pixelpass/src/host/taint/tests.rs

//! The taint-engine fixture matrix — design v3.4 §12 plus the impl plan's
//! degenerate-snapshot addition.
//!
//! **Every test asserts an exact partition of the whole candidate universe**,
//! never a spot check on one named node. Checking only the node a test cares
//! about constrains nothing about the others, and an exclude-everything
//! implementation would pass. So each test names *every* `Stream/Output/Audio`
//! node in its graph as either eligible or excluded-with-a-reason-code.
//!
//! Fixture realism that is load-bearing: an ordinary app holds **one client
//! connection**, each pactl module holds its own, and every device node
//! shares the session manager's. Getting that wrong makes the engine look
//! broken (or, worse, makes a leak look fine).

use std::collections::BTreeSet;

use super::fixture::{Graph, NodeRef, PULSE_PID, app};
use super::owner::{OwnerKey, strongest_shared_key};
use super::snapshot::{MediaRole, NodeProps, PortDirection, Serial};
use super::{Decisions, Eligibility, ExclusionCtx, ObjectRef, Reason, StickyState, evaluate};

fn ctx() -> ExclusionCtx {
    ExclusionCtx {
        aec_module_id: None,
        pipewire_pulse_pid: Some(PULSE_PID),
        pixelpass_owned: BTreeSet::new(),
        graph_ready: true,
    }
}

fn run(graph: &Graph, ctx: &ExclusionCtx) -> Decisions {
    evaluate(&graph.build(), ctx, &StickyState::default()).0
}

/// Assert the complete candidate partition. `excluded` names reason codes.
#[track_caller]
fn assert_partition(
    decisions: &Decisions,
    eligible: &[(&str, NodeRef)],
    excluded: &[(&str, NodeRef, &str)],
) {
    let mut expected_eligible: Vec<Serial> = eligible.iter().map(|(_, n)| n.serial).collect();
    expected_eligible.sort_unstable();
    let mut expected_excluded: Vec<(Serial, &str)> = excluded
        .iter()
        .map(|(_, n, code)| (n.serial, *code))
        .collect();
    expected_excluded.sort_unstable();

    let label = |serial: Serial| -> String {
        eligible
            .iter()
            .map(|(name, n)| (*name, *n))
            .chain(excluded.iter().map(|(name, n, _)| (*name, *n)))
            .find(|(_, n)| n.serial == serial)
            .map_or_else(|| format!("<unnamed {serial:?}>"), |(name, _)| name.into())
    };
    let actual: Vec<String> = decisions
        .candidates
        .values()
        .map(|d| match d.reason() {
            None => format!("{} = eligible", label(d.serial)),
            Some(reason) => format!("{} = {}", label(d.serial), reason.code()),
        })
        .collect();

    assert_eq!(
        (decisions.eligible(), decisions.excluded()),
        (expected_eligible, expected_excluded),
        "actual decisions: {actual:#?}"
    );
}

#[track_caller]
fn assert_tainted(decisions: &Decisions, node: NodeRef, reason: &str) {
    let entry = decisions
        .taint
        .get(&node.serial)
        .unwrap_or_else(|| panic!("expected {:?} to be tainted", node.serial));
    assert_eq!(entry.reason.code(), reason);
}

#[track_caller]
fn assert_untainted(decisions: &Decisions, node: NodeRef) {
    assert_eq!(
        decisions.taint.get(&node.serial).map(|e| e.reason.code()),
        None,
        "expected {:?} to be untainted",
        node.serial
    );
}

// ──────────────────────────────────────────────────────────────────────
// Boundary / degenerate cases — the fail-closed default
// ──────────────────────────────────────────────────────────────────────

#[test]
fn empty_snapshot_yields_nothing_eligible() {
    let decisions = run(&Graph::new(), &ctx());
    assert!(decisions.candidates.is_empty());
    assert!(decisions.eligible().is_empty());
}

#[test]
fn a_graph_with_only_untainted_streams_still_partitions() {
    // The other half of the degenerate case: "nothing eligible" must not be
    // reached by excluding everything unconditionally.
    let mut graph = Graph::new();
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    assert_partition(&run(&graph, &ctx()), &[("firefox", firefox)], &[]);
}

#[test]
fn graph_not_ready_excludes_every_candidate() {
    let mut graph = Graph::new();
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    let decisions = run(
        &graph,
        &ExclusionCtx {
            graph_ready: false,
            ..ctx()
        },
    );
    assert_partition(&decisions, &[], &[("firefox", firefox, "graph-not-ready")]);
}

#[test]
fn decisions_do_not_depend_on_insertion_order() {
    // The reported reason must come from an explicit priority, not from
    // traversal order, or the audit output is unstable between recomputes.
    let build = |reverse: bool| {
        let mut graph = Graph::new();
        let sink = graph.device_node("sink", MediaRole::Sink);
        let call = graph.peerspeak_node("peerspeak", 7);
        let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
        if reverse {
            graph.link(firefox, sink);
            graph.link(call, sink);
        } else {
            graph.link(call, sink);
            graph.link(firefox, sink);
        }
        run(&graph, &ctx()).excluded()
    };
    assert_eq!(build(false), build(true));
}

// ──────────────────────────────────────────────────────────────────────
// Node-local roots (v3.4 §5.1, §5.2, §6.2, §6.6)
// ──────────────────────────────────────────────────────────────────────

#[test]
fn peerspeak_tagged_nodes_are_excluded_and_plain_apps_are_not() {
    let mut graph = Graph::new();
    let sink = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak-call", 7);
    let mpv = graph.peerspeak_node("peerspeak-mpv", 8);
    let notify = graph.peerspeak_node("peerspeak-notify", 9);
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    for node in [call, mpv, notify, firefox] {
        graph.link(node, sink);
    }

