## Why
The split filesystem policy stack already supports exact and glob
`access = none` read restrictions on macOS and Linux. Windows still
needed subprocess handling for those deny-read policies without claiming
enforcement from a backend that cannot provide it.
## Key finding
The unelevated restricted-token backend cannot safely enforce deny-read
overlays. Its `WRITE_RESTRICTED` token model is authoritative for write
checks, not read denials, so this PR intentionally fails that backend
closed when deny-read overrides are present instead of claiming
unsupported enforcement.
## What changed
This PR adds the Windows deny-read enforcement layer and makes the
backend split explicit:
- Resolves Windows deny-read filesystem policy entries into concrete ACL
targets.
- Preserves exact missing paths so they can be materialized and denied
before an enforceable sandboxed process starts.
- Snapshot-expands existing glob matches into ACL targets for Windows
subprocess enforcement.
- Honors `glob_scan_max_depth` when expanding Windows deny-read globs.
- Plans both the configured lexical path and the canonical target for
existing paths so reparse-point aliases are covered.
- Threads deny-read overrides through the elevated/logon-user Windows
sandbox backend and unified exec.
- Applies elevated deny-read ACLs synchronously before command launch
rather than delegating them to the background read-grant helper.
- Reconciles persistent deny-read ACEs per sandbox principal so policy
changes do not leave stale deny-read ACLs behind.
- Fails closed on the unelevated restricted-token backend when deny-read
overrides are present, because its `WRITE_RESTRICTED` token model is not
authoritative for read denials.
## Landed prerequisites
These prerequisite PRs are already on `main`:
1. #15979 `feat(permissions): add glob deny-read policy support`
2. #18096 `feat(sandbox): add glob deny-read platform enforcement`
3. #17740 `feat(config): support managed deny-read requirements`
This PR targets `main` directly and contains only the Windows deny-read
enforcement layer.
## Implementation notes
- Exact deny-read paths remain enforceable on the elevated path even
when they do not exist yet: Windows materializes the missing path before
applying the deny ACE, so the sandboxed command cannot create and read
it during the same run.
- Existing exact deny paths are preserved lexically until the ACL
planner, which then adds the canonical target as a second ACL target
when needed. That keeps both the configured alias and the resolved
object covered.
- Windows ACLs do not consume Codex glob syntax directly, so glob
deny-read entries are expanded to the concrete matches that exist before
process launch.
- Glob traversal deduplicates directory visits within each pattern walk
to avoid cycles, without collapsing distinct lexical roots that happen
to resolve to the same target.
- Persistent deny-read ACL state is keyed by sandbox principal SID, so
cleanup only removes ACEs owned by the same backend principal.
- Deny-read ACEs are fail-closed on the elevated path: setup aborts if
mandatory deny-read ACL application fails.
- Unelevated restricted-token sessions reject deny-read overrides early
instead of running with a silently unenforceable read policy.
## Verification
- `cargo test -p codex-core
windows_restricted_token_rejects_unreadable_split_carveouts`
- `just fmt`
- `just fix -p codex-core`
- `just fix -p codex-windows-sandbox`
- GitHub Actions rerun is in progress on the pushed head.
---------
Co-authored-by: Codex <noreply@openai.com>
## Why
Windows Bazel runs in the permissions stack exposed that app-server
integration tests were launching normal plugin startup warmups in every
subprocess. Those warmups can call
`https://chatgpt.com/backend-api/plugins/featured` when a test is not
specifically exercising plugin startup, which adds slow background work,
noisy stderr, and dependence on external network state. The relevant
startup/featured-plugin behavior was introduced across #15042 and
#15264.
A few app-server tests also had long optional waits or unbounded cleanup
paths, making failures expensive to diagnose and contributing to slow
Windows shards. One external-agent config test from #18246 used a
GitHub-style marketplace source, which was enough to exercise the
pending remote-import path but also meant the background completion task
could attempt a real clone.
## What Changed
- Adds explicit `AppServerRuntimeOptions` / `PluginStartupTasks`
plumbing and a hidden debug-only
`--disable-plugin-startup-tasks-for-tests` app-server flag, so
integration tests can suppress startup plugin warmups without adding a
production env-var gate.
- Has the app-server test harness pass that hidden flag by default,
while opting plugin-startup coverage back in for tests that
intentionally exercise startup sync and featured-plugin warmup behavior.
- Lowers normal app-server subprocess logging from `info`/`debug` to
`warn` to avoid multi-megabyte stderr output in Bazel logs.
- Prevents the external-agent config test from attempting a real
marketplace clone by using an invalid non-local source while still
exercising the pending-import completion path.
- Bounds optional filesystem/realtime waits and fake WebSocket
test-server shutdown so failures produce targeted timeouts instead of
hanging a shard.
- Fixes the Unix script-resolution test in `rmcp-client` to exercise
PATH resolution directly and include the actual spawn error in failures.
