feat: introduce codex-utils-cargo-bin as an alternative to assert_cmd::Command

AGENTS.md

@@ -77,6 +77,12 @@ If you don’t have the tool:
 - Prefer deep equals comparisons whenever possible. Perform `assert_eq!()` on entire objects, rather than individual fields.
 - Avoid mutating process environment in tests; prefer passing environment-derived flags or dependencies from above.
 
+### Spawning workspace binaries in tests (Cargo vs Buck2)
+
+- Prefer `codex_utils_cargo_bin::cargo_bin("...")` over `assert_cmd::Command::cargo_bin(...)` or `escargot` when tests need to spawn first-party binaries.
+  - Under Buck2, `CARGO_BIN_EXE_*` may be project-relative (e.g. `buck-out/...`), which breaks if a test changes its working directory. `codex_utils_cargo_bin::cargo_bin` resolves to an absolute path first.
+- When locating fixture files under Buck2, avoid `env!("CARGO_MANIFEST_DIR")` (Buck codegen sets it to `"."`). Prefer deriving paths from `codex_utils_cargo_bin::buck_project_root()` when needed.
+
 ### Integration tests (core)
 
 - Prefer the utilities in `core_test_support::responses` when writing end-to-end Codex tests.

codex-rs/Cargo.lock

@@ -329,12 +329,12 @@ name = "app_test_support"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "assert_cmd",
  "base64",
  "chrono",
  "codex-app-server-protocol",
  "codex-core",
  "codex-protocol",
+ "codex-utils-cargo-bin",
  "core_test_support",
  "serde",
  "serde_json",
@@ -993,7 +993,6 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "app_test_support",
- "assert_cmd",
  "base64",
  "chrono",
  "codex-app-server-protocol",
@@ -1064,6 +1063,7 @@ dependencies = [
  "anyhow",
  "assert_cmd",
  "assert_matches",
+ "codex-utils-cargo-bin",
  "pretty_assertions",
  "similar",
  "tempfile",
@@ -1161,6 +1161,7 @@ dependencies = [
  "codex-tui",
  "codex-tui2",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
  "codex-windows-sandbox",
  "ctor 0.5.0",
  "libc",
@@ -1285,6 +1286,7 @@ dependencies = [
  "codex-protocol",
  "codex-rmcp-client",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
  "codex-utils-pty",
  "codex-utils-readiness",
  "codex-utils-string",
@@ -1360,6 +1362,7 @@ dependencies = [
  "codex-core",
  "codex-protocol",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
  "core_test_support",
  "libc",
  "mcp-types",
@@ -1385,11 +1388,11 @@ name = "codex-exec-server"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "assert_cmd",
  "async-trait",
  "clap",
  "codex-core",
  "codex-execpolicy",
+ "codex-utils-cargo-bin",
  "exec_server_test_support",
  "libc",
  "maplit",
@@ -1548,7 +1551,6 @@ name = "codex-mcp-server"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "assert_cmd",
  "codex-arg0",
  "codex-common",
  "codex-core",
@@ -1672,8 +1674,8 @@ dependencies = [
  "axum",
  "codex-keyring-store",
  "codex-protocol",
+ "codex-utils-cargo-bin",
  "dirs",
- "escargot",
  "futures",
  "keyring",
  "mcp-types",
@@ -1700,6 +1702,7 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "assert_cmd",
+ "codex-utils-cargo-bin",
  "pretty_assertions",
  "tempfile",
  "uds_windows",
@@ -1866,6 +1869,14 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "codex-utils-cargo-bin"
+version = "0.0.0"
+dependencies = [
+ "assert_cmd",
+ "thiserror 2.0.17",
+]
+
 [[package]]
 name = "codex-utils-image"
 version = "0.0.0"
@@ -2069,6 +2080,7 @@ dependencies = [
  "codex-core",
  "codex-protocol",
  "codex-utils-absolute-path",
+ "codex-utils-cargo-bin",
  "notify",
  "pretty_assertions",
  "regex-lite",
@@ -2788,8 +2800,8 @@ name = "exec_server_test_support"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "assert_cmd",
  "codex-core",
+ "codex-utils-cargo-bin",
  "rmcp",
  "serde_json",
  "tokio",
@@ -4157,9 +4169,9 @@ name = "mcp_test_support"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "assert_cmd",
  "codex-core",
  "codex-mcp-server",
+ "codex-utils-cargo-bin",
  "core_test_support",
  "mcp-types",
  "os_info",

