Streamline thread mutation handlers

[pakrym-oai]

Why

Thread mutation handlers had many short error branches whose only job was to emit a JSON-RPC error and stop. This slice keeps those errors visible, but lets each handler build a result and return early from validation helpers instead of nesting the main path.

What Changed

• Streamlined thread archive/unarchive, rename, memory, metadata, rollback, compact, background terminal, shell, and guardian handlers in codex-rs/app-server/src/codex_message_processor.rs.
• Reused shared JSON-RPC error constructors in codex-rs/app-server/src/bespoke_event_handling.rs for rollback-related request failures.
• Preserved direct send_error calls where they remain the simplest boundary for pending async event responses.

Verification

• cargo check -p codex-app-server
• cargo test -p codex-app-server --test all v2::thread_rollback -- --test-threads=1

[chatgpt-codex-connector]

💡 Codex Review

codex/codex-rs/app-server/src/codex_message_processor.rs

Line 3555 in b8828ca

self.outgoing.send_error(request_id, error).await;

Make thread_list_response return a proper Result

thread_list now delegates to thread_list_response, but this helper still calls send_error(request_id, ...) and uses bare return;. In this function, request_id is out of scope and the control flow no longer returns Result<ThreadListResponse, JSONRPCErrorError>. This introduces a build-breaking regression in the thread/list path.

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