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("mpv", mpv, "peerspeak-owned"),
            ("notify", notify, "peerspeak-owned"),
        ],
    );
    // The sink carried peerspeak audio, so it is tainted — that is what
    // makes every monitor reader downstream of it tainted too.
    assert_tainted(&decisions, sink, "tainted-upstream");
}

#[test]
fn aec_identity_is_exact_equality_and_other_modules_stay_eligible() {
    let mut graph = Graph::new();
    let ours = graph.module_node("echo-cancel-playback", MediaRole::StreamOutput, 536_870_919);
    // A tunnel/RTP module: it has a `pulse.module.id`, just not ours.
    // "Has any pulse.module.id" is explicitly rejected as an exclusion rule
    // — such a module may be the only carrier of audio the user wants
    // shared (v3.4 §5.2 correction 2).
    let tunnel = graph.module_node("tunnel-out", MediaRole::StreamOutput, 536_870_921);
    let plain = graph.app_node("firefox", MediaRole::StreamOutput, 11114);

    let decisions = run(
        &graph,
        &ExclusionCtx {
            aec_module_id: Some(536_870_919),
            ..ctx()
        },
    );
    assert_partition(
        &decisions,
        &[("tunnel", tunnel), ("plain", plain)],
        &[("ours", ours, "aec-identity")],
    );
}

#[test]
fn aec_module_id_is_compared_beyond_u32() {
    // Guards the phase 0a widening at the engine boundary too: these two
    // differ only above bit 32.
    let big = u64::from(u32::MAX) + 7;
    let mut graph = Graph::new();
    let ours = graph.module_node("aec", MediaRole::StreamOutput, big);
    let other = graph.module_node("other", MediaRole::StreamOutput, big ^ 0x1_0000_0000);
    let decisions = run(
        &graph,
        &ExclusionCtx {
            aec_module_id: Some(big),
            ..ctx()
        },
    );
    assert_partition(
        &decisions,
        &[("other", other)],
        &[("ours", ours, "aec-identity")],
    );
}

#[test]
fn foreign_echo_cancel_group_is_excluded_not_shared() {
    // Decision D3: warn and exclude. The group prefix is hazard detection,
    // never ownership — it cannot tell peerspeak's AEC from anyone else's.
    let mut graph = Graph::new();
    let foreign = graph.group_node(
        "echo-cancel-playback",
        MediaRole::StreamOutput,
        "echo-cancel-9999-13",
        4321,
    );
    let plain = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    assert_partition(
        &run(&graph, &ctx()),
        &[("plain", plain)],
        &[("foreign", foreign, "foreign-echo-cancel")],
    );
}

#[test]
fn pixelpass_capture_sink_and_its_downstream_are_excluded() {
    // v3.4 §6.2 cycle prevention, and impl-plan §5.1 row 7: observing the
    // capture sink is not enough — a *downstream* candidate must be named,
    // or recognising `pixelpass_capture_*` as a mere sink name would pass
    // without any transitive propagation.
    let mut graph = Graph::new();
    let other_host_sink = graph.module_node("pixelpass_capture_31337", MediaRole::Sink, 42);
    let fwd_in = graph.module_node("fwd-in", MediaRole::StreamInput, 77);
    let fwd_out = graph.module_node("fwd-out", MediaRole::StreamOutput, 77);
    graph.link(other_host_sink, fwd_in);
    let plain = graph.app_node("firefox", MediaRole::StreamOutput, 11114);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("plain", plain)],
        &[("fwd-out", fwd_out, "tainted-owner-bridge")],
    );
    assert_tainted(&decisions, other_host_sink, "pixelpass-owned");
    assert_tainted(&decisions, fwd_in, "tainted-upstream");
}

#[test]
fn pixelpass_owned_serials_are_roots_even_without_a_capture_sink_name() {
    let mut graph = Graph::new();
    let ours = graph.device_node("some-sink", MediaRole::Sink);
    let reader = graph.app_node("reader-in", MediaRole::StreamInput, 5150);
    let leg = graph.app_node("reader-out", MediaRole::StreamOutput, 5150);
    graph.link(ours, reader);
    let decisions = run(
        &graph,
        &ExclusionCtx {
            pixelpass_owned: BTreeSet::from([ours.serial]),
            ..ctx()
        },
    );
    assert_partition(&decisions, &[], &[("leg", leg, "tainted-owner-bridge")]);
    assert_tainted(&decisions, ours, "pixelpass-owned");
}

#[test]
fn port_exclusive_and_passthrough_are_local_exclusions() {
    let mut graph = Graph::new();
    let exclusive = graph.app_node("exclusive", MediaRole::StreamOutput, 100);
    graph.port(exclusive, PortDirection::Out, true);
    let client = graph.client_of_app(101);
    let passthrough = graph.node(
        "passthrough",
        MediaRole::StreamOutput,
        NodeProps {
            passthrough: true,
            ..app(client, 101)
        },
    );
    let ok = graph.app_node("ok", MediaRole::StreamOutput, 102);
    graph.port(ok, PortDirection::Out, false);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("ok", ok)],
        &[
            ("exclusive", exclusive, "port-exclusive"),
            ("passthrough", passthrough, "passthrough"),
        ],
    );
    // Neither is hazardous — an unlinkable stream must not taint anything.
    assert_untainted(&decisions, exclusive);
    assert_untainted(&decisions, passthrough);
}

