# Motivation
Browser Use origin-access prompts are MCP elicitations, not direct
tool-call approval prompts, so they were bypassing the Guardian approval
path. We need a generic opt-in that lets eligible MCP elicitations use
Guardian when the current turn already routes approvals there.
# Description
Add a generic elicitation reviewer hook in codex-mcp and wire codex-core
to pass a Guardian reviewer callback when creating the MCP connection
manager. The reviewer validates explicit mcp_tool_call opt-in metadata,
builds a Guardian MCP tool-call review request from
server/tool/connector metadata and tool params, and maps Guardian
approval, denial, timeout, and cancellation decisions back to MCP
elicitation responses.
The new option to trigger this in the `_meta` object is:
```
"codex_request_type": "approval_request",
```
# Testing
- RUST_MIN_STACK=8388608 NEXTEST_STATUS_LEVEL=leak cargo nextest run
--no-fail-fast --cargo-profile ci-test --test-threads 2
- cargo clippy --tests -- -D warnings
- cargo fmt -- --config imports_granularity=Item --check
- cargo shear
- pnpm run format
- python3 .github/scripts/verify_cargo_workspace_manifests.py
- python3 .github/scripts/verify_tui_core_boundary.py
- python3 .github/scripts/verify_bazel_clippy_lints.py
- git diff --check
## Summary
Xcode 26.4 was built against app-server behavior from before MCP
elicitation requests became client-visible in CLI 0.120.0 via #17043.
That client line does not expect the new events/messages, so this PR
restores the old behavior for exactly that client/version combination.
The compatibility handling stays in the app-server layer: when the
initialized client is `Xcode` and its version starts with `26.4`, the
app server marks the live Codex thread so MCP elicitations are
auto-denied. The flag is applied on thread start/resume/fork/turn
attachment, carried through `Codex`/`CodexThread`, and stored on
`McpConnectionManager` so refreshed MCP managers preserve the behavior.
## Notes
This is intentionally narrow and includes a TODO to remove the
compatibility path once Xcode 26.4 ages out.
## Why
When an MCP or app tool is configured with approval mode `approve`
(always allow), users expect that decision to be authoritative. In
guardian auto-review mode, ARC could still return `ask-user`, which then
routed the approval question into guardian with the ARC reason as
context. That meant a tool explicitly configured as always allowed still
went through both safety monitors before running.
This change keeps the existing ARC behavior for non-auto-review
sessions, but avoids the ARC-to-guardian sequence when
`approvals_reviewer = auto_review` and the tool approval mode is
`approve`.
## What changed
- Short-circuit MCP tool approval handling when `approval_mode ==
approve` and `approvals_reviewer == auto_review`.
- Updated the MCP approval regression test so the auto-review case
asserts neither ARC nor guardian is called.
- Preserved existing tests that verify ARC can still block always-allow
MCP tools outside guardian auto-review mode.
## Verification
- `cargo test -p codex-core --lib mcp_tool_call`
Gabriel Peal