## Why
The post-merge `rust-ci-full` run for #18999 still failed the Ubuntu
remote `suite::remote_env` sandboxed filesystem tests. That run checked
out merge commit `ddde50c611e4800cb805f243ed3c50bbafe7d011`, so the arg0
guard lifetime fix was present.
The Docker-backed failure had two remaining pieces:
- The sandboxed filesystem helper needs to execute Codex through the
`codex-linux-sandbox` arg0 alias path. The helper sandbox was only
granting read access to the real Codex executable parent, so the alias
parent also has to be visible inside the helper sandbox.
- The remote-env tests were building sandbox contexts with
`FileSystemSandboxContext::new()`, which captures the local test runner
cwd. In the Docker remote exec-server, that host checkout path does not
exist, so spawning the filesystem helper failed with `No such file or
directory` before the helper could process the request.
## What Changed
- Track all helper runtime read roots instead of a single root.
- Add both the real Codex executable parent and the
`codex-linux-sandbox` alias parent to sandbox readable roots.
- Avoid sending an unused local cwd in remote filesystem sandbox
contexts when the permission profile has no cwd-dependent entries.
- Build the Docker remote-env test sandbox contexts with a cwd path that
exists inside the container.
- Add unit coverage for the alias-parent root and remote sandbox cwd
handling.
## Verification
- `cargo test -p codex-exec-server`
- `cargo test -p codex-core
remote_test_env_sandboxed_read_allows_readable_root`
- `just fix -p codex-exec-server`
- `just fix -p codex-core`
###### Why/Context/Summary
Repro: start a session outside Full Access, switch permissions to Full
Access, then submit a new turn that triggers MCP/CUA permission
handling.
The turn used the live Full Access `SessionConfiguration`, but the MCP
coordinator was still synced from the stale `original_config_do_not_use`
/ per-turn config copy. That left the coordinator with an old sandbox
policy, so empty MCP permission elicitations could be denied instead of
auto-accepted.
Fix: update/rebuild the MCP connection manager from the live
turn/session approval and sandbox policy fields.
###### Test plan
```sh
just fmt
cargo test -p codex-core --lib
cargo test -p codex-core --lib mcp_tool_call::tests
```