#[test]
fn a_node_with_no_props_at_all_is_eligible_and_non_streams_are_not_candidates() {
    let mut graph = Graph::new();
    let bare = graph.node("bare", MediaRole::StreamOutput, NodeProps::default());
    graph.node("video", MediaRole::Other, NodeProps::default());
    graph.node("mic", MediaRole::Source, NodeProps::default());
    assert_partition(&run(&graph, &ctx()), &[("bare", bare)], &[]);
}

// ──────────────────────────────────────────────────────────────────────
// Edge type 2 — sink → monitor, free at node granularity
// ──────────────────────────────────────────────────────────────────────

#[test]
fn taint_crosses_app_then_sink_then_monitor_reader() {
    let mut graph = Graph::new();
    let sink = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, sink);
    // A recorder reading the sink's monitor. The monitor connection IS a
    // real Link whose output node is the sink itself, so no synthetic edge
    // is needed at node granularity.
    let rec_in = graph.app_node("recorder-in", MediaRole::StreamInput, 555);
    graph.link(sink, rec_in);
    let rec_out = graph.app_node("recorder-out", MediaRole::StreamOutput, 555);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("rec-out", rec_out, "tainted-owner-bridge"),
        ],
    );
    assert_tainted(&decisions, rec_in, "tainted-upstream");
}

#[test]
fn playing_into_a_tainted_sink_does_not_taint_the_player() {
    // Taint flows downstream only. Every app on the box plays into the same
    // sink peerspeak does; if that tainted them, nothing would ever be
    // shareable and the feature would ship as silence.
    let mut graph = Graph::new();
    let sink = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    graph.link(call, sink);
    graph.link(firefox, sink);

    assert_partition(
        &run(&graph, &ctx()),
        &[("firefox", firefox)],
        &[("call", call, "peerspeak-owned")],
    );
}

// ──────────────────────────────────────────────────────────────────────
// Edge type 3 — the owner bridge (v3.4 §6.1.1, §6.1.2)
// ──────────────────────────────────────────────────────────────────────

/// The measured `module-null-sink` + `module-loopback` shape. Walking Links
/// alone from the leaking output leg finds *no inbound links at all* — a
/// dead end that reads as "clean".
#[test]
fn loopback_forwarder_output_leg_is_excluded_via_the_owner_bridge() {
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let null_sink = graph.module_node("fabletest_sink", MediaRole::Sink, 536_870_917);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, null_sink);

    // The tainted forwarder: legs share `pulse.module.id`, no Link between.
    let lb_in = graph.module_node("input.loopback", MediaRole::StreamInput, 536_870_918);
    let lb_out = graph.module_node("output.loopback", MediaRole::StreamOutput, 536_870_918);
    graph.link(null_sink, lb_in);
    graph.link(lb_out, hw);

    // The same shape with a clean input — impl-plan §5.1 row 1's eligible
    // half. Without it the test would also pass on "exclude all forwarders".
    let clean_sink = graph.device_node("clean-sink", MediaRole::Sink);
    let clean_in = graph.module_node("clean-in", MediaRole::StreamInput, 536_870_920);
    let clean_out = graph.module_node("clean-out", MediaRole::StreamOutput, 536_870_920);
    graph.link(clean_sink, clean_in);
    graph.link(clean_out, hw);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("clean-out", clean_out)],
        &[
            ("call", call, "peerspeak-owned"),
            ("lb-out", lb_out, "tainted-owner-bridge"),
        ],
    );
    // ...and it was the bridge, naming the key — not a Link walk.
    assert_eq!(
        decisions.taint[&lb_out.serial].reason,
        Reason::TaintedOwnerBridge {
            key: Some(OwnerKey::PulseModuleId)
        }
    );
}

#[test]
fn easyeffects_shape_bridges_from_an_audio_sink_to_its_re_emitting_leg() {
    // The canonical installed case. The tainted member here is an
    // `Audio/Sink`, not a `Stream/Input/Audio` — if the bridge only fired
    // from stream inputs, EasyEffects would forward the whole call into the
    // share at full level.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let ee_sink = graph.group_node("ee_sink", MediaRole::Sink, "ee", 4321);
    let ee_out = graph.group_node("easyeffects-out", MediaRole::StreamOutput, "ee", 4321);
    graph.link(ee_out, hw);
    let call = graph.peerspeak_node("peerspeak", 7);
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    graph.link(call, ee_sink);
    graph.link(firefox, ee_sink);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("ee-out", ee_out, "tainted-owner-bridge"),
        ],
    );
    assert_eq!(
        decisions.taint[&ee_out.serial].reason,
        Reason::TaintedOwnerBridge {
            key: Some(OwnerKey::LinkGroup)
        }
    );
}

#[test]
fn gstreamer_split_clients_bridge_on_process_id() {
    // The C2 refutation, measured: one `gst-launch pulsesrc ! pulsesink`
    // process produced TWO client objects (209 and 210) for its two legs.
    let mut graph = Graph::new();
    let tainted_sink = graph.device_node("null-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, tainted_sink);

    let client_in = graph.client(Some(PULSE_PID));
    let client_out = graph.client(Some(PULSE_PID));
    let gst_in = graph.node("gst-in", MediaRole::StreamInput, app(client_in, 20172));
    let gst_out = graph.node("gst-out", MediaRole::StreamOutput, app(client_out, 20172));
    graph.link(tainted_sink, gst_in);

