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/core/src/tools/events.rs

@@ -6,6 +6,8 @@ use crate::tools::sandboxing::ToolError;
 use codex_protocol::error::CodexErr;
 use codex_protocol::error::SandboxErr;
 use codex_protocol::exec_output::ExecToolCallOutput;
+use codex_protocol::items::FileChangeItem;
+use codex_protocol::items::TurnItem;
 use codex_protocol::parse_command::ParsedCommand;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::ExecCommandBeginEvent;
@@ -13,8 +15,6 @@ use codex_protocol::protocol::ExecCommandEndEvent;
 use codex_protocol::protocol::ExecCommandSource;
 use codex_protocol::protocol::ExecCommandStatus;
 use codex_protocol::protocol::FileChange;
-use codex_protocol::protocol::PatchApplyBeginEvent;
-use codex_protocol::protocol::PatchApplyEndEvent;
 use codex_protocol::protocol::PatchApplyStatus;
 use codex_protocol::protocol::TurnDiffEvent;
 use codex_shell_command::parse_command::parse_command;
@@ -183,13 +183,15 @@ impl ToolEmitter {
                     guard.on_patch_begin(changes);
                 }
                 ctx.session
-                    .send_event(
+                    .emit_turn_item_started(
                         ctx.turn,
-                        EventMsg::PatchApplyBegin(PatchApplyBeginEvent {
-                            call_id: ctx.call_id.to_string(),
-                            turn_id: ctx.turn.sub_id.clone(),
-                            auto_approved: *auto_approved,
+                        &TurnItem::FileChange(FileChangeItem {
+                            id: ctx.call_id.to_string(),
                             changes: changes.clone(),
+                            status: None,
+                            auto_approved: Some(*auto_approved),
+                            stdout: None,
+                            stderr: None,
                         }),
                     )
                     .await;
@@ -200,7 +202,6 @@ impl ToolEmitter {
                     changes.clone(),
                     output.stdout.text.clone(),
                     output.stderr.text.clone(),
-                    output.exit_code == 0,
                     if output.exit_code == 0 {
                         PatchApplyStatus::Completed
                     } else {
@@ -218,7 +219,6 @@ impl ToolEmitter {
                     changes.clone(),
                     output.stdout.text.clone(),
                     output.stderr.text.clone(),
-                    output.exit_code == 0,
                     if output.exit_code == 0 {
                         PatchApplyStatus::Completed
                     } else {
@@ -236,7 +236,6 @@ impl ToolEmitter {
                     changes.clone(),
                     String::new(),
                     (*message).to_string(),
-                    /*success*/ false,
                     PatchApplyStatus::Failed,
                 )
                 .await;
@@ -250,7 +249,6 @@ impl ToolEmitter {
                     changes.clone(),
                     String::new(),
                     (*message).to_string(),
-                    /*success*/ false,
                     PatchApplyStatus::Declined,
                 )
                 .await;
@@ -496,20 +494,18 @@ async fn emit_patch_end(
     changes: HashMap<PathBuf, FileChange>,
     stdout: String,
     stderr: String,
-    success: bool,
     status: PatchApplyStatus,
 ) {
     ctx.session
-        .send_event(
+        .emit_turn_item_completed(
             ctx.turn,
-            EventMsg::PatchApplyEnd(PatchApplyEndEvent {
-                call_id: ctx.call_id.to_string(),
-                turn_id: ctx.turn.sub_id.clone(),
-                stdout,
-                stderr,
-                success,
+            TurnItem::FileChange(FileChangeItem {
+                id: ctx.call_id.to_string(),
                 changes,
-                status,
+                status: Some(status),
+                auto_approved: None,
+                stdout: Some(stdout),
+                stderr: Some(stderr),
             }),
         )
         .await;