fix: support arm64 build for Linux (#1225)

Users were running into issues with glibc mismatches on arm64 linux. In
the past, we did not provide a musl build for arm64 Linux because we had
trouble getting the openssl dependency to build correctly. Though today
I just tried the same trick in `Cargo.toml` that we were doing for
`x86_64-unknown-linux-musl` (using `openssl-sys` with `features =
["vendored"]`), so I'm not sure what problem we had in the past the
builds "just worked" today!

Though one tweak that did have to be made is that the integration tests
for Seccomp/Landlock empirically require longer timeouts on arm64 linux,
or at least on the `ubuntu-24.04-arm` GitHub Runner. As such, we change
the timeouts for arm64 in `codex-rs/linux-sandbox/tests/landlock.rs`.

Though in solving this problem, I decided I needed a turnkey solution
for testing the Linux build(s) from my Mac laptop, so this PR introduces
`.devcontainer/Dockerfile` and `.devcontainer/devcontainer.json` to
facilitate this. Detailed instructions are in `.devcontainer/README.md`.

We will update `dotslash-config.json` and other release-related scripts
in a follow-up PR.

.devcontainer/Dockerfile

@@ -0,0 +1,29 @@
+FROM ubuntu:22.04
+
+ARG DEBIAN_FRONTEND=noninteractive
+# enable 'universe' because musl-tools & clang live there
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+    software-properties-common && \
+    add-apt-repository --yes universe
+
+# now install build deps
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+    build-essential curl git ca-certificates \
+    pkg-config clang musl-tools libssl-dev && \
+    rm -rf /var/lib/apt/lists/*
+
+# non-root dev user
+ARG USER=dev
+ARG UID=1000
+RUN useradd -m -u $UID $USER
+USER $USER
+
+# install Rust + musl target as dev user
+RUN curl -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal && \
+    ~/.cargo/bin/rustup target add aarch64-unknown-linux-musl
+
+ENV PATH="/home/${USER}/.cargo/bin:${PATH}"
+
+WORKDIR /workspace

.devcontainer/README.md

@@ -0,0 +1,30 @@
+# 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.
+
+## Docker
+
+To build the Docker image locally for x64 and then run it with the repo mounted under `/workspace`:
+
+```shell
+CODEX_DOCKER_IMAGE_NAME=codex-linux-dev
+docker build --platform=linux/amd64 -t "$CODEX_DOCKER_IMAGE_NAME" ./.devcontainer
+docker run --platform=linux/amd64 --rm -it -e CARGO_TARGET_DIR=/workspace/codex-rs/target-amd64 -v "$PWD":/workspace -w /workspace/codex-rs "$CODEX_DOCKER_IMAGE_NAME"
+```
+
+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`.
+
+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
+```

.devcontainer/devcontainer.json

@@ -0,0 +1,29 @@
+{
+  "name": "Codex",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "context": "..",
+    "platform": "linux/arm64"
+  },
+
+  /* Force VS Code to run the container as arm64 in
+     case your host is x86 (or vice-versa). */
+  "runArgs": ["--platform=linux/arm64"],
+
+  "containerEnv": {
+    "RUST_BACKTRACE": "1",
+    "CARGO_TARGET_DIR": "${containerWorkspaceFolder}/codex-rs/target-arm64"
+  },
+
+  "remoteUser": "dev",
+  "customizations": {
+    "vscode": {
+      "settings": {
+          "terminal.integrated.defaultProfile.linux": "bash"
+      },
+      "extensions": [
+          "rust-lang.rust-analyzer"
+      ],
+    }
+  }
+}