## Verification
- `cargo check -p codex-app-server`
- `cargo clippy -p codex-app-server --tests -- -D warnings`
- `cargo test -p codex-rmcp-client
program_resolver::tests::test_unix_executes_script_without_extension`
- `cargo test -p codex-app-server --test all
external_agent_config_import_sends_completion_notification_after_pending_plugins_finish
-- --nocapture`
- `cargo test -p codex-app-server --test all
plugin_list_uses_warmed_featured_plugin_ids_cache_on_first_request --
--nocapture`
- Windows Local Bazel passed with this test-hardening bundle before it
was extracted from #19606.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/19683).
* #19395
* #19394
* #19393
* #19392
* #19606
* __->__ #19683
## Summary
- add experimental turn/start.environments params for per-turn
environment id + cwd selections
- pass selections through core protocol ops and resolve them with
EnvironmentManager before TurnContext creation
- treat omitted selections as default behavior, empty selections as no
environment, and non-empty selections as first environment/cwd as the
turn primary
## Testing
- ran `just fmt`
- ran `just write-app-server-schema`
- not run: unit tests for this stacked PR
---------
Co-authored-by: Codex <noreply@openai.com>
## Summary
- Add the executor-backed RMCP stdio transport.
- Wire MCP stdio placement through the executor environment config.
- Cover local and executor-backed stdio paths with the existing MCP test
helpers.
## Stack
```text
o #18027 [6/6] Fail exec client operations after disconnect
│
@ #18212 [5/6] Wire executor-backed MCP stdio
│
o #18087 [4/6] Abstract MCP stdio server launching
│
o #18020 [3/6] Add pushed exec process events
│
o #18086 [2/6] Support piped stdin in exec process API
│
o #18085 [1/6] Add MCP server environment config
│
o main
```
---------
Co-authored-by: Codex <noreply@openai.com>
## Why
This is a follow-up to #15360. That change fixed the `arg0` helper
setup, but `rmcp-client` still coerced stdio transport environment
values into UTF-8 `String`s before program resolution and process spawn.
If `PATH` or another inherited environment value contains non-UTF-8
bytes, that loses fidelity before it reaches `which` and `Command`.
## What changed
- change `create_env_for_mcp_server()` to return `HashMap<OsString,
OsString>` and read inherited values with `std::env::var_os()`
- change `TransportRecipe::Stdio.env`, `RmcpClient::new_stdio_client()`,
and `program_resolver::resolve()` to keep stdio transport env values in
`OsString` form within `rmcp-client`
- keep the `codex-core` config boundary stringly, but convert configured
stdio env values to `OsString` once when constructing the transport
- update the rmcp-client stdio test fixtures and callers to use
`OsString` env maps
- add a Unix regression test that verifies `create_env_for_mcp_server()`
preserves a non-UTF-8 `PATH`
## How to verify
- `cargo test -p codex-rmcp-client`
- `cargo test -p codex-core mcp_connection_manager`
- `just argument-comment-lint`
Targeted coverage in this change includes
`utils::tests::create_env_preserves_path_when_it_is_not_utf8`, while the
updated stdio transport path is exercised by the existing rmcp-client
tests that construct `RmcpClient::new_stdio_client()`.
## What?
Fixes MCP server initialization failures on Windows when using
script-based tools like `npx`, `pnpm`, and `yarn` that rely on
`.cmd`/`.bat` files rather than `.exe` binaries.
Fixes#2945
## Why?
Windows users encounter "program not found" errors when configuring MCP
servers with commands like `npx` in their `~/.codex/config.toml`. This
happens because:
- Tools like `npx` are batch scripts (`npx.cmd`) on Windows, not
executable binaries
- Rust's `std::process::Command` bypasses the shell and cannot execute
these scripts directly
- The Windows shell normally handles this by checking `PATHEXT` for
executable extensions
Without this fix, Windows users must specify full paths or add `.cmd`
extensions manually, which breaks cross-platform compatibility.
## How?
Added platform-specific program resolution using the `which` crate to
find the correct executable path:
- **Windows**: Resolves programs through PATH/PATHEXT to find
`.cmd`/`.bat` scripts
- **Unix**: Returns the program unchanged (no-op, as Unix handles
scripts natively)
### Changes
- Added `which = "6"` dependency to `mcp-client/Cargo.toml`
- Implemented `program_resolver` module in `mcp_client.rs` with
platform-specific resolution
- Added comprehensive tests for both Windows and Unix behavior
### Testing
Added platform-specific tests to verify:
- Unix systems execute scripts without extensions
- Windows fails without proper extensions
- Windows succeeds with explicit extensions
- Cross-platform resolution enables successful execution
**Tested on:**
- Windows 11 (NT 10.0.26100.0 x64)
- PowerShell 5.1 & 7+, CMD, Git Bash
- MCP servers: playwright, context7, supabase
- WSL (verified no regression)
**Local checks passed:**
```bash
cargo test && cargo clippy --tests && cargo fmt -- --config imports_granularity=Item
```
### Results
**Before:**
```
🖐 MCP client for `playwright` failed to start: program not found
```
**After:**
```
🖐 MCP client for `playwright` failed to start: request timed out
```
Windows users can now use simple commands like `npx` in their config
without specifying full paths or extensions. The timeout issue is a
separate concern that will be addressed in a follow-up PR.
---------
Co-authored-by: Eric Traut <etraut@openai.com>
