plushie-renderer 0.7.1

//! Integration test: verify session multiplexing in mock mode.
//!
//! Spawns `plushie --mock --max-sessions 4 --json` as a subprocess,
//! sends interleaved messages with different session IDs, and verifies
//! that responses come back tagged with the correct session.

use std::io::{BufRead, BufReader, Read, Write};
use std::process::{Child, ChildStderr, Command, Stdio};
use std::sync::mpsc;
use std::sync::{Arc, Mutex};
use std::time::Duration;

/// Default timeout for reading a single response from the subprocess.
/// Long enough for CI, short enough to catch real hangs.
const RECV_TIMEOUT: Duration = Duration::from_secs(10);

fn send(stdin: &mut impl Write, msg: &serde_json::Value) {
    let line = serde_json::to_string(msg).unwrap();
    writeln!(stdin, "{line}").unwrap();
    stdin.flush().unwrap();
}

/// A line receiver backed by a dedicated reader thread.
///
/// The blocking `read_line` loop runs on a background thread and
/// sends parsed JSON values through a channel. Tests call `recv()`
/// with a timeout so they fail with a clear message instead of
/// hanging forever if the subprocess stops responding.
struct LineReceiver {
    rx: mpsc::Receiver<serde_json::Value>,
    _handle: std::thread::JoinHandle<()>,
}

impl LineReceiver {
    fn new(stdout: std::process::ChildStdout) -> Self {
        let (tx, rx) = mpsc::channel();
        let handle = std::thread::spawn(move || {
            let mut reader = BufReader::new(stdout);
            loop {
                let mut line = String::new();
                match reader.read_line(&mut line) {
                    Ok(0) => break, // EOF
                    Ok(_) => {
                        let trimmed = line.trim();
                        if trimmed.is_empty() {
                            continue;
                        }
                        match serde_json::from_str(trimmed) {
                            Ok(val) => {
                                if tx.send(val).is_err() {
                                    break; // receiver dropped
                                }
                            }
                            Err(e) => {
                                panic!("failed to parse JSON from subprocess: {e}\nraw: {line:?}");
                            }
                        }
                    }
                    Err(e) => {
                        panic!("read_line failed: {e}");
                    }
                }
            }
        });
        Self {
            rx,
            _handle: handle,
        }
    }

    fn recv(&self) -> serde_json::Value {
        self.recv_timeout(RECV_TIMEOUT)
    }

    /// Receive the next non-status message, skipping any status events.
    fn recv_skip_status(&self) -> serde_json::Value {
        loop {
            let msg = self.recv();
            if msg.get("family").and_then(|f| f.as_str()) == Some("status") {
                continue;
            }
            return msg;
        }
    }

    fn recv_timeout(&self, timeout: Duration) -> serde_json::Value {
        match self.rx.recv_timeout(timeout) {
            Ok(val) => val,
            Err(mpsc::RecvTimeoutError::Timeout) => {
                panic!(
                    "recv timed out after {:.1}s waiting for subprocess response",
                    timeout.as_secs_f64()
                );
            }
            Err(mpsc::RecvTimeoutError::Disconnected) => {
                panic!("subprocess stdout closed unexpectedly (reader thread exited)");
            }
        }
    }
}

fn plushie_binary() -> String {
    // The integration test binary is in target/debug/deps. The plushie
    // binary is in target/debug.
    let mut path = std::env::current_exe().unwrap();
    path.pop(); // remove test binary name
    path.pop(); // remove deps/
    path.push("plushie-renderer");
    path.to_string_lossy().to_string()
}

/// Capture the child's stderr in a background thread and expose a
/// drop-time guard that dumps the captured text to the test's stderr
/// if the test panics. Non-panic drops stay silent so successful runs
/// don't leak log spam.
struct StderrCapture {
    buffer: Arc<Mutex<Vec<u8>>>,
    _handle: std::thread::JoinHandle<()>,
}

impl StderrCapture {
    fn spawn(stderr: ChildStderr) -> Self {
        let buffer = Arc::new(Mutex::new(Vec::new()));
        let buf_for_thread = Arc::clone(&buffer);
        let handle = std::thread::spawn(move || {
            let mut reader = stderr;
            let mut chunk = [0u8; 4096];
            loop {
                match reader.read(&mut chunk) {
                    Ok(0) => break,
                    Ok(n) => {
                        if let Ok(mut guard) = buf_for_thread.lock() {
                            guard.extend_from_slice(&chunk[..n]);
                        }
                    }
                    Err(_) => break,
                }
            }
        });
        Self {
            buffer,
            _handle: handle,
        }
    }

    fn snapshot(&self) -> String {
        let guard = self.buffer.lock().unwrap();
        String::from_utf8_lossy(&guard).into_owned()
    }
}

impl Drop for StderrCapture {
    fn drop(&mut self) {
        if std::thread::panicking() {
            let text = self.snapshot();
            if !text.is_empty() {
                eprintln!("---- captured renderer stderr ----\n{text}\n---- end ----");
            }
        }
    }
}

