[app-server] feat: v2 apply_patch approval flow (#6760)

This PR adds the API V2 version of the apply_patch approval flow, which
centers around `ThreadItem::FileChange`.

This PR wires the new RPC (`item/fileChange/requestApproval`, V2 only)
and related events (`item/started`, `item/completed` for
`ThreadItem::FileChange`, which are emitted in both V1 and V2) through
the app-server
protocol. The new approval RPC is only sent when the user initiates a
turn with the new `turn/start` API so we don't break backwards
compatibility with VSCE.

Similar to https://github.com/openai/codex/pull/6758, the approach I
took was to make as few changes to the Codex core as possible,
leveraging existing `EventMsg` core events, and translating those in
app-server. I did have to add a few additional fields to
`EventMsg::PatchApplyBegin` and `EventMsg::PatchApplyEnd`, but those
were fairly lightweight.

However, the `EventMsg`s emitted by core are the following:
```
1) Auto-approved (no request for approval)

- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

2) Approved by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

3) Declined by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd
```

For a request triggering an approval, this would result in:
```
item/fileChange/requestApproval
item/started
item/completed
```

which is different from the `ThreadItem::CommandExecution` flow
introduced in https://github.com/openai/codex/pull/6758, which does the
below and is preferable:
```
item/started
item/commandExecution/requestApproval
item/completed
```

To fix this, we leverage `TurnSummaryStore` on codex_message_processor
to store a little bit of state, allowing us to fire `item/started` and
`item/fileChange/requestApproval` whenever we receive the underlying
`EventMsg::ApplyPatchApprovalRequest`, and no-oping when we receive the
`EventMsg::PatchApplyBegin` later.

This is much less invasive than modifying the order of EventMsg within
core (I tried).

The resulting payloads:
```
{
  "method": "item/started",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "inProgress",
      "type": "fileChange"
    }
  }
}
```

```
{
  "id": 0,
  "method": "item/fileChange/requestApproval",
  "params": {
    "grantRoot": null,
    "itemId": "call_Nxnwj7B3YXigfV6Mwh03d686",
    "reason": null,
    "threadId": "019a9e11-8295-7883-a283-779e06502c6f",
    "turnId": "1"
  }
}
```

```
{
  "id": 0,
  "result": {
    "decision": "accept"
  }
}
```

```
{
  "method": "item/completed",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "completed",
      "type": "fileChange"
    }
  }
}
```