    // Control: the same split-client shape reading an *untainted* source.
    let mic = graph.device_node("mic", MediaRole::Source);
    let ok_client_in = graph.client(Some(PULSE_PID));
    let ok_client_out = graph.client(Some(PULSE_PID));
    let ok_in = graph.node("ok-in", MediaRole::StreamInput, app(ok_client_in, 30000));
    let ok_out = graph.node("ok-out", MediaRole::StreamOutput, app(ok_client_out, 30000));
    graph.link(mic, ok_in);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("ok-out", ok_out)],
        &[
            ("call", call, "peerspeak-owned"),
            ("gst-out", gst_out, "tainted-owner-bridge"),
        ],
    );
    assert_eq!(
        decisions.taint[&gst_out.serial].reason,
        Reason::TaintedOwnerBridge {
            key: Some(OwnerKey::ProcessId)
        }
    );
}

#[test]
fn owner_key_union_falls_through_a_present_but_unequal_key() {
    // The §6.1.2 wording trap, asserted on the key resolver itself: a
    // first-present implementation stops at `client.id`, sees 209 != 210,
    // concludes "different owners", and the leak survives.
    let mut graph = Graph::new();
    let a_client = graph.client(Some(PULSE_PID));
    let b_client = graph.client(Some(PULSE_PID));
    let a = graph.node("a", MediaRole::StreamInput, app(a_client, 20172));
    let b = graph.node("b", MediaRole::StreamOutput, app(b_client, 20172));
    let snapshot = graph.build();
    let (a, b) = (
        snapshot.node(a.serial).unwrap(),
        snapshot.node(b.serial).unwrap(),
    );
    assert_ne!(a.props.client_id, b.props.client_id);
    assert_eq!(
        strongest_shared_key(a, b, Some(PULSE_PID)),
        Some(OwnerKey::ProcessId)
    );
}

#[test]
fn the_strongest_shared_key_wins_when_several_match() {
    let mut graph = Graph::new();
    let a = graph.group_node("a", MediaRole::StreamInput, "g", 500);
    let b = graph.group_node("b", MediaRole::StreamOutput, "g", 500);
    let snapshot = graph.build();
    assert_eq!(
        strongest_shared_key(
            snapshot.node(a.serial).unwrap(),
            snapshot.node(b.serial).unwrap(),
            Some(PULSE_PID)
        ),
        Some(OwnerKey::LinkGroup)
    );
}

#[test]
fn the_pipewire_pulse_pid_does_not_fuse_unrelated_modules() {
    // impl-plan §5.1 row 3: two Pulse modules, one tainted input. The other
    // module's output MUST stay eligible — that is the only thing that
    // makes wrong pipewire-pulse-PID fusion observable at all.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);

    let a_in = graph.module_node("a-in", MediaRole::StreamInput, 1);
    let a_out = graph.module_node("a-out", MediaRole::StreamOutput, 1);
    graph.link(hw, a_in);

    let mic = graph.device_node("mic", MediaRole::Source);
    let b_in = graph.module_node("b-in", MediaRole::StreamInput, 2);
    let b_out = graph.module_node("b-out", MediaRole::StreamOutput, 2);
    graph.link(mic, b_in);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("b-out", b_out)],
        &[
            ("call", call, "peerspeak-owned"),
            ("a-out", a_out, "tainted-owner-bridge"),
        ],
    );
    assert_untainted(&decisions, b_in);
}

#[test]
fn an_unknown_pipewire_pulse_pid_over_excludes_rather_than_leaks() {
    // v3.4 §6.1.2's failure-mode paragraph: if pixelpass cannot identify
    // the daemon PID, key 4 stops being suppressed, every module-created
    // stream fuses into one owner, and the result is broad over-exclusion —
    // annoying and safe. This test pins that direction; flipping it to
    // "leave key 4 out when the PID is unknown" would be a leak.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);
    let a_in = graph.module_node("a-in", MediaRole::StreamInput, 1);
    let a_out = graph.module_node("a-out", MediaRole::StreamOutput, 1);
    graph.link(hw, a_in);
    let mic = graph.device_node("mic", MediaRole::Source);
    let b_in = graph.module_node("b-in", MediaRole::StreamInput, 2);
    let b_out = graph.module_node("b-out", MediaRole::StreamOutput, 2);
    graph.link(mic, b_in);

    let decisions = run(
        &graph,
        &ExclusionCtx {
            pipewire_pulse_pid: None,
            ..ctx()
        },
    );
    assert_partition(
        &decisions,
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("a-out", a_out, "tainted-owner-bridge"),
            ("b-out", b_out, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn coarse_keys_do_not_bridge_device_nodes() {
    // ⚠️ A rule added during implementation, NOT present in design v3.4.
    // Every ALSA device node is created by one WirePlumber process, so all
    // of them share one `client.id` and one `application.process.id`.
    // peerspeak's playback taints the default sink on every recompute; if
    // coarse keys bridged devices, that taint would jump to the microphone
    // source, and then every app holding a mic would lose its playback —
    // the exact §6.1.1 catastrophe by another route.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let mic = graph.device_node("mic", MediaRole::Source);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);
    let ff_in = graph.app_node("firefox-mic", MediaRole::StreamInput, 11114);
    let ff_out = graph.app_node("firefox-out", MediaRole::StreamOutput, 11114);
    graph.link(mic, ff_in);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("ff-out", ff_out)],
        &[("call", call, "peerspeak-owned")],
    );
    assert_tainted(&decisions, hw, "tainted-upstream");
    assert_untainted(&decisions, mic);
    assert_untainted(&decisions, ff_in);
}

