Fail closed when fixture ACK publish fails

cai

2026-08-12 da9563428e990244ff2145eb6a9cb453f9ef9d22

 src/main.rs

@@ -6,6 +6,7 @@
    borrow::Cow,
    collections::HashSet,
    env, fs,
    future::Future,
    path::{Path, PathBuf},
    sync::{
        Arc,
@@ -63,9 +64,23 @@
const CONTROLLED_FIXTURE_ACK_TOPIC: &str = "controlled_fixture_attribute_ack";
const CONTROLLED_FIXTURE_PROTOCOL_VERSION: u64 = 1;
const CONTROLLED_FIXTURE_GENERATION: u64 = 1;
const CONTROLLED_FIXTURE_PROBE_RECHECKS: usize = 3;
const CONTROLLED_FIXTURE_PROBE_RECHECK_DELAY: Duration = Duration::from_millis(25);
const CONTROLLED_FIXTURE_PROBE_TTL: Duration = Duration::from_millis(250);

const CONTROLLED_FIXTURE_ACK_RESULTS: [&str; 4] =
    ["observed", "rejected", "timeout", "publish_failed"];
const CONTROLLED_FIXTURE_REJECT_REASONS: [&str; 10] = [
    "missing_attributes",
    "wrong_source",
    "missing_sequence",
    "wrong_sequence",
    "wrong_participant",
    "expired",
    "duplicate_or_old_sequence",
    "no_current_participant",
    "ack_publish_failed",
    "unknown",
];

#[derive(Debug, Deserialize)]
#[serde(rename_all = "camelCase")]
@@ -111,6 +126,129 @@
        .iter()
        .map(|byte| format!("{byte:02x}"))
        .collect()
}

fn controlled_fixture_ack_classification(
    decision: Result<(), &'static str>,
) -> (&'static str, Option<&'static str>, bool) {
    match decision {
        Ok(()) => ("observed", None, true),
        Err("timeout") => ("timeout", Some("expired"), false),
        Err(reason) if CONTROLLED_FIXTURE_REJECT_REASONS.contains(&reason) => {
            ("rejected", Some(reason), false)
        }
        Err(_) => ("rejected", Some("unknown"), false),
    }
}

fn record_controlled_fixture_probe_event(
    stage: &'static str,
    call_id: &str,
    trace_id: &str,
    sequence: &str,
    observed: bool,
    ack_result: Option<&'static str>,
    reject_reason: Option<&'static str>,
) {
    debug_assert!(ack_result.is_none_or(|value| CONTROLLED_FIXTURE_ACK_RESULTS.contains(&value)));
    debug_assert!(
        reject_reason.is_none_or(|value| CONTROLLED_FIXTURE_REJECT_REASONS.contains(&value))
    );
    if let Some(ack_result) = ack_result {
        info!(
            event = "controlled_fixture_attribute_probe",
            stage,
            observed,
            ack_result,
            reject_reason = reject_reason.unwrap_or("unknown"),
            call_id_hash = %sha256_hex(call_id),
            trace_id_hash = %sha256_hex(trace_id),
            generation = CONTROLLED_FIXTURE_GENERATION,
            sequence_hash = %sha256_hex(sequence),
            "runtime helper controlled fixture probe state"
        );
    } else if let Some(reject_reason) = reject_reason {
        info!(
            event = "controlled_fixture_attribute_probe",
            stage,
            observed,
            reject_reason,
            call_id_hash = %sha256_hex(call_id),
            trace_id_hash = %sha256_hex(trace_id),
            generation = CONTROLLED_FIXTURE_GENERATION,
            sequence_hash = %sha256_hex(sequence),
            "runtime helper controlled fixture probe state"
        );
    } else {
        info!(
            event = "controlled_fixture_attribute_probe",
            stage,
            observed,
            call_id_hash = %sha256_hex(call_id),
            trace_id_hash = %sha256_hex(trace_id),
            generation = CONTROLLED_FIXTURE_GENERATION,
            sequence_hash = %sha256_hex(sequence),
            "runtime helper controlled fixture probe state"
        );
    }
}

fn record_controlled_fixture_attribute_decision(
    decision: Result<(), &'static str>,
    call_id: &str,
    trace_id: &str,
    sequence: &str,
) -> (&'static str, Option<&'static str>, bool) {
    let classification = controlled_fixture_ack_classification(decision);
    record_controlled_fixture_probe_event(
        "attributes_classified",
        call_id,
        trace_id,
        sequence,
        classification.2,
        Some(classification.0),
        classification.1,
    );
    classification
}

