diff --git a/codex-rs/core/src/chat_completions.rs b/codex-rs/core/src/chat_completions.rs
index 76cbdf9f0a..1fb2230d79 100644
--- a/codex-rs/core/src/chat_completions.rs
+++ b/codex-rs/core/src/chat_completions.rs
@@ -17,6 +17,7 @@ use crate::util::backoff;
 use bytes::Bytes;
 use codex_otel::otel_event_manager::OtelEventManager;
 use codex_protocol::models::ContentItem;
+use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::ReasoningItemContent;
 use codex_protocol::models::ResponseItem;
 use eventsource_stream::Eventsource;
@@ -159,16 +160,26 @@ pub(crate) async fn stream_chat_completions(
     for (idx, item) in input.iter().enumerate() {
         match item {
             ResponseItem::Message { role, content, .. } => {
+                // Build content either as a plain string (typical for assistant text)
+                // or as an array of content items when images are present (user/tool multimodal).
                 let mut text = String::new();
+                let mut items: Vec<serde_json::Value> = Vec::new();
+                let mut saw_image = false;
+
                 for c in content {
                     match c {
                         ContentItem::InputText { text: t }
                         | ContentItem::OutputText { text: t } => {
                             text.push_str(t);
+                            items.push(json!({"type":"text","text": t}));
+                        }
+                        ContentItem::InputImage { image_url } => {
+                            saw_image = true;
+                            items.push(json!({"type":"image_url","image_url": {"url": image_url}}));
                         }
-                        _ => {}
                     }
                 }
+
                 // Skip exact-duplicate assistant messages.
                 if role == "assistant" {
                     if let Some(prev) = &last_assistant_text
@@ -179,7 +190,17 @@ pub(crate) async fn stream_chat_completions(
                     last_assistant_text = Some(text.clone());
                 }
 
-                let mut msg = json!({"role": role, "content": text});
+                // For assistant messages, always send a plain string for compatibility.
+                // For user messages, if an image is present, send an array of content items.
+                let content_value = if role == "assistant" {
+                    json!(text)
+                } else if saw_image {
+                    json!(items)
+                } else {
+                    json!(text)
+                };
+
+                let mut msg = json!({"role": role, "content": content_value});
                 if role == "assistant"
                     && let Some(reasoning) = reasoning_by_anchor_index.get(&idx)
                     && let Some(obj) = msg.as_object_mut()
@@ -238,10 +259,29 @@ pub(crate) async fn stream_chat_completions(
                 messages.push(msg);
             }
             ResponseItem::FunctionCallOutput { call_id, output } => {
+                // Prefer structured content items when available (e.g., images)
+                // otherwise fall back to the legacy plain-string content.
+                let content_value = if let Some(items) = &output.content_items {
+                    let mapped: Vec<serde_json::Value> = items
+                        .iter()
+                        .map(|it| match it {
+                            FunctionCallOutputContentItem::InputText { text } => {
+                                json!({"type":"text","text": text})
+                            }
+                            FunctionCallOutputContentItem::InputImage { image_url } => {
+                                json!({"type":"image_url","image_url": {"url": image_url}})
+                            }
+                        })
+                        .collect();
+                    json!(mapped)
+                } else {
+                    json!(output.content)
+                };
+
                 messages.push(json!({
                     "role": "tool",
                     "tool_call_id": call_id,
-                    "content": output.content,
+                    "content": content_value,
                 }));
             }
             ResponseItem::CustomToolCall {
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index f811211c4f..6342635775 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -2047,7 +2047,7 @@ async fn try_run_turn(
                             call_id: String::new(),
                             output: FunctionCallOutputPayload {
                                 content: msg.to_string(),
-                                success: None,
+                                ..Default::default()
                             },
                         };
                         add_completed(ProcessedResponseItem {
@@ -2061,7 +2061,7 @@ async fn try_run_turn(
                             call_id: String::new(),
                             output: FunctionCallOutputPayload {
                                 content: message,
-                                success: None,
+                                ..Default::default()
                             },
                         };
                         add_completed(ProcessedResponseItem {
@@ -2199,41 +2199,6 @@ pub(super) fn get_last_assistant_message_from_turn(responses: &[ResponseItem]) -
         }
     })
 }
-pub(crate) fn convert_call_tool_result_to_function_call_output_payload(
-    call_tool_result: &CallToolResult,
-) -> FunctionCallOutputPayload {
-    let CallToolResult {
-        content,
-        is_error,
-        structured_content,
-    } = call_tool_result;
-
-    // In terms of what to send back to the model, we prefer structured_content,
-    // if available, and fallback to content, otherwise.
-    let mut is_success = is_error != &Some(true);
-    let content = if let Some(structured_content) = structured_content
-        && structured_content != &serde_json::Value::Null
-        && let Ok(serialized_structured_content) = serde_json::to_string(&structured_content)
-    {
-        serialized_structured_content
-    } else {
-        match serde_json::to_string(&content) {
-            Ok(serialized_content) => serialized_content,
-            Err(err) => {
-                // If we could not serialize either content or structured_content to
-                // JSON, flag this as an error.
-                is_success = false;
-                err.to_string()
-            }
-        }
-    };
-
-    FunctionCallOutputPayload {
-        content,
-        success: Some(is_success),
-    }
-}
-
 /// Emits an ExitedReviewMode Event with optional ReviewOutput,
 /// and records a developer message with the review output.
 pub(crate) async fn exit_review_mode(
@@ -2443,7 +2408,7 @@ mod tests {
             })),
         };
 
-        let got = convert_call_tool_result_to_function_call_output_payload(&ctr);
+        let got = FunctionCallOutputPayload::from(&ctr);
         let expected = FunctionCallOutputPayload {
             content: serde_json::to_string(&json!({
                 "ok": true,
@@ -2451,6 +2416,7 @@ mod tests {
             }))
             .unwrap(),
             success: Some(true),
+            ..Default::default()
         };
 
         assert_eq!(expected, got);
@@ -2572,11 +2538,12 @@ mod tests {
             structured_content: Some(serde_json::Value::Null),
         };
 
-        let got = convert_call_tool_result_to_function_call_output_payload(&ctr);
+        let got = FunctionCallOutputPayload::from(&ctr);
         let expected = FunctionCallOutputPayload {
             content: serde_json::to_string(&vec![text_block("hello"), text_block("world")])
                 .unwrap(),
             success: Some(true),
+            ..Default::default()
         };
 
         assert_eq!(expected, got);
@@ -2590,10 +2557,11 @@ mod tests {
             structured_content: Some(json!({ "message": "bad" })),
         };
 
