Preserve image transparency metadata in app-server items (#37178)

## What changed - Add `transparentBackground` to image-generation items and legacy completion events. - Map Images API backgrounds to `true` for transparent, `false` for opaque, and `null` for automatic or unavailable values. - Preserve the metadata in live notifications and persisted or resumed thread history while continuing to deserialize older items that omit it. ## Testing - Cover transparent, opaque, and automatic backgrounds, including image edits and thread read/resume flows. - Verify the stable JSON shape and optional TypeScript field. GitOrigin-RevId: 08527f37f23431df45fab1ed34eb82b2139b49d7
2026-10-18 17:18:52 +00:00 · 2026-08-05 23:42:29 +00:00
parent a3ebd19fa4
commit 928bda82cf
35 changed files with 407 additions and 9 deletions
@@ -4786,6 +4786,7 @@ async fn turn_event_counts_completed_tool_items() {
            status: "completed".to_string(),
            revised_prompt: None,
            result: "ok".to_string(),
+            transparent_background: None,
            saved_path: None,
        }),
    ];
@@ -4731,6 +4731,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -19779,6 +19779,13 @@
              "status": {
                "type": "string"
              },
+              "transparentBackground": {
+                "default": null,
+                "type": [
+                  "boolean",
+                  "null"
+                ]
+              },
              "type": {
                "enum": [
                  "imageGeneration"
@@ -17538,6 +17538,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1241,6 +1241,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1241,6 +1241,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1386,6 +1386,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1935,6 +1935,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1935,6 +1935,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1935,6 +1935,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1726,6 +1726,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1386,6 +1386,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1386,6 +1386,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -1386,6 +1386,13 @@
            "status": {
              "type": "string"
            },
+            "transparentBackground": {
+              "default": null,
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
            "type": {
              "enum": [
                "imageGeneration"
@@ -3,4 +3,4 @@
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 import type { AbsolutePathBuf } from "./AbsolutePathBuf";

