cu29_runtime/

cutask.rs

//! This module contains all the main definition of the traits you need to implement
//! or interact with to create a Copper task.

use crate::config::ComponentConfig;
use crate::context::CuContext;
use crate::reflect::{GetTypeRegistration, Reflect, TypePath, TypeRegistry};
#[cfg(feature = "reflect")]
use bevy_reflect;
use bincode::de::{Decode, Decoder};
use bincode::enc::{Encode, Encoder};
use bincode::error::{DecodeError, EncodeError};
use compact_str::{CompactString, ToCompactString};
use core::any::{TypeId, type_name};
use cu29_clock::{PartialCuTimeRange, Tov};
use cu29_traits::{
    COMPACT_STRING_CAPACITY, CuCompactString, CuError, CuMsgMetadataTrait, CuMsgOrigin, CuResult,
    ErasedCuStampedData, Metadata,
};
use serde::de::DeserializeOwned;
use serde::{Deserialize, Serialize};

use alloc::format;
use core::fmt::{Debug, Display, Formatter, Result as FmtResult};

/// The state of a task.
// Everything that is stateful in copper for zero copy constraints need to be restricted to this trait.
#[cfg(feature = "reflect")]
pub trait CuMsgPayload:
    Default
    + Debug
    + Clone
    + Encode
    + Decode<()>
    + Serialize
    + DeserializeOwned
    + Reflect
    + TypePath
    + GetTypeRegistration
    + Sized
{
}

#[cfg(not(feature = "reflect"))]
pub trait CuMsgPayload:
    Default + Debug + Clone + Encode + Decode<()> + Serialize + DeserializeOwned + Reflect + Sized
{
}

pub trait CuMsgPack {}

// Also anything that follows this contract can be a payload (blanket implementation)
#[cfg(feature = "reflect")]
impl<T> CuMsgPayload for T where
    T: Default
        + Debug
        + Clone
        + Encode
        + Decode<()>
        + Serialize
        + DeserializeOwned
        + Reflect
        + TypePath
        + GetTypeRegistration
        + Sized
{
}

#[cfg(not(feature = "reflect"))]
impl<T> CuMsgPayload for T where
    T: Default
        + Debug
        + Clone
        + Encode
        + Decode<()>
        + Serialize
        + DeserializeOwned
        + Reflect
        + Sized
{
}

macro_rules! impl_cu_msg_pack {
    ($($name:ident),+) => {
        impl<'cl, $($name),+> CuMsgPack for ($(&CuMsg<$name>,)+)
        where
            $($name: CuMsgPayload),+
        {}
    };
}

macro_rules! impl_cu_msg_pack_up_to {
    ($first:ident, $second:ident $(, $rest:ident)* $(,)?) => {
        impl_cu_msg_pack!($first, $second);
        impl_cu_msg_pack_up_to!(@accumulate ($first, $second); $($rest),*);
    };
    (@accumulate ($($acc:ident),+);) => {};
    (@accumulate ($($acc:ident),+); $next:ident $(, $rest:ident)*) => {
        impl_cu_msg_pack!($($acc),+, $next);
        impl_cu_msg_pack_up_to!(@accumulate ($($acc),+, $next); $($rest),*);
    };
}

impl<T: CuMsgPayload> CuMsgPack for CuMsg<T> {}
impl<T: CuMsgPayload> CuMsgPack for &CuMsg<T> {}
impl<T: CuMsgPayload> CuMsgPack for (&CuMsg<T>,) {}
impl CuMsgPack for () {}

// Apply the macro to generate implementations for tuple sizes up to 12.
impl_cu_msg_pack_up_to!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12);

// A convenience macro to get from a payload or a list of payloads to a proper CuMsg or CuMsgPack
// declaration for your tasks used for input messages.
#[macro_export]
macro_rules! input_msg {
    ($lt:lifetime, $first:ty, $($rest:ty),+) => {
        ( & $lt CuMsg<$first>, $( & $lt CuMsg<$rest> ),+ )
    };
    ($ty:ty) => {
        CuMsg<$ty>
    };
}