async fn complete_controlled_fixture_ack_publish<F, E>(
    publish: F,
    observed: bool,
    ack_result: &'static str,
    reject_reason: Option<&'static str>,
    call_id: &str,
    trace_id: &str,
    sequence: &str,
    acknowledged_probe_sequences: &mut HashSet<String>,
) -> bool
where
    F: Future<Output = Result<(), E>>,
{
    if publish.await.is_ok() {
        record_controlled_fixture_probe_event(
            "ack_publish_completed",
            call_id,
            trace_id,
            sequence,
            observed,
            Some(ack_result),
            reject_reason,
        );
        acknowledged_probe_sequences.insert(sequence.to_string());
        observed
    } else {
        record_controlled_fixture_probe_event(
            "ack_publish_completed",
            call_id,
            trace_id,
            sequence,
            false,
            Some("publish_failed"),
            Some("ack_publish_failed"),
        );
        false
    }
}

fn controlled_fixture_probe(
@@ -171,6 +309,59 @@
        return Err("wrong_sequence");
    }
    Ok(())
}

async fn observe_controlled_fixture_attributes<F>(
    expires_at: Instant,
    actual_participant: &str,
    expected_participant: Option<&str>,
    requested_sequence: &str,
    mut read_attributes: F,
) -> Result<(), &'static str>
where
    F: FnMut() -> std::collections::HashMap<String, String>,
{
    loop {
        if Instant::now() > expires_at {
            return Err("timeout");
        }
        let decision = classify_controlled_fixture_attributes(
            actual_participant,
            expected_participant,
            &read_attributes(),
            requested_sequence,
        );
        if decision.is_ok() || !matches!(decision, Err("missing_attributes")) {
            return decision;
        }
        let Some(next_check) = Instant::now().checked_add(CONTROLLED_FIXTURE_PROBE_RECHECK_DELAY)
        else {
            return Err("timeout");
        };
        if next_check > expires_at {
            return Err("timeout");
        }
        sleep(CONTROLLED_FIXTURE_PROBE_RECHECK_DELAY).await;
    }
}

fn controlled_fixture_observer_gate(pending_probe: bool, probe_result: Option<bool>) -> bool {
    !pending_probe || probe_result == Some(true)
}

fn start_observer_after_controlled_fixture_probe<F>(
    pending_probe: bool,
    probe_result: Option<bool>,
    spawn: F,
) -> bool
where
    F: FnOnce(),
{
    if !controlled_fixture_observer_gate(pending_probe, probe_result) {
        return false;
    }
    spawn();
    true
}