#[test]
fn a_module_owned_device_still_bridges_on_its_strong_key() {
    // The other side of that rule: exception 2 must not disarm the bridge
    // for virtual sinks that genuinely belong to a module.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    let virt = graph.module_node("virtual-sink", MediaRole::Sink, 900_001);
    let leg = graph.module_node("virtual-out", MediaRole::StreamOutput, 900_001);
    graph.link(call, virt);
    graph.link(leg, hw);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("leg", leg, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn firefox_three_cases() {
    // v3.4 §6.1.1's table, as one graph with an exact partition.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let mic = graph.device_node("mic", MediaRole::Source);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);

    // 1. music only
    let music = graph.app_node("ff-music", MediaRole::StreamOutput, 1001);
    graph.link(music, hw);
    // 2. a Meet call: a mic input leg on an untainted source
    let meet_in = graph.app_node("ff-meet-in", MediaRole::StreamInput, 1002);
    let meet_out = graph.app_node("ff-meet-out", MediaRole::StreamOutput, 1002);
    graph.link(mic, meet_in);
    graph.link(meet_out, hw);
    // 3. screen-sharing with desktop audio: an input leg on a tainted monitor
    let share_in = graph.app_node("ff-share-in", MediaRole::StreamInput, 1003);
    let share_out = graph.app_node("ff-share-out", MediaRole::StreamOutput, 1003);
    graph.link(hw, share_in);
    graph.link(share_out, hw);

    assert_partition(
        &run(&graph, &ctx()),
        &[("music", music), ("meet-out", meet_out)],
        &[
            ("call", call, "peerspeak-owned"),
            ("share-out", share_out, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn an_unbounded_module_forwarder_fails_closed() {
    // v3.4 §12: "a module forwarder with neither link-group nor
    // pulse.module.id ⇒ unresolved ⇒ excluded". Its process id is the
    // daemon's (so key 4 is suppressed) and its legs carry different
    // `client.id`s, so nothing can enumerate its siblings.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);

    let in_client = graph.client(Some(PULSE_PID));
    let out_client = graph.client(Some(PULSE_PID));
    let fwd_in = graph.node("fwd-in", MediaRole::StreamInput, app(in_client, PULSE_PID));
    let fwd_out = graph.node(
        "fwd-out",
        MediaRole::StreamOutput,
        app(out_client, PULSE_PID),
    );
    graph.link(hw, fwd_in);

    // The blast radius must stay small: an ordinary app is bounded by its
    // own PID and must not be swept up.
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    graph.link(firefox, hw);

    assert_partition(
        &run(&graph, &ctx()),
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("fwd-out", fwd_out, "unresolved-owner"),
        ],
    );
}

#[test]
fn audio_duplex_over_taints_known_accepted() {
    // v3.4 §6.1 edge-type-2 caveat, asserted so that fixing it later is a
    // deliberate change and not a silent regression. A duplex device whose
    // playback side is tainted has its capture side treated as tainted too,
    // so an app recording from it loses its playback leg.
    let mut graph = Graph::new();
    let duplex = graph.device_node("duplex-card", MediaRole::Duplex);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, duplex);
    let rec_in = graph.app_node("rec-in", MediaRole::StreamInput, 4444);
    let rec_out = graph.app_node("rec-out", MediaRole::StreamOutput, 4444);
    graph.link(duplex, rec_in);

    assert_partition(
        &run(&graph, &ctx()),
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("rec-out", rec_out, "tainted-owner-bridge"),
        ],
    );
}

// ──────────────────────────────────────────────────────────────────────
// Unresolved ancestry — fail closed (v3.4 §6.1.4)
// ──────────────────────────────────────────────────────────────────────

#[test]
fn a_link_from_an_unknown_node_fails_closed() {
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let mystery_in = graph.app_node("mystery-in", MediaRole::StreamInput, 6000);
    let mystery_out = graph.app_node("mystery-out", MediaRole::StreamOutput, 6000);
    let ghost = graph.dangling_id();
    graph.link_ids(ghost, mystery_in.id);
    graph.link(mystery_out, hw);
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[("firefox", firefox)],
        &[("mystery-out", mystery_out, "tainted-owner-bridge")],
    );
    assert_tainted(&decisions, mystery_in, "unresolved-ancestry");
}

#[test]
fn an_ambiguous_recycled_global_id_fails_closed() {
    // Two live nodes claiming one id means the observer missed a removal,
    // so every edge touching that id is untrustworthy.
    let mut graph = Graph::new();
    let shared = graph.dangling_id();
    let client = graph.client_of_app(7001);
    let first = graph.node_with_id("first", MediaRole::StreamOutput, shared, app(client, 7001));
    let second = graph.node_with_id("second", MediaRole::StreamOutput, shared, app(client, 7002));
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);

    assert_partition(
        &run(&graph, &ctx()),
        &[("firefox", firefox)],
        &[
            ("first", first, "unresolved-ancestry"),
            ("second", second, "unresolved-ancestry"),
        ],
    );
}

// ──────────────────────────────────────────────────────────────────────
// Stickiness and lifetime-awareness (v3.4 §6.1.3)
// ──────────────────────────────────────────────────────────────────────

/// The scene the sticky tests share: one owner with a tainted input leg and
/// an output leg, plus an untouched bystander.
fn sticky_scene() -> (Graph, NodeRef, NodeRef, NodeRef, NodeRef) {
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);
    let rec_in = graph.app_node("rec-in", MediaRole::StreamInput, 8080);
    let rec_out = graph.app_node("rec-out", MediaRole::StreamOutput, 8080);
    graph.link(hw, rec_in);
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    (graph, call, rec_in, rec_out, firefox)
}