-export type ImageGenerationItem = { id: string, status: string, revisedPrompt: string | null, result: string, savedPath?: AbsolutePathBuf, };
+export type ImageGenerationItem = { id: string, status: string, revisedPrompt: string | null, result: string, transparentBackground?: boolean, savedPath?: AbsolutePathBuf, };
@@ -862,6 +862,7 @@ impl ThreadHistoryBuilder {
            status: String::new(),
            revised_prompt: None,
            result: String::new(),
+            transparent_background: None,
            saved_path: None,
        });
        self.upsert_item_in_current_turn(item);
@@ -873,6 +874,7 @@ impl ThreadHistoryBuilder {
            status: payload.status.clone(),
            revised_prompt: payload.revised_prompt.clone(),
            result: payload.result.clone(),
+            transparent_background: payload.transparent_background,
            saved_path: payload.saved_path.clone(),
        });
        self.upsert_item_in_current_turn(item);
@@ -2076,6 +2078,7 @@ mod tests {
                        status: "completed".to_string(),
                        revised_prompt: Some("A blue square".to_string()),
                        result: "cG5n".to_string(),
+                        transparent_background: Some(true),
                        saved_path: Some(saved_path.clone()),
                    },
                )),
@@ -2106,6 +2109,7 @@ mod tests {
                status: "completed".to_string(),
                revised_prompt: Some("A blue square".to_string()),
                result: "cG5n".to_string(),
+                transparent_background: Some(true),
                saved_path: Some(saved_path),
            })]
        );
@@ -2368,6 +2372,7 @@ mod tests {
                status: "completed".into(),
                revised_prompt: Some("final prompt".into()),
                result: "Zm9v".into(),
+                transparent_background: Some(true),
                saved_path: Some(test_path_buf("/tmp/ig_123.png").abs()),
            })),
            RolloutItem::EventMsg(EventMsg::TurnComplete(TurnCompleteEvent {
@@ -2407,6 +2412,7 @@ mod tests {
                        status: "completed".into(),
                        revised_prompt: Some("final prompt".into()),
                        result: "Zm9v".into(),
+                        transparent_background: Some(true),
                        saved_path: Some(test_path_buf("/tmp/ig_123.png").abs()),
                    }),
                ],
@@ -928,6 +928,7 @@ impl From<CoreTurnItem> for ThreadItem {
                    status: image.status,
                    revised_prompt: image.revised_prompt,
                    result: image.result,
+                    transparent_background: None,
                    saved_path: image.saved_path,
                })
            }
@@ -1544,6 +1544,7 @@ The app-server streams JSON-RPC notifications while a turn is running. Each turn
 - `mcpToolCall` — `{id, server, tool, status, arguments, appContext, mcpAppResourceUri?, pluginId, readOnlyHint, result?, error?}` describing MCP calls; `appContext` is `{connectorId, linkId, resourceUri, appName, actionName}` for calls through a trusted MCP app, where `connectorId` identifies the connector that owns the tool, `linkId` identifies the app link, `resourceUri` points to the widget template, `appName` is the connector's display name, and `actionName` is the stable connector `Action.name`. `readOnlyHint` is `true` for read-only tools, `false` for write-capable tools, and `null` when the annotation is unavailable, including older rollout entries. The hint describes tool capability, not whether an invocation succeeded or performed a write; use `status`, `result`, and `error` to determine the execution outcome. `appName` and `actionName` may be null for older rollout entries. The top-level `mcpAppResourceUri` is deprecated and temporarily duplicated for client migration. `tool` identifies the raw MCP tool. `status` is `inProgress`, `completed`, or `failed`.
 - `collabToolCall` — `{id, tool, status, senderThreadId, receiverThreadId?, newThreadId?, prompt?, agentStatus?}` describing collab tool calls (`spawn_agent`, `send_input`, `resume_agent`, `wait`, `close_agent`); `status` is `inProgress`, `completed`, or `failed`.
 - `webSearch` — `{id, query, action?, results?}` for a web search request issued by the agent; `action` mirrors the Responses API web_search action payload (`search`, `open_page`, `find_in_page`) and may be omitted until completion. For standalone web search, `results` contains the out-of-band structured result DTOs returned by `/v1/alpha/search`; clients should ignore result types and fields they do not understand.
+- `imageGeneration` — `{id, status, revisedPrompt, result, transparentBackground, savedPath?}` for a generated image. `transparentBackground` is `true` when the Images API reports a transparent background, `false` when it reports an opaque background, and `null` when the background is automatic, unavailable, or the item has not completed. The field is always present on v2 item payloads, including persisted and resumed items.
 - `imageView` — `{id, path}` emitted when the agent invokes the image viewer tool.
 - `sleep` — `{id, durationMs}` emitted while the agent waits for a duration or new input.
 - `enteredReviewMode` — `{id, review}` sent when the reviewer starts; `review` is a short user-facing label such as `"current changes"` or the requested target description.
@@ -106,6 +106,7 @@ mod tests {
                status: "completed".to_string(),
                revised_prompt: Some("revised".to_string()),
                result: "base64-result".to_string(),
+                transparent_background: None,
                saved_path: Some(test_path_buf("/tmp/ig-1.png").abs()),
            }),
        ]);
@@ -10,6 +10,10 @@ use app_test_support::write_chatgpt_auth;
 use codex_app_server_protocol::ImageGenerationItem;
 use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ThreadItem;
+use codex_app_server_protocol::ThreadReadParams;
+use codex_app_server_protocol::ThreadReadResponse;
+use codex_app_server_protocol::ThreadResumeParams;
+use codex_app_server_protocol::ThreadResumeResponse;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::TurnStartParams;
@@ -117,6 +121,7 @@ async fn standalone_image_generation_returns_saved_path_hint_to_model() -> Resul
        status,
        revised_prompt,
        result,
+        transparent_background,
        saved_path: Some(saved_path),
        ..
    }) = completed.item
@@ -126,6 +131,7 @@ async fn standalone_image_generation_returns_saved_path_hint_to_model() -> Resul
    assert_eq!(status, "completed");
    assert_eq!(revised_prompt.as_deref(), Some("paint a blue whale"));
    assert_eq!(result, RESULT);
+    assert_eq!(transparent_background, Some(false));
    assert_eq!(std::fs::read(&saved_path)?, TINY_PNG_BYTES);

    let image_request = server
@@ -179,6 +185,179 @@ async fn standalone_image_generation_returns_saved_path_hint_to_model() -> Resul
    Ok(())
 }