-        let got = convert_call_tool_result_to_function_call_output_payload(&ctr);
+        let got = FunctionCallOutputPayload::from(&ctr);
         let expected = FunctionCallOutputPayload {
             content: serde_json::to_string(&json!({ "message": "bad" })).unwrap(),
             success: Some(false),
+            ..Default::default()
         };
 
         assert_eq!(expected, got);
@@ -2607,10 +2575,11 @@ mod tests {
             structured_content: None,
         };
 
-        let got = convert_call_tool_result_to_function_call_output_payload(&ctr);
+        let got = FunctionCallOutputPayload::from(&ctr);
         let expected = FunctionCallOutputPayload {
             content: serde_json::to_string(&vec![text_block("alpha")]).unwrap(),
             success: Some(true),
+            ..Default::default()
         };
 
         assert_eq!(expected, got);
diff --git a/codex-rs/core/src/conversation_history.rs b/codex-rs/core/src/conversation_history.rs
index 08fa8cebed..bf37351086 100644
--- a/codex-rs/core/src/conversation_history.rs
+++ b/codex-rs/core/src/conversation_history.rs
@@ -110,7 +110,7 @@ impl ConversationHistory {
                                 call_id: call_id.clone(),
                                 output: FunctionCallOutputPayload {
                                     content: "aborted".to_string(),
-                                    success: None,
+                                    ..Default::default()
                                 },
                             },
                         ));
@@ -157,7 +157,7 @@ impl ConversationHistory {
                                     call_id: call_id.clone(),
                                     output: FunctionCallOutputPayload {
                                         content: "aborted".to_string(),
-                                        success: None,
+                                        ..Default::default()
                                     },
                                 },
                             ));
@@ -454,7 +454,7 @@ mod tests {
                 call_id: "call-1".to_string(),
                 output: FunctionCallOutputPayload {
                     content: "ok".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
         ];
@@ -470,7 +470,7 @@ mod tests {
                 call_id: "call-2".to_string(),
                 output: FunctionCallOutputPayload {
                     content: "ok".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
             ResponseItem::FunctionCall {
@@ -504,7 +504,7 @@ mod tests {
                 call_id: "call-3".to_string(),
                 output: FunctionCallOutputPayload {
                     content: "ok".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
         ];
@@ -560,7 +560,7 @@ mod tests {
                     call_id: "call-x".to_string(),
                     output: FunctionCallOutputPayload {
                         content: "aborted".to_string(),
-                        success: None,
+                        ..Default::default()
                     },
                 },
             ]
@@ -637,7 +637,7 @@ mod tests {
                     call_id: "shell-1".to_string(),
                     output: FunctionCallOutputPayload {
                         content: "aborted".to_string(),
-                        success: None,
+                        ..Default::default()
                     },
                 },
             ]
@@ -651,7 +651,7 @@ mod tests {
             call_id: "orphan-1".to_string(),
             output: FunctionCallOutputPayload {
                 content: "ok".to_string(),
-                success: None,
+                ..Default::default()
             },
         }];
         let mut h = create_history_with_items(items);
@@ -691,7 +691,7 @@ mod tests {
                 call_id: "c2".to_string(),
                 output: FunctionCallOutputPayload {
                     content: "ok".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
             // Will get an inserted custom tool output
@@ -733,7 +733,7 @@ mod tests {
                     call_id: "c1".to_string(),
                     output: FunctionCallOutputPayload {
                         content: "aborted".to_string(),
-                        success: None,
+                        ..Default::default()
                     },
                 },
                 ResponseItem::CustomToolCall {
@@ -763,7 +763,7 @@ mod tests {
                     call_id: "s1".to_string(),
                     output: FunctionCallOutputPayload {
                         content: "aborted".to_string(),
-                        success: None,
+                        ..Default::default()
                     },
                 },
             ]
@@ -828,7 +828,7 @@ mod tests {
             call_id: "orphan-1".to_string(),
             output: FunctionCallOutputPayload {
                 content: "ok".to_string(),
-                success: None,
+                ..Default::default()
             },
         }];
         let mut h = create_history_with_items(items);
@@ -862,7 +862,7 @@ mod tests {
                 call_id: "c2".to_string(),
                 output: FunctionCallOutputPayload {
                     content: "ok".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
             ResponseItem::CustomToolCall {
diff --git a/codex-rs/core/src/mcp_tool_call.rs b/codex-rs/core/src/mcp_tool_call.rs
index 09846b719a..5166410372 100644
--- a/codex-rs/core/src/mcp_tool_call.rs
+++ b/codex-rs/core/src/mcp_tool_call.rs
@@ -35,6 +35,7 @@ pub(crate) async fn handle_mcp_tool_call(
                     output: FunctionCallOutputPayload {
                         content: format!("err: {e}"),
                         success: Some(false),
+                        ..Default::default()
                     },
                 };
             }
diff --git a/codex-rs/core/src/response_processing.rs b/codex-rs/core/src/response_processing.rs
index e18fdd45c8..5c30c1126c 100644
--- a/codex-rs/core/src/response_processing.rs
+++ b/codex-rs/core/src/response_processing.rs
@@ -61,14 +61,11 @@ pub(crate) async fn process_items(
             ) => {
                 items_to_record_in_conversation_history.push(item);
                 let output = match result {
-                    Ok(call_tool_result) => {
-                        crate::codex::convert_call_tool_result_to_function_call_output_payload(
-                            call_tool_result,
-                        )
-                    }
+                    Ok(call_tool_result) => FunctionCallOutputPayload::from(call_tool_result),
                     Err(err) => FunctionCallOutputPayload {
                         content: err.clone(),
                         success: Some(false),
+                        ..Default::default()
                     },
                 };
                 items_to_record_in_conversation_history.push(ResponseItem::FunctionCallOutput {
diff --git a/codex-rs/core/src/tools/context.rs b/codex-rs/core/src/tools/context.rs
index 27d309dc25..d2e47f926f 100644
--- a/codex-rs/core/src/tools/context.rs
+++ b/codex-rs/core/src/tools/context.rs
@@ -5,6 +5,7 @@ use crate::tools::TELEMETRY_PREVIEW_MAX_LINES;
 use crate::tools::TELEMETRY_PREVIEW_TRUNCATION_NOTICE;
 use crate::turn_diff_tracker::TurnDiffTracker;
 use codex_otel::otel_event_manager::OtelEventManager;
+use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::FunctionCallOutputPayload;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::models::ShellToolCallParams;
@@ -65,7 +66,10 @@ impl ToolPayload {
 #[derive(Clone)]
 pub enum ToolOutput {
     Function {
+        // Plain text representation of the tool output.
         content: String,
+        // Some tool calls such as MCP calls may return structured content that can get parsed into an array of polymorphic content items.
+        content_items: Option<Vec<FunctionCallOutputContentItem>>,
         success: Option<bool>,
     },
     Mcp {
@@ -90,7 +94,11 @@ impl ToolOutput {
 