codex-rs/Cargo.toml

@@ -36,6 +36,7 @@ members = [
     "tui",
     "tui2",
     "utils/absolute-path",
+    "utils/cargo-bin",
     "utils/git",
     "utils/cache",
     "utils/image",
@@ -93,6 +94,7 @@ codex-tui = { path = "tui" }
 codex-tui2 = { path = "tui2" }
 codex-utils-absolute-path = { path = "utils/absolute-path" }
 codex-utils-cache = { path = "utils/cache" }
+codex-utils-cargo-bin = { path = "utils/cargo-bin" }
 codex-utils-image = { path = "utils/image" }
 codex-utils-json-to-toml = { path = "utils/json-to-toml" }
 codex-utils-pty = { path = "utils/pty" }

codex-rs/app-server/Cargo.toml

@@ -48,7 +48,6 @@ uuid = { workspace = true, features = ["serde", "v7"] }
 
 [dev-dependencies]
 app_test_support = { workspace = true }
-assert_cmd = { workspace = true }
 base64 = { workspace = true }
 core_test_support = { workspace = true }
 mcp-types = { workspace = true }

codex-rs/app-server/tests/common/Cargo.toml

@@ -9,12 +9,12 @@ path = "lib.rs"
 
 [dependencies]
 anyhow = { workspace = true }
-assert_cmd = { workspace = true }
 base64 = { workspace = true }
 chrono = { workspace = true }
 codex-app-server-protocol = { workspace = true }
 codex-core = { workspace = true, features = ["test-support"] }
 codex-protocol = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true, features = [

codex-rs/app-server/tests/common/mcp_process.rs

@@ -11,7 +11,6 @@ use tokio::process::ChildStdin;
 use tokio::process::ChildStdout;
 
 use anyhow::Context;
-use assert_cmd::prelude::*;
 use codex_app_server_protocol::AddConversationListenerParams;
 use codex_app_server_protocol::ArchiveConversationParams;
 use codex_app_server_protocol::CancelLoginAccountParams;
@@ -49,7 +48,6 @@ use codex_app_server_protocol::ThreadResumeParams;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::TurnInterruptParams;
 use codex_app_server_protocol::TurnStartParams;
-use std::process::Command as StdCommand;
 use tokio::process::Command;
 
 pub struct McpProcess {
@@ -78,12 +76,8 @@ impl McpProcess {
         codex_home: &Path,
         env_overrides: &[(&str, Option<&str>)],
     ) -> anyhow::Result<Self> {
-        // Use assert_cmd to locate the binary path and then switch to tokio::process::Command
-        let std_cmd = StdCommand::cargo_bin("codex-app-server")
-            .context("should find binary for codex-mcp-server")?;
-
-        let program = std_cmd.get_program().to_owned();
-
+        let program = codex_utils_cargo_bin::cargo_bin("codex-app-server")
+            .context("should find binary for codex-app-server")?;
         let mut cmd = Command::new(program);
 
         cmd.stdin(Stdio::piped());

codex-rs/apply-patch/Cargo.toml

@@ -25,5 +25,6 @@ tree-sitter-bash = { workspace = true }
 [dev-dependencies]
 assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 pretty_assertions = { workspace = true }
 tempfile = { workspace = true }

codex-rs/apply-patch/tests/suite/cli.rs

@@ -1,6 +1,5 @@
-use assert_cmd::prelude::*;
+use assert_cmd::Command;
 use std::fs;
-use std::process::Command;
 use tempfile::tempdir;
 
