fix(translation): normalize Responses built-in tool roles

crates/switchyard-translation/src/codecs/openai_chat/buffered.rs

@@ -1090,6 +1090,11 @@ pub(crate) fn encode_openai_content(
         return Ok(Value::String(text_from_blocks(content, "\n")));
     }
     if role != Role::User {
+        for block in content {
+            if let ContentBlock::Unknown { provider, raw } = block {
+                reject_responses_builtin_tool_item(provider, raw, WireFormat::OpenAiChat)?;
+            }
+        }
         push_lossy(
             diagnostics,
             policy,

crates/switchyard-translation/src/codecs/responses/buffered.rs

@@ -731,7 +731,20 @@ fn decode_responses_input(
                     Some("additional_tools") => {}
                     _ => {
                         let message = Message {
-                            role: Role::User,
+                            role: match item_type {
+                                Some(
+                                    "shell_call"
+                                    | "apply_patch_call"
+                                    | "computer_call"
+                                    | "image_generation_call",
+                                ) => Role::Assistant,
+                                Some(
+                                    "shell_call_output"
+                                    | "apply_patch_call_output"
+                                    | "computer_call_output",
+                                ) => Role::Tool,
+                                _ => Role::User,
+                            },
                             content: vec![ContentBlock::Unknown {
                                 provider: WireFormat::OpenAiResponses.into(),
                                 raw: Value::Object(item.clone()),
@@ -1288,8 +1301,7 @@ fn encode_responses_input(
     for message in messages {
         // The decoder carries each valid top-level built-in tool item as one
         // provider-qualified block, so replay that block in place.
-        if message.role == Role::User
-            && let [ContentBlock::Unknown { provider, raw }] = message.content.as_slice()
+        if let [ContentBlock::Unknown { provider, raw }] = message.content.as_slice()
             && provider.as_str() == WireFormat::OpenAiResponses.as_str()
             && is_responses_builtin_tool_item(raw)
         {

crates/switchyard-translation/src/util.rs

@@ -110,6 +110,7 @@ pub(crate) fn is_responses_builtin_tool_item(item: &Value) -> bool {
                 | "shell_call_output"
                 | "computer_call"
                 | "computer_call_output"
+                | "image_generation_call"
         )
     )
 }

crates/switchyard-translation/tests/request_translation.rs

@@ -836,6 +836,8 @@ fn anthropic_tool_result_error_survives_target_prompt() -> TestResult {
 // Target prompts force normalized re-encoding; built-in tool history must retain its wire shape.
 #[test]
 fn responses_builtin_tool_history_survives_target_prompt() -> TestResult {
+    use switchyard_translation::Role;
+
     let engine = TranslationEngine::default();
     let policy = TranslationPolicy::default();
     let input = json!([
@@ -873,6 +875,13 @@ fn responses_builtin_tool_history_survives_target_prompt() -> TestResult {
         .decode_request(WireFormat::OpenAiResponses, &body, &policy)?
         .request;
 
+    let roles: Vec<_> = request
+        .messages
+        .iter()
+        .map(|message| message.role)
+        .collect();
+    assert_eq!(roles, [Role::Assistant, Role::Tool].repeat(3));
+
     prepare_request_for_target(&mut request, &"target".into(), Some("target prompt"));
 
     let output = engine