#[tokio::main(flavor = "multi_thread")]
@@ -914,33 +1105,68 @@
                    track_source = %track_source,
                    "runtime helper user_track_subscribed"
                );
                let pending_sequence = pending_probe.as_ref().map(|probe| probe.sequence.clone());
                let participant_for_probe = participant.clone();
                spawn_user_audio_frame_observer(
                    track,
                    call_id.clone(),
                    trace_id.clone(),
                    participant_alias,
                    track_sid_alias,
                    simple_vad_enabled,
                    simple_vad_config.clone(),
                    vad_enabled_gate.clone(),
                    turn_bridge_config.clone(),
                    http.clone(),
                    sink.clone(),
                    user_participant_identity.clone(),
                    participant,
                );
                current_user_participant = Some(participant_for_probe);
                process_controlled_fixture_probe(
                let probe_result = process_controlled_fixture_probe(
                    &mut pending_probe,
                    &mut acknowledged_probe_sequences,
                    current_user_participant.as_ref(),
                    Some(&participant_for_probe),
                    &sink,
                    &call_id,
                    &trace_id,
                    user_participant_identity.as_deref(),
                )
                .await;
                let observer_started = start_observer_after_controlled_fixture_probe(
                    pending_sequence.is_some(),
                    probe_result,
                    || {
                        spawn_user_audio_frame_observer(
                            track,
                            call_id.clone(),
                            trace_id.clone(),
                            participant_alias,
                            track_sid_alias,
                            simple_vad_enabled,
                            simple_vad_config.clone(),
                            vad_enabled_gate.clone(),
                            turn_bridge_config.clone(),
                            http.clone(),
                            sink.clone(),
                            user_participant_identity.clone(),
                            participant,
                        );
                    },
                );
                if let Some(sequence) = pending_sequence.as_deref() {
                    let (ack_result, reject_reason, observed) = match probe_result {
                        Some(true) => (Some("observed"), None, true),
                        Some(false) => (Some("rejected"), Some("unknown"), false),
                        None => (None, Some("no_current_participant"), false),
                    };
                    record_controlled_fixture_probe_event(
                        if observer_started {
                            "audio_observer_allowed"
                        } else {
                            "audio_observer_blocked"
                        },
                        &call_id,
                        &trace_id,
                        sequence,
                        observed,
                        ack_result,
                        reject_reason,
                    );
                }
                if !observer_started {
                    warn!(
                        call_id = %call_id,
                        trace_id = %trace_id,
                        "runtime helper withheld audio observer until controlled fixture ACK"
                    );
                    continue;
                }
                current_user_participant = Some(participant_for_probe);
            }
            RoomEvent::DataReceived {
                payload,
@@ -952,6 +1178,15 @@
                    serde_json::from_slice::<ControlledFixtureAttributeProbe>(&payload)
                {
                    if acknowledged_probe_sequences.contains(&probe.client_fixture_sequence) {
                        record_controlled_fixture_probe_event(
                            "data_received",
                            &call_id,
                            &trace_id,
                            &probe.client_fixture_sequence,
                            false,
                            Some("rejected"),
                            Some("duplicate_or_old_sequence"),
                        );
                        continue;
                    }
                }
@@ -962,6 +1197,17 @@
                    &sender.identity(),
                    user_participant_identity.as_deref(),
                );
                if let Some(probe) = pending_probe.as_ref() {
                    record_controlled_fixture_probe_event(
                        "data_received",
                        &call_id,
                        &trace_id,
                        &probe.sequence,
                        false,
                        None,
                        None,
                    );
                }
                process_controlled_fixture_probe(
                    &mut pending_probe,
                    &mut acknowledged_probe_sequences,
@@ -1022,43 +1268,72 @@
    call_id: &str,
    trace_id: &str,
    expected_participant: Option<&str>,
) {
) -> Option<bool> {
    let Some(probe) = pending_probe.take() else {
        return;
        return None;
    };
    if acknowledged_probe_sequences.contains(&probe.sequence) || Instant::now() > probe.expires_at {
        return;
    if acknowledged_probe_sequences.contains(&probe.sequence) {
        record_controlled_fixture_probe_event(
            "attributes_classified",
            call_id,
            trace_id,
            &probe.sequence,
            false,
            Some("rejected"),
            Some("duplicate_or_old_sequence"),
        );
        return Some(false);
    }
    if Instant::now() > probe.expires_at {
        record_controlled_fixture_probe_event(
            "attributes_classified",
            call_id,
            trace_id,
            &probe.sequence,
            false,
            Some("timeout"),
            Some("expired"),
        );
        return Some(false);
    }
    let Some(participant) = participant else {
        record_controlled_fixture_probe_event(
            "attributes_classified",
            call_id,
            trace_id,
            &probe.sequence,
            false,
            None,
            Some("no_current_participant"),
        );
        *pending_probe = Some(probe);
        return;
        return None;
    };
    if participant.identity() != probe.sender {
        return;
    }
    let mut decision = Err("timeout");
    for attempt in 0..CONTROLLED_FIXTURE_PROBE_RECHECKS {
        if Instant::now() > probe.expires_at {
            break;
        }
        let attributes = participant.attributes();
        decision = classify_controlled_fixture_attributes(
            &participant.identity().to_string(),
            expected_participant,
            &attributes,
        record_controlled_fixture_probe_event(
            "attributes_classified",
            call_id,
            trace_id,
            &probe.sequence,
            false,
            Some("rejected"),
            Some("wrong_participant"),
        );
        if decision.is_ok() || !matches!(decision, Err("missing_attributes")) {
            break;
        }
        if attempt + 1 < CONTROLLED_FIXTURE_PROBE_RECHECKS {
            sleep(CONTROLLED_FIXTURE_PROBE_RECHECK_DELAY).await;
        }
        return Some(false);
    }
    let (result, input_source_category, reject_reason) = match decision {
        Ok(()) => ("observed", Some("controlled_fixture"), None),
        Err(reason) => ("rejected", None, Some(reason)),
    };
    let decision = observe_controlled_fixture_attributes(
        probe.expires_at,
        &participant.identity().to_string(),
        expected_participant,
        &probe.sequence,
        || participant.attributes(),
    )
    .await;
    let protocol_reject_reason = decision.err();
    let (ack_result, reject_reason, observed) =
        record_controlled_fixture_attribute_decision(decision, call_id, trace_id, &probe.sequence);
    let result = if observed { "observed" } else { "rejected" };
    let input_source_category = observed.then_some("controlled_fixture");
    let ack = ControlledFixtureAttributeAck {
        message_type: CONTROLLED_FIXTURE_ACK_TOPIC,
        protocol_version: CONTROLLED_FIXTURE_PROTOCOL_VERSION,
@@ -1068,22 +1343,41 @@
        client_fixture_sequence: probe.sequence.clone(),
        result,
        input_source_category,
        reject_reason,
        reject_reason: protocol_reject_reason,
    };
    let payload = match serde_json::to_vec(&ack) {
        Ok(payload) => payload,
        Err(_) => return,
        Err(_) => return Some(false),
    };
    let local_participant = sink.room.local_participant();
    record_controlled_fixture_probe_event(
        "ack_publish_started",
        call_id,
        trace_id,
        &probe.sequence,
        observed,
        Some(ack_result),
        reject_reason,
    );
    let publish = local_participant.publish_data(DataPacket {
        payload,
        topic: Some(CONTROLLED_FIXTURE_ACK_TOPIC.to_string()),
        reliable: true,
        destination_identities: vec![probe.sender],
    });
    if publish.await.is_ok() {
        acknowledged_probe_sequences.insert(probe.sequence);
    }
    Some(
        complete_controlled_fixture_ack_publish(
            publish,
            observed,
            ack_result,
            reject_reason,
            call_id,
            trace_id,
            &probe.sequence,
            acknowledged_probe_sequences,
        )
        .await,
    )
}