     pub fn into_response(self, call_id: &str, payload: &ToolPayload) -> ResponseInputItem {
         match self {
-            ToolOutput::Function { content, success } => {
+            ToolOutput::Function {
+                content,
+                content_items,
+                success,
+            } => {
                 if matches!(payload, ToolPayload::Custom { .. }) {
                     ResponseInputItem::CustomToolCallOutput {
                         call_id: call_id.to_string(),
@@ -99,7 +107,11 @@ impl ToolOutput {
                 } else {
                     ResponseInputItem::FunctionCallOutput {
                         call_id: call_id.to_string(),
-                        output: FunctionCallOutputPayload { content, success },
+                        output: FunctionCallOutputPayload {
+                            content,
+                            content_items,
+                            success,
+                        },
                     }
                 }
             }
@@ -163,6 +175,7 @@ mod tests {
         };
         let response = ToolOutput::Function {
             content: "patched".to_string(),
+            content_items: None,
             success: Some(true),
         }
         .into_response("call-42", &payload);
@@ -183,6 +196,7 @@ mod tests {
         };
         let response = ToolOutput::Function {
             content: "ok".to_string(),
+            content_items: None,
             success: Some(true),
         }
         .into_response("fn-1", &payload);
@@ -191,6 +205,7 @@ mod tests {
             ResponseInputItem::FunctionCallOutput { call_id, output } => {
                 assert_eq!(call_id, "fn-1");
                 assert_eq!(output.content, "ok");
+                assert!(output.content_items.is_none());
                 assert_eq!(output.success, Some(true));
             }
             other => panic!("expected FunctionCallOutput, got {other:?}"),
diff --git a/codex-rs/core/src/tools/handlers/apply_patch.rs b/codex-rs/core/src/tools/handlers/apply_patch.rs
index 126b734242..1e82b9cf10 100644
--- a/codex-rs/core/src/tools/handlers/apply_patch.rs
+++ b/codex-rs/core/src/tools/handlers/apply_patch.rs
@@ -82,6 +82,7 @@ impl ToolHandler for ApplyPatchHandler {
                         let content = item?;
                         Ok(ToolOutput::Function {
                             content,
+                            content_items: None,
                             success: Some(true),
                         })
                     }
@@ -126,6 +127,7 @@ impl ToolHandler for ApplyPatchHandler {
                         let content = emitter.finish(event_ctx, out).await?;
                         Ok(ToolOutput::Function {
                             content,
+                            content_items: None,
                             success: Some(true),
                         })
                     }
diff --git a/codex-rs/core/src/tools/handlers/grep_files.rs b/codex-rs/core/src/tools/handlers/grep_files.rs
index de3cd3411c..5473f86935 100644
--- a/codex-rs/core/src/tools/handlers/grep_files.rs
+++ b/codex-rs/core/src/tools/handlers/grep_files.rs
@@ -90,11 +90,13 @@ impl ToolHandler for GrepFilesHandler {
         if search_results.is_empty() {
             Ok(ToolOutput::Function {
                 content: "No matches found.".to_string(),
+                content_items: None,
                 success: Some(false),
             })
         } else {
             Ok(ToolOutput::Function {
                 content: search_results.join("\n"),
+                content_items: None,
                 success: Some(true),
             })
         }
diff --git a/codex-rs/core/src/tools/handlers/list_dir.rs b/codex-rs/core/src/tools/handlers/list_dir.rs
index bcea4a756d..1c08243f72 100644
--- a/codex-rs/core/src/tools/handlers/list_dir.rs
+++ b/codex-rs/core/src/tools/handlers/list_dir.rs
@@ -106,6 +106,7 @@ impl ToolHandler for ListDirHandler {
         output.extend(entries);
         Ok(ToolOutput::Function {
             content: output.join("\n"),
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/mcp.rs b/codex-rs/core/src/tools/handlers/mcp.rs
index 4b2bf3b80e..9798fb8241 100644
--- a/codex-rs/core/src/tools/handlers/mcp.rs
+++ b/codex-rs/core/src/tools/handlers/mcp.rs
@@ -56,8 +56,16 @@ impl ToolHandler for McpHandler {
                 Ok(ToolOutput::Mcp { result })
             }
             codex_protocol::models::ResponseInputItem::FunctionCallOutput { output, .. } => {
-                let codex_protocol::models::FunctionCallOutputPayload { content, success } = output;
-                Ok(ToolOutput::Function { content, success })
+                let codex_protocol::models::FunctionCallOutputPayload {
+                    content,
+                    content_items,
+                    success,
+                } = output;
+                Ok(ToolOutput::Function {
+                    content,
+                    content_items,
+                    success,
+                })
             }
             _ => Err(FunctionCallError::RespondToModel(
                 "mcp handler received unexpected response variant".to_string(),
diff --git a/codex-rs/core/src/tools/handlers/mcp_resource.rs b/codex-rs/core/src/tools/handlers/mcp_resource.rs
index be496f01ec..b601591ac1 100644
--- a/codex-rs/core/src/tools/handlers/mcp_resource.rs
+++ b/codex-rs/core/src/tools/handlers/mcp_resource.rs
@@ -297,7 +297,10 @@ async fn handle_list_resources(
     match payload_result {
         Ok(payload) => match serialize_function_output(payload) {
             Ok(output) => {
-                let ToolOutput::Function { content, success } = &output else {
+                let ToolOutput::Function {
+                    content, success, ..
+                } = &output
+                else {
                     unreachable!("MCP resource handler should return function output");
                 };
                 let duration = start.elapsed();
@@ -403,7 +406,10 @@ async fn handle_list_resource_templates(
     match payload_result {
         Ok(payload) => match serialize_function_output(payload) {
             Ok(output) => {
-                let ToolOutput::Function { content, success } = &output else {
+                let ToolOutput::Function {
+                    content, success, ..
+                } = &output
+                else {
                     unreachable!("MCP resource handler should return function output");
                 };
                 let duration = start.elapsed();
@@ -489,7 +495,10 @@ async fn handle_read_resource(
     match payload_result {
         Ok(payload) => match serialize_function_output(payload) {
             Ok(output) => {
-                let ToolOutput::Function { content, success } = &output else {
+                let ToolOutput::Function {
+                    content, success, ..
+                } = &output
+                else {
                     unreachable!("MCP resource handler should return function output");
                 };
                 let duration = start.elapsed();
@@ -618,6 +627,7 @@ where
 