codex-rs/app-server/src/bespoke_event_handling.rs

@@ -15,12 +15,17 @@ use codex_app_server_protocol::CommandExecutionRequestApprovalResponse;
 use codex_app_server_protocol::CommandExecutionStatus;
 use codex_app_server_protocol::ExecCommandApprovalParams;
 use codex_app_server_protocol::ExecCommandApprovalResponse;
+use codex_app_server_protocol::FileChangeRequestApprovalParams;
+use codex_app_server_protocol::FileChangeRequestApprovalResponse;
+use codex_app_server_protocol::FileUpdateChange;
 use codex_app_server_protocol::InterruptConversationResponse;
 use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ItemStartedNotification;
 use codex_app_server_protocol::McpToolCallError;
 use codex_app_server_protocol::McpToolCallResult;
 use codex_app_server_protocol::McpToolCallStatus;
+use codex_app_server_protocol::PatchApplyStatus;
+use codex_app_server_protocol::PatchChangeKind as V2PatchChangeKind;
 use codex_app_server_protocol::ReasoningSummaryPartAddedNotification;
 use codex_app_server_protocol::ReasoningSummaryTextDeltaNotification;
 use codex_app_server_protocol::ReasoningTextDeltaNotification;
@@ -40,6 +45,7 @@ use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::ExecApprovalRequestEvent;
 use codex_core::protocol::ExecCommandEndEvent;
+use codex_core::protocol::FileChange as CoreFileChange;
 use codex_core::protocol::McpToolCallBeginEvent;
 use codex_core::protocol::McpToolCallEndEvent;
 use codex_core::protocol::Op;
@@ -47,7 +53,9 @@ use codex_core::protocol::ReviewDecision;
 use codex_core::review_format::format_review_findings_block;
 use codex_protocol::ConversationId;
 use codex_protocol::protocol::ReviewOutputEvent;
+use std::collections::HashMap;
 use std::convert::TryFrom;
+use std::path::PathBuf;
 use std::sync::Arc;
 use tokio::sync::oneshot;
 use tracing::error;
@@ -70,24 +78,74 @@ pub(crate) async fn apply_bespoke_event_handling(
         }
         EventMsg::ApplyPatchApprovalRequest(ApplyPatchApprovalRequestEvent {
             call_id,
+            turn_id,
             changes,
             reason,
             grant_root,
-        }) => {
-            let params = ApplyPatchApprovalParams {
-                conversation_id,
-                call_id,
-                file_changes: changes,
-                reason,
-                grant_root,
-            };
-            let rx = outgoing
-                .send_request(ServerRequestPayload::ApplyPatchApproval(params))
-                .await;
-            tokio::spawn(async move {
-                on_patch_approval_response(event_id, rx, conversation).await;
-            });
-        }
+        }) => match api_version {
+            ApiVersion::V1 => {
+                let params = ApplyPatchApprovalParams {
+                    conversation_id,
+                    call_id,
+                    file_changes: changes.clone(),
+                    reason,
+                    grant_root,
+                };
+                let rx = outgoing
+                    .send_request(ServerRequestPayload::ApplyPatchApproval(params))
+                    .await;
+                tokio::spawn(async move {
+                    on_patch_approval_response(event_id, rx, conversation).await;
+                });
+            }
+            ApiVersion::V2 => {
+                // Until we migrate the core to be aware of a first class FileChangeItem
+                // and emit the corresponding EventMsg, we repurpose the call_id as the item_id.
+                let item_id = call_id.clone();
+                let patch_changes = convert_patch_changes(&changes);
+
+                let first_start = {
+                    let mut map = turn_summary_store.lock().await;
+                    let summary = map.entry(conversation_id).or_default();
+                    summary.file_change_started.insert(item_id.clone())
+                };
+                if first_start {