async fn handle_finished_turn(
@@ -4331,17 +4625,97 @@
mod tests {
    use super::*;
    use std::{
        collections::HashSet,
        collections::{HashMap, HashSet},
        io::{Read, Write},
        net::TcpListener,
        sync::{
            Arc,
            Arc, Mutex,
            atomic::{AtomicUsize, Ordering},
            mpsc,
        },
        thread,
        time::Duration,
    };

    #[derive(Debug)]
    enum PreAudioOrderEvent {
        DataReceived {
            sender: String,
            sequence: String,
        },
        TrackSubscribed {
            participant: String,
            attributes: HashMap<String, String>,
        },
    }

    #[derive(Clone, Default)]
    struct CapturedLogs(Arc<Mutex<Vec<u8>>>);

    struct CapturedLogWriter(Arc<Mutex<Vec<u8>>>);

    impl Write for CapturedLogWriter {
        fn write(&mut self, bytes: &[u8]) -> std::io::Result<usize> {
            self.0.lock().unwrap().extend_from_slice(bytes);
            Ok(bytes.len())
        }

        fn flush(&mut self) -> std::io::Result<()> {
            Ok(())
        }
    }

    impl<'a> tracing_subscriber::fmt::MakeWriter<'a> for CapturedLogs {
        type Writer = CapturedLogWriter;

        fn make_writer(&'a self) -> Self::Writer {
            CapturedLogWriter(self.0.clone())
        }
    }

    fn drive_pre_audio_order_test_seam(events: &[PreAudioOrderEvent]) -> Vec<&'static str> {
        let mut pending_sequence = None;
        let mut effects = Vec::new();
        for event in events {
            match event {
                PreAudioOrderEvent::DataReceived { sender, sequence } if sender == "user-1" => {
                    pending_sequence = Some(sequence.as_str());
                }
                PreAudioOrderEvent::TrackSubscribed {
                    participant,
                    attributes,
                } => {
                    let pending = pending_sequence.is_some();
                    let probe_result = pending_sequence.map(|sequence| {
                        classify_controlled_fixture_attributes(
                            participant,
                            Some("user-1"),
                            attributes,
                            sequence,
                        )
                        .is_ok()
                    });
                    let mut ack_observed = false;
                    let mut observer_started = false;
                    start_observer_after_controlled_fixture_probe(pending, probe_result, || {
                        if pending && probe_result == Some(true) {
                            ack_observed = true;
                        }
                        observer_started = true;
                    });
                    if ack_observed {
                        effects.push("ack_observed");
                    }
                    if observer_started {
                        effects.push("observer_started");
                    }
                    pending_sequence = None;
                }
                PreAudioOrderEvent::DataReceived { .. } => {}
            }
        }
        effects
    }