+#[tokio::test]
+async fn transparent_image_preserves_output_metadata_and_persisted_history() -> Result<()> {
+    let call_id = "transparent-image-run-1";
+    let server = responses::start_mock_server().await;
+    mount_image_response_with_background(&server, "transparent").await;
+    responses::mount_sse_sequence(
+        &server,
+        vec![
+            responses::sse(vec![
+                responses::ev_response_created("resp-1"),
+                responses::ev_function_call_with_namespace(
+                    call_id,
+                    "image_gen",
+                    "imagegen",
+                    &json!({"prompt": "a blue whale on a transparent background"}).to_string(),
+                ),
+                responses::ev_completed("resp-1"),
+            ]),
+            responses::sse(vec![
+                responses::ev_assistant_message("msg-1", "Done"),
+                responses::ev_completed("resp-2"),
+            ]),
+        ],
+    )
+    .await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml(codex_home.path(), &server.uri(), ImagegenTestMode::Direct)?;
+    write_chatgpt_auth(
+        codex_home.path(),
+        ChatGptAuthFixture::new("access-chatgpt"),
+        AuthCredentialsStoreMode::File,
+    )?;
+    let mut mcp = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .with_env_overrides(&[("OPENAI_API_KEY", None)])
+        .build_initialized_with_timeout(DEFAULT_READ_TIMEOUT)
+        .await?;
+    start_image_generation_turn(&mut mcp, ThreadStartParams::default()).await?;
+
+    let completed = timeout(
+        DEFAULT_READ_TIMEOUT,
+        wait_for_image_generation_completed(&mut mcp),
+    )
+    .await??;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+    let thread_id = completed.thread_id.clone();
+    let ThreadItem::ImageGeneration(ImageGenerationItem {
+        status,
+        result,
+        transparent_background,
+        ..
+    }) = completed.item
+    else {
+        panic!("expected completed image-generation item");
+    };
+    assert_eq!(status, "completed");
+    assert_eq!(result, RESULT);
+    assert_eq!(transparent_background, Some(true));
+
+    drop(mcp);
+    let mut resumed = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .with_env_overrides(&[("OPENAI_API_KEY", None)])
+        .build_initialized_with_timeout(DEFAULT_READ_TIMEOUT)
+        .await?;
+    let read_id = resumed
+        .send_thread_read_request(ThreadReadParams {
+            thread_id: thread_id.clone(),
+            include_turns: true,
+        })
+        .await?;
+    let ThreadReadResponse { thread, .. } =
+        timeout(DEFAULT_READ_TIMEOUT, resumed.read_response(read_id)).await??;
+    let persisted_image = thread
+        .turns
+        .iter()
+        .flat_map(|turn| turn.items.iter())
+        .find_map(|item| match item {
+            ThreadItem::ImageGeneration(item) => Some(item),
+            _ => None,
+        })
+        .context("persisted legacy history should contain the generated image")?;
+    assert_eq!(persisted_image.transparent_background, Some(true));
+
+    let resume_id = resumed
+        .send_thread_resume_request(ThreadResumeParams {
+            thread_id,
+            ..Default::default()
+        })
+        .await?;
+    let ThreadResumeResponse { thread, .. } =
+        timeout(DEFAULT_READ_TIMEOUT, resumed.read_response(resume_id)).await??;
+    let resumed_image = thread
+        .turns
+        .iter()
+        .flat_map(|turn| turn.items.iter())
+        .find_map(|item| match item {
+            ThreadItem::ImageGeneration(item) => Some(item),
+            _ => None,
+        })
+        .context("resumed legacy history should contain the generated image")?;
+    assert_eq!(resumed_image.transparent_background, Some(true));
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn automatic_image_background_preserves_unknown_transparency() -> Result<()> {
+    let call_id = "automatic-image-run-1";
+    let server = responses::start_mock_server().await;
+    mount_image_response_with_background(&server, "auto").await;
+    responses::mount_sse_sequence(
+        &server,
+        vec![
+            responses::sse(vec![
+                responses::ev_response_created("resp-1"),
+                responses::ev_function_call_with_namespace(
+                    call_id,
+                    "image_gen",
+                    "imagegen",
+                    &json!({"prompt": "paint a blue whale"}).to_string(),
+                ),
+                responses::ev_completed("resp-1"),
+            ]),
+            responses::sse(vec![
+                responses::ev_assistant_message("msg-1", "Done"),
+                responses::ev_completed("resp-2"),
+            ]),
+        ],
+    )
+    .await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml(codex_home.path(), &server.uri(), ImagegenTestMode::Direct)?;
+    write_chatgpt_auth(
+        codex_home.path(),
+        ChatGptAuthFixture::new("access-chatgpt"),
+        AuthCredentialsStoreMode::File,
+    )?;
+    let mut mcp = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .with_env_overrides(&[("OPENAI_API_KEY", None)])
+        .build_initialized_with_timeout(DEFAULT_READ_TIMEOUT)
+        .await?;
+    start_image_generation_turn(&mut mcp, ThreadStartParams::default()).await?;
+    let completed = timeout(
+        DEFAULT_READ_TIMEOUT,
+        wait_for_image_generation_completed(&mut mcp),
+    )
+    .await??;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+    let ThreadItem::ImageGeneration(image) = completed.item else {
+        panic!("expected completed image-generation item");
+    };
+    assert_eq!(image.transparent_background, None);
+    let value = serde_json::to_value(&image)?;
+    assert_eq!(
+        value.get("transparentBackground"),
+        Some(&serde_json::Value::Null),
+        "v2 image-generation items must always include nullable transparency metadata"
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn standalone_image_generation_failure_emits_terminal_item() -> Result<()> {
    let call_id = "image-run-failed";
@@ -236,6 +415,7 @@ async fn standalone_image_generation_failure_emits_terminal_item() -> Result<()>
            status: "failed".to_string(),
            revised_prompt: Some("paint a blue whale".to_string()),
            result: String::new(),
+            transparent_background: None,
            saved_path: None,
        })
    );
@@ -266,7 +446,7 @@ async fn standalone_image_edit_uses_attached_model_visible_image() -> Result<()>
        "remote executors use different imagegen storage approaches, so host-local image paths are unavailable"
    );

