test: generalize exec-server fixture (#31422)

## Why

Remote-executor integration tests need one host-agnostic exec-server
fixture target instead of a Windows-only wrapper.

## What

- rename the testing binary target to exec-server
- make the fixture source and target host-agnostic
- update Windows remote-executor test wiring to use the shared target

## Validation

- bazel build //codex-rs/exec-server/testing:exec-server
- bazel cquery --config=ci-windows-cross
'set(//codex-rs/exec-server/testing:exec-server
//codex-rs/core/tests/remote_env_windows:smoke-test)'

## Stack

1. [#31422 test: generalize exec-server
fixture](https://github.com/openai/codex/pull/31422)
2. [#31425 test: add TestAppServer
builder](https://github.com/openai/codex/pull/31425)
3. [#31427 test: add delayed exec-server
transport](https://github.com/openai/codex/pull/31427)
4. [#31295 bench: add cold skill load
macrobenchmark](https://github.com/openai/codex/pull/31295)
5. [#31428 bench: add e2e benchmark
entrypoints](https://github.com/openai/codex/pull/31428)
6. [#31429 ci: smoke Bazel e2e
benchmarks](https://github.com/openai/codex/pull/31429)

codex-rs/core/tests/remote_env_windows/BUILD.bazel

@@ -7,7 +7,7 @@ wine_rust_test(
     crate_name = "remote_env_windows_test",
     crate_root = "remote_env_windows_test.rs",
     windows_binaries = {
-        "wine-windows-exec-server": "//codex-rs/exec-server/testing:windows-exec-server",
+        "wine-windows-exec-server": "//codex-rs/exec-server/testing:exec-server",
     },
     deps = [
         "//codex-rs/core/tests/common",

codex-rs/exec-server/testing/BUILD.bazel

@@ -32,13 +32,11 @@ rust_binary(
 )
 
 rust_binary(
-    name = "windows-exec-server",
+    name = "exec-server",
     testonly = True,
-    srcs = ["windows_exec_server.rs"],
-    crate_name = "windows_exec_server",
-    crate_root = "windows_exec_server.rs",
-    tags = ["manual"],
-    target_compatible_with = ["@platforms//os:windows"],
+    srcs = ["exec_server.rs"],
+    crate_name = "exec_server",
+    crate_root = "exec_server.rs",
     visibility = ["//visibility:public"],
     deps = [
         "//codex-rs/exec-server",

codex-rs/exec-server/testing/exec_server.rs

@@ -0,0 +1,14 @@
+//! Minimal exec-server fixture for Bazel-only integration tests.
+//!
+//! Linking only exec-server avoids depending on the full Codex CLI binary
+//! when a test only needs a WebSocket executor endpoint.
+
+use codex_exec_server::ExecServerRuntimePaths;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    let current_exe = std::env::current_exe()?;
+    let runtime_paths =
+        ExecServerRuntimePaths::new(current_exe, /*codex_linux_sandbox_exe*/ None)?;
+    codex_exec_server::run_main("ws://127.0.0.1:0", runtime_paths).await
+}

codex-rs/exec-server/testing/windows_exec_server.rs

@@ -1,18 +0,0 @@
-//! Minimal Windows exec-server fixture for cross-platform tests.
-//!
-//! Keeping this wrapper separate avoids depending on the full Codex binary's
-//! Windows cross-build, which is not yet supported by the Bazel graph. Linking
-//! only the exec-server also makes the Wine test substantially faster to
-//! iterate on.
-
-use codex_exec_server::ExecServerRuntimePaths;
-
-#[tokio::main]
-async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
-    let current_exe = std::env::current_exe()?;
-    // This fixture is always a Windows executable, so it neither invokes nor
-    // needs the separate Linux sandbox binary.
-    let runtime_paths =
-        ExecServerRuntimePaths::new(current_exe, /*codex_linux_sandbox_exe*/ None)?;
-    codex_exec_server::run_main("ws://127.0.0.1:0", runtime_paths).await
-}

defs.bzl

@@ -538,7 +538,7 @@ def codex_rust_crate(
             wine_exec_server = wine_test_name + "-windows-exec-server"
             foreign_platform_binary(
                 name = wine_exec_server,
-                binary = "//codex-rs/exec-server/testing:windows-exec-server",
+                binary = "//codex-rs/exec-server/testing:exec-server",
                 extra_rustc_flags = WINDOWS_GNULLVM_RUSTC_LINK_FLAGS,
                 platform = "//:windows_x86_64_gnullvm",
                 tags = ["manual"],