Why

codex-rs/app-server-protocol/src/protocol/v2.rs had grown into a single ~12k-line definition file for the entire app-server v2 API.

This is purely a mechanical refactor to break up the monolithic v2.rs file that contains all app-server API v2 types into more modular files, grouped by resource (e.g. account, thread, turn, etc.).

just write-app-server-schema shows no real changes, so we can be sure that this is purely an internal organizational change.

What changed

• Replaced the monolithic protocol/v2.rs with a protocol/v2/ module tree and a small mod.rs that only declares and reexports modules.
• Grouped v2 API definitions by conceptual owner, including account, apps, collaboration_mode, command_exec, config, device_key, experimental_feature, feedback, fs, hook, item, mcp, model, notification, permissions, plugin, process, realtime, review, thread, thread_data, turn, and windows_sandbox.
• Moved v2 tests into protocol/v2/tests.rs so mod.rs stays small.
• Kept shared protocol helpers in protocol/v2/shared.rs, including the enum mirroring macro and common cross-resource types.
• Co-located resource-specific notifications and server-request payloads with the modules that own those resources.
• Regenerated app-server protocol schema fixtures. The schema diffs are non-semantic newline-only changes after the refactor.

Verification

• cargo check -p codex-app-server-protocol
• cargo test -p codex-app-server-protocol
• just write-app-server-schema