core: strip image detail from Responses Lite requests (#27246)

## Summary

- Strip image `detail` fields from every Responses Lite request.
- Apply stripping to message images and function/custom tool-output
images.
- Transform only the formatted request copy without mutating stored
history.
- Preserve image URLs byte-for-byte, including HTTP(S) URLs, without
downloading, validating, or resizing them.
- Preserve all image `detail` fields for non-Responses-Lite models.

## Motivation

Responses Lite does not support image `detail` tags, so Codex must omit
them whenever `model_info.use_responses_lite` is enabled. This transport
requirement is independent of the `resize_all_images` feature.

Stored history retains the original detail values. This keeps
request-specific formatting isolated from conversation state and
preserves the information for local image preparation and
non-Responses-Lite requests.


#### [git stack](https://github.com/magus/git-stack-cli)
- ✅ `1` https://github.com/openai/codex/pull/27245
- ✅ `2` https://github.com/openai/codex/pull/27247
- 👉 `3` https://github.com/openai/codex/pull/27246
- ⏳ `4` https://github.com/openai/codex/pull/27266

codex-rs/core/src/client.rs

@@ -746,7 +746,7 @@ impl ModelClient {
         window_id: &str,
     ) -> Result<ResponsesApiRequest> {
         let instructions = &prompt.base_instructions.text;
-        let input = prompt.get_formatted_input();
+        let input = prompt.get_formatted_input_for_request(model_info.use_responses_lite);
         let tools = create_tools_json_for_responses_api(&prompt.tools)?;
         let reasoning = Self::build_reasoning(model_info, effort, summary);
         let include = if reasoning.is_some() {

codex-rs/core/src/client_common.rs

@@ -2,6 +2,8 @@ pub use codex_api::ResponseEvent;
 use codex_config::types::Personality;
 use codex_protocol::error::Result;
 use codex_protocol::models::BaseInstructions;
+use codex_protocol::models::ContentItem;
+use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::protocol::InterAgentCommunication;
 use codex_tools::ToolSpec;
@@ -71,6 +73,56 @@ impl Prompt {
             })
             .collect()
     }
+
+    pub(crate) fn get_formatted_input_for_request(
+        &self,
+        use_responses_lite: bool,
+    ) -> Vec<ResponseItem> {
+        let mut input = self.get_formatted_input();
+        if use_responses_lite {
+            strip_image_details(&mut input);
+        }
+        input
+    }
+}
+
+fn strip_image_details(items: &mut [ResponseItem]) {
+    for item in items {
+        match item {
+            ResponseItem::Message { content, .. } => {
+                for content_item in content {
+                    if let ContentItem::InputImage { detail, .. } = content_item {
+                        *detail = None;
+                    }
+                }
+            }
+            ResponseItem::FunctionCallOutput { output, .. }
+            | ResponseItem::CustomToolCallOutput { output, .. } => {
+                if let Some(content) = output.content_items_mut() {
+                    for content_item in content {
+                        if let FunctionCallOutputContentItem::InputImage { detail, .. } =
+                            content_item
+                        {
+                            *detail = None;
+                        }
+                    }
+                }
+            }
+            ResponseItem::Reasoning { .. }
+            | ResponseItem::AgentMessage { .. }
+            | ResponseItem::LocalShellCall { .. }
+            | ResponseItem::FunctionCall { .. }
+            | ResponseItem::ToolSearchCall { .. }
+            | ResponseItem::CustomToolCall { .. }
+            | ResponseItem::ToolSearchOutput { .. }
+            | ResponseItem::WebSearchCall { .. }
+            | ResponseItem::ImageGenerationCall { .. }
+            | ResponseItem::Compaction { .. }
+            | ResponseItem::CompactionTrigger
+            | ResponseItem::ContextCompaction { .. }
+            | ResponseItem::Other => {}
+        }
+    }
 }
 
 pub struct ResponseStream {

codex-rs/core/src/client_common_tests.rs

@@ -3,10 +3,95 @@ use codex_api::ResponsesApiRequest;
 use codex_api::TextControls;
 use codex_api::create_text_param_for_request;
 use codex_protocol::config_types::ServiceTier;
+use codex_protocol::models::FunctionCallOutputPayload;
+use codex_protocol::models::ImageDetail;
 use pretty_assertions::assert_eq;
 
 use super::*;
 
+fn prompt_with_image_outputs() -> Prompt {
+    Prompt {
+        input: vec![
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputImage {
+                    image_url: "https://example.com/image.png".to_string(),
+                    detail: Some(ImageDetail::Original),
+                }],
+                phase: None,
+            },
+            ResponseItem::FunctionCallOutput {
+                call_id: "function-call".to_string(),
+                output: FunctionCallOutputPayload::from_content_items(vec![
+                    FunctionCallOutputContentItem::InputImage {
+                        image_url: "data:image/png;base64,function".to_string(),
+                        detail: Some(ImageDetail::High),
+                    },
+                ]),
+            },
+            ResponseItem::CustomToolCallOutput {
+                call_id: "custom-call".to_string(),
+                name: None,
+                output: FunctionCallOutputPayload::from_content_items(vec![
+                    FunctionCallOutputContentItem::InputImage {
+                        image_url: "data:image/png;base64,custom".to_string(),
+                        detail: Some(ImageDetail::Auto),
+                    },
+                ]),
+            },
+        ],
+        ..Default::default()
+    }
+}
+
+#[test]
+fn responses_lite_request_copies_strip_image_details() {
+    let prompt = prompt_with_image_outputs();
+    let original = prompt.input.clone();
+
+    let stripped = prompt.get_formatted_input_for_request(/*use_responses_lite*/ true);
+
+    assert_eq!(
+        stripped,
+        vec![
+            ResponseItem::Message {
+                id: None,
+                role: "user".to_string(),
+                content: vec![ContentItem::InputImage {
+                    image_url: "https://example.com/image.png".to_string(),
+                    detail: None,
+                }],
+                phase: None,
+            },
+            ResponseItem::FunctionCallOutput {
+                call_id: "function-call".to_string(),
+                output: FunctionCallOutputPayload::from_content_items(vec![
+                    FunctionCallOutputContentItem::InputImage {
+                        image_url: "data:image/png;base64,function".to_string(),
+                        detail: None,
+                    },
+                ]),
+            },
+            ResponseItem::CustomToolCallOutput {
+                call_id: "custom-call".to_string(),
+                name: None,
+                output: FunctionCallOutputPayload::from_content_items(vec![
+                    FunctionCallOutputContentItem::InputImage {
+                        image_url: "data:image/png;base64,custom".to_string(),
+                        detail: None,
+                    },
+                ]),
+            },
+        ]
+    );
+    assert_eq!(prompt.input, original);
+    assert_eq!(
+        prompt.get_formatted_input_for_request(/*use_responses_lite*/ false),
+        original
+    );
+}
+
 #[test]
 fn serializes_text_verbosity_when_set() {
     let input: Vec<ResponseItem> = vec![];