+                    let item = ThreadItem::FileChange {
+                        id: item_id.clone(),
+                        changes: patch_changes.clone(),
+                        status: PatchApplyStatus::InProgress,
+                    };
+                    let notification = ItemStartedNotification { item };
+                    outgoing
+                        .send_server_notification(ServerNotification::ItemStarted(notification))
+                        .await;
+                }
+
+                let params = FileChangeRequestApprovalParams {
+                    thread_id: conversation_id.to_string(),
+                    turn_id: turn_id.clone(),
+                    item_id: item_id.clone(),
+                    reason,
+                    grant_root,
+                };
+                let rx = outgoing
+                    .send_request(ServerRequestPayload::FileChangeRequestApproval(params))
+                    .await;
+                tokio::spawn(async move {
+                    on_file_change_request_approval_response(
+                        event_id,
+                        conversation_id,
+                        item_id,
+                        patch_changes,
+                        rx,
+                        conversation,
+                        outgoing,
+                        turn_summary_store,
+                    )
+                    .await;
+                });
+            }
+        },
         EventMsg::ExecApprovalRequest(ExecApprovalRequestEvent {
             call_id,
             turn_id,
@@ -244,6 +302,49 @@ pub(crate) async fn apply_bespoke_event_handling(
                 .send_server_notification(ServerNotification::ItemCompleted(notification))
                 .await;
         }
+        EventMsg::PatchApplyBegin(patch_begin_event) => {
+            // Until we migrate the core to be aware of a first class FileChangeItem
+            // and emit the corresponding EventMsg, we repurpose the call_id as the item_id.
+            let item_id = patch_begin_event.call_id.clone();
+
+            let first_start = {
+                let mut map = turn_summary_store.lock().await;
+                let summary = map.entry(conversation_id).or_default();
+                summary.file_change_started.insert(item_id.clone())
+            };
+            if first_start {
+                let item = ThreadItem::FileChange {
+                    id: item_id.clone(),
+                    changes: convert_patch_changes(&patch_begin_event.changes),
+                    status: PatchApplyStatus::InProgress,
+                };
+                let notification = ItemStartedNotification { item };
+                outgoing
+                    .send_server_notification(ServerNotification::ItemStarted(notification))
+                    .await;
+            }
+        }
+        EventMsg::PatchApplyEnd(patch_end_event) => {
+            // Until we migrate the core to be aware of a first class FileChangeItem
+            // and emit the corresponding EventMsg, we repurpose the call_id as the item_id.
+            let item_id = patch_end_event.call_id.clone();
+
+            let status = if patch_end_event.success {
+                PatchApplyStatus::Completed
+            } else {
+                PatchApplyStatus::Failed
+            };
+            let changes = convert_patch_changes(&patch_end_event.changes);
+            complete_file_change_item(
+                conversation_id,
+                item_id,
+                changes,
+                status,
+                outgoing.as_ref(),
+                &turn_summary_store,
+            )
+            .await;
+        }
         EventMsg::ExecCommandBegin(exec_command_begin_event) => {
             let item = ThreadItem::CommandExecution {
                 id: exec_command_begin_event.call_id.clone(),
@@ -365,6 +466,32 @@ async fn emit_turn_completed_with_status(
         .await;
 }
 