/// Spawn the renderer with stdin/stdout piped and stderr captured
/// into a guard that dumps on test panic. Replaces the prior
/// `Stdio::null()` usage so renderer diagnostics are visible when
/// subprocess-driven tests fail.
fn spawn_renderer(args: &[&str]) -> (Child, StderrCapture) {
    let mut child = Command::new(plushie_binary())
        .args(args)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped())
        .spawn()
        .expect("failed to spawn plushie");
    let stderr = child
        .stderr
        .take()
        .expect("renderer subprocess should expose stderr");
    let capture = StderrCapture::spawn(stderr);
    (child, capture)
}

/// Render mode selector for parity helpers. `Mock` runs the
/// protocol-only path, `Headless` runs the real iced pipeline via
/// tiny-skia. Any widget-event test that lands in `Mock` should
/// also pass in `Headless`; use `run_in_both_modes` to make that
/// a compile-time-obvious invariant.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Mode {
    Mock,
    Headless,
}

impl Mode {
    fn flag(self) -> &'static str {
        match self {
            Mode::Mock => "--mock",
            Mode::Headless => "--headless",
        }
    }

    fn label(self) -> &'static str {
        match self {
            Mode::Mock => "mock",
            Mode::Headless => "headless",
        }
    }
}

/// Run a test body against the named renderer modes.
///
/// A panic in one mode is reported with the mode name so the failure
/// message identifies which branch diverged.
fn run_in_modes(modes: &[Mode], body: impl Fn(Mode)) {
    for &mode in modes {
        let label = mode.label();
        let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| body(mode)));
        if let Err(payload) = result {
            let msg = payload
                .downcast_ref::<&'static str>()
                .copied()
                .or_else(|| payload.downcast_ref::<String>().map(|s| s.as_str()))
                .unwrap_or("(non-string panic)");
            panic!("test body failed in {label} mode: {msg}");
        }
    }
}

/// Run a test body against both mock and headless renderer modes.
///
/// This is the pattern new widget-event tests should follow: write
/// the scenario once, then exercise both backends to keep mock and
/// headless in sync.
fn run_in_both_modes(body: impl Fn(Mode)) {
    run_in_modes(&[Mode::Mock, Mode::Headless], body);
}

#[test]
fn hello_message_has_empty_session() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    // Send initial settings to trigger hello.
    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );

    let hello = stdout.recv();
    assert_eq!(hello["type"], "hello");
    assert_eq!(hello["session"], "");

    drop(stdin);
    child.wait().unwrap();
}

#[test]
fn hello_message_fields() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );

    let hello = stdout.recv();
    assert_eq!(hello["type"], "hello");

    let protocol_version = serde_json::json!(plushie_widget_sdk::protocol::PROTOCOL_VERSION);
    assert_eq!(
        hello["protocol_version"], protocol_version,
        "hello.protocol_version should match PROTOCOL_VERSION"
    );
    assert_eq!(
        hello["protocol"], protocol_version,
        "hello.protocol should mirror hello.protocol_version"
    );
    assert_eq!(
        hello["codec"], "json",
        "hello.codec should confirm the JSON transport codec"
    );
    assert!(hello.get("extensions").is_none());

    let native_widgets = hello["native_widgets"]
        .as_array()
        .expect("hello.native_widgets should be an array");
    assert!(native_widgets.is_empty());

    assert_eq!(hello["widget_sets"], serde_json::json!(["iced"]));

    let widgets = hello["widgets"]
        .as_array()
        .expect("hello.widgets should be an array");
    assert!(widgets.iter().any(|name| name.as_str() == Some("button")));
    assert!(widgets.iter().any(|name| name.as_str() == Some("text")));

    // Mode: the test uses --mock.
    assert_eq!(
        hello["mode"], "mock",
        "hello.mode should be \"mock\" for --mock flag"
    );

