Shijie RaoandGitHub
fc8c6b7384
## Why Multi-agent v2 currently carries an explicit-request-only delegation rule in its static usage hint. That provides a safe default, but it prevents clients from selecting proactive delegation per turn without changing static guidance or rewriting prior model context. This change makes delegation mode a session selection that can be updated through `turn/start`, while deriving the effective model-visible mode separately for each turn. Eligible multi-agent v2 turns remain explicit-request-only unless proactive mode is both selected and enabled. ## What changed - Add the experimental `turn/start.multiAgentMode` parameter with `explicitRequestOnly` and `proactive` values. Omission retains the loaded session's current optional selection. - Add the default-off `features.multi_agent_mode` feature gate. Eligible multi-agent v2 turns use the selected mode when enabled; an unset selection or disabled gate resolves to `explicitRequestOnly`. - Treat mode prompting as inapplicable for multi-agent v1 and other unsupported session configurations, producing no multi-agent mode developer message rather than rejecting the turn. - Move the explicit-request-only rule out of the static v2 usage hint and into a bounded, tagged developer context fragment. - Emit the effective mode in initial context and only when that effective mode changes on later turns. - Persist the effective mode in `TurnContextItem` as the durable baseline for resume and context-update comparisons. Historical rollout items are not rewritten. Later mode developer messages establish the current rule incrementally. ## Not covered - Initial selection through `thread/start` and selected-mode reporting from thread lifecycle/settings APIs; those are isolated in the stacked #28792. - A TUI control or slash command for selecting the mode. - Persisting a preferred mode to `config.toml`; selection remains session/turn scoped. - Changes to multi-agent concurrency limits, tool availability, or model catalog capability declarations. - Rewriting historical rollout prompt items. Cold resume restores the latest persisted effective mode when available while leaving historical developer messages intact. ## Verification - `CARGO_INCREMENTAL=0 just test -p codex-core multi_agent_mode` - Focused app-server coverage verifies that `turn/start.multiAgentMode` produces proactive developer instructions for an eligible v2 turn. ## Stack Followed by #28792, which adds `thread/start` initialization and lifecycle/settings observability.
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. Temporary blockers use a
source-local skip_if_wine_exec! call and reason.
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.