// A convenience macro to get from a payload to a proper CuMsg used as output.
#[macro_export]
macro_rules! output_msg {
    ($lt:lifetime, $first:ty, $($rest:ty),+) => {
        ( CuMsg<$first>, $( CuMsg<$rest> ),+ )
    };
    ($first:ty, $($rest:ty),+) => {
        ( CuMsg<$first>, $( CuMsg<$rest> ),+ )
    };
    ($ty:ty) => {
        CuMsg<$ty>
    };
}

/// Helper trait used by codegen when Copper needs to treat a task output as a
/// single message slot without relying on config-declared output edges.
pub trait CuSingleOutputMsg {
    type Payload: CuMsgPayload;
}

impl<T: CuMsgPayload> CuSingleOutputMsg for CuMsg<T> {
    type Payload = T;
}

/// CuMsgMetadata is a structure that contains metadata common to all CuStampedDataSet.
#[derive(Debug, Clone, bincode::Encode, bincode::Decode, Serialize, Deserialize, Reflect)]
#[reflect(opaque, from_reflect = false, no_field_bounds)]
pub struct CuMsgMetadata {
    /// The time range used for the processing of this message
    pub process_time: PartialCuTimeRange,
    /// A small string for real time feedback purposes.
    /// This is useful for to display on the field when the tasks are operating correctly.
    pub status_txt: CuCompactString,
    /// Remote Copper provenance captured on receive, when available.
    pub origin: Option<CuMsgOrigin>,
}

impl Metadata for CuMsgMetadata {}

impl CuMsgMetadata {
    pub fn set_status(&mut self, status: impl ToCompactString) {
        self.status_txt = CuCompactString(status.to_compact_string());
    }

    pub fn set_origin(&mut self, origin: CuMsgOrigin) {
        self.origin = Some(origin);
    }

    pub fn clear_origin(&mut self) {
        self.origin = None;
    }
}

impl CuMsgMetadataTrait for CuMsgMetadata {
    fn process_time(&self) -> PartialCuTimeRange {
        self.process_time
    }

    fn status_txt(&self) -> &CuCompactString {
        &self.status_txt
    }

    fn origin(&self) -> Option<&CuMsgOrigin> {
        self.origin.as_ref()
    }
}

impl Display for CuMsgMetadata {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        write!(
            f,
            "process_time start: {}, process_time end: {}",
            self.process_time.start, self.process_time.end
        )
    }
}

/// CuMsg is the envelope holding the msg payload and the metadata between tasks.
#[derive(Default, Debug, Clone, bincode::Decode, Serialize, Deserialize, Reflect)]
#[reflect(opaque, from_reflect = false, no_field_bounds)]
#[serde(bound(
    serialize = "T: Serialize, M: Serialize",
    deserialize = "T: DeserializeOwned, M: DeserializeOwned"
))]
pub struct CuStampedData<T, M>
where
    T: CuMsgPayload,
    M: Metadata,
{
    /// This payload is the actual data exchanged between tasks.
    payload: Option<T>,

    /// The time of validity of the message.
    /// It can be undefined (None), one measure point or a range of measures (TimeRange).
    pub tov: Tov,

    /// This metadata is the data that is common to all messages.
    pub metadata: M,
}

