": "root", "content": "R"},
+                {"role": "system", "content": "S"},
+                {"role": "user", "content": "U"},
+            ]),
+        )
+        .unwrap();
+        assert_eq!(out, "[system]R[developer]S[user]U");
+    }
+
     #[test]
     fn strict_leading_template_demotes_mid_system_but_keeps_user_turns_apart() {
         let f = formatter_for(STRICT_LEADING_TMPL);