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## Why When Codex uses a remote `ExecutorFileSystem`, every `get_metadata` call is an exec-server round trip. Upward discovery currently pays those round trips serially in two latency-sensitive places: - session startup, while locating the configured project root before loading `AGENTS.md`; and - Git-root discovery, which runs before per-turn Git diff enrichment. The goal is to remove the serial ancestor dependency without adding a new filesystem RPC, JSON-RPC batch method, Git executable dependency, or cache. ## Example Assume this layout, with `.git` as the configured project-root marker: ```text /workspace/repo/.git /workspace/repo/AGENTS.md /workspace/repo/crates/core/ <- cwd ``` The marker probes have this required precedence: ```text 1. /workspace/repo/crates/core/.git 2. /workspace/repo/crates/.git 3. /workspace/repo/.git 4. /workspace/.git 5. /.git ``` Previously, probe 2 was not sent until probe 1 returned, and probe 3 was not sent until probe 2 returned. With this change, the client lazily keeps up to eight ordinary `fs/getMetadata` requests in flight, but consumes their results in the order above. Codex must still learn that probes 1 and 2 are absent before accepting probe 3, so the nearest root always wins. Once probe 3 succeeds, the client has its answer and stops awaiting probes 4 and 5. Requests that were already sent may still finish on the worker. For the marker phase alone, with a 50 ms client-to-worker round trip and fast local metadata calls, finding the root at probe 3 changes from roughly three serialized round trips (150 ms) to one round trip plus worker processing. The later `AGENTS.md` candidate phase remains separate and ordered. Only after `/workspace/repo` is selected does `AGENTS.md` discovery check instruction candidates, in root-to-cwd order: ```text /workspace/repo/AGENTS.override.md /workspace/repo/AGENTS.md /workspace/repo/crates/AGENTS.override.md /workspace/repo/crates/AGENTS.md /workspace/repo/crates/core/AGENTS.override.md /workspace/repo/crates/core/AGENTS.md ``` The first configured candidate found in each directory wins. These checks remain ordered and no instruction candidate above `/workspace/repo` is issued. Git-root discovery uses the same bounded lookup with only `.git` as the marker. ## What changed - Added a client-side find-up helper that generates `ancestor x marker` probes lazily, nearest directory first and configured marker order within each directory. - Uses an ordered concurrency window of eight scalar metadata requests. This bounds executor load while preserving nearest-root and marker precedence. - Reuses the helper for both configured project-root discovery and remote Git-root discovery. - Keeps Git ancestor and marker construction in `AbsolutePathBuf`, converting only each complete `.git` probe to `PathUri`. This preserves native paths that require an opaque URI fallback, such as Windows namespace paths. - Preserves existing error behavior: `AGENTS.md` discovery propagates non-`NotFound` metadata errors, while Git discovery treats a failed marker probe as absent and continues upward. - Reads each discovered `AGENTS.md` directly instead of statting it a second time. No filesystem trait or exec-server protocol method is added. An empty `project_root_markers` list performs no ancestor-marker I/O and checks instruction candidates only in `cwd`. This change also deliberately does not cache roots across turns. ## Symlinks Upward traversal remains **lexical**. The helper does not canonicalize `cwd`; it appends marker names to the supplied path and walks that path's textual parents. The filesystem performs the actual metadata/read operation, and the current local and exec-server implementations follow live symlink targets. For example: ```text /tmp/pkg -> /workspace/repo/packages/pkg cwd = /tmp/pkg/src actual Git marker = /workspace/repo/.git ``` The lexical probes are `/tmp/pkg/src/.git`, `/tmp/pkg/.git`, `/tmp/.git`, and `/.git`. They do not jump from `/tmp/pkg` to the target's parent `/workspace/repo`, so this spelling of `cwd` does not discover `/workspace/repo/.git`. That is the existing behavior and is unchanged by this PR. Conversely, if `/tmp/repo -> /workspace/repo`, then probing `/tmp/repo/.git` follows the directory symlink and finds `/workspace/repo/.git`; the reported root remains the lexical path `/tmp/repo`. A live symlink used directly as `.git`, another configured marker, or `AGENTS.md` is also followed. A symlinked `AGENTS.md` is loaded when its target is a regular file, while a broken symlink behaves as `NotFound`.
codex-core
This crate implements the business logic for Codex. It is designed to be used by the various Codex UIs written in Rust.
Wine-exec integration tests
On x86-64 Linux, run the shared suite against the Windows exec server with
bazel test //codex-rs/core:core-all-wine-exec-test.
Local execution targets the host OS, Docker targets Linux, and Wine exec targets Windows. Choose the skip macro by what the test depends on:
skip_if_target_windows!: Windows target behavior.skip_if_host_windows!: Windows host constraints.skip_if_remote!: Local-only test behavior.skip_if_no_remote_env!: Remote-only test behavior.skip_if_wine_exec!: Wine-specific runner debt.
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.