impl<T, M> Encode for CuStampedData<T, M>
where
    T: CuMsgPayload,
    M: Metadata,
{
    fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
        // NOTE: the `HandleContent` policy decision (TouchedOnly / None) is NOT made
        // here. It can't be: this impl is generic over `T`, so method resolution at
        // the `payload_should_log()` call site would always pick the trait blanket
        // default (true) — autoref-specialization only works at concrete-type sites.
        // The codegen-emitted per-slot encoder in cu29_derive consults the policy at
        // the concrete payload type and routes to `encode_metadata_only` when the
        // bytes should be skipped. This generic impl just writes the full payload.
        match &self.payload {
            None => {
                0u8.encode(encoder)?;
            }
            Some(payload) => {
                1u8.encode(encoder)?;
                let encoded_start = cu29_traits::observed_encode_bytes();
                let handle_start = crate::monitoring::current_payload_handle_bytes();
                payload.encode(encoder)?;
                let encoded_bytes =
                    cu29_traits::observed_encode_bytes().saturating_sub(encoded_start);
                let handle_bytes =
                    crate::monitoring::current_payload_handle_bytes().saturating_sub(handle_start);
                crate::monitoring::record_current_slot_payload_io_stats(
                    core::mem::size_of::<T>(),
                    encoded_bytes,
                    handle_bytes,
                );
            }
        }
        self.tov.encode(encoder)?;
        self.metadata.encode(encoder)?;
        Ok(())
    }
}

/// Write a metadata-only record for a stamped message: presence tag = 0u8 (no payload),
/// followed by `tov` and `metadata`. Wire-compatible with the existing decode path —
/// a reader sees `payload: None` for the frame, same as if the source had been
/// disabled entirely, but the surrounding timestamp/status are preserved.
///
/// Codegen emits a call to this helper when a slot's producing task is configured with
/// `HandleContent::None` or `HandleContent::TouchedOnly` and the handle wasn't touched.
pub fn encode_metadata_only<T, M, E>(
    msg: &CuStampedData<T, M>,
    encoder: &mut E,
) -> Result<(), EncodeError>
where
    T: CuMsgPayload,
    M: Metadata,
    E: Encoder,
{
    0u8.encode(encoder)?;
    msg.tov.encode(encoder)?;
    msg.metadata.encode(encoder)?;
    Ok(())
}

impl Default for CuMsgMetadata {
    fn default() -> Self {
        CuMsgMetadata {
            process_time: PartialCuTimeRange::default(),
            status_txt: CuCompactString(CompactString::with_capacity(COMPACT_STRING_CAPACITY)),
            origin: None,
        }
    }
}

impl<T, M> CuStampedData<T, M>
where
    T: CuMsgPayload,
    M: Metadata,
{
    /// Initializes an empty message directly in preallocated pool storage.
    ///
    /// # Safety
    /// `dst` must point to aligned, writable storage for one `Self`. Its previous
    /// contents are overwritten without being dropped.
    #[doc(hidden)]
    pub unsafe fn init_in_place(dst: *mut Self) {
        // SAFETY: Each field is written independently before a reference to the
        // message is formed. An empty payload does not construct a T.
        unsafe {
            // Copy from a promoted constant so debug builds do not materialize
            // a potentially large Option<T> temporary on the startup stack.
            core::ptr::copy_nonoverlapping(
                const { &None::<T> },
                core::ptr::addr_of_mut!((*dst).payload),
                1,
            );
            core::ptr::addr_of_mut!((*dst).tov).write(Tov::default());
            core::ptr::addr_of_mut!((*dst).metadata).write(M::default());
        }
    }

    pub(crate) fn from_parts(payload: Option<T>, tov: Tov, metadata: M) -> Self {
        CuStampedData {
            payload,
            tov,
            metadata,
        }
    }

    pub fn new(payload: Option<T>) -> Self {
        Self::from_parts(payload, Tov::default(), M::default())
    }
    pub fn payload(&self) -> Option<&T> {
        self.payload.as_ref()
    }

    pub fn set_payload(&mut self, payload: T) {
        self.payload = Some(payload);
    }

    pub fn clear_payload(&mut self) {
        self.payload = None;
    }

    pub fn payload_mut(&mut self) -> &mut Option<T> {
        &mut self.payload
    }
}

impl<T, M> ErasedCuStampedData for CuStampedData<T, M>
where
    T: CuMsgPayload,
    M: CuMsgMetadataTrait + Metadata,
{
    fn payload(&self) -> Option<&dyn erased_serde::Serialize> {
        self.payload
            .as_ref()
            .map(|p| p as &dyn erased_serde::Serialize)
    }