     Ok(ToolOutput::Function {
         content,
+        content_items: None,
         success: Some(true),
     })
 }
diff --git a/codex-rs/core/src/tools/handlers/plan.rs b/codex-rs/core/src/tools/handlers/plan.rs
index ba8de6bef7..073319bf1c 100644
--- a/codex-rs/core/src/tools/handlers/plan.rs
+++ b/codex-rs/core/src/tools/handlers/plan.rs
@@ -88,6 +88,7 @@ impl ToolHandler for PlanHandler {
 
         Ok(ToolOutput::Function {
             content,
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/read_file.rs b/codex-rs/core/src/tools/handlers/read_file.rs
index f9b6ae4dab..58b6ea6888 100644
--- a/codex-rs/core/src/tools/handlers/read_file.rs
+++ b/codex-rs/core/src/tools/handlers/read_file.rs
@@ -149,6 +149,7 @@ impl ToolHandler for ReadFileHandler {
         };
         Ok(ToolOutput::Function {
             content: collected.join("\n"),
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/shell.rs b/codex-rs/core/src/tools/handlers/shell.rs
index cab313077f..76650992b9 100644
--- a/codex-rs/core/src/tools/handlers/shell.rs
+++ b/codex-rs/core/src/tools/handlers/shell.rs
@@ -136,6 +136,7 @@ impl ShellHandler {
                         let content = item?;
                         return Ok(ToolOutput::Function {
                             content,
+                            content_items: None,
                             success: Some(true),
                         });
                     }
@@ -179,6 +180,7 @@ impl ShellHandler {
                         let content = emitter.finish(event_ctx, out).await?;
                         return Ok(ToolOutput::Function {
                             content,
+                            content_items: None,
                             success: Some(true),
                         });
                     }
@@ -226,6 +228,7 @@ impl ShellHandler {
         let content = emitter.finish(event_ctx, out).await?;
         Ok(ToolOutput::Function {
             content,
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/test_sync.rs b/codex-rs/core/src/tools/handlers/test_sync.rs
index e340ab47f7..d217c1e8a6 100644
--- a/codex-rs/core/src/tools/handlers/test_sync.rs
+++ b/codex-rs/core/src/tools/handlers/test_sync.rs
@@ -95,6 +95,7 @@ impl ToolHandler for TestSyncHandler {
 
         Ok(ToolOutput::Function {
             content: "ok".to_string(),
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/unified_exec.rs b/codex-rs/core/src/tools/handlers/unified_exec.rs
index 7d1102121e..32ace6c959 100644
--- a/codex-rs/core/src/tools/handlers/unified_exec.rs
+++ b/codex-rs/core/src/tools/handlers/unified_exec.rs
@@ -171,6 +171,7 @@ impl ToolHandler for UnifiedExecHandler {
 
         Ok(ToolOutput::Function {
             content,
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/handlers/view_image.rs b/codex-rs/core/src/tools/handlers/view_image.rs
index b25642d803..6b308c0944 100644
--- a/codex-rs/core/src/tools/handlers/view_image.rs
+++ b/codex-rs/core/src/tools/handlers/view_image.rs
@@ -85,6 +85,7 @@ impl ToolHandler for ViewImageHandler {
 
         Ok(ToolOutput::Function {
             content: "attached local image path".to_string(),
+            content_items: None,
             success: Some(true),
         })
     }
diff --git a/codex-rs/core/src/tools/parallel.rs b/codex-rs/core/src/tools/parallel.rs
index 449b8e6553..7340f5cc9c 100644
--- a/codex-rs/core/src/tools/parallel.rs
+++ b/codex-rs/core/src/tools/parallel.rs
@@ -105,7 +105,7 @@ impl ToolCallRuntime {
                 call_id: call.call_id.clone(),
                 output: FunctionCallOutputPayload {
                     content: "aborted".to_string(),
-                    success: None,
+                    ..Default::default()
                 },
             },
         }
diff --git a/codex-rs/core/src/tools/router.rs b/codex-rs/core/src/tools/router.rs
index 161997fb6c..19098aa80d 100644
--- a/codex-rs/core/src/tools/router.rs
+++ b/codex-rs/core/src/tools/router.rs
@@ -181,6 +181,7 @@ impl ToolRouter {
                 output: codex_protocol::models::FunctionCallOutputPayload {
                     content: message,
                     success: Some(false),
+                    ..Default::default()
                 },
             }
         }
diff --git a/codex-rs/core/tests/suite/rmcp_client.rs b/codex-rs/core/tests/suite/rmcp_client.rs
index 99c863b8f9..85698e9216 100644
--- a/codex-rs/core/tests/suite/rmcp_client.rs
+++ b/codex-rs/core/tests/suite/rmcp_client.rs
@@ -14,6 +14,8 @@ use codex_core::features::Feature;
 
 use codex_core::protocol::AskForApproval;
 use codex_core::protocol::EventMsg;
+use codex_core::protocol::McpInvocation;
+use codex_core::protocol::McpToolCallBeginEvent;
 use codex_core::protocol::Op;
 use codex_core::protocol::SandboxPolicy;
 use codex_protocol::config_types::ReasoningSummary;
@@ -25,7 +27,9 @@ use core_test_support::test_codex::test_codex;
 use core_test_support::wait_for_event;
 use core_test_support::wait_for_event_with_timeout;
 use escargot::CargoBuild;
+use mcp_types::ContentBlock;
 use serde_json::Value;
+use serde_json::json;
 use serial_test::serial;
 use tempfile::tempdir;
 use tokio::net::TcpStream;
@@ -35,6 +39,8 @@ use tokio::time::Instant;
 use tokio::time::sleep;
 use wiremock::matchers::any;
 
