[MCP] Render MCP tool call result images to the model (#5600)

It's pretty amazing we have gotten here without the ability for the
model to see image content from MCP tool calls.

This PR builds off of 4391 and fixes #4819. I would like @KKcorps to get
adequete credit here but I also want to get this fix in ASAP so I gave
him a week to update it and haven't gotten a response so I'm going to
take it across the finish line.


This test highlights how absured the current situation is. I asked the
model to read this image using the Chrome MCP
<img width="2378" height="674" alt="image"
src="https://github.com/user-attachments/assets/9ef52608-72a2-4423-9f5e-7ae36b2b56e0"
/>

After this change, it correctly outputs:
> Captured the page: image dhows a dark terminal-style UI labeled
`OpenAI Codex (v0.0.0)` with prompt `model: gpt-5-codex medium` and
working directory `/codex/codex-rs`
(and more)  

Before this change, it said:
> Took the full-page screenshot you asked for. It shows a long,
horizontally repeating pattern of stylized people in orange, light-blue,
and mustard clothing, holding hands in alternating poses against a white
background. No text or other graphics-just rows of flat illustration
stretching off to the right.

Without this change, the Figma, Playwright, Chrome, and other visual MCP
servers are pretty much entirely useless.

I tested this change with the openai respones api as well as a third
party completions api

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:?}"),