-    let edit_request = run_image_edit_test(|codex_home| {
+    let (edit_request, _) = run_image_edit_test(|codex_home| {
        let image_path = codex_home.join("attached.png");
        std::fs::write(&image_path, TINY_PNG_BYTES)?;
        Ok((
@@ -294,9 +474,9 @@ async fn standalone_image_edit_uses_attached_model_visible_image() -> Result<()>
 }

 #[tokio::test]
-async fn standalone_image_edit_uses_recent_pathless_image() -> Result<()> {
+async fn transparent_image_edit_preserves_metadata_and_recent_pathless_image() -> Result<()> {
    let image_url = TINY_PNG_DATA_URL;
-    let edit_request = run_image_edit_test(|_| {
+    let (edit_request, completed_image) = run_image_edit_test(|_| {
        Ok((
            json!({
                "prompt": "add a red hat",
@@ -317,6 +497,7 @@ async fn standalone_image_edit_uses_recent_pathless_image() -> Result<()> {
    .await?;
    assert_eq!(edit_request["prompt"], "add a red hat");
    assert_eq!(edit_request["images"][0]["image_url"], image_url);
+    assert_eq!(completed_image.transparent_background, Some(true));

    Ok(())
 }
@@ -461,7 +642,7 @@ async fn start_image_generation_turn(

 async fn run_image_edit_test(
    input: impl FnOnce(&Path) -> Result<(serde_json::Value, Vec<V2UserInput>)>,
-) -> Result<serde_json::Value> {
+) -> Result<(serde_json::Value, ImageGenerationItem)> {
    let call_id = "image-edit-1";
    let server = responses::start_mock_server().await;
    mount_image_edit_response(&server).await;
@@ -510,11 +691,14 @@ async fn run_image_edit_test(
        input,
    )
    .await?;
-    timeout(
+    let completed = timeout(
        DEFAULT_READ_TIMEOUT,
        wait_for_image_generation_completed(&mut mcp),
    )
    .await??;
+    let ThreadItem::ImageGeneration(completed_image) = completed.item else {
+        panic!("expected completed image-generation item");
+    };
    timeout(
        DEFAULT_READ_TIMEOUT,
        mcp.read_stream_until_notification_message("turn/completed"),
@@ -540,7 +724,10 @@ async fn run_image_edit_test(
        "chatgpt_cca"
    );
    assert_image_turn_id_header(image_request, &turn_id)?;
-    Ok(image_request.body_json::<serde_json::Value>()?)
+    Ok((
+        image_request.body_json::<serde_json::Value>()?,
+        completed_image,
+    ))
 }