    #[cfg(feature = "reflect")]
    fn payload_reflect(&self) -> Option<&dyn cu29_traits::Reflect> {
        self.payload
            .as_ref()
            .map(|p| p as &dyn cu29_traits::Reflect)
    }

    fn tov(&self) -> Tov {
        self.tov
    }

    fn metadata(&self) -> &dyn CuMsgMetadataTrait {
        &self.metadata
    }
}

/// This is the robotics message type for Copper with the correct Metadata type
/// that will be used by the runtime.
pub type CuMsg<T> = CuStampedData<T, CuMsgMetadata>;

impl<T: CuMsgPayload> CuStampedData<T, CuMsgMetadata> {
    /// Reinterprets the payload type carried by this message.
    ///
    /// # Safety
    ///
    /// The caller must guarantee that the message really contains a payload of type `U`. Failing
    /// to do so is undefined behaviour.
    pub unsafe fn assume_payload<U: CuMsgPayload>(&self) -> &CuMsg<U> {
        // SAFETY: Caller guarantees that the underlying payload is of type U.
        unsafe { &*(self as *const CuMsg<T> as *const CuMsg<U>) }
    }

    /// Mutable variant of [`assume_payload`](Self::assume_payload).
    ///
    /// # Safety
    ///
    /// The caller must guarantee that mutating the returned message is sound for the actual
    /// payload type stored in the buffer.
    pub unsafe fn assume_payload_mut<U: CuMsgPayload>(&mut self) -> &mut CuMsg<U> {
        // SAFETY: Caller guarantees that the underlying payload is of type U.
        unsafe { &mut *(self as *mut CuMsg<T> as *mut CuMsg<U>) }
    }
}

impl<T: CuMsgPayload + 'static> CuStampedData<T, CuMsgMetadata> {
    fn downcast_err<U: CuMsgPayload + 'static>() -> CuError {
        CuError::from(format!(
            "CuMsg payload mismatch: {} cannot be reinterpreted as {}",
            type_name::<T>(),
            type_name::<U>()
        ))
    }

    /// Attempts to view this message as carrying payload `U`.
    pub fn downcast_ref<U: CuMsgPayload + 'static>(&self) -> CuResult<&CuMsg<U>> {
        if TypeId::of::<T>() == TypeId::of::<U>() {
            // SAFETY: We just proved that T == U.
            Ok(unsafe { self.assume_payload::<U>() })
        } else {
            Err(Self::downcast_err::<U>())
        }
    }

    /// Mutable variant of [`downcast_ref`](Self::downcast_ref).
    pub fn downcast_mut<U: CuMsgPayload + 'static>(&mut self) -> CuResult<&mut CuMsg<U>> {
        if TypeId::of::<T>() == TypeId::of::<U>() {
            // SAFETY: We just proved that T == U.
            Ok(unsafe { self.assume_payload_mut::<U>() })
        } else {
            Err(Self::downcast_err::<U>())
        }
    }
}

/// The internal state of a task needs to be serializable
/// so the framework can take a snapshot of the task graph.
pub trait Freezable {
    /// This method is called by the framework when it wants to save the task state.
    /// The default implementation is to encode nothing (stateless).
    /// If you have a state, you need to implement this method.
    fn freeze<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
        Encode::encode(&(), encoder) // default is stateless
    }

    /// This method is called by the framework when it wants to restore the task to a specific state.
    /// Here it is similar to Decode but the framework will give you a new instance of the task (the new method will be called)
    fn thaw<D: Decoder>(&mut self, _decoder: &mut D) -> Result<(), DecodeError> {
        Ok(())
    }
}

/// Bincode Adapter for Freezable tasks
/// This allows the use of the bincode API directly to freeze and thaw tasks.
pub struct BincodeAdapter<'a, T: Freezable + ?Sized>(pub &'a T);

impl<'a, T: Freezable + ?Sized> Encode for BincodeAdapter<'a, T> {
    fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
        self.0.freeze(encoder)
    }
}