+static OPENAI_PNG: &str = "data:image/png;base64,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";
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 #[serial(mcp_test_value)]
 async fn stdio_server_round_trip() -> anyhow::Result<()> {
@@ -175,6 +181,352 @@ async fn stdio_server_round_trip() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+#[serial(mcp_test_value)]
+async fn stdio_image_responses_round_trip() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+
+    let call_id = "img-1";
+    let server_name = "rmcp";
+    let tool_name = format!("mcp__{server_name}__image");
+
+    // First stream: model decides to call the image tool.
+    mount_sse_once_match(
+        &server,
+        any(),
+        responses::sse(vec![
+            responses::ev_response_created("resp-1"),
+            responses::ev_function_call(call_id, &tool_name, "{}"),
+            responses::ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+    // Second stream: after tool execution, assistant emits a message and completes.
+    let final_mock = mount_sse_once_match(
+        &server,
+        any(),
+        responses::sse(vec![
+            responses::ev_assistant_message("msg-1", "rmcp image tool completed successfully."),
+            responses::ev_completed("resp-2"),
+        ]),
+    )
+    .await;
+
+    // Build the stdio rmcp server and pass the image as data URL so it can construct ImageContent.
+    let rmcp_test_server_bin = CargoBuild::new()
+        .package("codex-rmcp-client")
+        .bin("test_stdio_server")
+        .run()?
+        .path()
+        .to_string_lossy()
+        .into_owned();
+
+    let fixture = test_codex()
+        .with_config(move |config| {
+            config.features.enable(Feature::RmcpClient);
+            config.mcp_servers.insert(
+                server_name.to_string(),
+                McpServerConfig {
+                    transport: McpServerTransportConfig::Stdio {
+                        command: rmcp_test_server_bin,
+                        args: Vec::new(),
+                        env: Some(HashMap::from([(
+                            "MCP_TEST_IMAGE_DATA_URL".to_string(),
+                            OPENAI_PNG.to_string(),
+                        )])),
+                        env_vars: Vec::new(),
+                        cwd: None,
+                    },
+                    enabled: true,
+                    startup_timeout_sec: Some(Duration::from_secs(10)),
+                    tool_timeout_sec: None,
+                    enabled_tools: None,
+                    disabled_tools: None,
+                },
+            );
+        })
+        .build(&server)
+        .await?;
+    let session_model = fixture.session_configured.model.clone();
+
+    fixture
+        .codex
+        .submit(Op::UserTurn {
+            items: vec![UserInput::Text {
+                text: "call the rmcp image tool".into(),
+            }],
+            final_output_json_schema: None,
+            cwd: fixture.cwd.path().to_path_buf(),
+            approval_policy: AskForApproval::Never,
+            sandbox_policy: SandboxPolicy::ReadOnly,
+            model: session_model,
+            effort: None,
+            summary: ReasoningSummary::Auto,
+        })
+        .await?;
+
+    // Wait for tool begin/end and final completion.
+    let begin_event = wait_for_event_with_timeout(
+        &fixture.codex,
+        |ev| matches!(ev, EventMsg::McpToolCallBegin(_)),
+        Duration::from_secs(10),
+    )
+    .await;
+    let EventMsg::McpToolCallBegin(begin) = begin_event else {
+        unreachable!("begin");
+    };
+    assert_eq!(
+        begin,
+        McpToolCallBeginEvent {
+            call_id: call_id.to_string(),
+            invocation: McpInvocation {
+                server: server_name.to_string(),
+                tool: "image".to_string(),
+                arguments: Some(json!({})),
+            },
+        },
+    );
+
+    let end_event = wait_for_event(&fixture.codex, |ev| {
+        matches!(ev, EventMsg::McpToolCallEnd(_))
+    })
+    .await;
+    let EventMsg::McpToolCallEnd(end) = end_event else {
+        unreachable!("end");
+    };
+    assert_eq!(end.call_id, call_id);
+    assert_eq!(
+        end.invocation,
+        McpInvocation {
+            server: server_name.to_string(),
+            tool: "image".to_string(),
+            arguments: Some(json!({})),
+        }
+    );
+    let result = end.result.expect("rmcp image tool should return success");
+    assert_eq!(result.is_error, Some(false));
+    assert_eq!(result.content.len(), 1);
+    let base64_only = OPENAI_PNG
+        .strip_prefix("data:image/png;base64,")
+        .expect("data url prefix");
+    match &result.content[0] {
+        ContentBlock::ImageContent(img) => {
+            assert_eq!(img.mime_type, "image/png");
+            assert_eq!(img.r#type, "image");
+            assert_eq!(img.data, base64_only);
+        }
+        other => panic!("expected image content, got {other:?}"),
+    }
+
+    wait_for_event(&fixture.codex, |ev| matches!(ev, EventMsg::TaskComplete(_))).await;
+
+    let output_item = final_mock.single_request().function_call_output(call_id);
+    assert_eq!(
+        output_item,
+        json!({
+            "type": "function_call_output",
+            "call_id": call_id,
+            "output": [{
+                "type": "input_image",
+                "image_url": OPENAI_PNG
+            }]
+        })
+    );
+    server.verify().await;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+#[serial(mcp_test_value)]
+async fn stdio_image_completions_round_trip() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+
+    let call_id = "img-cc-1";
+    let server_name = "rmcp";
+    let tool_name = format!("mcp__{server_name}__image");
+
+    let tool_call = json!({
+        "choices": [
+            {
+                "delta": {
+                    "tool_calls": [
+                        {
+                            "id": call_id,
+                            "type": "function",
+                            "function": {"name": tool_name, "arguments": "{}"}
+                        }
+                    ]
+                },
+                "finish_reason": "tool_calls"
+            }
+        ]
+    });
+    let sse_tool_call = format!(
+        "data: {}\n\ndata: [DONE]\n\n",
+        serde_json::to_string(&tool_call)?
+    );
+
+    let final_assistant = json!({
+        "choices": [
+            {
+                "delta": {"content": "rmcp image tool completed successfully."},
+                "finish_reason": "stop"
+            }
+        ]
+    });
+    let sse_final = format!(
+        "data: {}\n\ndata: [DONE]\n\n",
+        serde_json::to_string(&final_assistant)?
+    );
+
+    use std::sync::atomic::AtomicUsize;
+    use std::sync::atomic::Ordering;
+    struct ChatSeqResponder {
+        num_calls: AtomicUsize,
+        bodies: Vec<String>,
+    }
+    impl wiremock::Respond for ChatSeqResponder {
+        fn respond(&self, _: &wiremock::Request) -> wiremock::ResponseTemplate {
+            let idx = self.num_calls.fetch_add(1, Ordering::SeqCst);
+            match self.bodies.get(idx) {
+                Some(body) => wiremock::ResponseTemplate::new(200)
+                    .insert_header("content-type", "text/event-stream")
+                    .set_body_string(body.clone()),
+                None => panic!("no chat completion response for index {idx}"),
