## Why
Thread-scoped config needs a stable boundary between the app/session
owner and the config stack. Instead of having call sites manually copy
thread config fields into individual overrides, this adds the proto and
Rust plumbing needed for a `ThreadConfigLoader` implementation to return
typed sources that can be translated into ordinary config layer entries.
Keeping the remote payload typed also makes precedence easier to reason
about: session-owned thread config maps back to the existing session
config source, while user-owned thread config is represented separately
without introducing a new config-layer source until it has TOML-backed
fields.
## What changed
- Added the `codex.thread_config.v1` protobuf service and generated Rust
module for loading thread config sources.
- Added `RemoteThreadConfigLoader`, which calls the gRPC service, parses
`SessionThreadConfig` / `UserThreadConfig`, and validates provider
fields such as `wire_api`, auth timeout, and absolute auth cwd.
- Added proto generation tooling under
`config/scripts/generate-proto.sh` and
`config/examples/generate-proto.rs`.
- Added `ThreadConfigLoader::load_config_layers`, plus static/no-op
loader helpers, so tests and callers can use the same typed loader
interface while config-layer translation stays centralized.
## Verification
- `cargo test -p codex-config thread_config`
## Why
Codex needs a first-class `amazon-bedrock` model provider so users can
select Bedrock without copying a full provider definition into
`config.toml`. The provider has Codex-owned defaults for the pieces that
should stay consistent across users: the display `name`, Bedrock
`base_url`, and `wire_api`.
At the same time, users still need a way to choose the AWS credential
profile used by their local environment. This change makes
`amazon-bedrock` a partially modifiable built-in provider: code owns the
provider identity and endpoint defaults, while user config can set
`model_providers.amazon-bedrock.aws.profile`.
For example:
```toml
model_provider = "amazon-bedrock"
[model_providers.amazon-bedrock.aws]
profile = "codex-bedrock"
```
## What Changed
- Added `amazon-bedrock` to the built-in model provider map with:
- `name = "Amazon Bedrock"`
- `base_url = "https://bedrock-mantle.us-east-1.api.aws/v1"`
- `wire_api = "responses"`
- Added AWS provider auth config with a profile-only shape:
`model_providers.<id>.aws.profile`.
- Kept AWS auth config restricted to `amazon-bedrock`; custom providers
that set `aws` are rejected.
- Allowed `model_providers.amazon-bedrock` through reserved-provider
validation so it can act as a partial override.
- During config loading, only `aws.profile` is copied from the
user-provided `amazon-bedrock` entry onto the built-in provider. Other
Bedrock provider fields remain hard-coded by the built-in definition.
- Updated the generated config schema for the new provider AWS profile
config.
## Why
Cloud-hosted sessions need a way for the service that starts or manages
a thread to provide session-owned config without treating all config as
if it came from the same user/project/workspace TOML stack.
The important boundary is ownership: some values should be controlled by
the session/orchestrator, some by the authenticated user, and later some
may come from the executor. The earlier broad config-store shape made
that boundary too fuzzy and overlapped heavily with the existing
filesystem-backed config loader. This PR starts with the smaller piece
we need now: a typed session config loader that can feed the existing
config layer stack while preserving the normal precedence and merge
behavior.
## What Changed
- Added `ThreadConfigLoader` and related typed payloads in
`codex-config`.
- `SessionThreadConfig` currently supports `model_provider`,
`model_providers`, and feature flags.
- `UserThreadConfig` is present as an ownership boundary, but does not
yet add TOML-backed fields.
- `NoopThreadConfigLoader` preserves existing behavior when no external
loader is configured.
- `StaticThreadConfigLoader` supports tests and simple callers.
- Taught thread config sources to produce ordinary `ConfigLayerEntry`
values so the existing `ConfigLayerStack` remains the place where
precedence and merging happen.
- Wired the loader through `ConfigBuilder`, the config loader, and
app-server startup paths so app-server can provide session-owned config
before deriving a thread config.
- Added coverage for:
- translating typed thread config into config layers,
- inserting thread config layers into the stack at the right precedence,
- applying session-provided model provider and feature settings when
app-server derives config from thread params.
## Follow-Ups
This intentionally stops short of adding the remote/service transport.
The next pieces are expected to be:
1. Define the proto/API shape for this interface.
2. Add a client implementation that can source session config from the
service side.
## Verification
- Added unit coverage in `codex-config` for the loader and layer
conversion.
- Added `codex-core` config loader coverage for thread config layer
precedence.
- Added app-server coverage that verifies session thread config wins
over request-provided config for model provider and feature settings.
Rasmus Rygaard