+async fn complete_file_change_item(
+    conversation_id: ConversationId,
+    item_id: String,
+    changes: Vec<FileUpdateChange>,
+    status: PatchApplyStatus,
+    outgoing: &OutgoingMessageSender,
+    turn_summary_store: &TurnSummaryStore,
+) {
+    {
+        let mut map = turn_summary_store.lock().await;
+        if let Some(summary) = map.get_mut(&conversation_id) {
+            summary.file_change_started.remove(&item_id);
+        }
+    }
+
+    let item = ThreadItem::FileChange {
+        id: item_id,
+        changes,
+        status,
+    };
+    let notification = ItemCompletedNotification { item };
+    outgoing
+        .send_server_notification(ServerNotification::ItemCompleted(notification))
+        .await;
+}
+
 async fn find_and_remove_turn_summary(
     conversation_id: ConversationId,
     turn_summary_store: &TurnSummaryStore,
@@ -512,6 +639,110 @@ fn render_review_output_text(output: &ReviewOutputEvent) -> String {
     }
 }
 
+fn convert_patch_changes(changes: &HashMap<PathBuf, CoreFileChange>) -> Vec<FileUpdateChange> {
+    let mut converted: Vec<FileUpdateChange> = changes
+        .iter()
+        .map(|(path, change)| FileUpdateChange {
+            path: path.to_string_lossy().into_owned(),
+            kind: map_patch_change_kind(change),
+            diff: format_file_change_diff(change),
+        })
+        .collect();
+    converted.sort_by(|a, b| a.path.cmp(&b.path));
+    converted
+}
+
+fn map_patch_change_kind(change: &CoreFileChange) -> V2PatchChangeKind {
+    match change {
+        CoreFileChange::Add { .. } => V2PatchChangeKind::Add,
+        CoreFileChange::Delete { .. } => V2PatchChangeKind::Delete,
+        CoreFileChange::Update { move_path, .. } => V2PatchChangeKind::Update {
+            move_path: move_path.clone(),
+        },
+    }
+}
+
+fn format_file_change_diff(change: &CoreFileChange) -> String {
+    match change {
+        CoreFileChange::Add { content } => content.clone(),
+        CoreFileChange::Delete { content } => content.clone(),
+        CoreFileChange::Update {
+            unified_diff,
+            move_path,
+        } => {
+            if let Some(path) = move_path {
+                format!("{unified_diff}\n\nMoved to: {}", path.display())
+            } else {
+                unified_diff.clone()
+            }
+        }
+    }
+}
+
+#[allow(clippy::too_many_arguments)]
+async fn on_file_change_request_approval_response(
+    event_id: String,
+    conversation_id: ConversationId,
+    item_id: String,
+    changes: Vec<FileUpdateChange>,
+    receiver: oneshot::Receiver<JsonValue>,
+    codex: Arc<CodexConversation>,
+    outgoing: Arc<OutgoingMessageSender>,
+    turn_summary_store: TurnSummaryStore,
+) {
+    let response = receiver.await;
+    let (decision, completion_status) = match response {
+        Ok(value) => {
+            let response = serde_json::from_value::<FileChangeRequestApprovalResponse>(value)
+                .unwrap_or_else(|err| {
+                    error!("failed to deserialize FileChangeRequestApprovalResponse: {err}");
+                    FileChangeRequestApprovalResponse {
+                        decision: ApprovalDecision::Decline,
+                    }
+                });
+
+            let (decision, completion_status) = match response.decision {
+                ApprovalDecision::Accept => (ReviewDecision::Approved, None),
+                ApprovalDecision::Decline => {
+                    (ReviewDecision::Denied, Some(PatchApplyStatus::Declined))
+                }
+                ApprovalDecision::Cancel => {
+                    (ReviewDecision::Abort, Some(PatchApplyStatus::Declined))
+                }
+            };
+            // Allow EventMsg::PatchApplyEnd to emit ItemCompleted for accepted patches.
+            // Only short-circuit on declines/cancels/failures.
+            (decision, completion_status)
+        }
+        Err(err) => {
+            error!("request failed: {err:?}");
+            (ReviewDecision::Denied, Some(PatchApplyStatus::Failed))
+        }
+    };
+
+    if let Some(status) = completion_status {
+        complete_file_change_item(
+            conversation_id,
+            item_id,
+            changes,
+            status,
+            outgoing.as_ref(),
+            &turn_summary_store,
+        )
+        .await;
+    }
+
+    if let Err(err) = codex
+        .submit(Op::PatchApproval {
+            id: event_id,
+            decision,
+        })
+        .await
+    {
+        error!("failed to submit PatchApproval: {err}");
+    }
+}
+
 async fn on_command_execution_request_approval_response(
     event_id: String,
     receiver: oneshot::Receiver<JsonValue>,