+            }
+        }
+    }
+
+    let chat_seq = ChatSeqResponder {
+        num_calls: AtomicUsize::new(0),
+        bodies: vec![sse_tool_call, sse_final],
+    };
+    wiremock::Mock::given(wiremock::matchers::method("POST"))
+        .and(wiremock::matchers::path("/v1/chat/completions"))
+        .respond_with(chat_seq)
+        .expect(2)
+        .mount(&server)
+        .await;
+
+    let rmcp_test_server_bin = CargoBuild::new()
+        .package("codex-rmcp-client")
+        .bin("test_stdio_server")
+        .run()?
+        .path()
+        .to_string_lossy()
+        .into_owned();
+
+    let fixture = test_codex()
+        .with_config(move |config| {
+            config.model_provider.wire_api = codex_core::WireApi::Chat;
+            config.features.enable(Feature::RmcpClient);
+            config.mcp_servers.insert(
+                server_name.to_string(),
+                McpServerConfig {
+                    transport: McpServerTransportConfig::Stdio {
+                        command: rmcp_test_server_bin,
+                        args: Vec::new(),
+                        env: Some(HashMap::from([(
+                            "MCP_TEST_IMAGE_DATA_URL".to_string(),
+                            OPENAI_PNG.to_string(),
+                        )])),
+                        env_vars: Vec::new(),
+                        cwd: None,
+                    },
+                    enabled: true,
+                    startup_timeout_sec: Some(Duration::from_secs(10)),
+                    tool_timeout_sec: None,
+                    enabled_tools: None,
+                    disabled_tools: None,
+                },
+            );
+        })
+        .build(&server)
+        .await?;
+    let session_model = fixture.session_configured.model.clone();
+
+    fixture
+        .codex
+        .submit(Op::UserTurn {
+            items: vec![UserInput::Text {
+                text: "call the rmcp image tool".into(),
+            }],
+            final_output_json_schema: None,
+            cwd: fixture.cwd.path().to_path_buf(),
+            approval_policy: AskForApproval::Never,
+            sandbox_policy: SandboxPolicy::ReadOnly,
+            model: session_model,
+            effort: None,
+            summary: ReasoningSummary::Auto,
+        })
+        .await?;
+
+    let begin_event = wait_for_event_with_timeout(
+        &fixture.codex,
+        |ev| matches!(ev, EventMsg::McpToolCallBegin(_)),
+        Duration::from_secs(10),
+    )
+    .await;
+    let EventMsg::McpToolCallBegin(begin) = begin_event else {
+        unreachable!("begin");
+    };
+    assert_eq!(
+        begin,
+        McpToolCallBeginEvent {
+            call_id: call_id.to_string(),
+            invocation: McpInvocation {
+                server: server_name.to_string(),
+                tool: "image".to_string(),
+                arguments: Some(json!({})),
+            },
+        },
+    );
+
+    let end_event = wait_for_event(&fixture.codex, |ev| {
+        matches!(ev, EventMsg::McpToolCallEnd(_))
+    })
+    .await;
+    let EventMsg::McpToolCallEnd(end) = end_event else {
+        unreachable!("end");
+    };
+    assert!(end.result.as_ref().is_ok(), "tool call should succeed");
+
+    wait_for_event(&fixture.codex, |ev| matches!(ev, EventMsg::TaskComplete(_))).await;
+
+    // Chat Completions assertion: the second POST should include a tool role message
+    // with an array `content` containing an item with the expected data URL.
+    let requests = server.received_requests().await.expect("requests captured");
+    assert!(requests.len() >= 2, "expected two chat completion calls");
+    let second = &requests[1];
+    let body: Value = serde_json::from_slice(&second.body)?;
+    let messages = body
+        .get("messages")
+        .and_then(Value::as_array)
+        .cloned()
+        .expect("messages array");
+    let tool_msg = messages
+        .iter()
+        .find(|m| {
+            m.get("role") == Some(&json!("tool")) && m.get("tool_call_id") == Some(&json!(call_id))
+        })
+        .cloned()
+        .expect("tool message present");
+    assert_eq!(
+        tool_msg,
+        json!({
+            "role": "tool",
+            "tool_call_id": call_id,
+            "content": [{"type": "image_url", "image_url": {"url": OPENAI_PNG}}]
+        })
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 #[serial(mcp_test_value)]
 async fn stdio_server_propagates_whitelisted_env_vars() -> anyhow::Result<()> {
diff --git a/codex-rs/protocol/src/models.rs b/codex-rs/protocol/src/models.rs
index 4430a0998a..614a5ff2b0 100644
--- a/codex-rs/protocol/src/models.rs
+++ b/codex-rs/protocol/src/models.rs
@@ -3,6 +3,7 @@ use std::collections::HashMap;
 use base64::Engine;
 use codex_utils_image::load_and_resize_to_fit;
 use mcp_types::CallToolResult;
+use mcp_types::ContentBlock;
 use serde::Deserialize;
 use serde::Deserializer;
 use serde::Serialize;
@@ -83,9 +84,8 @@ pub enum ResponseItem {
     // NOTE: The input schema for `function_call_output` objects that clients send to the
     // OpenAI /v1/responses endpoint is NOT the same shape as the objects the server returns on the
     // SSE stream. When *sending* we must wrap the string output inside an object that includes a
-    // required `success` boolean. The upstream TypeScript CLI does this implicitly. To ensure we
-    // serialize exactly the expected shape we introduce a dedicated payload struct and flatten it
-    // here.
+    // required `success` boolean. To ensure we serialize exactly the expected shape we introduce
+    // a dedicated payload struct and flatten it here.
     FunctionCallOutput {
         call_id: String,
         output: FunctionCallOutputPayload,
@@ -160,19 +160,17 @@ impl From<ResponseInputItem> for ResponseItem {
             ResponseInputItem::FunctionCallOutput { call_id, output } => {
                 Self::FunctionCallOutput { call_id, output }
             }
-            ResponseInputItem::McpToolCallOutput { call_id, result } => Self::FunctionCallOutput {
-                call_id,
-                output: FunctionCallOutputPayload {
-                    success: Some(result.is_ok()),
-                    content: result.map_or_else(
-                        |tool_call_err| format!("err: {tool_call_err:?}"),
-                        |result| {
-                            serde_json::to_string(&result)
-                                .unwrap_or_else(|e| format!("JSON serialization error: {e}"))
-                        },
-                    ),
-                },
-            },
+            ResponseInputItem::McpToolCallOutput { call_id, result } => {
+                let output = match result {
+                    Ok(result) => FunctionCallOutputPayload::from(&result),
+                    Err(tool_call_err) => FunctionCallOutputPayload {
+                        content: format!("err: {tool_call_err:?}"),
+                        success: Some(false),
+                        ..Default::default()
+                    },
+                };
+                Self::FunctionCallOutput { call_id, output }
+            }
             ResponseInputItem::CustomToolCallOutput { call_id, output } => {
                 Self::CustomToolCallOutput { call_id, output }
             }
@@ -290,31 +288,53 @@ pub struct ShellToolCallParams {
     pub justification: Option<String>,
 }
 