    // Version: non-empty string (crate version).
    let version = hello["version"]
        .as_str()
        .expect("hello.version should be a string");
    assert!(
        !version.is_empty(),
        "hello.version should be a non-empty string"
    );

    // Name: should be "plushie-renderer".
    assert_eq!(
        hello["name"], "plushie-renderer",
        "hello.name should be \"plushie-renderer\""
    );

    drop(stdin);
    child.wait().unwrap();
}

#[test]
fn single_session_echoes_session_id() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    send(
        &mut stdin,
        &serde_json::json!({"session": "test_1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let _hello = stdout.recv();

    // Send a reset and verify session is echoed.
    send(
        &mut stdin,
        &serde_json::json!({"session": "test_1", "type": "reset", "id": "r1"}),
    );
    let resp = stdout.recv();
    assert_eq!(resp["type"], "reset_response");
    assert_eq!(resp["session"], "test_1");
    assert_eq!(resp["id"], "r1");

    drop(stdin);
    child.wait().unwrap();
}

#[test]
fn multiplexed_sessions_are_isolated() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--max-sessions", "4", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    // Consume hello.
    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let _hello = stdout.recv();

    // Send snapshots to two different sessions with different trees.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "snapshot",
            "tree": {"id": "root", "type": "text", "props": {"content": "session one"}, "children": []}
        }),
    );
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s2",
            "type": "snapshot",
            "tree": {"id": "root", "type": "text", "props": {"content": "session two"}, "children": []}
        }),
    );

    // Query tree from each session: they should have different content.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "query",
            "id": "q1",
            "target": "tree",
            "selector": {}
        }),
    );
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s2",
            "type": "query",
            "id": "q2",
            "target": "tree",
            "selector": {}
        }),
    );

    // Collect both responses (order may vary due to threading).
    let r1 = stdout.recv();
    let r2 = stdout.recv();

    let mut responses: std::collections::HashMap<String, serde_json::Value> =
        std::collections::HashMap::new();
    responses.insert(r1["session"].as_str().unwrap().to_string(), r1);
    responses.insert(r2["session"].as_str().unwrap().to_string(), r2);

    let s1_tree = &responses["s1"];
    assert_eq!(s1_tree["type"], "query_response");
    assert_eq!(s1_tree["id"], "q1");
    assert_eq!(s1_tree["data"]["props"]["content"], "session one");

    let s2_tree = &responses["s2"];
    assert_eq!(s2_tree["type"], "query_response");
    assert_eq!(s2_tree["id"], "q2");
    assert_eq!(s2_tree["data"]["props"]["content"], "session two");

    drop(stdin);
    child.wait().unwrap();
}

#[test]
fn reset_tears_down_session() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--max-sessions", "4", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let _hello = stdout.recv();

    // Create a session, send a tree, reset it.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "snapshot",
            "tree": {"id": "root", "type": "text", "props": {"content": "before"}, "children": []}
        }),
    );
    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "reset", "id": "r1"}),
    );

    // After reset, the session thread emits both a reset_response
    // (for the reset request) and a session_closed event (as the
    // final lifecycle message before the session thread exits).
    // The relative order is not load-bearing; collect both and
    // assert on the multiset.
    let first = stdout.recv();
    let second = stdout.recv();
    let messages = [first, second];

    let reset_response = messages
        .iter()
        .find(|m| m["type"] == "reset_response")
        .unwrap_or_else(|| panic!("expected a reset_response, got: {messages:?}"));
    assert_eq!(reset_response["id"], "r1");

    let closed_event = messages
        .iter()
        .find(|m| m["type"] == "event" && m["family"] == "session_closed")
        .unwrap_or_else(|| panic!("expected a session_closed event, got: {messages:?}"));
    assert_eq!(closed_event["session"], "s1");

    // Reuse the same session ID: should get a fresh session.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "query",
            "id": "q1",
            "target": "tree",
            "selector": {}
        }),
    );

    let tree_resp = stdout.recv();
    assert_eq!(tree_resp["session"], "s1");
    // Tree should be null (fresh session, no snapshot sent).
    assert!(tree_resp["data"].is_null());

    drop(stdin);
    child.wait().unwrap();
}

// FIXME: skipped on Windows. The renderer subprocess hangs in
// `--headless` mode when a synthetic click reaches iced's tiny-skia
// event-injection path; the test times out at 10s waiting for the
// `interact_response`. The mock-mode equivalents in this file pass on
// Windows, so the protocol contract is fine; the issue is in the
// headless rendering loop on that platform. Needs a Windows debugging
// pass to root-cause; until then we keep the test exercising the path
// on Linux and macOS where it's known good.
#[cfg(not(target_os = "windows"))]
#[test]
fn headless_interact_step_round_trip() {
    let (mut child, _stderr) = spawn_renderer(&["--headless", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    // Bootstrap: settings + hello.
    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let _hello = stdout.recv();

