acpmux tests: stand-in harnesses keep normal CPU class (3 codex-steer reds on loaded fleet Macs)

cmux-tui/crates/acpmux/src/hub/steer_end_race_tests.rs

@@ -9,7 +9,12 @@ async fn unsent_steer_after_completion(steer_only: bool) {
     use crate::config::{Config, StoreMode};
     let fake = concat!(env!("CARGO_MANIFEST_DIR"), "/tests/fake_agent.py");
     let mut cfg: Config = serde_json::from_value(json!({
-        "harnesses": {"fake": {"argv": ["/usr/bin/env", "FAKE_CODEX_STEER=1", "python3", fake]}},
+        // At normal CPU class (`cpu_class.rs`), as in the hermetic integration tests: at
+        // background class a loaded fleet Mac did not end the stand-in's steer turn in 20 s.
+        "harnesses": {"fake": {
+            "argv": ["/usr/bin/env", "FAKE_CODEX_STEER=1", "python3", fake],
+            "env": {"ACPMUX_SESSION_CPU_CLASS": "normal"},
+        }},
         "defaultHarness": "fake",
     }))
     .unwrap();

cmux-tui/crates/acpmux/tests/cpu_class.rs

@@ -20,8 +20,13 @@ mod daemon_env;
 // agent hosts this process starts in background class (`qos.rs`), so a hosted harness would
 // inherit it: the hosted test checks that its harness clears it at its exec. The in-process hubs
 // start their harnesses directly and read no `ACPMUX_QOS`.
-const HERMETIC: daemon_env::Process = daemon_env::Process::stand_in()
-    .with_env(&[("ACPMUX_TEST_CPU_CLASS_REF", "normal"), ("ACPMUX_QOS", "background")]);
+// The hermetic environment keeps stand-ins at normal class (`daemon_env::vars`); these tests
+// check the product's background class, so this process and its daemons ask for it.
+const HERMETIC: daemon_env::Process = daemon_env::Process::stand_in().with_env(&[
+    ("ACPMUX_TEST_CPU_CLASS_REF", "normal"),
+    ("ACPMUX_QOS", "background"),
+    ("ACPMUX_SESSION_CPU_CLASS", "background"),
+]);
 
 use acpmux::agent::{Attached, ChildAgent};
 use acpmux::agent_host::link::{self, HostLauncher};
@@ -427,6 +432,7 @@ impl RealDaemon {
             .env("ACPMUX_HEALTH_FETCH", "0")
             .env("ACPMUX_CATALOG_FETCH", "0")
             .env("ACPMUX_PROBE_HARNESSES", "fake")
+            .env(acpmux::cpu_class::ENV, "background")
             .env_remove("ACPMUX_SESSION_ID")
             .stdin(std::process::Stdio::null());
         cmd

cmux-tui/crates/acpmux/tests/hub_integration/stop.rs

@@ -705,3 +705,15 @@ async fn a_long_replayed_history_stays_out_of_the_resumed_sessions_last_message(
     let summary = hub.session_summary(&hub.resolve(&id).unwrap());
     assert_eq!(summary["lastMessage"], json!({"role": "agent", "text": "echo: second"}));
 }
+
+/// A test's stand-in harness runs at normal CPU class once its start is over, not at the
+/// product's background default (`cpu_class.rs`). The stand-ins time their turns with short
+/// sleeps (a Codex-steer turn polls 300 x 10 ms for a joined prompt), and on a loaded fleet Mac
+/// (load 13 to 21 on 10 performance cores) a background-class stand-in did not end that turn in
+/// 18 to 30 s: this test, the forum's steered rule and the steer race failed only on macOS.
+/// `tests/cpu_class.rs` asks for background itself and checks the product's class.
+#[cfg(target_os = "macos")]
+#[test]
+fn a_stand_in_harness_runs_at_normal_class_in_tests() {
+    assert_eq!(acpmux::cpu_class::CpuClass::for_session([]), acpmux::cpu_class::CpuClass::Normal);
+}

cmux-tui/crates/acpmux/tests/support/daemon_env.rs

@@ -30,6 +30,8 @@
 //!   daemon's home or a chat's folder, and the daemon refuses to start an
 //!   agent in the user's home folder unless a person picks it;
 //! - `TMPDIR`: the test process's temp directory (macOS: the per-user one);
+//! - `ACPMUX_SESSION_CPU_CLASS=normal`: a stand-in harness keeps its normal CPU class (see
+//!   [`vars`]);
 //! - `ACPMUX_AGENT_LAUNCH=deny`: no agent starts at all (cx-9ettq). A test
 //!   that drives a stand-in agent (fake_agent.py, fake_claude.py) opts out
 //!   with [`Agents::StandIn`]; it keeps the bare PATH, so only its stand-in
@@ -293,6 +295,11 @@ pub fn vars(scratch: &Path, agents: Agents, tools: &[&str]) -> Vec<(String, Stri
     if agents == Agents::Deny {
         env.push(("ACPMUX_AGENT_LAUNCH".into(), "deny".into()));
     }
+    // Stand-in harnesses at normal CPU class once their start is over, not the product's
+    // background default (`cpu_class.rs`): they time their turns with short sleeps, and at
+    // background class on a loaded fleet Mac (load 13 to 21 on 10 performance cores) a Codex-steer
+    // turn did not end in 18 to 30 s. `tests/cpu_class.rs` sets background itself.
+    env.push((acpmux::cpu_class::ENV.into(), "normal".into()));
     env
 }