 fn assert_image_turn_id_header(request: &wiremock::Request, expected_turn_id: &str) -> Result<()> {
@@ -592,10 +779,15 @@ async fn wait_for_image_generation_completed(
 }

 async fn mount_image_response(server: &MockServer) {
+    mount_image_response_with_background(server, "opaque").await;
+}
+
+async fn mount_image_response_with_background(server: &MockServer, background: &str) {
    Mock::given(method("POST"))
        .and(path("/api/codex/images/generations"))
        .respond_with(ResponseTemplate::new(200).set_body_json(json!({
            "created": 1,
+            "background": background,
            "data": [{"b64_json": RESULT}],
        })))
        .expect(1)
@@ -608,6 +800,7 @@ async fn mount_image_edit_response(server: &MockServer) {
        .and(path("/api/codex/images/edits"))
        .respond_with(ResponseTemplate::new(200).set_body_json(json!({
            "created": 1,
+            "background": "transparent",
            "data": [{"b64_json": RESULT}],
        })))
        .expect(1)
@@ -1681,6 +1681,7 @@ fn append_resume_redaction_history(
            status: "completed".to_string(),
            revised_prompt: Some("secret revised prompt".to_string()),
            result: "base64-image-result".to_string(),
+            transparent_background: None,
            saved_path: Some(test_absolute_path("/tmp/ig-1.png")),
        }),
    ]
@@ -472,6 +472,7 @@ mod tests {
            status: "in_progress".to_string(),
            revised_prompt: None,
            result: String::new(),
+            transparent_background: None,
            saved_path: None,
        });
        let expected_completed_item = ExtensionItem::ImageGeneration(ImageGenerationItem {
@@ -479,6 +480,7 @@ mod tests {
            status: "completed".to_string(),
            revised_prompt: Some("A tiny blue square".to_string()),
            result: "cG5n".to_string(),
+            transparent_background: Some(true),
            saved_path: Some(expected_path.clone()),
        });
        codex_tools::TurnItemEmitter::emit_started(
@@ -500,6 +502,7 @@ mod tests {
                    status: "completed".to_string(),
                    revised_prompt: Some("A tiny blue square".to_string()),
                    result: "cG5n".to_string(),
+                    transparent_background: Some(true),
                    saved_path: Some(expected_path.clone()),
                })],
            },
@@ -96,6 +96,7 @@ fn legacy_end_event(item: &ImageGenerationItem) -> EventMsg {
        status: item.status.clone(),
        revised_prompt: item.revised_prompt.clone(),
        result: item.result.clone(),
+        transparent_background: item.transparent_background,
        saved_path: item.saved_path.clone(),
    })
 }
@@ -142,6 +143,7 @@ impl ImageGenerationTool {
                    status: "in_progress".to_string(),
                    revised_prompt: None,
                    result: String::new(),
+                    transparent_background: None,
                    saved_path: None,
                },
                EventMsg::ImageGenerationBegin(ImageGenerationBeginEvent {
@@ -155,14 +157,19 @@ impl ImageGenerationTool {
        }
        .map_err(|err| format!("image generation failed: {err}"))
        .and_then(|response| {
+            let transparent_background = match response.background {
+                Some(ImageBackground::Transparent) => Some(true),
+                Some(ImageBackground::Opaque) => Some(false),
+                Some(ImageBackground::Auto) | None => None,
+            };
            response
                .data
                .into_iter()
                .next()
-                .map(|data| data.b64_json)
+                .map(|data| (data.b64_json, transparent_background))
                .ok_or_else(|| "image generation returned no image data".to_string())
        });
-        let result = match result {
+        let (result, transparent_background) = match result {
            Ok(result) => result,
            Err(message) => {
                let item = ImageGenerationItem {
@@ -170,6 +177,7 @@ impl ImageGenerationTool {
                    status: "failed".to_string(),
                    revised_prompt: Some(args.prompt),
                    result: String::new(),
+                    transparent_background: None,
                    saved_path: None,
                };
                let legacy_event = legacy_end_event(&item);
@@ -209,6 +217,7 @@ impl ImageGenerationTool {
            status: "completed".to_string(),
            revised_prompt: Some(args.prompt),
            result: result.clone(),
+            transparent_background,
            saved_path: saved_path.clone(),
        };
        let legacy_event = legacy_end_event(&item);
@@ -15,6 +15,9 @@ pub struct ImageGenerationItem {
    pub status: String,
    pub revised_prompt: Option<String>,
    pub result: String,
+    #[serde(default)]
+    #[ts(optional)]
+    pub transparent_background: Option<bool>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    #[ts(optional)]
    pub saved_path: Option<AbsolutePathBuf>,
@@ -1,5 +1,6 @@
 use pretty_assertions::assert_eq;
 use serde_json::json;
+use ts_rs::TS;