-#[derive(Debug, Clone, PartialEq, JsonSchema, TS)]
+/// Responses API compatible content items that can be returned by a tool call.
+/// This is a subset of ContentItem with the types we support as function call outputs.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, JsonSchema, TS)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum FunctionCallOutputContentItem {
+    // Do not rename, these are serialized and used directly in the responses API.
+    InputText { text: String },
+    // Do not rename, these are serialized and used directly in the responses API.
+    InputImage { image_url: String },
+}
+
+/// The payload we send back to OpenAI when reporting a tool call result.
+///
+/// `content` preserves the historical plain-string payload so downstream
+/// integrations (tests, logging, etc.) can keep treating tool output as
+/// `String`. When an MCP server returns richer data we additionally populate
+/// `content_items` with the structured form that the Responses/Chat
+/// Completions APIs understand.
+#[derive(Debug, Default, Clone, PartialEq, JsonSchema, TS)]
 pub struct FunctionCallOutputPayload {
     pub content: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub content_items: Option<Vec<FunctionCallOutputContentItem>>,
     // TODO(jif) drop this.
     pub success: Option<bool>,
 }
 
+#[derive(Deserialize)]
+#[serde(untagged)]
+enum FunctionCallOutputPayloadSerde {
+    Text(String),
+    Items(Vec<FunctionCallOutputContentItem>),
+}
+
 // The Responses API expects two *different* shapes depending on success vs failure:
 //   • success → output is a plain string (no nested object)
 //   • failure → output is an object { content, success:false }
-// The upstream TypeScript CLI implements this by special‑casing the serialize path.
-// We replicate that behavior with a manual Serialize impl.
-
 impl Serialize for FunctionCallOutputPayload {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
     {
-        // The upstream TypeScript CLI always serializes `output` as a *plain string* regardless
-        // of whether the function call succeeded or failed. The boolean is purely informational
-        // for local bookkeeping and is NOT sent to the OpenAI endpoint. Sending the nested object
-        // form `{ content, success:false }` triggers the 400 we are still seeing. Mirror the JS CLI
-        // exactly: always emit a bare string.
-
-        serializer.serialize_str(&self.content)
+        if let Some(items) = &self.content_items {
+            items.serialize(serializer)
+        } else {
+            serializer.serialize_str(&self.content)
+        }
     }
 }
 
@@ -323,14 +343,106 @@ impl<'de> Deserialize<'de> for FunctionCallOutputPayload {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
-        Ok(FunctionCallOutputPayload {
-            content: s,
-            success: None,
-        })
+        match FunctionCallOutputPayloadSerde::deserialize(deserializer)? {
+            FunctionCallOutputPayloadSerde::Text(content) => Ok(FunctionCallOutputPayload {
+                content,
+                ..Default::default()
+            }),
+            FunctionCallOutputPayloadSerde::Items(items) => {
+                let content = serde_json::to_string(&items).map_err(serde::de::Error::custom)?;
+                Ok(FunctionCallOutputPayload {
+                    content,
+                    content_items: Some(items),
+                    success: None,
+                })
+            }
+        }
+    }
+}
+
+impl From<&CallToolResult> for FunctionCallOutputPayload {
+    fn from(call_tool_result: &CallToolResult) -> Self {
+        let CallToolResult {
+            content,
+            structured_content,
+            is_error,
+        } = call_tool_result;
+
+        let is_success = is_error != &Some(true);
+
+        if let Some(structured_content) = structured_content
+            && !structured_content.is_null()
+        {
+            match serde_json::to_string(structured_content) {
+                Ok(serialized_structured_content) => {
+                    return FunctionCallOutputPayload {
+                        content: serialized_structured_content,
+                        success: Some(is_success),
+                        ..Default::default()
+                    };
+                }
+                Err(err) => {
+                    return FunctionCallOutputPayload {
+                        content: err.to_string(),
+                        success: Some(false),
+                        ..Default::default()
+                    };
+                }
+            }
+        }
+
+        let serialized_content = match serde_json::to_string(content) {
+            Ok(serialized_content) => serialized_content,
+            Err(err) => {
+                return FunctionCallOutputPayload {
+                    content: err.to_string(),
+                    success: Some(false),
+                    ..Default::default()
+                };
+            }
+        };
+
+        let content_items = convert_content_blocks_to_items(content);
+
+        FunctionCallOutputPayload {
+            content: serialized_content,
+            content_items,
+            success: Some(is_success),
+        }
     }
 }
 
+fn convert_content_blocks_to_items(
+    blocks: &[ContentBlock],
+) -> Option<Vec<FunctionCallOutputContentItem>> {
+    let mut saw_image = false;
+    let mut items = Vec::with_capacity(blocks.len());
+
+    for block in blocks {
+        match block {
+            ContentBlock::TextContent(text) => {
+                items.push(FunctionCallOutputContentItem::InputText {
+                    text: text.text.clone(),
+                });
+            }
+            ContentBlock::ImageContent(image) => {
+                saw_image = true;
+                // Just in case the content doesn't include a data URL, add it.
+                let image_url = if image.data.starts_with("data:") {
+                    image.data.clone()
+                } else {
+                    format!("data:{};base64,{}", image.mime_type, image.data)
+                };
+                items.push(FunctionCallOutputContentItem::InputImage { image_url });
+            }
+            // TODO: render audio, resource, and embedded resource content to the model.
+            _ => return None,
+        }
+    }
+
+    if saw_image { Some(items) } else { None }
+}
+
 // Implement Display so callers can treat the payload like a plain string when logging or doing
 // trivial substring checks in tests (existing tests call `.contains()` on the output). Display
 // returns the raw `content` field.
@@ -354,6 +466,8 @@ impl std::ops::Deref for FunctionCallOutputPayload {
 mod tests {
     use super::*;
     use anyhow::Result;
+    use mcp_types::ImageContent;
+    use mcp_types::TextContent;
     use tempfile::tempdir;
 
     #[test]
@@ -362,7 +476,7 @@ mod tests {
             call_id: "call1".into(),
             output: FunctionCallOutputPayload {
                 content: "ok".into(),
-                success: None,
+                ..Default::default()
             },
         };
 
@@ -381,6 +495,7 @@ mod tests {
             output: FunctionCallOutputPayload {
                 content: "bad".into(),
                 success: Some(false),
+                ..Default::default()
             },
         };
 
