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codex/codex-rs/core
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iceweasel-oai e7a9988d1a Add Windows unified exec yield floor (#27086)
## Why

The Windows `unified_exec` experiment regressed at the turn level in a
way that points to premature backgrounding / extra command cycles rather
than individual responses getting heavier:

- `codex_local_tool_calls_per_turn` was up about 20.7%.
- `codex_local_blended_tokens_per_turn` was up about 4.1%, and
`codex_local_output_tokens_per_turn` was up about 4.0%.
- `codex_local_response_latency_per_turn` was up about 8.3%.
- The primary activity metrics also moved down: `codex_turns` about
-6.6%, `codex_dau` about -1.0%, and `codex_local_hourly_active_users`
about -3.0%.

At the same time, the per-response metrics moved in the other direction:
blended tokens per response, output tokens per response, and latency per
response were all lower in test. That suggests the bad turn-level shape
is largely about extra tool/model cycles, not each response being slower
or more expensive on its own.

Local Windows benchmarking showed the likely mechanism: shell-wrapped
commands pay a large PowerShell startup/teardown tax before the actual
command has much time to run. In the benchmark, the PowerShell wrapper
added roughly 0.7-1.0s versus direct exec:

- Windows PowerShell: about 740ms p50 / 800ms p90 overhead versus direct
exec.
- PowerShell 7 (`pwsh`): about 930ms p50 / 980ms p90 overhead versus
direct exec.

The model commonly asks for a 1s initial yield. On Windows, that can
spend nearly the whole window waiting on PowerShell machinery, so
otherwise-short commands are more likely to return as background
sessions and require follow-up polling/tool calls.

This is intentionally a temporary unlock. It gives Windows closer to the
same useful post-shell command window as other platforms while we work
on reducing the PowerShell tax directly, for example with persistent
PowerShell workers or conservative direct-exec paths for commands that
do not need shell semantics.

## What changed

- Adds a Windows-only 2s floor to `unified_exec`'s initial
`yield_time_ms` clamp.
- Keeps larger model-requested waits unchanged, including the existing
10s default.
- Keeps the existing 30s max clamp.
- Leaves non-Windows behavior unchanged.
- Adds platform-gated tests for both the Windows floor and the
non-Windows clamp behavior.

## Verification

- `just test -p codex-core unified_exec`
e7a9988d1a ยท 2026-06-15 13:56:18 -07:00
History
..

codex-core

This crate implements the business logic for Codex. It is designed to be used by the various Codex UIs written in Rust.

Dependencies

Note that codex-core makes some assumptions about certain helper utilities being available in the environment. Currently, this support matrix is:

macOS

Expects /usr/bin/sandbox-exec to be present.

When using the workspace-write sandbox policy, the Seatbelt profile allows writes under the configured writable roots while keeping .git (directory or pointer file), the resolved gitdir: target, and .codex read-only.

Network access and filesystem read/write roots are controlled by SandboxPolicy. Seatbelt consumes the resolved policy and enforces it.

Seatbelt also keeps the legacy default preferences read access (user-preference-read) needed for cfprefs-backed macOS behavior.

Linux

Expects the binary containing codex-core to run the equivalent of codex sandbox when arg0 is codex-linux-sandbox. See the codex-arg0 crate for details.

Legacy SandboxPolicy / sandbox_mode configs are still supported on Linux. They can continue to use the legacy Landlock path when the split filesystem policy is sandbox-equivalent to the legacy model after cwd resolution. Split filesystem policies that need direct FileSystemSandboxPolicy enforcement, such as read-only or denied carveouts under a broader writable root, automatically route through bubblewrap. The legacy Landlock path is used only when the split filesystem policy round-trips through the legacy SandboxPolicy model without changing semantics. That includes overlapping cases like /repo = write, /repo/a = none, /repo/a/b = write, where the more specific writable child must reopen under a denied parent.

The Linux sandbox helper prefers the first bwrap found on PATH outside the current working directory whenever it is available. If bwrap is present but too old to support --argv0, the helper keeps using system bubblewrap and switches to a no---argv0 compatibility path for the inner re-exec. If bwrap is missing, it falls back to the bundled codex-resources/bwrap binary shipped with Codex and Codex surfaces a startup warning through its normal notification path instead of printing directly from the sandbox helper. Codex also surfaces a startup warning when bubblewrap cannot create user namespaces. WSL2 uses the normal Linux bubblewrap path. WSL1 is not supported for bubblewrap sandboxing because it cannot create the required user namespaces, so Codex rejects sandboxed shell commands that would enter the bubblewrap path before invoking bwrap.

Windows

Legacy SandboxPolicy / sandbox_mode configs are still supported on Windows. Legacy read-only and workspace-write policies imply full filesystem read access; exact readable roots are represented by split filesystem policies instead.

The elevated Windows sandbox also supports:

  • legacy ReadOnly and WorkspaceWrite behavior
  • split filesystem policies that need exact readable roots, exact writable roots, or extra read-only carveouts under writable roots
  • backend-managed system read roots required for basic execution, such as C:\Windows, C:\Program Files, C:\Program Files (x86), and C:\ProgramData, when a split filesystem policy requests platform defaults

The unelevated restricted-token backend still supports the legacy full-read Windows model for legacy ReadOnly and WorkspaceWrite behavior. It also supports a narrow split-filesystem subset: full-read split policies whose writable roots still match the legacy WorkspaceWrite root set, but add extra read-only carveouts under those writable roots.

New [permissions] / split filesystem policies remain supported on Windows only when they can be enforced directly by the selected Windows backend or round-trip through the legacy SandboxPolicy model without changing semantics. Policies that would require direct explicit unreadable carveouts (none) or reopened writable descendants under read-only carveouts still fail closed instead of running with weaker enforcement.

All Platforms

Expects the binary containing codex-core to simulate the virtual apply_patch CLI when arg1 is --codex-run-as-apply-patch. See the codex-arg0 crate for details.