#[test]
fn sticky_taint_survives_the_tainted_input_leg_disappearing() {
    // The C3 buffered-audio defect: the recorder stops capturing, but its
    // 5-second ring buffer is still full of peerspeak's audio and no graph
    // event marks the moment it drains.
    let (graph, call, rec_in, rec_out, firefox) = sticky_scene();
    let c = ctx();
    let (first, sticky) = evaluate(&graph.build(), &c, &StickyState::default());
    assert_partition(
        &first,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("rec-out", rec_out, "tainted-owner-bridge"),
        ],
    );

    let (second, _) = evaluate(&graph.build_without(&[rec_in]), &c, &sticky);
    assert_partition(
        &second,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("rec-out", rec_out, "tainted-owner-bridge"),
        ],
    );
    assert!(
        matches!(
            second.candidates[&rec_out.serial].eligibility,
            Eligibility::NotEligible { sticky: true, .. }
        ),
        "the second exclusion must be recorded as sticky, not re-derived"
    );
}

#[test]
fn a_new_leg_of_a_still_tainted_owner_inherits_the_taint() {
    // Stickiness is per *owner*, not per node: the recorder opening a
    // second output stream after its input leg closed must not escape.
    let (mut graph, _, rec_in, _, _) = sticky_scene();
    let c = ctx();
    let (_, sticky) = evaluate(&graph.build(), &c, &StickyState::default());
    let late = graph.app_node("rec-out-2", MediaRole::StreamOutput, 8080);
    let (second, _) = evaluate(&graph.build_without(&[rec_in]), &c, &sticky);
    assert_eq!(
        second.candidates[&late.serial].reason().map(Reason::code),
        Some("tainted-owner-bridge")
    );
}

#[test]
fn sticky_taint_clears_once_every_owner_member_is_gone() {
    // Otherwise an app is unshareable forever, which is the over-exclusion
    // half of the trade and just as much a bug.
    let (mut graph, call, rec_in, rec_out, firefox) = sticky_scene();
    let c = ctx();
    let (_, sticky) = evaluate(&graph.build(), &c, &StickyState::default());

    // Full teardown: both legs and the client object.
    let recorder_client = graph.client_of_app(8080);
    graph.drop_clients(&[recorder_client]);
    let torn_down = graph.build_without(&[rec_in, rec_out]);
    let (_, sticky) = evaluate(&torn_down, &c, &sticky);
    assert!(
        sticky
            .owners
            .iter()
            .all(|owner| !owner.members.contains(&ObjectRef::Node(rec_out.serial))),
        "the recorder's sticky entry should have been dropped: {sticky:#?}"
    );

    // A brand-new recorder with the same PID starts clean.
    let fresh = graph.app_node("rec-out-fresh", MediaRole::StreamOutput, 8080);
    let (third, _) = evaluate(&graph.build_without(&[rec_in, rec_out]), &c, &sticky);
    assert_partition(
        &third,
        &[("firefox", firefox), ("fresh", fresh)],
        &[("call", call, "peerspeak-owned")],
    );
}

#[test]
fn recycled_ids_module_indices_and_link_groups_do_not_inherit_taint() {
    // Every one of these recycles on this stack — measured for module
    // indices, node ids and link-group strings. Only `object.serial` does
    // not, which is exactly why stickiness is keyed on it.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);
    let old_in = graph.group_node("old-in", MediaRole::StreamInput, "loopback-2541-13", 6100);
    let old_out = graph.group_node("old-out", MediaRole::StreamOutput, "loopback-2541-13", 6100);
    graph.link(hw, old_in);

    let c = ctx();
    let (first, sticky) = evaluate(&graph.build(), &c, &StickyState::default());
    assert_eq!(
        first.candidates[&old_out.serial].reason().map(Reason::code),
        Some("tainted-owner-bridge")
    );

    // Teardown, then a brand-new module reusing the global id, the PID and
    // the link-group string verbatim — everything except the serial.
    let old_client = graph.client_of_app(6100);
    graph.drop_clients(&[old_client]);
    let reborn_client = graph.client(Some(PULSE_PID));
    let reborn = graph.node_with_id(
        "reborn-out",
        MediaRole::StreamOutput,
        old_out.id,
        super::fixture::link_group("loopback-2541-13", reborn_client, 6100),
    );
    let (second, _) = evaluate(&graph.build_without(&[old_in, old_out]), &c, &sticky);
    assert_partition(
        &second,
        &[("reborn", reborn)],
        &[("call", call, "peerspeak-owned")],
    );
}

// ──────────────────────────────────────────────────────────────────────
// Regressions from Codex round 1 — each of these was a leak or a lost
// taint history, and each mutation-tests the fix that closed it.
// ──────────────────────────────────────────────────────────────────────

#[test]
fn sticky_taint_survives_when_only_the_client_object_remains() {
    // Finding 1. An app can close every stream it holds while keeping its
    // PipeWire connection open, then open a fresh one — Firefox does this
    // constantly. Seeding sticky taint only from live *nodes* let the new
    // leg come back Eligible while the owner's buffers were still full of
    // the call.
    let (mut graph, call, rec_in, rec_out, firefox) = sticky_scene();
    let c = ctx();
    let (_, sticky) = evaluate(&graph.build(), &c, &StickyState::default());