    // Send a tree with a button.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "snapshot",
            "tree": {
                "id": "main", "type": "window", "props": {}, "children": [
                    {"id": "root", "type": "column", "props": {}, "children": [
                        {"id": "btn1", "type": "button", "props": {"label": "Click me"}, "children": []}
                    ]}
                ]
            }
        }),
    );

    // Click the button. In headless mode, this injects CursorMoved +
    // ButtonPressed + ButtonReleased. The ButtonReleased should
    // produce a Click message, emitted as an interact_step.
    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "interact",
            "id": "i1",
            "action": "click",
            "selector": {"by": "id", "value": "btn1"},
            "payload": {}
        }),
    );

    // Semantic actions (click, toggle, select) use the synthetic path
    // in all modes. Returns a single interact_response with events.
    // Skip any status events emitted during the interaction.
    let resp = stdout.recv_skip_status();
    assert_eq!(resp["type"], "interact_response");
    assert_eq!(resp["session"], "s1");
    assert_eq!(resp["id"], "i1");
    assert!(resp["events"].is_array());
    let events = resp["events"].as_array().unwrap();
    assert!(!events.is_empty(), "response should have events");
    assert_eq!(events[0]["family"], "click");
    assert_eq!(events[0]["id"], "btn1");

    drop(stdin);
    child.wait().unwrap();
}

#[test]
fn headless_advance_frame_emits_timestamp_object() {
    let (mut child, _stderr) = spawn_renderer(&["--headless", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let stdout = LineReceiver::new(child.stdout.take().unwrap());

    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let _hello = stdout.recv();

    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "subscribe",
            "kind": "on_animation_frame",
            "tag": "anim",
        }),
    );

    send(
        &mut stdin,
        &serde_json::json!({
            "session": "s1",
            "type": "advance_frame",
            "timestamp": 16_000,
        }),
    );

    let msg = stdout.recv_skip_status();
    assert_eq!(msg["type"], "event");
    assert_eq!(msg["session"], "s1");
    assert_eq!(msg["family"], "animation_frame");
    assert_eq!(msg["tag"], "anim");
    assert_eq!(msg["value"], serde_json::json!({"timestamp": 16_000}));

    drop(stdin);
    child.wait().unwrap();
}

// ---------------------------------------------------------------------------
// Widget render, concurrent session, and validate_props tests below
// use the LineReceiver defined at the top of this file.

// ---------------------------------------------------------------------------
// Widget-event tests: each runs against both mock and headless mode
// through run_in_both_modes so parity can't drift silently.
// ---------------------------------------------------------------------------

#[test]
fn text_input_emits_input_event_in_both_modes() {
    // FIXME: the headless arm hangs on Windows when the synthetic
    // text-input commit path reaches iced's tiny-skia event loop.
    // See `headless_interact_step_round_trip` for the same symptom.
    // Mock mode still validates the wire contract on Windows; the
    // headless arm runs everywhere else.
    #[cfg(target_os = "windows")]
    let modes: &[Mode] = &[Mode::Mock];
    #[cfg(not(target_os = "windows"))]
    let modes: &[Mode] = &[Mode::Mock, Mode::Headless];
    run_in_modes(modes, |mode| {
        let (mut child, _stderr) = spawn_renderer(&[mode.flag(), "--json"]);

        let mut stdin = child.stdin.take().unwrap();
        let receiver = LineReceiver::new(child.stdout.take().unwrap());
        let timeout = Duration::from_secs(10);

        // Bootstrap.
        send(
            &mut stdin,
            &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
        );
        let hello = receiver.recv_timeout(timeout);
        assert_eq!(hello["type"], "hello");

        // Send a tree with a text_input widget.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "snapshot",
                "tree": {
                    "id": "main", "type": "window", "props": {}, "children": [
                        {"id": "root", "type": "column", "props": {}, "children": [
                            {"id": "inp1", "type": "text_input", "props": {"value": "", "placeholder": "Type here"}, "children": []}
                        ]}
                    ]
                }
            }),
        );

        // Interact: type_text on the text_input.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "interact",
                "id": "i1",
                "action": "type_text",
                "selector": {"by": "id", "value": "inp1"},
                "payload": {"text": "hello"}
            }),
        );