 #[test]
@@ -16,8 +15,7 @@ fn test_apply_patch_cli_add_and_update() -> anyhow::Result<()> {
 +hello
 *** End Patch"#
     );
-    Command::cargo_bin("apply_patch")
-        .expect("should find apply_patch binary")
+    Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?)
         .arg(add_patch)
         .current_dir(tmp.path())
         .assert()
@@ -34,8 +32,7 @@ fn test_apply_patch_cli_add_and_update() -> anyhow::Result<()> {
 +world
 *** End Patch"#
     );
-    Command::cargo_bin("apply_patch")
-        .expect("should find apply_patch binary")
+    Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?)
         .arg(update_patch)
         .current_dir(tmp.path())
         .assert()
@@ -59,8 +56,7 @@ fn test_apply_patch_cli_stdin_add_and_update() -> anyhow::Result<()> {
 +hello
 *** End Patch"#
     );
-    let mut cmd =
-        assert_cmd::Command::cargo_bin("apply_patch").expect("should find apply_patch binary");
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(tmp.path());
     cmd.write_stdin(add_patch)
         .assert()
@@ -77,8 +73,7 @@ fn test_apply_patch_cli_stdin_add_and_update() -> anyhow::Result<()> {
 +world
 *** End Patch"#
     );
-    let mut cmd =
-        assert_cmd::Command::cargo_bin("apply_patch").expect("should find apply_patch binary");
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(tmp.path());
     cmd.write_stdin(update_patch)
         .assert()

codex-rs/apply-patch/tests/suite/scenarios.rs

@@ -1,4 +1,3 @@
-use assert_cmd::prelude::*;
 use pretty_assertions::assert_eq;
 use std::collections::BTreeMap;
 use std::fs;
@@ -36,7 +35,7 @@ fn run_apply_patch_scenario(dir: &Path) -> anyhow::Result<()> {
     // Run apply_patch in the temporary directory. We intentionally do not assert
     // on the exit status here; the scenarios are specified purely in terms of
     // final filesystem state, which we compare below.
-    Command::cargo_bin("apply_patch")?
+    Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?)
         .arg(patch)
         .current_dir(tmp.path())
         .output()?;

codex-rs/apply-patch/tests/suite/tool.rs

@@ -5,13 +5,13 @@ use std::path::Path;
 use tempfile::tempdir;
 
 fn run_apply_patch_in_dir(dir: &Path, patch: &str) -> anyhow::Result<assert_cmd::assert::Assert> {
-    let mut cmd = Command::cargo_bin("apply_patch")?;
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(dir);
     Ok(cmd.arg(patch).assert())
 }
 
 fn apply_patch_command(dir: &Path) -> anyhow::Result<Command> {
-    let mut cmd = Command::cargo_bin("apply_patch")?;
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(dir);
     Ok(cmd)
 }

codex-rs/cli/Cargo.toml

@@ -60,6 +60,7 @@ codex_windows_sandbox = { package = "codex-windows-sandbox", path = "../windows-
 [dev-dependencies]
 assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 predicates = { workspace = true }
 pretty_assertions = { workspace = true }
 tempfile = { workspace = true }

codex-rs/cli/tests/execpolicy.rs

@@ -24,7 +24,7 @@ prefix_rule(
 "#,
     )?;
 
-    let output = Command::cargo_bin("codex")?
+    let output = Command::new(codex_utils_cargo_bin::cargo_bin("codex")?)
         .env("CODEX_HOME", codex_home.path())
         .args([
             "execpolicy",

codex-rs/cli/tests/mcp_add_remove.rs

@@ -8,7 +8,7 @@ use pretty_assertions::assert_eq;
 use tempfile::TempDir;
 
 fn codex_command(codex_home: &Path) -> Result<assert_cmd::Command> {
-    let mut cmd = assert_cmd::Command::cargo_bin("codex")?;
+    let mut cmd = assert_cmd::Command::new(codex_utils_cargo_bin::cargo_bin("codex")?);
     cmd.env("CODEX_HOME", codex_home);
     Ok(cmd)
 }

codex-rs/cli/tests/mcp_list.rs

@@ -12,7 +12,7 @@ use serde_json::json;
 use tempfile::TempDir;
 
 fn codex_command(codex_home: &Path) -> Result<assert_cmd::Command> {
-    let mut cmd = assert_cmd::Command::cargo_bin("codex")?;
+    let mut cmd = assert_cmd::Command::new(codex_utils_cargo_bin::cargo_bin("codex")?);
     cmd.env("CODEX_HOME", codex_home);
     Ok(cmd)
 }

