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/protocol/src/items.rs

@@ -8,7 +8,11 @@ use crate::protocol::AgentReasoningEvent;
 use crate::protocol::AgentReasoningRawContentEvent;
 use crate::protocol::ContextCompactedEvent;
 use crate::protocol::EventMsg;
+use crate::protocol::FileChange;
 use crate::protocol::ImageGenerationEndEvent;
+use crate::protocol::PatchApplyBeginEvent;
+use crate::protocol::PatchApplyEndEvent;
+use crate::protocol::PatchApplyStatus;
 use crate::protocol::UserMessageEvent;
 use crate::protocol::WebSearchEndEvent;
 use crate::user_input::ByteRange;
@@ -20,6 +24,8 @@ use quick_xml::se::to_string as to_xml_string;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde::Serialize;
+use std::collections::HashMap;
+use std::path::PathBuf;
 use ts_rs::TS;
 
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
@@ -33,6 +39,7 @@ pub enum TurnItem {
     Reasoning(ReasoningItem),
     WebSearch(WebSearchItem),
     ImageGeneration(ImageGenerationItem),
+    FileChange(FileChangeItem),
     ContextCompaction(ContextCompactionItem),
 }
 
@@ -127,6 +134,24 @@ pub struct ImageGenerationItem {
     pub saved_path: Option<AbsolutePathBuf>,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq)]
+pub struct FileChangeItem {
+    pub id: String,
+    pub changes: HashMap<PathBuf, FileChange>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub status: Option<PatchApplyStatus>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub auto_approved: Option<bool>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub stdout: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub stderr: Option<String>,
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
 pub struct ContextCompactionItem {
     pub id: String,
@@ -381,6 +406,30 @@ impl ImageGenerationItem {
     }
 }
 
+impl FileChangeItem {
+    pub fn as_legacy_begin_event(&self, turn_id: String) -> EventMsg {
+        EventMsg::PatchApplyBegin(PatchApplyBeginEvent {
+            call_id: self.id.clone(),
+            turn_id,
+            auto_approved: self.auto_approved.unwrap_or(false),
+            changes: self.changes.clone(),
+        })
+    }
+
+    pub fn as_legacy_end_event(&self, turn_id: String) -> Option<EventMsg> {
+        let status = self.status.clone()?;
+        Some(EventMsg::PatchApplyEnd(PatchApplyEndEvent {
+            call_id: self.id.clone(),
+            turn_id,
+            stdout: self.stdout.clone().unwrap_or_default(),
+            stderr: self.stderr.clone().unwrap_or_default(),
+            success: status == PatchApplyStatus::Completed,
+            changes: self.changes.clone(),
+            status,
+        }))
+    }
+}
+
 impl TurnItem {
     pub fn id(&self) -> String {
         match self {
@@ -391,6 +440,7 @@ impl TurnItem {
             TurnItem::Reasoning(item) => item.id.clone(),
             TurnItem::WebSearch(item) => item.id.clone(),
             TurnItem::ImageGeneration(item) => item.id.clone(),
+            TurnItem::FileChange(item) => item.id.clone(),
             TurnItem::ContextCompaction(item) => item.id.clone(),
         }
     }
@@ -403,6 +453,10 @@ impl TurnItem {
             TurnItem::Plan(_) => Vec::new(),
             TurnItem::WebSearch(item) => vec![item.as_legacy_event()],
             TurnItem::ImageGeneration(item) => vec![item.as_legacy_event()],
+            TurnItem::FileChange(item) => item
+                .as_legacy_end_event(String::new())
+                .into_iter()
+                .collect(),
             TurnItem::Reasoning(item) => item.as_legacy_events(show_raw_agent_reasoning),
             TurnItem::ContextCompaction(item) => vec![item.as_legacy_event()],
         }