/// A Src Task is a task that only produces messages. For example drivers for sensors are Src Tasks.
/// They are in push mode from the runtime.
/// To set the frequency of the pulls and align them to any hw, see the runtime configuration.
/// Note: A source has the privilege to have a clock passed to it vs a frozen clock.
pub trait CuSrcTask: Freezable + Reflect {
    type Output<'m>: CuMsgPayload;
    /// Resources required by the task.
    type Resources<'r>;

    /// Registers the reflected type used as this task's debug-state contract.
    ///
    /// The default exposes the task struct itself. Override this when the task
    /// contains ignored, third-party, hardware, or otherwise non-inspectable
    /// internals and should expose a purpose-built debug-state view instead.
    fn register_debug_state_types(registry: &mut TypeRegistry)
    where
        Self: GetTypeRegistration + Sized,
    {
        registry.register::<Self>();
    }

    /// Returns the reflected type path used as this task's debug-state schema.
    fn debug_state_type_path() -> &'static str
    where
        Self: TypePath + Sized,
    {
        Self::type_path()
    }

    /// Borrows this task's current debug-state view.
    ///
    /// Override this together with [`debug_state_type_path`](Self::debug_state_type_path)
    /// when the debug state is a projected view rather than the task struct.
    fn with_debug_state<R>(&self, f: impl FnOnce(&dyn Reflect) -> R) -> R
    where
        Self: Sized,
    {
        f(self)
    }

    /// Here you need to initialize everything your task will need for the duration of its lifetime.
    /// The config allows you to access the configuration of the task.
    fn new(_config: Option<&ComponentConfig>, _resources: Self::Resources<'_>) -> CuResult<Self>
    where
        Self: Sized;

    /// Start is called between the creation of the task and the first call to pre/process.
    fn start(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// This is a method called by the runtime before "process". This is a kind of best effort,
    /// as soon as possible call to give a chance for the task to do some work before to prepare
    /// to make "process" as short as possible.
    fn preprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Process is the most critical execution of the task.
    /// The goal will be to produce the output message as soon as possible.
    /// Use preprocess to prepare the task to make this method as short as possible.
    fn process<'o>(&mut self, ctx: &CuContext, new_msg: &mut Self::Output<'o>) -> CuResult<()>;

    /// This is a method called by the runtime after "process". It is best effort a chance for
    /// the task to update some state after process is out of the way.
    /// It can be use for example to maintain statistics etc. that are not time-critical for the robot.
    fn postprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Called to stop the task. It signals that the *process method won't be called until start is called again.
    fn stop(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }
}

/// This is the most generic Task of copper. It is a "transform" task deriving an output from an input.
pub trait CuTask: Freezable + Reflect {
    type Input<'m>: CuMsgPack;
    type Output<'m>: CuMsgPayload;
    /// Resources required by the task.
    type Resources<'r>;

    /// Registers the reflected type used as this task's debug-state contract.
    ///
    /// The default exposes the task struct itself. Override this when the task
    /// contains ignored, third-party, hardware, or otherwise non-inspectable
    /// internals and should expose a purpose-built debug-state view instead.
    fn register_debug_state_types(registry: &mut TypeRegistry)
    where
        Self: GetTypeRegistration + Sized,
    {
        registry.register::<Self>();
    }

    /// Returns the reflected type path used as this task's debug-state schema.
    fn debug_state_type_path() -> &'static str
    where
        Self: TypePath + Sized,
    {
        Self::type_path()
    }

    /// Borrows this task's current debug-state view.
    ///
    /// Override this together with [`debug_state_type_path`](Self::debug_state_type_path)
    /// when the debug state is a projected view rather than the task struct.
    fn with_debug_state<R>(&self, f: impl FnOnce(&dyn Reflect) -> R) -> R
    where
        Self: Sized,
    {
        f(self)
    }

    /// Here you need to initialize everything your task will need for the duration of its lifetime.
    /// The config allows you to access the configuration of the task.
    fn new(_config: Option<&ComponentConfig>, _resources: Self::Resources<'_>) -> CuResult<Self>
    where
        Self: Sized;