    // Both legs vanish; the client object does not.
    let late = graph.app_node("rec-out-late", MediaRole::StreamOutput, 8080);
    let (next, _) = evaluate(&graph.build_without(&[rec_in, rec_out]), &c, &sticky);
    assert_partition(
        &next,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("late", late, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn an_inbound_linked_node_of_unknown_role_still_bridges() {
    // Finding 2. "Receives audio" cannot be inferred from `media.class`
    // alone: a node with an absent or unexpected class sits on a real
    // inbound link carrying the call, and if it cannot start an owner
    // bridge its sibling output leg re-emits the call as Eligible.
    let mut graph = Graph::new();
    let sink = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, sink);

    let client = graph.client_of_app(8080);
    let unknown_in = graph.node("unknown-in", MediaRole::Other, app(client, 8080));
    let leaked_out = graph.node("leaked-out", MediaRole::StreamOutput, app(client, 8080));
    graph.link(sink, unknown_in);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("leaked-out", leaked_out, "tainted-owner-bridge"),
        ],
    );
    assert_tainted(&decisions, unknown_in, "tainted-upstream");
}

#[test]
fn a_candidate_that_is_itself_a_receiver_still_bridges_to_its_siblings() {
    // The other half of finding 2: a `Stream/Output/Audio` on an inbound
    // link is excluded by the link walk, but it must also be able to carry
    // taint across the owner bridge to its siblings.
    let mut graph = Graph::new();
    let sink = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, sink);

    let odd_in = graph.app_node("odd-in", MediaRole::StreamOutput, 9100);
    let sibling = graph.app_node("sibling-out", MediaRole::StreamOutput, 9100);
    graph.link(sink, odd_in);

    assert_partition(
        &run(&graph, &ctx()),
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("odd-in", odd_in, "tainted-upstream"),
            ("sibling", sibling, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn a_native_virtual_sink_bridges_on_its_client() {
    // Finding 3. The device exception is keyed on `device.id`, not on the
    // node's role: an app that creates its own `Audio/Sink` plus a
    // re-emitting stream on one client has no `device.id`, no link-group
    // and no `pulse.module.id`, so `client.id` is the *only* thing relating
    // the two. Suppressing coarse keys by role stripped it and leaked the
    // whole call.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    let virtual_sink = graph.native_virtual_node("native-virtual-sink", MediaRole::Sink, 4321);
    let reemitter = graph.native_virtual_node("native-output", MediaRole::StreamOutput, 4321);
    graph.link(call, virtual_sink);
    graph.link(reemitter, hw);

    let decisions = run(&graph, &ctx());
    assert_partition(
        &decisions,
        &[],
        &[
            ("call", call, "peerspeak-owned"),
            ("reemitter", reemitter, "tainted-owner-bridge"),
        ],
    );
    assert_eq!(
        decisions.taint[&reemitter.serial].reason,
        Reason::TaintedOwnerBridge {
            key: Some(OwnerKey::ClientId)
        }
    );
}

#[test]
fn an_asymmetric_forwarder_fails_closed() {
    // Finding 4. The reader carries a `node.link-group` and is therefore
    // "bounded", but its re-emitting leg carries none, so the strong key
    // finds no sibling. Requiring the *source* to be unbounded let this
    // through as Eligible.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);

    let in_client = graph.client(Some(PULSE_PID));
    let out_client = graph.client(Some(PULSE_PID));
    let fwd_in = graph.node(
        "fwd-in",
        MediaRole::StreamInput,
        NodeProps {
            link_group: Some("asymmetric-forwarder".into()),
            client_id: Some(in_client),
            process_id: Some(PULSE_PID),
            ..NodeProps::default()
        },
    );
    let fwd_out = graph.node(
        "fwd-out",
        MediaRole::StreamOutput,
        app(out_client, PULSE_PID),
    );
    graph.link(hw, fwd_in);

    // Blast radius control: a real app is bounded by its own PID.
    let firefox = graph.app_node("firefox", MediaRole::StreamOutput, 11114);
    graph.link(firefox, hw);

    assert_partition(
        &run(&graph, &ctx()),
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("fwd-out", fwd_out, "unresolved-owner"),
        ],
    );
}

#[test]
fn a_not_ready_snapshot_never_retires_sticky_owners() {
    // Finding 5. `graph_ready == false` says "this view of the graph is not
    // trustworthy". Retiring sticky owners because their members are absent
    // from an untrustworthy snapshot erases the taint history, and the next
    // ready recompute hands back a clean bill of health for an owner that
    // never went away.
    let (graph, call, rec_in, rec_out, firefox) = sticky_scene();
    let c = ctx();
    let (_, sticky) = evaluate(&graph.build(), &c, &StickyState::default());

    let not_ready = ExclusionCtx {
        graph_ready: false,
        ..ctx()
    };
    let (_, carried) = evaluate(
        &super::snapshot::GraphSnapshot::default(),
        &not_ready,
        &sticky,
    );
    assert_eq!(
        carried, sticky,
        "a not-ready recompute must not edit history"
    );

    let (after, _) = evaluate(&graph.build_without(&[rec_in]), &c, &carried);
    assert_partition(
        &after,
        &[("firefox", firefox)],
        &[
            ("call", call, "peerspeak-owned"),
            ("rec-out", rec_out, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn taint_crosses_two_chained_forwarders() {
    // Finding 6. Every earlier fixture needed at most one owner hop, so
    // replacing the fixpoint with a single pass of each rule survived the
    // whole suite. Two chained forwarders need two.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    let sink1 = graph.module_node("sink1", MediaRole::Sink, 100);
    graph.link(call, sink1);

    let fwd1_in = graph.module_node("fwd1-in", MediaRole::StreamInput, 101);
    let fwd1_out = graph.module_node("fwd1-out", MediaRole::StreamOutput, 101);
    graph.link(sink1, fwd1_in);

    let sink2 = graph.module_node("sink2", MediaRole::Sink, 102);
    graph.link(fwd1_out, sink2);
    let fwd2_in = graph.module_node("fwd2-in", MediaRole::StreamInput, 103);
    let fwd2_out = graph.module_node("fwd2-out", MediaRole::StreamOutput, 103);
    graph.link(sink2, fwd2_in);
    graph.link(fwd2_out, hw);