codex-rs/core/Cargo.toml

@@ -123,6 +123,7 @@ assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
 codex-arg0 = { workspace = true }
 codex-core = { path = ".", features = ["deterministic_process_ids"] }
+codex-utils-cargo-bin = { workspace = true }
 core_test_support = { workspace = true }
 ctor = { workspace = true }
 escargot = { workspace = true }

codex-rs/core/tests/common/Cargo.toml

@@ -14,6 +14,7 @@ base64 = { workspace = true }
 codex-core = { workspace = true, features = ["test-support"] }
 codex-protocol = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 notify = { workspace = true }
 regex-lite = { workspace = true }
 serde_json = { workspace = true }

codex-rs/core/tests/common/lib.rs

@@ -10,9 +10,6 @@ use codex_utils_absolute_path::AbsolutePathBuf;
 use regex_lite::Regex;
 use std::path::PathBuf;
 
-#[cfg(target_os = "linux")]
-use assert_cmd::cargo::cargo_bin;
-
 pub mod process;
 pub mod responses;
 pub mod streaming_sse;
@@ -87,7 +84,10 @@ pub async fn load_default_config_for_test(codex_home: &TempDir) -> Config {
 #[cfg(target_os = "linux")]
 fn default_test_overrides() -> ConfigOverrides {
     ConfigOverrides {
-        codex_linux_sandbox_exe: Some(cargo_bin("codex-linux-sandbox")),
+        codex_linux_sandbox_exe: Some(
+            codex_utils_cargo_bin::cargo_bin("codex-linux-sandbox")
+                .expect("should find binary for codex-linux-sandbox"),
+        ),
         ..ConfigOverrides::default()
     }
 }

codex-rs/core/tests/common/test_codex.rs

@@ -184,8 +184,8 @@ impl TestCodexBuilder {
         for hook in self.pre_build_hooks.drain(..) {
             hook(home.path());
         }
-        if let Ok(cmd) = assert_cmd::Command::cargo_bin("codex") {
-            config.codex_linux_sandbox_exe = Some(PathBuf::from(cmd.get_program().to_os_string()));
+        if let Ok(path) = codex_utils_cargo_bin::cargo_bin("codex") {
+            config.codex_linux_sandbox_exe = Some(path);
         }
 
         let mut mutators = vec![];

codex-rs/core/tests/common/test_codex_exec.rs

@@ -11,8 +11,10 @@ pub struct TestCodexExecBuilder {
 
 impl TestCodexExecBuilder {
     pub fn cmd(&self) -> assert_cmd::Command {
-        let mut cmd = assert_cmd::Command::cargo_bin("codex-exec")
-            .expect("should find binary for codex-exec");
+        let mut cmd = assert_cmd::Command::new(
+            codex_utils_cargo_bin::cargo_bin("codex-exec")
+                .expect("should find binary for codex-exec"),
+        );
         cmd.current_dir(self.cwd.path())
             .env("CODEX_HOME", self.home.path())
             .env(CODEX_API_KEY_ENV_VAR, "dummy");

codex-rs/core/tests/suite/cli_stream.rs

@@ -1,5 +1,4 @@
 use assert_cmd::Command as AssertCommand;
-use assert_cmd::cargo::cargo_bin;
 use codex_core::RolloutRecorder;
 use codex_core::protocol::GitInfo;
 use core_test_support::fs_wait;
@@ -45,7 +44,7 @@ async fn chat_mode_stream_cli() {
         "model_providers.mock={{ name = \"mock\", base_url = \"{}/v1\", env_key = \"PATH\", wire_api = \"chat\" }}",
         server.uri()
     );
-    let bin = cargo_bin("codex");
+    let bin = codex_utils_cargo_bin::cargo_bin("codex").unwrap();
     let mut cmd = AssertCommand::new(bin);
     cmd.arg("exec")
         .arg("--skip-git-repo-check")
@@ -128,7 +127,7 @@ async fn exec_cli_applies_experimental_instructions_file() {
     );
 
     let home = TempDir::new().unwrap();
-    let bin = cargo_bin("codex");
+    let bin = codex_utils_cargo_bin::cargo_bin("codex").unwrap();
     let mut cmd = AssertCommand::new(bin);
     cmd.arg("exec")
         .arg("--skip-git-repo-check")
@@ -182,7 +181,7 @@ async fn responses_api_stream_cli() {
         std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/cli_responses_fixture.sse");
 
     let home = TempDir::new().unwrap();
-    let bin = cargo_bin("codex");
+    let bin = codex_utils_cargo_bin::cargo_bin("codex").unwrap();
     let mut cmd = AssertCommand::new(bin);
     cmd.arg("exec")
         .arg("--skip-git-repo-check")
@@ -218,7 +217,7 @@ async fn integration_creates_and_checks_session_file() -> anyhow::Result<()> {
         std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/cli_responses_fixture.sse");
 
