[codex] Restore setup helper UAC manifest (#25949)

## Why

#23764 removed Windows resource stamping from `codex-windows-sandbox`,
but it also removed the setup helper's UAC manifest. That manifest was
doing more than cosmetic version metadata: Microsoft documents
`requestedExecutionLevel level="asInvoker"` as the setting that makes an
executable run at the same permission level as the process that started
it:
https://learn.microsoft.com/en-us/windows/win32/sbscs/application-manifests#trustinfo

In the reported session, `codex-windows-sandbox-setup.exe` was launched
for a non-elevated setup refresh and `CreateProcess` failed with `os
error 740` (`The requested operation requires elevation`). Restoring an
explicit `asInvoker` manifest records the helper's intended default
launch contract: normal launches inherit the caller's token, and
elevation only happens through the code paths that request it
explicitly.

The setup helper has two launch modes:

- setup refresh uses a normal `Command::new(...)` spawn and should never
trigger UAC
- full setup explicitly uses `ShellExecuteExW` with the `runas` verb
when elevation is required

Restoring `asInvoker` keeps refresh non-elevated by default while
preserving the explicit elevated path for full setup.

## What changed

- Restored a minimal `codex-windows-sandbox-setup.manifest` containing
only `requestedExecutionLevel level="asInvoker"`.
- Added a small build script that passes setup-helper-scoped manifest
linker args for MSVC and the Windows GNU/LLVM target used by Bazel.
- Wired the manifest into Bazel build-script data.

This does not restore `winres`, `FileDescription`, `ProductName`, or
package-wide resource stamping, so other Codex binaries that link
`codex-windows-sandbox` do not inherit metadata from this package.

## Verification

- `cargo fmt -p codex-windows-sandbox`
- `cargo build -p codex-windows-sandbox --bin
codex-windows-sandbox-setup`
- `cargo build -p codex-windows-sandbox --bin codex-command-runner`
- `cargo build -p codex-windows-sandbox --lib`
- Build-script output simulation for `CARGO_CFG_TARGET_ENV=msvc` emits
`/MANIFEST:EMBED` and `/MANIFESTINPUT:<manifest>`.
- Build-script output simulation for `CARGO_CFG_TARGET_ENV=gnu` +
`CARGO_CFG_TARGET_ABI=llvm` emits `-Wl,-Xlink=/manifest:embed` and
`-Wl,-Xlink=/manifestinput:<manifest>`.
- Inspected the built binaries and confirmed:
- `codex-windows-sandbox-setup.exe` contains `requestedExecutionLevel` /
`asInvoker`
  - `codex-command-runner.exe` does not contain those manifest strings
- Windows `VersionInfo` remains blank for `FileDescription` /
`ProductName`
- `just test -p codex-windows-sandbox` ran through Nextest, with 114
passing, 2 skipped, and 1 existing Windows sandbox failure:
`unified_exec::tests::legacy_non_tty_cmd_emits_output` fails with
`CreateRestrictedToken failed: 87`.

codex-rs/windows-sandbox-rs/BUILD.bazel

@@ -3,4 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "windows-sandbox-rs",
     crate_name = "codex_windows_sandbox",
+    build_script_data = [
+        "codex-windows-sandbox-setup.manifest",
+    ],
 )

codex-rs/windows-sandbox-rs/Cargo.toml

@@ -1,4 +1,5 @@
 [package]
+build = "build.rs"
 edition.workspace = true
 license.workspace = true
 name = "codex-windows-sandbox"

codex-rs/windows-sandbox-rs/build.rs

@@ -0,0 +1,39 @@
+use std::env;
+use std::path::PathBuf;
+
+const SETUP_BIN: &str = "codex-windows-sandbox-setup";
+const SETUP_MANIFEST: &str = "codex-windows-sandbox-setup.manifest";
+
+fn main() {
+    println!("cargo:rerun-if-changed={SETUP_MANIFEST}");
+
+    if env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("windows") {
+        return;
+    }
+
+    let manifest_path = PathBuf::from(
+        env::var_os("CARGO_MANIFEST_DIR")
+            .expect("CARGO_MANIFEST_DIR should be set for build scripts"),
+    )
+    .join(SETUP_MANIFEST);
+    let manifest_path = manifest_path.display();
+
+    // Keep this scoped to the setup helper so Codex binaries that link the
+    // library do not inherit any resource metadata from this package.
+    match (
+        env::var("CARGO_CFG_TARGET_ENV").as_deref(),
+        env::var("CARGO_CFG_TARGET_ABI").as_deref(),
+    ) {
+        (Ok("msvc"), _) => {
+            println!("cargo:rustc-link-arg-bin={SETUP_BIN}=/MANIFEST:EMBED");
+            println!("cargo:rustc-link-arg-bin={SETUP_BIN}=/MANIFESTINPUT:{manifest_path}");
+        }
+        (Ok("gnu"), Ok("llvm")) => {
+            println!("cargo:rustc-link-arg-bin={SETUP_BIN}=-Wl,-Xlink=/manifest:embed");
+            println!(
+                "cargo:rustc-link-arg-bin={SETUP_BIN}=-Wl,-Xlink=/manifestinput:{manifest_path}"
+            );
+        }
+        _ => {}
+    }
+}

codex-rs/windows-sandbox-rs/codex-windows-sandbox-setup.manifest

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
+  <trustInfo xmlns="urn:schemas-microsoft-com:asm.v2">
+    <security>
+      <requestedPrivileges>
+        <requestedExecutionLevel level="asInvoker" uiAccess="false"/>
+      </requestedPrivileges>
+    </security>
+  </trustInfo>
+</assembly>