        // Collect events from interact_step and interact_response messages.
        // The type_text action may produce steps that require snapshot replies.
        let mut all_events = Vec::new();
        loop {
            let msg = receiver.recv_skip_status();
            if msg["type"] == "interact_step" {
                assert_eq!(msg["session"], "s1");
                if let Some(evts) = msg["events"].as_array() {
                    all_events.extend(evts.clone());
                }
                send(
                    &mut stdin,
                    &serde_json::json!({
                        "session": "s1",
                        "type": "snapshot",
                        "tree": {
                            "id": "main", "type": "window", "props": {}, "children": [
                                {"id": "root", "type": "column", "props": {}, "children": [
                                    {"id": "inp1", "type": "text_input", "props": {"value": "hello"}, "children": []}
                                ]}
                            ]
                        }
                    }),
                );
            } else if msg["type"] == "interact_response" {
                assert_eq!(msg["session"], "s1");
                assert_eq!(msg["id"], "i1");
                if let Some(evts) = msg["events"].as_array() {
                    all_events.extend(evts.clone());
                }
                break;
            } else {
                panic!("unexpected message type: {}", msg["type"]);
            }
        }

        let input_event = all_events
            .iter()
            .find(|e| e["family"] == "input")
            .unwrap_or_else(|| panic!("expected an input event in: {all_events:?}"));
        assert_eq!(input_event["id"], "inp1");
        assert_eq!(input_event["value"], "hello");

        drop(stdin);
        child.wait().unwrap();
    });
}

#[test]
fn checkbox_emits_toggle_event_in_both_modes() {
    // FIXME: see `text_input_emits_input_event_in_both_modes`. The
    // headless arm hangs on Windows during synthetic click injection.
    #[cfg(target_os = "windows")]
    let modes: &[Mode] = &[Mode::Mock];
    #[cfg(not(target_os = "windows"))]
    let modes: &[Mode] = &[Mode::Mock, Mode::Headless];
    run_in_modes(modes, |mode| {
        let (mut child, _stderr) = spawn_renderer(&[mode.flag(), "--json"]);

        let mut stdin = child.stdin.take().unwrap();
        let receiver = LineReceiver::new(child.stdout.take().unwrap());
        let timeout = Duration::from_secs(10);

        send(
            &mut stdin,
            &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
        );
        let hello = receiver.recv_timeout(timeout);
        assert_eq!(hello["type"], "hello");

        // Send a tree with a checkbox widget.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "snapshot",
                "tree": {
                    "id": "main", "type": "window", "props": {}, "children": [
                        {"id": "root", "type": "column", "props": {}, "children": [
                            {"id": "chk1", "type": "checkbox", "props": {"label": "Accept", "checked": false}, "children": []}
                        ]}
                    ]
                }
            }),
        );

        // Interact: toggle the checkbox. Both modes use the full iced
        // pipeline, so toggle injects real mouse events which produce
        // interact_step messages followed by the final interact_response.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "interact",
                "id": "i1",
                "action": "toggle",
                "selector": {"by": "id", "value": "chk1"},
                "payload": {"value": true}
            }),
        );

        // Collect all interact_step events, sending back a snapshot after
        // each step (the renderer blocks waiting for the host's tree update).
        let mut toggle_events = Vec::new();
        loop {
            let msg = receiver.recv_timeout(timeout);
            if msg["type"] == "interact_step" {
                assert_eq!(msg["session"], "s1");
                assert_eq!(msg["id"], "i1");
                if let Some(evts) = msg["events"].as_array() {
                    toggle_events.extend(evts.clone());
                }
                // Send back the same tree so the renderer can proceed.
                send(
                    &mut stdin,
                    &serde_json::json!({
                        "session": "s1",
                        "type": "snapshot",
                        "tree": {
                            "id": "main", "type": "window", "props": {}, "children": [
                                {"id": "root", "type": "column", "props": {}, "children": [
                                    {"id": "chk1", "type": "checkbox", "props": {"label": "Accept", "checked": true}, "children": []}
                                ]}
                            ]
                        }
                    }),
                );
            } else if msg["type"] == "interact_response" {
                assert_eq!(msg["session"], "s1");
                assert_eq!(msg["id"], "i1");
                // Any remaining events from the final response.
                if let Some(evts) = msg["events"].as_array() {
                    toggle_events.extend(evts.clone());
                }
                break;
            } else if msg.get("family").and_then(|f| f.as_str()) == Some("status") {
                // Skip status change events during interaction.
                continue;
            } else {
                panic!("unexpected message type: {}", msg["type"]);
            }
        }