    #[test]
    fn production_vad_session_boundary_reads_updated_attributes() {
@@ -4951,6 +5325,197 @@
    }

    #[test]
    fn controlled_fixture_probe_failure_log_is_fixed_redacted_and_has_no_audio_effect() {
        let logs = CapturedLogs::default();
        let subscriber = tracing_subscriber::fmt()
            .without_time()
            .with_ansi(false)
            .with_writer(logs.clone())
            .finish();
        let call_id = "private-call-value";
        let trace_id = "private-trace-value";
        let sequence = "private-sequence-value";
        let mut observer_starts = 0;
        tracing::subscriber::with_default(subscriber, || {
            let decision = Err("wrong_source");
            let (ack_result, reject_reason, observed) =
                record_controlled_fixture_attribute_decision(decision, call_id, trace_id, sequence);
            record_controlled_fixture_probe_event(
                "audio_observer_blocked",
                call_id,
                trace_id,
                sequence,
                observed,
                Some(ack_result),
                reject_reason,
            );
            assert!(!start_observer_after_controlled_fixture_probe(
                true,
                Some(observed),
                || observer_starts += 1,
            ));
        });
        let output = String::from_utf8(logs.0.lock().unwrap().clone()).unwrap();
        assert!(output.contains("ack_result=\"rejected\""));
        assert!(output.contains("reject_reason=\"wrong_source\""));
        assert!(output.contains("observed=false"));
        assert!(output.contains(&sha256_hex(call_id)));
        assert!(output.contains(&sha256_hex(trace_id)));
        assert!(output.contains(&sha256_hex(sequence)));
        assert!(!output.contains(call_id));
        assert!(!output.contains(trace_id));
        assert!(!output.contains(sequence));
        assert_eq!(observer_starts, 0);
    }

    #[test]
    fn controlled_fixture_probe_observed_and_failure_enums_are_stable() {
        assert_eq!(
            controlled_fixture_ack_classification(Ok(())),
            ("observed", None, true)
        );
        assert_eq!(
            controlled_fixture_ack_classification(Err("timeout")),
            ("timeout", Some("expired"), false)
        );
        for reason in [
            "missing_attributes",
            "wrong_source",
            "missing_sequence",
            "wrong_sequence",
            "wrong_participant",
        ] {
            assert_eq!(
                controlled_fixture_ack_classification(Err(reason)),
                ("rejected", Some(reason), false)
            );
        }
        assert_eq!(
            controlled_fixture_ack_classification(Err("unclassified")),
            ("rejected", Some("unknown"), false)
        );
    }

    #[tokio::test]
    async fn production_ack_publish_failure_keeps_observer_session_and_audio_closed() {
        let mut acknowledged = HashSet::new();
        let probe_result = complete_controlled_fixture_ack_publish(
            async { Err::<(), ()>(()) },
            true,
            "observed",
            None,
            "call-publish-failure",
            "trace-publish-failure",
            "fixture-01",
            &mut acknowledged,
        )
        .await;
        let mut observer_starts = 0;
        let mut session_starts = 0;
        let mut audio_starts = 0;
        let mut speaking_starts = 0;
        assert!(!start_observer_after_controlled_fixture_probe(
            true,
            Some(probe_result),
            || {
                observer_starts += 1;
                session_starts += 1;
                audio_starts += 1;
                speaking_starts += 1;
            },
        ));
        assert!(!probe_result);
        assert!(acknowledged.is_empty());
        assert_eq!(observer_starts, 0);
        assert_eq!(session_starts, 0);
        assert_eq!(audio_starts, 0);
        assert_eq!(speaking_starts, 0);

        let observed_result = complete_controlled_fixture_ack_publish(
            async { Ok::<(), ()>(()) },
            true,
            "observed",
            None,
            "call-publish-success",
            "trace-publish-success",
            "fixture-02",
            &mut acknowledged,
        )
        .await;
        let mut successful_observer_starts = 0;
        assert!(start_observer_after_controlled_fixture_probe(
            true,
            Some(observed_result),
            || successful_observer_starts += 1,
        ));
        assert!(observed_result);
        assert!(acknowledged.contains("fixture-02"));
        assert_eq!(successful_observer_starts, 1);
    }