     // 4. Run the codex CLI and invoke `exec`, which is what records a session.
-    let bin = cargo_bin("codex");
+    let bin = codex_utils_cargo_bin::cargo_bin("codex").unwrap();
     let mut cmd = AssertCommand::new(bin);
     cmd.arg("exec")
         .arg("--skip-git-repo-check")
@@ -339,7 +338,7 @@ async fn integration_creates_and_checks_session_file() -> anyhow::Result<()> {
     // Second run: resume should update the existing file.
     let marker2 = format!("integration-resume-{}", Uuid::new_v4());
     let prompt2 = format!("echo {marker2}");
-    let bin2 = cargo_bin("codex");
+    let bin2 = codex_utils_cargo_bin::cargo_bin("codex").unwrap();
     let mut cmd2 = AssertCommand::new(bin2);
     cmd2.arg("exec")
         .arg("--skip-git-repo-check")

codex-rs/core/tests/suite/live_cli.rs

@@ -30,7 +30,7 @@ fn run_live(prompt: &str) -> (assert_cmd::assert::Assert, TempDir) {
     // implementation). Instead we configure the std `Command` ourselves, then later hand the
     // resulting `Output` to `assert_cmd` for the familiar assertions.
 
-    let mut cmd = Command::cargo_bin("codex-rs").unwrap();
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("codex-rs").unwrap());
     cmd.current_dir(dir.path());
     cmd.env("OPENAI_API_KEY", require_api_key());
 

codex-rs/exec-server/Cargo.toml

@@ -56,7 +56,7 @@ tracing = { workspace = true }
 tracing-subscriber = { workspace = true, features = ["env-filter", "fmt"] }
 
 [dev-dependencies]
-assert_cmd = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 exec_server_test_support = { workspace = true }
 maplit = { workspace = true }
 pretty_assertions = { workspace = true }

codex-rs/exec-server/tests/common/Cargo.toml

@@ -8,9 +8,9 @@ license.workspace = true
 path = "lib.rs"
 
 [dependencies]
-assert_cmd = { workspace = true }
 anyhow = { workspace = true }
 codex-core = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 rmcp = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true }

codex-rs/exec-server/tests/common/lib.rs

@@ -32,14 +32,16 @@ pub async fn create_transport<P>(
 where
     P: AsRef<Path>,
 {
-    let mcp_executable = assert_cmd::Command::cargo_bin("codex-exec-mcp-server")?;
-    let execve_wrapper = assert_cmd::Command::cargo_bin("codex-execve-wrapper")?;
-    let bash = Path::new(env!("CARGO_MANIFEST_DIR"))
-        .join("..")
-        .join("..")
-        .join("tests")
-        .join("suite")
-        .join("bash");
+    let mcp_executable = codex_utils_cargo_bin::cargo_bin("codex-exec-mcp-server")?;
+    let execve_wrapper = codex_utils_cargo_bin::cargo_bin("codex-execve-wrapper")?;
+    let bash = if let Some(root) = codex_utils_cargo_bin::buck_project_root()? {
+        root.join("codex-rs/exec-server/tests/suite/bash")
+    } else {
+        Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("..")
+            .join("suite")
+            .join("bash")
+    };
 
     // Need to ensure the artifact associated with the bash DotSlash file is
     // available before it is run in a read-only sandbox.
@@ -52,20 +54,19 @@ where
         .await?;
     assert!(status.success(), "dotslash fetch failed: {status:?}");
 
