Make the curated iOS app plugin discoverable

What would this improve?

Codex already has an OpenAI-curated build-ios-apps@openai-curated plugin in the curated marketplace, but it is not currently included in TOOL_SUGGEST_DISCOVERABLE_PLUGIN_ALLOWLIST. That means the tool-suggestion path can surface curated plugins such as GitHub, Slack, Figma, and bundled desktop tools, but not the existing iOS app workflow.

For users building iOS apps, the lower-risk path seems to be making the existing curated plugin discoverable instead of adding a new Simulator UI surface or encouraging duplicate manual xcodebuildmcp setup. This also lines up with the user-impact seen in #17448, where having both a manual MCP entry and the curated iOS plugin configured can create confusing duplicate MCP startup behavior.

Minimal patch prepared

I prepared a narrow branch in my fork in case maintainers want this direction:

• Branch: https://github.com/mitre88/codex/tree/chore/discoverable-build-ios-apps-plugin
• Compare: https://github.com/openai/codex/compare/main...mitre88:chore/discoverable-build-ios-apps-plugin

The branch is currently rebased onto main and is one commit ahead. The patch only:

• adds build-ios-apps@openai-curated to TOOL_SUGGEST_DISCOVERABLE_PLUGIN_ALLOWLIST
• adds a focused discoverable-plugin test for build-ios-apps
• updates the existing marketplace reload test so its negative fixture still uses non-allowlisted plugins

No runtime iOS build logic, CLI command behavior, MCP startup behavior, or Simulator UI is changed.

Validation

On the initial base, the focused discoverable-plugin tests passed:

• cargo fmt --package codex-core-plugins --package codex-core --check
• cargo test -p codex-core list_tool_suggest_discoverable_plugins -- --nocapture
• git diff --check

After rebasing onto the latest main, I re-ran:

• cargo fmt --package codex-core-plugins --package codex-core --check
• cargo check -p codex-core --lib -p codex-core-plugins
• git diff --check origin/main..HEAD

Those pass. Re-running cargo test -p codex-core list_tool_suggest_discoverable_plugins -- --nocapture is currently blocked by an unrelated main test-support compile error: core/tests/common/context_snapshot.rs imports similar, but core_test_support does not list that dependency. I did not include that unrelated dependency fix in this branch to keep the scope narrow.

Given the current contributing policy for code PRs, I did not open a PR directly. Happy to turn this branch into a PR if maintainers want the curated iOS plugin to be discoverable.