## Why
This is a prep PR in the multi-environment process-tool stack. It
separates ownership/config cleanup from the behavior change that teaches
process tools to route by selected environment, so the follow-up PR can
focus on model-facing `environment_id` behavior.
## Stack
1. https://github.com/openai/codex/pull/20646 - `EnvironmentContext`
rendering for selected environments
2. https://github.com/openai/codex/pull/20669 - selected-environment
ownership and tool config prep (this PR)
3. https://github.com/openai/codex/pull/20647 - process-tool
`environment_id` routing
## What Changed
- keep the resolved turn environment list wrapped in
`ResolvedTurnEnvironments` through `TurnContext` instead of unwrapping
it back to a raw `Vec`
- add `TurnContext::resolve_path_against` so cwd-relative path
resolution has one shared helper
- replace the old tool config boolean with `ToolEnvironmentMode::{None,
Single, Multiple}`
## Testing
- Tests not run locally; this prep refactor is covered by GitHub CI for
the stack.
Co-authored-by: Codex <noreply@openai.com>
## Why
The model needs a way to see which environments are available during a
multi-environment turn without changing the legacy single-environment
prompt surface or pulling replay/persistence changes into the same
review.
## Stack
1. https://github.com/openai/codex/pull/20646 - `EnvironmentContext`
rendering for selected environments (this PR)
2. https://github.com/openai/codex/pull/20669 - selected-environment
ownership and tool config prep
3. https://github.com/openai/codex/pull/20647 - process-tool
`environment_id` routing
## What Changed
- extend `environment_context` so multi-environment turns render an
`<environments>` block with the selected environment ids and cwd values
- keep zero- and single-environment turns on the existing cwd-only
render path
- keep replay and persistence paths on the legacy surface for now so
this PR stays scoped to live prompt rendering
- add focused coverage in
`codex-rs/core/src/context/environment_context_tests.rs`
## Testing
- CI
---------
Co-authored-by: Codex <noreply@openai.com>
## Summary
- make selected turn environments the source of truth for session
runtime cwd and MCP runtime environment selection
- keep local/no-selection fallback behavior intact
- add coverage for duplicate selected environments, cwd resolution, and
MCP runtime environment selection
## Validation
- git diff --check
- rustfmt was run on touched Rust files during the implementation
workflow
CI should provide the full Bazel/test signal.
---------
Co-authored-by: Codex <noreply@openai.com>
## Summary
- Change `EnvironmentProvider` to return concrete `Environment`
instances instead of `EnvironmentConfigurations`.
- Make `DefaultEnvironmentProvider` provide the provider-visible `local`
environment plus optional `remote` environment from
`CODEX_EXEC_SERVER_URL`.
- Keep `EnvironmentManager` as the concrete cache while exposing its own
explicit local environment for `local_environment()` fallback paths.
## Validation
- `just fmt`
- `git diff --check`
---------
Co-authored-by: Codex <noreply@openai.com>
