[codex] Emit image view as core item (#20512)

## Why

Image-view results should be represented as a core-produced turn item
instead of being reconstructed by app-server. At the same time, existing
rollout/history paths still understand the legacy `ViewImageToolCall`
event, so this keeps that event as compatibility output generated from
the new item lifecycle.

## What changed

- Added `TurnItem::ImageView` to `codex-protocol`.
- Emitted image-view item start/completion directly from the core
`view_image` handler.
- Kept `ViewImageToolCall` as a legacy event and generate it from
completed `TurnItem::ImageView` items.
- Kept `thread_history.rs` on the legacy `ViewImageToolCall` replay
path, with `ImageView` item lifecycle events ignored there.
- Updated app-server protocol conversion, rollout persistence, and
affected exhaustive event matches for the new item plus legacy fan-out
shape.

## Verification

- `cargo test -p codex-protocol -p codex-app-server-protocol -p
codex-rollout -p codex-rollout-trace -p codex-mcp-server -p
codex-app-server --lib`
- `cargo test -p codex-core --test all
view_image_tool_attaches_local_image`
- `just fix -p codex-protocol -p codex-core -p codex-app-server-protocol
-p codex-app-server -p codex-rollout -p codex-rollout-trace -p
codex-mcp-server`
- `git diff --check`

codex-rs/core/src/session/turn.rs

@@ -1470,9 +1470,9 @@ pub(super) fn realtime_text_for_event(msg: &EventMsg) -> Option<String> {
         | EventMsg::PatchApplyBegin(_)
         | EventMsg::PatchApplyUpdated(_)
         | EventMsg::PatchApplyEnd(_)
-        | EventMsg::ViewImageToolCall(_)
         | EventMsg::ImageGenerationBegin(_)
         | EventMsg::ImageGenerationEnd(_)
+        | EventMsg::ViewImageToolCall(_)
         | EventMsg::ExecApprovalRequest(_)
         | EventMsg::RequestPermissions(_)
         | EventMsg::RequestUserInput(_)

codex-rs/core/src/tools/handlers/view_image.rs

@@ -1,3 +1,5 @@
+use codex_protocol::items::ImageViewItem;
+use codex_protocol::items::TurnItem;
 use codex_protocol::models::DEFAULT_IMAGE_DETAIL;
 use codex_protocol::models::FunctionCallOutputBody;
 use codex_protocol::models::FunctionCallOutputContentItem;
@@ -17,8 +19,6 @@ use crate::tools::context::ToolPayload;
 use crate::tools::handlers::parse_arguments;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use codex_protocol::protocol::EventMsg;
-use codex_protocol::protocol::ViewImageToolCallEvent;
 
 pub struct ViewImageHandler;
 
@@ -152,15 +152,12 @@ impl ToolHandler for ViewImageHandler {
             })?;
         let image_url = image.into_data_url();
 
-        session
-            .send_event(
-                turn.as_ref(),
-                EventMsg::ViewImageToolCall(ViewImageToolCallEvent {
-                    call_id,
-                    path: event_path,
-                }),
-            )
-            .await;
+        let item = TurnItem::ImageView(ImageViewItem {
+            id: call_id,
+            path: event_path,
+        });
+        session.emit_turn_item_started(turn.as_ref(), &item).await;
+        session.emit_turn_item_completed(turn.as_ref(), item).await;
 
         Ok(ViewImageOutput {
             image_url,