    /// Start is called between the creation of the task and the first call to pre/process.
    fn start(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// This is a method called by the runtime before "process". This is a kind of best effort,
    /// as soon as possible call to give a chance for the task to do some work before to prepare
    /// to make "process" as short as possible.
    fn preprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Process is the most critical execution of the task.
    /// The goal will be to produce the output message as soon as possible.
    /// Use preprocess to prepare the task to make this method as short as possible.
    fn process<'i, 'o>(
        &mut self,
        _ctx: &CuContext,
        input: &Self::Input<'i>,
        output: &mut Self::Output<'o>,
    ) -> CuResult<()>;

    /// This is a method called by the runtime after "process". It is best effort a chance for
    /// the task to update some state after process is out of the way.
    /// It can be use for example to maintain statistics etc. that are not time-critical for the robot.
    fn postprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Called to stop the task. It signals that the *process method won't be called until start is called again.
    fn stop(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }
}

/// A Sink Task is a task that only consumes messages. For example drivers for actuators are Sink Tasks.
pub trait CuSinkTask: Freezable + Reflect {
    type Input<'m>: CuMsgPack;
    /// Resources required by the task.
    type Resources<'r>;

    /// Registers the reflected type used as this task's debug-state contract.
    ///
    /// The default exposes the task struct itself. Override this when the task
    /// contains ignored, third-party, hardware, or otherwise non-inspectable
    /// internals and should expose a purpose-built debug-state view instead.
    fn register_debug_state_types(registry: &mut TypeRegistry)
    where
        Self: GetTypeRegistration + Sized,
    {
        registry.register::<Self>();
    }

    /// Returns the reflected type path used as this task's debug-state schema.
    fn debug_state_type_path() -> &'static str
    where
        Self: TypePath + Sized,
    {
        Self::type_path()
    }

    /// Borrows this task's current debug-state view.
    ///
    /// Override this together with [`debug_state_type_path`](Self::debug_state_type_path)
    /// when the debug state is a projected view rather than the task struct.
    fn with_debug_state<R>(&self, f: impl FnOnce(&dyn Reflect) -> R) -> R
    where
        Self: Sized,
    {
        f(self)
    }

    /// Here you need to initialize everything your task will need for the duration of its lifetime.
    /// The config allows you to access the configuration of the task.
    fn new(_config: Option<&ComponentConfig>, _resources: Self::Resources<'_>) -> CuResult<Self>
    where
        Self: Sized;

    /// Start is called between the creation of the task and the first call to pre/process.
    fn start(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// This is a method called by the runtime before "process". This is a kind of best effort,
    /// as soon as possible call to give a chance for the task to do some work before to prepare
    /// to make "process" as short as possible.
    fn preprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Process is the most critical execution of the task.
    /// The goal will be to produce the output message as soon as possible.
    /// Use preprocess to prepare the task to make this method as short as possible.
    fn process<'i>(&mut self, _ctx: &CuContext, input: &Self::Input<'i>) -> CuResult<()>;

    /// This is a method called by the runtime after "process". It is best effort a chance for
    /// the task to update some state after process is out of the way.
    /// It can be use for example to maintain statistics etc. that are not time-critical for the robot.
    fn postprocess(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }

    /// Called to stop the task. It signals that the *process method won't be called until start is called again.
    fn stop(&mut self, _ctx: &CuContext) -> CuResult<()> {
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bincode::{config, decode_from_slice, encode_to_vec};

    #[test]
    fn test_cucompactstr_encode_decode() {
        let cstr = CuCompactString(CompactString::from("hello"));
        let config = config::standard();
        let encoded = encode_to_vec(&cstr, config).expect("Encoding failed");
        let (decoded, _): (CuCompactString, usize) =
            decode_from_slice(&encoded, config).expect("Decoding failed");
        assert_eq!(cstr.0, decoded.0);
    }

