## Why
Several legacy `EventMsg` variants were still emitted or mapped even
though clients either ignored them or had moved to item/lifecycle
events. `Op::Undo` had also degraded to an unavailable shim, so this
removes that dead task path instead of preserving a command that cannot
do useful work.
`McpStartupComplete`, `WebSearchBegin`, and `ImageGenerationBegin` are
intentionally kept because useful consumers still depend on them: MCP
startup completion drives readiness behavior, and the begin events let
app-server/core consumers surface in-progress web-search and
image-generation items before the final payload arrives.
## What Changed
- Removed weak legacy event variants and payloads from `codex-protocol`,
including legacy agent deltas, background events, and undo lifecycle
events.
- Kept/restored `EventMsg::McpStartupComplete`,
`EventMsg::WebSearchBegin`, and `EventMsg::ImageGenerationBegin` with
serializer and emission coverage.
- Updated core, rollout, MCP server, app-server thread history,
review/delegate filtering, and tests to rely on the useful replacement
events that remain.
- Removed `Op::Undo`, `UndoTask`, the undo test module, and stale TUI
slash-command comments.
- Stopped agent job/background progress and compaction retry notices
from emitting `BackgroundEvent` payloads.
## Verification
- `cargo check -p codex-protocol -p codex-app-server-protocol -p
codex-core -p codex-rollout -p codex-rollout-trace -p codex-mcp-server`
- `cargo test -p codex-protocol -p codex-app-server-protocol -p
codex-rollout -p codex-rollout-trace -p codex-mcp-server`
- `cargo test -p codex-core --test all suite::items`
- `just fix -p codex-protocol -p codex-app-server-protocol -p codex-core
-p codex-rollout -p codex-rollout-trace -p codex-mcp-server`
- Earlier coverage on this PR also included `codex-mcp`, `codex-tui`,
core library tests, MCP/plugin/delegate/review/agent job tests, and MCP
startup TUI tests.
## Summary
Remote plugin-service returns plugin availability separately from a
user's installed/enabled state. This adds `PluginAvailabilityStatus` to
the app-server protocol, propagates remote catalog `status` into
`PluginSummary`, and rejects install attempts for remote plugins marked
`DISABLED_BY_ADMIN` before downloading or caching the bundle.
This is the `openai/codex` half of the change. The companion
`openai/openai` webview PR is
https://github.com/openai/openai/pull/873269.
## Validation
- `cargo run -p codex-app-server-protocol --bin write_schema_fixtures`
- `cargo test -p codex-app-server --test all
plugin_list_marks_remote_plugin_disabled_by_admin`
- `cargo test -p codex-app-server --test all
plugin_list_includes_remote_marketplaces_when_remote_plugin_enabled`
- `cargo test -p codex-app-server --test all
plugin_install_rejects_remote_plugin_disabled_by_admin_before_download`
- `cargo test -p codex-app-server-protocol schema_fixtures`
Michael Bolin