@@ -391,6 +506,81 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn serializes_image_outputs_as_array() -> Result<()> {
+        let call_tool_result = CallToolResult {
+            content: vec![
+                ContentBlock::TextContent(TextContent {
+                    annotations: None,
+                    text: "caption".into(),
+                    r#type: "text".into(),
+                }),
+                ContentBlock::ImageContent(ImageContent {
+                    annotations: None,
+                    data: "BASE64".into(),
+                    mime_type: "image/png".into(),
+                    r#type: "image".into(),
+                }),
+            ],
+            is_error: None,
+            structured_content: None,
+        };
+
+        let payload = FunctionCallOutputPayload::from(&call_tool_result);
+        assert_eq!(payload.success, Some(true));
+        let items = payload.content_items.clone().expect("content items");
+        assert_eq!(
+            items,
+            vec![
+                FunctionCallOutputContentItem::InputText {
+                    text: "caption".into(),
+                },
+                FunctionCallOutputContentItem::InputImage {
+                    image_url: "data:image/png;base64,BASE64".into(),
+                },
+            ]
+        );
+
+        let item = ResponseInputItem::FunctionCallOutput {
+            call_id: "call1".into(),
+            output: payload,
+        };
+
+        let json = serde_json::to_string(&item)?;
+        let v: serde_json::Value = serde_json::from_str(&json)?;
+
+        let output = v.get("output").expect("output field");
+        assert!(output.is_array(), "expected array output");
+
+        Ok(())
+    }
+
+    #[test]
+    fn deserializes_array_payload_into_items() -> Result<()> {
+        let json = r#"[
+            {"type": "input_text", "text": "note"},
+            {"type": "input_image", "image_url": "data:image/png;base64,XYZ"}
+        ]"#;
+
+        let payload: FunctionCallOutputPayload = serde_json::from_str(json)?;
+
+        assert_eq!(payload.success, None);
+        let expected_items = vec![
+            FunctionCallOutputContentItem::InputText {
+                text: "note".into(),
+            },
+            FunctionCallOutputContentItem::InputImage {
+                image_url: "data:image/png;base64,XYZ".into(),
+            },
+        ];
+        assert_eq!(payload.content_items, Some(expected_items.clone()));
+
+        let expected_content = serde_json::to_string(&expected_items)?;
+        assert_eq!(payload.content, expected_content);
+
+        Ok(())
+    }
+
     #[test]
     fn deserialize_shell_tool_call_params() -> Result<()> {
         let json = r#"{
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index bb14f3797b..a7f5241bb3 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -814,7 +814,7 @@ pub struct AgentReasoningDeltaEvent {
     pub delta: String,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
+#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS, PartialEq)]
 pub struct McpInvocation {
     /// Name of the MCP server as defined in the config.
     pub server: String,
@@ -824,14 +824,14 @@ pub struct McpInvocation {
     pub arguments: Option<serde_json::Value>,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
+#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS, PartialEq)]
 pub struct McpToolCallBeginEvent {
     /// Identifier so this can be paired with the McpToolCallEnd event.
     pub call_id: String,
     pub invocation: McpInvocation,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
+#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS, PartialEq)]
 pub struct McpToolCallEndEvent {
     /// Identifier for the corresponding McpToolCallBegin that finished.
     pub call_id: String,
diff --git a/codex-rs/rmcp-client/src/bin/test_stdio_server.rs b/codex-rs/rmcp-client/src/bin/test_stdio_server.rs
index 44ae50f02f..aafba59324 100644
--- a/codex-rs/rmcp-client/src/bin/test_stdio_server.rs
+++ b/codex-rs/rmcp-client/src/bin/test_stdio_server.rs
@@ -40,7 +40,7 @@ pub fn stdio() -> (tokio::io::Stdin, tokio::io::Stdout) {
 }
 impl TestToolServer {
     fn new() -> Self {
-        let tools = vec![Self::echo_tool()];
+        let tools = vec![Self::echo_tool(), Self::image_tool()];
         let resources = vec![Self::memo_resource()];
         let resource_templates = vec![Self::memo_template()];
         Self {
@@ -70,6 +70,22 @@ impl TestToolServer {
         )
     }
 
+    fn image_tool() -> Tool {
+        #[expect(clippy::expect_used)]
+        let schema: JsonObject = serde_json::from_value(serde_json::json!({
+            "type": "object",
+            "properties": {},
+            "additionalProperties": false
+        }))
+        .expect("image tool schema should deserialize");
+
+        Tool::new(
+            Cow::Borrowed("image"),
+            Cow::Borrowed("Return a single image content block."),
+            Arc::new(schema),
+        )
+    }
+
     fn memo_resource() -> Resource {
         let raw = RawResource {
             uri: MEMO_URI.to_string(),
@@ -214,6 +230,35 @@ impl ServerHandler for TestToolServer {
                     meta: None,
                 })
             }
+            "image" => {
+                // Read a data URL (e.g. data:image/png;base64,AAA...) from env and convert to
+                // an MCP image content block. Tests set MCP_TEST_IMAGE_DATA_URL.
+                let data_url = std::env::var("MCP_TEST_IMAGE_DATA_URL").map_err(|_| {
+                    McpError::invalid_params(
+                        "missing MCP_TEST_IMAGE_DATA_URL env var for image tool",
+                        None,
+                    )
+                })?;
+
+                fn parse_data_url(url: &str) -> Option<(String, String)> {
+                    let rest = url.strip_prefix("data:")?;
+                    let (mime_and_opts, data) = rest.split_once(',')?;
+                    let (mime, _opts) =
+                        mime_and_opts.split_once(';').unwrap_or((mime_and_opts, ""));
+                    Some((mime.to_string(), data.to_string()))
+                }
+
+                let (mime_type, data_b64) = parse_data_url(&data_url).ok_or_else(|| {
+                    McpError::invalid_params(
+                        format!("invalid data URL for image tool: {data_url}"),
+                        None,
+                    )
+                })?;
+
+                Ok(CallToolResult::success(vec![rmcp::model::Content::image(
+                    data_b64, mime_type,
+                )]))
+            }
             other => Err(McpError::invalid_params(
                 format!("unknown tool: {other}"),
                 None,
diff --git a/codex-rs/tui/src/history_cell.rs b/codex-rs/tui/src/history_cell.rs
index e630e00175..406a892561 100644
--- a/codex-rs/tui/src/history_cell.rs
+++ b/codex-rs/tui/src/history_cell.rs
@@ -465,7 +465,7 @@ struct CompletedMcpToolCallWithImageOutput {
 }
 impl HistoryCell for CompletedMcpToolCallWithImageOutput {
     fn display_lines(&self, _width: u16) -> Vec<Line<'static>> {
-        vec!["tool result (image output omitted)".into()]
+        vec!["tool result (image output)".into()]
     }
 }