        // The toggle event should have been produced by the iced pipeline.
        assert!(
            toggle_events.iter().any(|e| e["family"] == "toggle"),
            "expected a toggle event in the interact flow, got: {toggle_events:?}"
        );

        drop(stdin);
        child.wait().unwrap();
    });
}

#[test]
fn slider_emits_slide_event_in_both_modes() {
    run_in_both_modes(|mode| {
        let (mut child, _stderr) = spawn_renderer(&[mode.flag(), "--json"]);

        let mut stdin = child.stdin.take().unwrap();
        let receiver = LineReceiver::new(child.stdout.take().unwrap());
        let timeout = Duration::from_secs(10);

        send(
            &mut stdin,
            &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
        );
        let hello = receiver.recv_timeout(timeout);
        assert_eq!(hello["type"], "hello");

        // Send a tree with a slider widget.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "snapshot",
                "tree": {
                    "id": "main", "type": "window", "props": {}, "children": [
                        {"id": "root", "type": "column", "props": {}, "children": [
                            {"id": "sld1", "type": "slider", "props": {"value": 50, "range": [0, 100]}, "children": []}
                        ]}
                    ]
                }
            }),
        );

        // Interact: slide to a new value.
        send(
            &mut stdin,
            &serde_json::json!({
                "session": "s1",
                "type": "interact",
                "id": "i1",
                "action": "slide",
                "selector": {"by": "id", "value": "sld1"},
                "payload": {"value": 75.0}
            }),
        );

        let resp = receiver.recv_skip_status();
        assert_eq!(resp["type"], "interact_response");
        assert_eq!(resp["session"], "s1");
        assert_eq!(resp["id"], "i1");

        let events = resp["events"]
            .as_array()
            .expect("events should be an array");
        let slide_event = events
            .iter()
            .find(|e| e["family"] == "slide")
            .expect("expected a slide event");
        assert_eq!(slide_event["id"], "sld1");
        assert_eq!(events[0]["value"], 75.0);

        drop(stdin);
        child.wait().unwrap();
    });
}

// ---------------------------------------------------------------------------
// Item 6: Concurrent session stress test
// ---------------------------------------------------------------------------

#[test]
fn concurrent_sessions_interleaved() {
    let (mut child, _stderr) = spawn_renderer(&["--mock", "--max-sessions", "4", "--json"]);

    let mut stdin = child.stdin.take().unwrap();
    let receiver = LineReceiver::new(child.stdout.take().unwrap());
    let timeout = Duration::from_secs(10);

    // Bootstrap.
    send(
        &mut stdin,
        &serde_json::json!({"session": "s1", "type": "settings", "settings": {"protocol_version": 1}}),
    );
    let hello = receiver.recv_timeout(timeout);
    assert_eq!(hello["type"], "hello");

    let session_ids = ["s1", "s2", "s3", "s4"];

    // Send snapshots to all 4 sessions interleaved.
    for &sid in &session_ids {
        send(
            &mut stdin,
            &serde_json::json!({
                "session": sid,
                "type": "snapshot",
                "tree": {
                    "id": "root",
                    "type": "text",
                    "props": {"content": format!("content-{sid}")},
                    "children": []
                }
            }),
        );
    }

    // Query each session's tree.
    for (i, &sid) in session_ids.iter().enumerate() {
        send(
            &mut stdin,
            &serde_json::json!({
                "session": sid,
                "type": "query",
                "id": format!("q{}", i + 1),
                "target": "tree",
                "selector": {}
            }),
        );
    }

    // Collect all 4 responses (order may vary due to threading).
    let mut responses: std::collections::HashMap<String, serde_json::Value> =
        std::collections::HashMap::new();
    for _ in 0..4 {
        let resp = receiver.recv_timeout(timeout);
        let session = resp["session"].as_str().unwrap().to_string();
        responses.insert(session, resp);
    }

    // Verify each response has the correct session ID and content.
    for &sid in &session_ids {
        let resp = responses
            .get(sid)
            .unwrap_or_else(|| panic!("missing response for session {sid}"));
        assert_eq!(resp["type"], "query_response");
        assert_eq!(
            resp["data"]["props"]["content"],
            format!("content-{sid}"),
            "session {sid} should have its own tree content"
        );
    }

    drop(stdin);
    child.wait().unwrap();
}