feat: enforce marketplace restrictions at plugin entry points

[viyatb-oai]

Why

The core plugin manager can reject disallowed marketplaces, but enterprise policy also needs to hold at the entry points that add marketplaces or call remote plugin APIs. Those paths are where a user or automation would otherwise keep widening the local state.

What changed

• Added a config-aware marketplace add helper that rejects user additions when managed requirements disable them.
• Routed CLI, app-server, and external-agent import flows through the managed add/install checks.
• Filtered remote marketplace reads, skill reads, installs, and listings against the managed allowlist, including the backend-resolved marketplace returned by plugin detail fetches.
• Updated the remote plugin skill-read fixture for the detail lookup now required before reading skill contents.

Example config.toml

With the managed requirements stack applied, an approved marketplace can still appear in user config.toml like this:

[features]
plugins = true

[marketplaces.approved-marketplace]
source_type = "git"
source = "https://github.com/example/approved-marketplace.git"

There is intentionally no user-writable allowed_sources key in config.toml; skill-source restrictions are enforced only from managed requirements.

Verification

• Added regression coverage for blocking managed marketplace additions in codex-rs/core-plugins/src/marketplace_add.rs.
• Updated app-server remote skill-read coverage in codex-rs/app-server/tests/suite/v2/plugin_read.rs.

Stack

• feat: prepare managed controls for skills and marketplaces #21462: internal managed artifact requirement plumbing
• feat: restrict which skill sources Codex can load #21457: managed skill enforcement
• feat: restrict which plugin marketplaces Codex can use #21458: core plugin allowlist enforcement
  --> feat: enforce marketplace restrictions at plugin entry points #21459: plugin entrypoint enforcement
• feat: let admins configure managed skill and marketplace controls #21413: managed artifact requirements activation