Move apply-patch file changes into turn items (#20540)

## Why

Apply-patch file changes are now part of the core turn item stream, so
v2 clients can consume the same first-class item lifecycle path used by
other turn items instead of relying on app-server-specific remapping
from legacy patch events.

## What changed

- Added a core `TurnItem::FileChange` carrying apply-patch changes and
completion metadata.
- Updated the apply-patch tool emitter to send `ItemStarted` /
`ItemCompleted` with the new `FileChange` item while preserving legacy
`PatchApplyBegin` / `PatchApplyEnd` fan-out.
- Updated app-server v2 conversion to render the new core item directly
and stopped `event_mapping` from remapping old patch begin/end events
into item notifications.
- Kept thread history reconstruction based on the existing old
apply-patch events for rollout compatibility.

## Verification

- `cargo test -p codex-protocol -p codex-app-server-protocol`
- `cargo test -p codex-core --test all
apply_patch_tool_executes_and_emits_patch_events`
- `cargo test -p codex-app-server bespoke_event_handling`

codex-rs/app-server-protocol/src/protocol/event_mapping.rs

@@ -1,7 +1,6 @@
 use crate::protocol::common::ServerNotification;
 use crate::protocol::item_builders::build_command_execution_begin_item;
 use crate::protocol::item_builders::build_command_execution_end_item;
-use crate::protocol::item_builders::build_file_change_begin_item;
 use crate::protocol::item_builders::convert_patch_changes;
 use crate::protocol::v2::AgentMessageDeltaNotification;
 use crate::protocol::v2::CollabAgentState;
@@ -450,13 +449,6 @@ pub fn item_event_to_server_notification(
                 item: item_completed_event.item.into(),
             })
         }
-        EventMsg::PatchApplyBegin(patch_begin_event) => {
-            ServerNotification::ItemStarted(ItemStartedNotification {
-                thread_id,
-                turn_id,
-                item: build_file_change_begin_item(&patch_begin_event),
-            })
-        }
         EventMsg::PatchApplyUpdated(event) => {
             ServerNotification::FileChangePatchUpdated(FileChangePatchUpdatedNotification {
                 thread_id,

codex-rs/app-server-protocol/src/protocol/item_builders.rs

@@ -1,9 +1,8 @@
-//! Shared builders for synthetic [`ThreadItem`] values emitted by the app-server layer.
+//! Shared builders for app-server [`ThreadItem`] values derived from compatibility events.
 //!
-//! These items do not come from first-class core `ItemStarted` / `ItemCompleted` events.
-//! Instead, the app-server synthesizes them so clients can render a coherent lifecycle for
-//! approvals and other pre-execution flows before the underlying tool has started or when the
-//! tool never starts at all.
+//! Most live tool items now come from first-class core `ItemStarted` / `ItemCompleted` events.
+//! These builders remain for approval flows, rebuilt legacy history, and other pre-execution
+//! paths where the underlying tool has not started or never starts at all.
 //!
 //! Keeping these builders in one place is useful for two reasons:
 //! - Live notifications and rebuilt `thread/read` history both need to construct the same

codex-rs/app-server-protocol/src/protocol/thread_history.rs

@@ -357,6 +357,7 @@ impl ThreadHistoryBuilder {
             | codex_protocol::items::TurnItem::Reasoning(_)
             | codex_protocol::items::TurnItem::WebSearch(_)
             | codex_protocol::items::TurnItem::ImageGeneration(_)
+            | codex_protocol::items::TurnItem::FileChange(_)
             | codex_protocol::items::TurnItem::ContextCompaction(_) => {}
         }
     }
@@ -378,6 +379,7 @@ impl ThreadHistoryBuilder {
             | codex_protocol::items::TurnItem::Reasoning(_)
             | codex_protocol::items::TurnItem::WebSearch(_)
             | codex_protocol::items::TurnItem::ImageGeneration(_)
+            | codex_protocol::items::TurnItem::FileChange(_)
             | codex_protocol::items::TurnItem::ContextCompaction(_) => {}
         }
     }

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -5,6 +5,7 @@ use std::path::PathBuf;
 
 use crate::RequestId;
 use crate::protocol::common::AuthMode;
+use crate::protocol::item_builders::convert_patch_changes;
 use codex_experimental_api_macros::ExperimentalApi;
 use codex_protocol::account::PlanType;
 use codex_protocol::account::ProviderAccount;
@@ -6469,6 +6470,15 @@ impl From<CoreTurnItem> for ThreadItem {
                 result: image.result,
                 saved_path: image.saved_path,
             },
+            CoreTurnItem::FileChange(file_change) => ThreadItem::FileChange {
+                id: file_change.id,
+                changes: convert_patch_changes(&file_change.changes),
+                status: file_change
+                    .status
+                    .as_ref()
+                    .map(PatchApplyStatus::from)
+                    .unwrap_or(PatchApplyStatus::InProgress),
+            },
             CoreTurnItem::ContextCompaction(compaction) => {
                 ThreadItem::ContextCompaction { id: compaction.id }
             }
@@ -8078,6 +8088,7 @@ mod tests {
     use super::*;
     use codex_protocol::items::AgentMessageContent;
     use codex_protocol::items::AgentMessageItem;
+    use codex_protocol::items::FileChangeItem;
     use codex_protocol::items::ReasoningItem;
     use codex_protocol::items::TurnItem;
     use codex_protocol::items::UserMessageItem;
@@ -10358,6 +10369,35 @@ mod tests {
                 }),
             }
         );
+
+        let file_change_item = TurnItem::FileChange(FileChangeItem {
+            id: "patch-1".to_string(),
+            changes: [(
+                PathBuf::from("README.md"),
+                codex_protocol::protocol::FileChange::Add {
+                    content: "hello\n".to_string(),
+                },
+            )]
+            .into_iter()
+            .collect(),
+            status: Some(codex_protocol::protocol::PatchApplyStatus::Completed),
+            auto_approved: None,
+            stdout: Some("Done!".to_string()),
+            stderr: Some(String::new()),
+        });
+
+        assert_eq!(
+            ThreadItem::from(file_change_item),
+            ThreadItem::FileChange {
+                id: "patch-1".to_string(),
+                changes: vec![FileUpdateChange {
+                    path: "README.md".to_string(),
+                    kind: PatchChangeKind::Add,
+                    diff: "hello\n".to_string(),
+                }],
+                status: PatchApplyStatus::Completed,
+            }
+        );
     }
 
     #[test]