[codex] Emit image view as core item

[pakrym-oai]

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

[chatgpt-codex-connector]

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