    // Negative control: an unrelated clean forwarder chain of the same shape.
    let clean_sink = graph.device_node("clean-sink", MediaRole::Sink);
    let clean_in = graph.module_node("clean-in", MediaRole::StreamInput, 200);
    let clean_out = graph.module_node("clean-out", MediaRole::StreamOutput, 200);
    graph.link(clean_sink, clean_in);
    graph.link(clean_out, hw);

    assert_partition(
        &run(&graph, &ctx()),
        &[("clean-out", clean_out)],
        &[
            ("call", call, "peerspeak-owned"),
            ("fwd1-out", fwd1_out, "tainted-owner-bridge"),
            ("fwd2-out", fwd2_out, "tainted-owner-bridge"),
        ],
    );
}

#[test]
fn a_stronger_reason_replaces_a_weaker_one_regardless_of_arrival_order() {
    // Finding 7. The old determinism test reversed two links that never
    // competed, so a first-write-wins `raise()` survived it. Here a node is
    // reached by the owner bridge on the first fixpoint pass and by a
    // direct tainted link on the second; the direct link is the stronger
    // reason and must win.
    let build = |reverse: bool| {
        let mut graph = Graph::new();
        let hw = graph.device_node("hw-sink", MediaRole::Sink);
        let call = graph.peerspeak_node("peerspeak", 7);
        graph.link(call, hw);
        let rec_in = graph.app_node("rec-in", MediaRole::StreamInput, 5000);
        let mid = graph.app_node("mid-out", MediaRole::StreamOutput, 5000);
        let owned_sink = graph.native_virtual_node("owned-sink", MediaRole::Sink, 5000);
        if reverse {
            graph.link(mid, owned_sink);
            graph.link(hw, rec_in);
        } else {
            graph.link(hw, rec_in);
            graph.link(mid, owned_sink);
        }
        let decisions = run(&graph, &ctx());
        (
            decisions.taint[&owned_sink.serial].reason.code(),
            decisions.excluded(),
        )
    };
    let forward = build(false);
    assert_eq!(
        forward.0, "tainted-upstream",
        "bridged first, then reached directly — the direct link is stronger"
    );
    assert_eq!(forward, build(true), "and it must not depend on link order");
}

#[test]
fn a_recycled_client_id_and_module_index_do_not_inherit_taint() {
    // Finding 8. The original recycling test never reused a
    // `pulse.module.id`, and its "fresh" client silently reused the dead
    // client's global id because the fixture cache was stale — so the node
    // pointed at a client object that no longer existed.
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    graph.link(call, hw);
    let old_in = graph.module_node("old-in", MediaRole::StreamInput, 536_870_919);
    let old_out = graph.module_node("old-out", MediaRole::StreamOutput, 536_870_919);
    graph.link(hw, old_in);

    let c = ctx();
    let (first, sticky) = evaluate(&graph.build(), &c, &StickyState::default());
    assert_eq!(
        first.candidates[&old_out.serial].reason().map(Reason::code),
        Some("tainted-owner-bridge")
    );

    // Full teardown, then a module that reuses the node id, the client id
    // and the module index verbatim. Only the serials are new — which is
    // the entire reason stickiness is keyed on them.
    let old_client = graph.client_of_module(536_870_919);
    graph.drop_clients(&[old_client]);
    let reborn_client = graph.client_with_id(old_client, Some(PULSE_PID));
    let reborn = graph.node_with_id(
        "reborn-out",
        MediaRole::StreamOutput,
        old_out.id,
        super::fixture::pulse_module(reborn_client, 536_870_919, PULSE_PID),
    );
    let (second, _) = evaluate(&graph.build_without(&[old_in, old_out]), &c, &sticky);
    assert_partition(
        &second,
        &[("reborn", reborn)],
        &[("call", call, "peerspeak-owned")],
    );
}

#[test]
fn a_deep_forwarder_chain_converges() {
    // Finding 9. The fixpoint is monotone so it terminates, but each pass
    // re-runs a full link BFS and a full owner scan, so a chain of owner
    // hops costs one pass per layer. This is the shape that would expose an
    // accidental blow-up; phase 5 measures the real distribution.
    const LAYERS: u64 = 60;
    let mut graph = Graph::new();
    let hw = graph.device_node("hw-sink", MediaRole::Sink);
    let call = graph.peerspeak_node("peerspeak", 7);
    let mut upstream = graph.module_node("sink-0", MediaRole::Sink, 1);
    graph.link(call, upstream);
    let mut last_out = None;
    for layer in 1..=LAYERS {
        let module = 1000 + layer;
        let leg_in = graph.module_node(&format!("fwd-{layer}-in"), MediaRole::StreamInput, module);
        let leg_out =
            graph.module_node(&format!("fwd-{layer}-out"), MediaRole::StreamOutput, module);
        graph.link(upstream, leg_in);
        let next = graph.module_node(&format!("sink-{layer}"), MediaRole::Sink, 2000 + layer);
        graph.link(leg_out, next);
        upstream = next;
        last_out = Some(leg_out);
    }
    graph.link(last_out.expect("at least one layer"), hw);

    let decisions = run(&graph, &ctx());
    assert_eq!(
        decisions.eligible(),
        Vec::new(),
        "every leg of the chain carries the call"
    );
    assert_eq!(
        decisions.candidates.len(),
        LAYERS as usize + 1,
        "the whole chain plus peerspeak's own playback"
    );
}