Charlie Marsh
41b4fabbb4
## Summary We originally addressed startup prewarming holding the read side of `RwLock<McpConnectionManager>` by snapshotting tool-list state. Review feedback identified the broader ownership problem: the outer synchronization should only publish or retrieve the current manager, while MCP operations rely on the manager's internal synchronization. A follow-up preserved operation retirement with a separate gate, but further review questioned whether that synchronization was actually required and whether we could support latest-wins replacement instead. This PR now stores the current MCP manager in `ArcSwap`. Each operation uses `load_full()` to obtain an owned `Arc<McpConnectionManager>`, then performs MCP I/O without retaining the publication mechanism. Refresh cancels obsolete startup work, constructs a replacement, and atomically publishes it. New operations see the latest manager, while operations that already loaded the previous manager retain a valid handle. Refresh happens at a turn boundary, so there should be no active user tool calls to drain. Git history supports dropping the outer `RwLock`. It was introduced in `03ffe4d595` on November 17, 2025 for non-blocking MCP startup: the session published an empty manager, startup initialized that same object while holding the write lock, and readers waited for initialization. `7cd2e84026` on February 19, 2026 removed that two-phase initialization in favor of constructing a fresh manager and swapping it in, explicitly noting that `Option` or `OnceCell` could replace the placeholder design. Hot reload later reused the existing lock to publish a replacement, but I found no indication that the lock was introduced to guarantee in-flight tool calls finish before refresh or shutdown. Terminal shutdown remains separate from refresh: it aborts startup prewarming and active tasks before shutting down the current manager, so tool calls may be interrupted and no model WebSocket work continues after shutdown. Focused regression coverage exercises pending tool-list cancellation, deferred refresh, and startup-prewarm shutdown.
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
ReadOnlyandWorkspaceWritebehavior - 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), andC:\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.