-    let transport =
-        TokioChildProcess::new(Command::new(mcp_executable.get_program()).configure(|cmd| {
-            cmd.arg("--bash").arg(bash);
-            cmd.arg("--execve").arg(execve_wrapper.get_program());
-            cmd.env("CODEX_HOME", codex_home.as_ref());
-            cmd.env("DOTSLASH_CACHE", dotslash_cache.as_ref());
+    let transport = TokioChildProcess::new(Command::new(&mcp_executable).configure(|cmd| {
+        cmd.arg("--bash").arg(bash);
+        cmd.arg("--execve").arg(&execve_wrapper);
+        cmd.env("CODEX_HOME", codex_home.as_ref());
+        cmd.env("DOTSLASH_CACHE", dotslash_cache.as_ref());
 
-            // Important: pipe stdio so rmcp can speak JSON-RPC over stdin/stdout
-            cmd.stdin(Stdio::piped());
-            cmd.stdout(Stdio::piped());
+        // Important: pipe stdio so rmcp can speak JSON-RPC over stdin/stdout
+        cmd.stdin(Stdio::piped());
+        cmd.stdout(Stdio::piped());
 
-            // Optional but very helpful while debugging:
-            cmd.stderr(Stdio::inherit());
-        }))?;
+        // Optional but very helpful while debugging:
+        cmd.stderr(Stdio::inherit());
+    }))?;
 
     Ok(transport)
 }

codex-rs/exec-server/tests/suite/accept_elicitation.rs

@@ -142,11 +142,7 @@ prefix_rule(
 }
 
 fn ensure_codex_cli() -> Result<PathBuf> {
-    let codex_cli = PathBuf::from(
-        assert_cmd::Command::cargo_bin("codex")?
-            .get_program()
-            .to_os_string(),
-    );
+    let codex_cli = codex_utils_cargo_bin::cargo_bin("codex")?;
 
     let metadata = codex_cli.metadata().with_context(|| {
         format!(

codex-rs/exec/Cargo.toml

@@ -51,6 +51,7 @@ ts-rs = { workspace = true, features = [
 
 [dev-dependencies]
 assert_cmd = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 core_test_support = { workspace = true }
 libc = { workspace = true }
 mcp-types = { workspace = true }

codex-rs/exec/tests/suite/apply_patch.rs

@@ -23,8 +23,7 @@ fn test_standalone_exec_cli_can_use_apply_patch() -> anyhow::Result<()> {
     let absolute_path = tmp.path().join(relative_path);
     fs::write(&absolute_path, "original content\n")?;
 
-    Command::cargo_bin("codex-exec")
-        .context("should find binary for codex-exec")?
+    Command::new(codex_utils_cargo_bin::cargo_bin("codex-exec")?)
         .arg(CODEX_APPLY_PATCH_ARG1)
         .arg(
             r#"*** Begin Patch

codex-rs/exec/tests/suite/sandbox.rs

@@ -42,7 +42,8 @@ async fn spawn_command_under_sandbox(
     env: HashMap<String, String>,
 ) -> std::io::Result<Child> {
     use codex_core::landlock::spawn_command_under_linux_sandbox;
-    let codex_linux_sandbox_exe = assert_cmd::cargo::cargo_bin("codex-exec");
+    let codex_linux_sandbox_exe = codex_utils_cargo_bin::cargo_bin("codex-exec")
+        .map_err(|err| io::Error::new(io::ErrorKind::NotFound, err))?;
     spawn_command_under_linux_sandbox(
         codex_linux_sandbox_exe,
         command,

codex-rs/mcp-server/Cargo.toml

@@ -38,7 +38,6 @@ tracing = { workspace = true, features = ["log"] }
 tracing-subscriber = { workspace = true, features = ["env-filter", "fmt"] }
 
 [dev-dependencies]
-assert_cmd = { workspace = true }
 core_test_support = { workspace = true }
 mcp_test_support = { workspace = true }
 os_info = { workspace = true }

codex-rs/mcp-server/tests/common/Cargo.toml

@@ -9,9 +9,9 @@ path = "lib.rs"
 
