Support original-detail metadata on MCP image outputs (#17714)

## Summary
- honor `_meta["codex/imageDetail"] == "original"` on MCP image content
and map it to `detail: "original"` where supported
- strip that detail back out when the active model does not support
original-detail image inputs
- update code-mode `image(...)` to accept individual MCP image blocks
- teach `js_repl` / `codex.emitImage(...)` to preserve the same hint
from raw MCP image outputs
- document the new `_meta` contract and add generic RMCP-backed coverage
across protocol, core, code-mode, and js_repl paths

codex-rs/tools/src/image_detail.rs

@@ -1,3 +1,4 @@
+use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::ImageDetail;
 use codex_protocol::openai_models::ModelInfo;
 
@@ -17,6 +18,23 @@ pub fn normalize_output_image_detail(
     }
 }
 
+pub fn sanitize_original_image_detail(
+    can_request_original_image_detail: bool,
+    items: &mut [FunctionCallOutputContentItem],
+) {
+    if can_request_original_image_detail {
+        return;
+    }
+
+    for item in items {
+        if let FunctionCallOutputContentItem::InputImage { detail, .. } = item
+            && matches!(detail, Some(ImageDetail::Original))
+        {
+            *detail = None;
+        }
+    }
+}
+
 #[cfg(test)]
 #[path = "image_detail_tests.rs"]
 mod tests;

codex-rs/tools/src/image_detail_tests.rs

@@ -1,4 +1,5 @@
 use super::*;
+use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::ImageDetail;
 use codex_protocol::openai_models::ModelInfo;
 use pretty_assertions::assert_eq;
@@ -73,3 +74,39 @@ fn unsupported_non_original_detail_is_dropped() {
         None
     );
 }
+
+#[test]
+fn sanitize_original_drops_original_without_support() {
+    let mut items = vec![
+        FunctionCallOutputContentItem::InputText {
+            text: "header".to_string(),
+        },
+        FunctionCallOutputContentItem::InputImage {
+            image_url: "data:image/png;base64,AAA".to_string(),
+            detail: Some(ImageDetail::Original),
+        },
+        FunctionCallOutputContentItem::InputImage {
+            image_url: "data:image/png;base64,BBB".to_string(),
+            detail: Some(ImageDetail::Low),
+        },
+    ];
+
+    sanitize_original_image_detail(/*can_request_original_image_detail*/ false, &mut items);
+
+    assert_eq!(
+        items,
+        vec![
+            FunctionCallOutputContentItem::InputText {
+                text: "header".to_string(),
+            },
+            FunctionCallOutputContentItem::InputImage {
+                image_url: "data:image/png;base64,AAA".to_string(),
+                detail: None,
+            },
+            FunctionCallOutputContentItem::InputImage {
+                image_url: "data:image/png;base64,BBB".to_string(),
+                detail: Some(ImageDetail::Low),
+            },
+        ]
+    );
+}

codex-rs/tools/src/lib.rs

@@ -53,6 +53,7 @@ pub use codex_protocol::ToolName;
 pub use dynamic_tool::parse_dynamic_tool;
 pub use image_detail::can_request_original_image_detail;
 pub use image_detail::normalize_output_image_detail;
+pub use image_detail::sanitize_original_image_detail;
 pub use js_repl_tool::create_js_repl_reset_tool;
 pub use js_repl_tool::create_js_repl_tool;
 pub use json_schema::AdditionalProperties;