codex-rs/app-server/src/codex_message_processor.rs

@@ -139,6 +139,7 @@ use codex_protocol::protocol::USER_MESSAGE_BEGIN;
 use codex_protocol::user_input::UserInput as CoreInputItem;
 use codex_utils_json_to_toml::json_to_toml;
 use std::collections::HashMap;
+use std::collections::HashSet;
 use std::ffi::OsStr;
 use std::io::Error as IoError;
 use std::path::Path;
@@ -162,6 +163,7 @@ pub(crate) type PendingInterrupts = Arc<Mutex<HashMap<ConversationId, PendingInt
 #[derive(Default, Clone)]
 pub(crate) struct TurnSummary {
     pub(crate) last_error_message: Option<String>,
+    pub(crate) file_change_started: HashSet<String>,
 }
 
 pub(crate) type TurnSummaryStore = Arc<Mutex<HashMap<ConversationId, TurnSummary>>>;

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -1,14 +1,20 @@
 use anyhow::Result;
 use app_test_support::McpProcess;
+use app_test_support::create_apply_patch_sse_response;
 use app_test_support::create_final_assistant_message_sse_response;
 use app_test_support::create_mock_chat_completions_server;
 use app_test_support::create_mock_chat_completions_server_unchecked;
 use app_test_support::create_shell_sse_response;
 use app_test_support::to_response;
+use codex_app_server_protocol::ApprovalDecision;
 use codex_app_server_protocol::CommandExecutionStatus;
+use codex_app_server_protocol::FileChangeRequestApprovalResponse;
+use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ItemStartedNotification;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::PatchApplyStatus;
+use codex_app_server_protocol::PatchChangeKind;
 use codex_app_server_protocol::RequestId;
 use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::ThreadItem;
@@ -471,6 +477,300 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn turn_start_file_change_approval_v2() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let tmp = TempDir::new()?;
+    let codex_home = tmp.path().join("codex_home");
+    std::fs::create_dir(&codex_home)?;
+    let workspace = tmp.path().join("workspace");
+    std::fs::create_dir(&workspace)?;
+
+    let patch = r#"*** Begin Patch
+*** Add File: README.md
++new line
+*** End Patch
+"#;
+    let responses = vec![
+        create_apply_patch_sse_response(patch, "patch-call")?,
+        create_final_assistant_message_sse_response("patch applied")?,
+    ];
+    let server = create_mock_chat_completions_server(responses).await;
+    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+
+    let mut mcp = McpProcess::new(&codex_home).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let start_req = mcp
+        .send_thread_start_request(ThreadStartParams {
+            model: Some("mock-model".to_string()),
+            cwd: Some(workspace.to_string_lossy().into_owned()),
+            ..Default::default()
+        })
+        .await?;
+    let start_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(start_req)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(start_resp)?;
+
+    let turn_req = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id.clone(),
+            input: vec![V2UserInput::Text {
+                text: "apply patch".into(),
+            }],
+            cwd: Some(workspace.clone()),
+            ..Default::default()
+        })
+        .await?;
+    let turn_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_req)),
+    )
+    .await??;
+    let TurnStartResponse { turn } = to_response::<TurnStartResponse>(turn_resp)?;
+
+    let started_file_change = timeout(DEFAULT_READ_TIMEOUT, async {
+        loop {
+            let started_notif = mcp
+                .read_stream_until_notification_message("item/started")
+                .await?;
+            let started: ItemStartedNotification =
+                serde_json::from_value(started_notif.params.clone().expect("item/started params"))?;
+            if let ThreadItem::FileChange { .. } = started.item {
+                return Ok::<ThreadItem, anyhow::Error>(started.item);
+            }
+        }
+    })
+    .await??;
+    let ThreadItem::FileChange {
+        ref id,
+        status,
+        ref changes,
+    } = started_file_change
+    else {
+        unreachable!("loop ensures we break on file change items");
+    };
+    assert_eq!(id, "patch-call");
+    assert_eq!(status, PatchApplyStatus::InProgress);
+    let started_changes = changes.clone();
+
+    let server_req = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_request_message(),
+    )
+    .await??;
+    let ServerRequest::FileChangeRequestApproval { request_id, params } = server_req else {
+        panic!("expected FileChangeRequestApproval request")
+    };
+    assert_eq!(params.item_id, "patch-call");
+    assert_eq!(params.thread_id, thread.id);
+    assert_eq!(params.turn_id, turn.id);
+    let expected_readme_path = workspace.join("README.md");
+    let expected_readme_path = expected_readme_path.to_string_lossy().into_owned();
+    pretty_assertions::assert_eq!(
+        started_changes,
+        vec![codex_app_server_protocol::FileUpdateChange {
+            path: expected_readme_path.clone(),
+            kind: PatchChangeKind::Add,
+            diff: "new line\n".to_string(),
+        }]
+    );
+
+    mcp.send_response(
+        request_id,
+        serde_json::to_value(FileChangeRequestApprovalResponse {
+            decision: ApprovalDecision::Accept,
+        })?,
+    )
+    .await?;
+
+    let completed_file_change = timeout(DEFAULT_READ_TIMEOUT, async {
+        loop {
+            let completed_notif = mcp
+                .read_stream_until_notification_message("item/completed")
+                .await?;
+            let completed: ItemCompletedNotification = serde_json::from_value(
+                completed_notif
+                    .params