 [dependencies]
 anyhow = { workspace = true }
-assert_cmd = { workspace = true }
 codex-core = { workspace = true }
 codex-mcp-server = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 mcp-types = { workspace = true }
 os_info = { workspace = true }
 pretty_assertions = { workspace = true }

codex-rs/mcp-server/tests/common/mcp_process.rs

@@ -10,7 +10,6 @@ use tokio::process::ChildStdin;
 use tokio::process::ChildStdout;
 
 use anyhow::Context;
-use assert_cmd::prelude::*;
 use codex_mcp_server::CodexToolCallParam;
 
 use mcp_types::CallToolRequestParams;
@@ -27,7 +26,6 @@ use mcp_types::ModelContextProtocolRequest;
 use mcp_types::RequestId;
 use pretty_assertions::assert_eq;
 use serde_json::json;
-use std::process::Command as StdCommand;
 use tokio::process::Command;
 
 pub struct McpProcess {
@@ -55,12 +53,8 @@ impl McpProcess {
         codex_home: &Path,
         env_overrides: &[(&str, Option<&str>)],
     ) -> anyhow::Result<Self> {
-        // Use assert_cmd to locate the binary path and then switch to tokio::process::Command
-        let std_cmd = StdCommand::cargo_bin("codex-mcp-server")
+        let program = codex_utils_cargo_bin::cargo_bin("codex-mcp-server")
             .context("should find binary for codex-mcp-server")?;
-
-        let program = std_cmd.get_program().to_owned();
-
         let mut cmd = Command::new(program);
 
         cmd.stdin(Stdio::piped());

codex-rs/rmcp-client/Cargo.toml

@@ -55,7 +55,7 @@ webbrowser = { workspace = true }
 which = { workspace = true }
 
 [dev-dependencies]
-escargot = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 pretty_assertions = { workspace = true }
 serial_test = { workspace = true }
 tempfile = { workspace = true }

codex-rs/rmcp-client/tests/resources.rs

@@ -5,7 +5,6 @@ use std::time::Duration;
 use codex_rmcp_client::ElicitationAction;
 use codex_rmcp_client::ElicitationResponse;
 use codex_rmcp_client::RmcpClient;
-use escargot::CargoBuild;
 use futures::FutureExt as _;
 use mcp_types::ClientCapabilities;
 use mcp_types::Implementation;
@@ -21,11 +20,7 @@ use serde_json::json;
 const RESOURCE_URI: &str = "memo://codex/example-note";
 
 fn stdio_server_bin() -> anyhow::Result<PathBuf> {
-    let build = CargoBuild::new()
-        .package("codex-rmcp-client")
-        .bin("test_stdio_server")
-        .run()?;
-    Ok(build.path().to_path_buf())
+    Ok(codex_utils_cargo_bin::cargo_bin("test_stdio_server")?)
 }
 
 fn init_params() -> InitializeRequestParams {

codex-rs/stdio-to-uds/Cargo.toml

@@ -23,5 +23,6 @@ uds_windows = { workspace = true }
 
 [dev-dependencies]
 assert_cmd = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 pretty_assertions = { workspace = true }
 tempfile = { workspace = true }

codex-rs/stdio-to-uds/tests/stdio_to_uds.rs

@@ -47,7 +47,7 @@ fn pipes_stdin_and_stdout_through_socket() -> anyhow::Result<()> {
         Ok(())
     });
 
-    Command::cargo_bin("codex-stdio-to-uds")?
+    Command::new(codex_utils_cargo_bin::cargo_bin("codex-stdio-to-uds")?)
         .arg(&socket_path)
         .write_stdin("request")
         .assert()

codex-rs/utils/cargo-bin/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "codex-utils-cargo-bin"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[lints]
+workspace = true
+
+[dependencies]
+assert_cmd = { workspace = true }
+thiserror = { workspace = true }