    /// Test wrapper proving that a composite payload can forward `payload_should_log`
    /// to an inner [`CuHandle`] via an inherent method — exactly the pattern real
    /// composite payloads like `CuImage` will use.
    ///
    /// Gated on the default (non-bevy_reflect) feature configuration where
    /// `Reflect` is auto-impl'd for any `'static`, so the wrapper satisfies
    /// `CuMsgPayload` without needing `#[derive(Reflect)]`.
    #[cfg(not(feature = "reflect"))]
    #[derive(Debug, Clone, bincode::Encode, bincode::Decode, Serialize, Deserialize)]
    struct TestHandlePayload {
        handle: crate::pool::CuHandle<Vec<u8>>,
    }

    #[cfg(not(feature = "reflect"))]
    impl Default for TestHandlePayload {
        fn default() -> Self {
            Self {
                handle: crate::pool::CuHandle::new_detached(Vec::new()),
            }
        }
    }

    #[cfg(not(feature = "reflect"))]
    impl TestHandlePayload {
        // Inherent specialization arm: real composite payloads (e.g. CuImage) provide
        // an identical method that forwards to their inner CuHandle.
        fn payload_should_log(&self) -> bool {
            self.handle.payload_should_log()
        }
    }

    /// Encoding a CuMsg whose payload wraps a CuHandle in `TouchedOnly` mode must:
    /// * skip the payload bytes when no consumer marked the handle touched, and
    /// * include them once `mark_touched` was called.
    /// The wire shape stays compatible with the existing `Option<T>` decode path
    /// (presence tag is 0u8 for skip, 1u8 + payload otherwise).
    #[cfg(not(feature = "reflect"))]
    #[test]
    fn test_encode_skips_payload_for_untouched_handle() {
        use crate::pool::{CuHandle, HandleContent};
        let cfg = config::standard();

        let untouched = TestHandlePayload {
            handle: CuHandle::new_detached_with_mode(
                vec![0xAA, 0xBB, 0xCC, 0xDD],
                HandleContent::TouchedOnly,
            ),
        };
        let msg_skip: CuMsg<TestHandlePayload> = CuMsg::new(Some(untouched));
        let skip_bytes = encode_to_vec(&msg_skip, cfg).expect("encode");

        let touched_payload = TestHandlePayload {
            handle: CuHandle::new_detached_with_mode(
                vec![0xAA, 0xBB, 0xCC, 0xDD],
                HandleContent::TouchedOnly,
            ),
        };
        touched_payload.handle.mark_touched();
        let msg_keep: CuMsg<TestHandlePayload> = CuMsg::new(Some(touched_payload));
        let keep_bytes = encode_to_vec(&msg_keep, cfg).expect("encode");

        assert_eq!(
            skip_bytes[0], 0u8,
            "first byte must be the no-payload presence tag for an untouched TouchedOnly handle"
        );
        assert_eq!(
            keep_bytes[0], 1u8,
            "first byte must be the payload-present tag once the handle was touched"
        );
        assert!(
            keep_bytes.len() > skip_bytes.len(),
            "touched encoding ({} bytes) must include payload content; skip is {} bytes",
            keep_bytes.len(),
            skip_bytes.len()
        );
    }

    /// `HandleContent::All` (the default for every existing source) must never drop
    /// payload bytes — regardless of whether the handle was touched.
    #[cfg(not(feature = "reflect"))]
    #[test]
    fn test_encode_keeps_payload_for_default_mode() {
        use crate::pool::{CuHandle, HandleContent};
        let cfg = config::standard();

        let payload = TestHandlePayload {
            handle: CuHandle::new_detached_with_mode(vec![1, 2, 3], HandleContent::All),
        };
        let msg: CuMsg<TestHandlePayload> = CuMsg::new(Some(payload));
        let bytes = encode_to_vec(&msg, cfg).expect("encode");
        assert_eq!(
            bytes[0], 1u8,
            "default (HandleContent::All) must keep emitting the payload"
        );
    }
}