sdk: make the IntentBody derive no_std

Cargo.toml

@@ -12,6 +12,7 @@ members = [
     "crates/nexum-venue-sdk",
     "crates/nexum-venue-test",
     "crates/nexum-world",
+    "crates/no-std-probe",
     "crates/shepherd",
     "crates/shepherd-backtest",
     "crates/shepherd-cow-host",

crates/cow-venue/src/composable.rs

@@ -8,6 +8,8 @@
 //! `static_input` is opaque to the venue; only the named handler parses
 //! it, so this crate never inspects its bytes.
 
+use alloc::vec::Vec;
+
 use borsh::{BorshDeserialize, BorshSerialize};
 
 use crate::order::Address;

crates/cow-venue/src/lib.rs

@@ -9,10 +9,9 @@
 //! venue SDK (for the [`IntentBody`](nexum_venue_sdk::IntentBody) derive)
 //! and borsh, so a venue adapter component or a strategy module can carry
 //! the body types and codec without dragging in the host-side CoW
-//! machinery. The one non-obvious constraint: the derive's generated code
-//! names `::std`, so the slice links std and is not a bare-metal
-//! `#![no_std]` crate; it is guest-consumable on the runtime's
-//! std-bearing wasm target rather than target-free.
+//! machinery. The crate is `#![no_std]` (tests aside): the derive's
+//! generated code reaches `alloc` through the venue SDK re-export, never
+//! `::std`.
 //!
 //! With `--no-default-features` the slice drops out entirely and the
 //! crate compiles empty, so a consumer can depend on a future slice
@@ -26,9 +25,13 @@
 //! so an adapter or a module that wants only the body types stays
 //! dependency-light.
 
+#![cfg_attr(not(test), no_std)]
 #![cfg_attr(not(test), warn(unused_crate_dependencies))]
 #![warn(missing_docs)]
 
+#[cfg(feature = "body")]
+extern crate alloc;
+
 #[cfg(feature = "body")]
 pub mod body;
 

crates/nexum-macros/src/intent_body.rs

@@ -12,7 +12,9 @@
 //!
 //! Generated code names the venue SDK by its crate path
 //! (`::nexum_venue_sdk`), so the derive is only usable through that
-//! crate's re-export.
+//! crate's re-export. The expansion names only `::core` and the SDK's
+//! `__private` re-exports (borsh, `alloc`), so a `#![no_std]` consumer
+//! needs no `extern crate alloc`.
 
 use proc_macro2::TokenStream;
 use quote::quote;
@@ -80,12 +82,12 @@ pub(crate) fn expand(input: &DeriveInput) -> syn::Result<TokenStream> {
 
         encode_arms.push(quote! {
             Self::#ident(payload) => {
-                let mut out = ::std::vec::Vec::new();
+                let mut out = ::nexum_venue_sdk::body::__private::alloc::vec::Vec::new();
                 out.push(#tag);
                 ::nexum_venue_sdk::body::__private::borsh::to_writer(&mut out, payload).map_err(
                     |err| ::nexum_venue_sdk::body::BodyError::Encode {
                         version: #tag,
-                        detail: ::std::string::ToString::to_string(&err),
+                        detail: ::nexum_venue_sdk::body::__private::alloc::string::ToString::to_string(&err),
                     },
                 )?;
                 ::core::result::Result::Ok(out)
@@ -96,7 +98,9 @@ pub(crate) fn expand(input: &DeriveInput) -> syn::Result<TokenStream> {
                 ::nexum_venue_sdk::body::__private::borsh::from_slice::<#payload_ty>(payload)
                     .map_err(|err| ::nexum_venue_sdk::body::BodyError::Malformed {
                         version: #tag,
-                        detail: ::std::string::ToString::to_string(&err),
+                        detail: ::nexum_venue_sdk::body::__private::alloc::string::ToString::to_string(
+                            &err,
+                        ),
                     })?,
             )),
         });
@@ -108,7 +112,7 @@ pub(crate) fn expand(input: &DeriveInput) -> syn::Result<TokenStream> {
             fn to_bytes(
                 &self,
             ) -> ::core::result::Result<
-                ::std::vec::Vec<u8>,
+                ::nexum_venue_sdk::body::__private::alloc::vec::Vec<u8>,
                 ::nexum_venue_sdk::body::BodyError,
             > {
                 match self {

crates/nexum-venue-sdk/src/body.rs

@@ -86,8 +86,11 @@ impl From<BodyError> for VenueError {
 }
 
 /// Re-exports for `#[derive(IntentBody)]` generated code only; not a
-/// public surface.
+/// public surface. `alloc` rides along so the expansion resolves in a
+/// `#![no_std]` consumer without its own `extern crate alloc`.
 #[doc(hidden)]
 pub mod __private {
+    pub extern crate alloc;
+
     pub use borsh;
 }

crates/no-std-probe/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "no-std-probe"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+description = "Compile-only #![no_std] probe: the IntentBody derive must expand without the consumer's std prelude."
+
+[lib]
+# Never shipped. Living in the workspace keeps the derive's no_std
+# contract under the workspace check/clippy gate.
+
+[lints]
+workspace = true
+
+[dependencies]
+# Source of the `IntentBody` derive and trait the probe enum implements.
+nexum-venue-sdk = { path = "../nexum-venue-sdk" }

crates/no-std-probe/src/lib.rs

@@ -0,0 +1,14 @@
+//! Compile-only `#![no_std]` probe: `#[derive(IntentBody)]` must expand
+//! without the consumer's std prelude or an `extern crate alloc`.
+
+#![no_std]
+#![warn(missing_docs)]
+
+use nexum_venue_sdk::IntentBody;
+
+/// The probe schema: one published version over a bare byte payload.
+#[derive(IntentBody, Clone, Debug, PartialEq, Eq)]
+pub enum ProbeBody {
+    /// First published version.
+    V1(u8),
+}