 use super::ExtensionItem;
 use super::image_generation::ImageGenerationItem;
@@ -13,6 +14,7 @@ fn completed_image_generation_item() -> ExtensionItem {
        status: "completed".to_string(),
        revised_prompt: Some("A blue square".to_string()),
        result: "cG5n".to_string(),
+        transparent_background: None,
        saved_path: None,
    })
 }
@@ -30,12 +32,58 @@ fn image_generation_item_preserves_stable_wire_shape() {
            "status": "completed",
            "revisedPrompt": "A blue square",
            "result": "cG5n",
+            "transparentBackground": null,
        })
    );
    assert_eq!(
        serde_json::from_value::<ExtensionItem>(value).expect("deserialize extension item"),
        item
    );
+    assert_eq!(
+        serde_json::from_value::<ExtensionItem>(json!({
+            "kind": "image_gen.generation",
+            "id": "image-1",
+            "status": "completed",
+            "revisedPrompt": "A blue square",
+            "result": "cG5n",
+        }))
+        .expect("deserialize legacy image-generation item without transparency metadata"),
+        item
+    );
+}
+
+#[test]
+fn image_generation_item_preserves_authoritative_transparency() {
+    let ExtensionItem::ImageGeneration(mut image) = completed_image_generation_item() else {
+        panic!("expected image-generation item");
+    };
+    image.transparent_background = Some(true);
+    let item = ExtensionItem::ImageGeneration(image);
+    let value = serde_json::to_value(&item).expect("serialize extension item");
+
+    assert_eq!(
+        value,
+        json!({
+            "kind": "image_gen.generation",
+            "id": "image-1",
+            "status": "completed",
+            "revisedPrompt": "A blue square",
+            "result": "cG5n",
+            "transparentBackground": true,
+        })
+    );
+    assert_eq!(
+        serde_json::from_value::<ExtensionItem>(value).expect("deserialize extension item"),
+        item
+    );
+}
+
+#[test]
+fn image_generation_transparency_is_optional_in_typescript() {
+    assert!(
+        ImageGenerationItem::inline().contains("transparentBackground?: boolean"),
+        "image-generation transparency must remain optional for existing TypeScript clients"
+    );
 }

 #[test]
@@ -429,6 +429,7 @@ impl ImageGenerationItem {
            status: self.status.clone(),
            revised_prompt: self.revised_prompt.clone(),
            result: self.result.clone(),
+            transparent_background: None,
            saved_path: self.saved_path.clone(),
        })
    }
@@ -2544,6 +2544,9 @@ pub struct ImageGenerationEndEvent {
    #[ts(optional)]
    pub revised_prompt: Option<String>,
    pub result: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub transparent_background: Option<bool>,
    #[serde(skip_serializing_if = "Option::is_none")]
    #[ts(optional)]
    pub saved_path: Option<AbsolutePathBuf>,
@@ -718,6 +718,7 @@ pub(super) fn handle_image_generation_end(
                status: status.into(),
                revised_prompt,
                result: String::new(),
+                transparent_background: None,
                saved_path,
            }),
        }),