codex-rs/utils/cargo-bin/src/lib.rs

@@ -0,0 +1,126 @@
+use std::ffi::OsString;
+use std::path::PathBuf;
+
+#[derive(Debug, thiserror::Error)]
+pub enum CargoBinError {
+    #[error("failed to read current exe")]
+    CurrentExe {
+        #[source]
+        source: std::io::Error,
+    },
+    #[error("failed to read current directory")]
+    CurrentDir {
+        #[source]
+        source: std::io::Error,
+    },
+    #[error("CARGO_BIN_EXE env var {key} resolved to {path:?}, but it does not exist")]
+    ResolvedPathDoesNotExist { key: String, path: PathBuf },
+    #[error("could not locate binary {name:?}; tried env vars {env_keys:?}; {fallback}")]
+    NotFound {
+        name: String,
+        env_keys: Vec<String>,
+        fallback: String,
+    },
+}
+
+/// Returns an absolute path to a binary target built for the current test run.
+///
+/// In `cargo test`, `CARGO_BIN_EXE_*` env vars are absolute, but Buck2 may set
+/// them to project-relative paths (e.g. `buck-out/...`). Those paths break if a
+/// test later changes its working directory. This helper makes the path
+/// absolute up-front so callers can safely `chdir` afterwards.
+pub fn cargo_bin(name: &str) -> Result<PathBuf, CargoBinError> {
+    let env_keys = cargo_bin_env_keys(name);
+    for key in &env_keys {
+        if let Some(value) = std::env::var_os(key) {
+            return resolve_bin_from_env(key, value);
+        }
+    }
+
+    match assert_cmd::Command::cargo_bin(name) {
+        Ok(cmd) => {
+            let abs = absolutize_from_buck_or_cwd(PathBuf::from(cmd.get_program()))?;
+            if abs.exists() {
+                Ok(abs)
+            } else {
+                Err(CargoBinError::ResolvedPathDoesNotExist {
+                    key: "assert_cmd::Command::cargo_bin".to_owned(),
+                    path: abs,
+                })
+            }
+        }
+        Err(err) => Err(CargoBinError::NotFound {
+            name: name.to_owned(),
+            env_keys,
+            fallback: format!("assert_cmd fallback failed: {err}"),
+        }),
+    }
+}
+
+fn cargo_bin_env_keys(name: &str) -> Vec<String> {
+    let mut keys = Vec::with_capacity(2);
+    keys.push(format!("CARGO_BIN_EXE_{name}"));
+
+    // Cargo replaces dashes in target names when exporting env vars.
+    let underscore_name = name.replace('-', "_");
+    if underscore_name != name {
+        keys.push(format!("CARGO_BIN_EXE_{underscore_name}"));
+    }
+
+    keys
+}
+
+fn resolve_bin_from_env(key: &str, value: OsString) -> Result<PathBuf, CargoBinError> {
+    let abs = absolutize_from_buck_or_cwd(PathBuf::from(value))?;
+
+    if abs.exists() {
+        Ok(abs)
+    } else {
+        Err(CargoBinError::ResolvedPathDoesNotExist {
+            key: key.to_owned(),
+            path: abs,
+        })
+    }
+}
+
+fn absolutize_from_buck_or_cwd(path: PathBuf) -> Result<PathBuf, CargoBinError> {
+    if path.is_absolute() {
+        return Ok(path);
+    }
+
+    if let Some(root) = buck_project_root().map_err(|source| CargoBinError::CurrentExe { source })?
+    {
+        return Ok(root.join(path));
+    }
+
+    Ok(std::env::current_dir()
+        .map_err(|source| CargoBinError::CurrentDir { source })?
+        .join(path))
+}
+
+/// Best-effort attempt to find the Buck project root for the currently running
+/// process.
+///
+/// Prefer this over `env!("CARGO_MANIFEST_DIR")` when running under Buck2: our
+/// Buck generator sets `CARGO_MANIFEST_DIR="."` for compilation, which makes
+/// `env!("CARGO_MANIFEST_DIR")` unusable for locating workspace files.
+pub fn buck_project_root() -> Result<Option<PathBuf>, std::io::Error> {
+    if let Some(root) = std::env::var_os("BUCK_PROJECT_ROOT") {
+        let root = PathBuf::from(root);
+        if root.is_absolute() {
+            return Ok(Some(root));
+        }
+    }
+
+    // Fall back to deriving the project root from the location of the test
+    // runner executable:
+    //   <project>/buck-out/v2/gen/.../__tests__/test-binary
+    let exe = std::env::current_exe()?;
+    for ancestor in exe.ancestors() {
+        if ancestor.file_name().is_some_and(|name| name == "buck-out") {
+            return Ok(ancestor.parent().map(PathBuf::from));
+        }
+    }
+
+    Ok(None)
+}