feat(devcontainer): add separate secure customer profile (#10431)

## Description

Keeps the existing Codex contributor devcontainer in place and adds a
separate secure profile for customer use.

## What changed

- leaves `.devcontainer/devcontainer.json` and the contributor
`Dockerfile` aligned with `main`
- adds `.devcontainer/devcontainer.secure.json` and
`.devcontainer/Dockerfile.secure`
- adds secure-profile bootstrap scripts:
  - `post_install.py`
  - `post-start.sh`
  - `init-firewall.sh`
- updates `.devcontainer/README.md` to explain when to use each path

## Secure profile behavior

The new secure profile is opt-in and is meant for running Codex in a
stricter project container:

- preinstalls the Codex CLI plus common build tools
- uses persistent volumes for Codex state, Cargo, Rustup, and GitHub
auth
- applies an allowlist-driven outbound firewall at startup
- blocks IPv6 by default so the allowlist cannot be bypassed via AAAA
routes
- keeps the stricter networking isolated from the default contributor
workflow

## Resulting behavior

- `devcontainer.json` remains the low-friction Codex contributor setup
- `devcontainer.secure.json` is the customer-facing secure option
- the repo supports both workflows without forcing the secure profile on
Codex contributors

.devcontainer/README.md

@@ -1,10 +1,36 @@
 # Containerized Development
 
-We provide the following options to facilitate Codex development in a container. This is particularly useful for verifying the Linux build when working on a macOS host.
+We provide two container paths:
+
+- `devcontainer.json` keeps the existing Codex contributor setup for working on this repository.
+- `devcontainer.secure.json` adds a customer-oriented profile with stricter outbound network controls.
+
+## Codex contributor profile
+
+Use `devcontainer.json` when you are developing Codex itself. This is the same lightweight arm64 container that already exists in the repo.
+
+## Secure customer profile
+
+Use `devcontainer.secure.json` when you want a stricter runtime profile for running Codex inside a project container:
+
+- installs the Codex CLI plus common build tools
+- enables firewall startup with an allowlist-driven outbound policy
+- blocks IPv6 by default so the allowlist cannot be bypassed over AAAA routes
+- requires `NET_ADMIN` and `NET_RAW` so the firewall can be installed at startup
+
+This profile keeps the stricter networking isolated to the customer path instead of changing the default Codex contributor container.
+
+Start it from the CLI with:
+
+```bash
+devcontainer up --workspace-folder . --config .devcontainer/devcontainer.secure.json
+```
+
+In VS Code, choose **Dev Containers: Open Folder in Container...** and select `.devcontainer/devcontainer.secure.json`.
 
 ## Docker
 
-To build the Docker image locally for x64 and then run it with the repo mounted under `/workspace`:
+To build the contributor image locally for x64 and then run it with the repo mounted under `/workspace`:
 
 ```shell
 CODEX_DOCKER_IMAGE_NAME=codex-linux-dev
@@ -14,17 +40,6 @@ docker run --platform=linux/amd64 --rm -it -e CARGO_TARGET_DIR=/workspace/codex-
 
 Note that `/workspace/target` will contain the binaries built for your host platform, so we include `-e CARGO_TARGET_DIR=/workspace/codex-rs/target-amd64` in the `docker run` command so that the binaries built inside your container are written to a separate directory.
 
-For arm64, specify `--platform=linux/amd64` instead for both `docker build` and `docker run`.
+For arm64, specify `--platform=linux/arm64` instead for both `docker build` and `docker run`.
 
-Currently, the `Dockerfile` works for both x64 and arm64 Linux, though you need to run `rustup target add x86_64-unknown-linux-musl` yourself to install the musl toolchain for x64.
-
-## VS Code
-
-VS Code recognizes the `devcontainer.json` file and gives you the option to develop Codex in a container. Currently, `devcontainer.json` builds and runs the `arm64` flavor of the container.
-
-From the integrated terminal in VS Code, you can build either flavor of the `arm64` build (GNU or musl):
-
-```shell
-cargo build --target aarch64-unknown-linux-musl
-cargo build --target aarch64-unknown-linux-gnu
-```
+Currently, the contributor `Dockerfile` works for both x64 and arm64 Linux, though you need to run `rustup target add x86_64-unknown-linux-musl` yourself to install the musl toolchain for x64.