+                    .clone()
+                    .expect("item/completed params"),
+            )?;
+            if let ThreadItem::FileChange { .. } = completed.item {
+                return Ok::<ThreadItem, anyhow::Error>(completed.item);
+            }
+        }
+    })
+    .await??;
+    let ThreadItem::FileChange { ref id, status, .. } = completed_file_change else {
+        unreachable!("loop ensures we break on file change items");
+    };
+    assert_eq!(id, "patch-call");
+    assert_eq!(status, PatchApplyStatus::Completed);
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("codex/event/task_complete"),
+    )
+    .await??;
+
+    let readme_contents = std::fs::read_to_string(expected_readme_path)?;
+    assert_eq!(readme_contents, "new line\n");
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn turn_start_file_change_approval_decline_v2() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let tmp = TempDir::new()?;
+    let codex_home = tmp.path().join("codex_home");
+    std::fs::create_dir(&codex_home)?;
+    let workspace = tmp.path().join("workspace");
+    std::fs::create_dir(&workspace)?;
+
+    let patch = r#"*** Begin Patch
+*** Add File: README.md
++new line
+*** End Patch
+"#;
+    let responses = vec![
+        create_apply_patch_sse_response(patch, "patch-call")?,
+        create_final_assistant_message_sse_response("patch declined")?,
+    ];
+    let server = create_mock_chat_completions_server(responses).await;
+    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+
+    let mut mcp = McpProcess::new(&codex_home).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let start_req = mcp
+        .send_thread_start_request(ThreadStartParams {
+            model: Some("mock-model".to_string()),
+            cwd: Some(workspace.to_string_lossy().into_owned()),
+            ..Default::default()
+        })
+        .await?;
+    let start_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(start_req)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(start_resp)?;
+
+    let turn_req = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id.clone(),
+            input: vec![V2UserInput::Text {
+                text: "apply patch".into(),
+            }],
+            cwd: Some(workspace.clone()),
+            ..Default::default()
+        })
+        .await?;
+    let turn_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_req)),
+    )
+    .await??;
+    let TurnStartResponse { turn } = to_response::<TurnStartResponse>(turn_resp)?;
+
+    let started_file_change = timeout(DEFAULT_READ_TIMEOUT, async {
+        loop {
+            let started_notif = mcp
+                .read_stream_until_notification_message("item/started")
+                .await?;
+            let started: ItemStartedNotification =
+                serde_json::from_value(started_notif.params.clone().expect("item/started params"))?;
+            if let ThreadItem::FileChange { .. } = started.item {
+                return Ok::<ThreadItem, anyhow::Error>(started.item);
+            }
+        }
+    })
+    .await??;
+    let ThreadItem::FileChange {
+        ref id,
+        status,
+        ref changes,
+    } = started_file_change
+    else {
+        unreachable!("loop ensures we break on file change items");
+    };
+    assert_eq!(id, "patch-call");
+    assert_eq!(status, PatchApplyStatus::InProgress);
+    let started_changes = changes.clone();
+
+    let server_req = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_request_message(),
+    )
+    .await??;
+    let ServerRequest::FileChangeRequestApproval { request_id, params } = server_req else {
+        panic!("expected FileChangeRequestApproval request")
+    };
+    assert_eq!(params.item_id, "patch-call");
+    assert_eq!(params.thread_id, thread.id);
+    assert_eq!(params.turn_id, turn.id);
+    let expected_readme_path = workspace.join("README.md");
+    let expected_readme_path_str = expected_readme_path.to_string_lossy().into_owned();
+    pretty_assertions::assert_eq!(
+        started_changes,
+        vec![codex_app_server_protocol::FileUpdateChange {
+            path: expected_readme_path_str.clone(),
+            kind: PatchChangeKind::Add,
+            diff: "new line\n".to_string(),
+        }]
+    );
+
+    mcp.send_response(
+        request_id,
+        serde_json::to_value(FileChangeRequestApprovalResponse {
+            decision: ApprovalDecision::Decline,
+        })?,
+    )
+    .await?;
+
+    let completed_file_change = timeout(DEFAULT_READ_TIMEOUT, async {
+        loop {
+            let completed_notif = mcp
+                .read_stream_until_notification_message("item/completed")
+                .await?;
+            let completed: ItemCompletedNotification = serde_json::from_value(
+                completed_notif
+                    .params
+                    .clone()
+                    .expect("item/completed params"),
+            )?;
+            if let ThreadItem::FileChange { .. } = completed.item {
+                return Ok::<ThreadItem, anyhow::Error>(completed.item);
+            }
+        }
+    })
+    .await??;
+    let ThreadItem::FileChange { ref id, status, .. } = completed_file_change else {
+        unreachable!("loop ensures we break on file change items");
+    };
+    assert_eq!(id, "patch-call");
+    assert_eq!(status, PatchApplyStatus::Declined);
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("codex/event/task_complete"),
+    )
+    .await??;
+
+    assert!(
+        !expected_readme_path.exists(),
+        "declined patch should not be applied"
+    );
+
+    Ok(())
+}
+
 // Helper to create a config.toml pointing at the mock model server.
 fn create_config_toml(
     codex_home: &Path,