    #[tokio::test]
    async fn production_attribute_observation_accepts_server_visibility_within_probe_ttl() {
        let expected = HashMap::from([
            (
                "inputSourceCategory".to_string(),
                "controlled_fixture".to_string(),
            ),
            (
                "clientFixtureSequence".to_string(),
                "fixture-01".to_string(),
            ),
        ]);
        let mut reads = 0;
        let result = observe_controlled_fixture_attributes(
            Instant::now() + CONTROLLED_FIXTURE_PROBE_TTL,
            "user-1",
            Some("user-1"),
            "fixture-01",
            || {
                reads += 1;
                if reads <= 3 {
                    HashMap::new()
                } else {
                    expected.clone()
                }
            },
        )
        .await;
        assert_eq!(result, Ok(()));
        assert_eq!(reads, 4);
    }

    #[tokio::test]
    async fn production_attribute_observation_rejects_wrong_sequence_without_audio_effect() {
        let attributes = HashMap::from([
            (
                "inputSourceCategory".to_string(),
                "controlled_fixture".to_string(),
            ),
            (
                "clientFixtureSequence".to_string(),
                "fixture-02".to_string(),
            ),
        ]);
        let result = observe_controlled_fixture_attributes(
            Instant::now() + CONTROLLED_FIXTURE_PROBE_TTL,
            "user-1",
            Some("user-1"),
            "fixture-01",
            || attributes.clone(),
        )
        .await;
        let mut observer_starts = 0;
        assert_eq!(result, Err("wrong_sequence"));
        assert!(!start_observer_after_controlled_fixture_probe(
            true,
            Some(result.is_ok()),
            || observer_starts += 1,
        ));
        assert_eq!(observer_starts, 0);
    }

    #[test]
    fn controlled_fixture_ack_payload_is_reliable_and_redacted() {
        let ack = ControlledFixtureAttributeAck {
            message_type: CONTROLLED_FIXTURE_ACK_TOPIC,
@@ -4998,4 +5563,76 @@
            "controlled_fixture_attribute_ack"
        );
    }

    #[test]
    fn controlled_fixture_probe_must_be_observed_before_audio_observer() {
        assert!(controlled_fixture_observer_gate(false, None));
        assert!(controlled_fixture_observer_gate(true, Some(true)));
        assert!(!controlled_fixture_observer_gate(true, Some(false)));
        assert!(!controlled_fixture_observer_gate(true, None));
    }

    #[test]
    fn production_event_order_probe_then_track_publishes_ack_before_observer() {
        let attributes = HashMap::from([
            (
                "inputSourceCategory".to_string(),
                "controlled_fixture".to_string(),
            ),
            (
                "clientFixtureSequence".to_string(),
                "fixture-01".to_string(),
            ),
        ]);
        let effects = drive_pre_audio_order_test_seam(&[
            PreAudioOrderEvent::DataReceived {
                sender: "user-1".to_string(),
                sequence: "fixture-01".to_string(),
            },
            PreAudioOrderEvent::TrackSubscribed {
                participant: "user-1".to_string(),
                attributes,
            },
        ]);
        assert_eq!(effects, ["ack_observed", "observer_started"]);
    }

    #[test]
    fn production_event_order_negative_probe_has_no_observer_or_session_effect() {
        let mut invalid = HashMap::new();
        invalid.insert(
            "inputSourceCategory".to_string(),
            "ordinary_mic".to_string(),
        );
        let effects = drive_pre_audio_order_test_seam(&[
            PreAudioOrderEvent::DataReceived {
                sender: "user-1".to_string(),
                sequence: "fixture-01".to_string(),
            },
            PreAudioOrderEvent::TrackSubscribed {
                participant: "user-1".to_string(),
                attributes: invalid,
            },
        ]);
        assert!(effects.is_empty());
    }

    #[test]
    fn production_audio_branch_orders_probe_before_spawn_callsite() {
        let source = include_str!("main.rs");
        let branch = source
            .find("RoomEvent::TrackSubscribed {\n                track: RemoteTrack::Audio")
            .expect("audio TrackSubscribed production branch");
        let branch_source = &source[branch..];
        let probe = branch_source
            .find("let probe_result = process_controlled_fixture_probe")
            .expect("probe must be processed in audio branch");
        let spawn = branch_source
            .find("start_observer_after_controlled_fixture_probe")
            .expect("spawn must use shared order entry");
        assert!(
            probe < spawn,
            "probe must precede shared observer spawn entry"
        );
    }
}