feat(ethflow-watcher): workspace + skeleton (BLEU-831)

Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "crates/nexum-engine",
+    "modules/ethflow-watcher",
     "modules/example",
 ]
 resolver = "2"

modules/ethflow-watcher/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "ethflow-watcher"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+cowprotocol = { version = "1.0.0-alpha.3", default-features = false }
+alloy-primitives = { version = "1.5", default-features = false, features = ["std"] }
+alloy-sol-types = { version = "1.5", default-features = false, features = ["std"] }
+wit-bindgen = { version = "0.57", default-features = false, features = ["macros", "realloc"] }

modules/ethflow-watcher/src/lib.rs

@@ -0,0 +1,35 @@
+// wit_bindgen::generate! expands to host-import shims whose arity matches
+// the WIT signatures, which can exceed clippy's too-many-arguments threshold.
+#![allow(clippy::too_many_arguments)]
+
+wit_bindgen::generate!({
+    path: ["../../wit/nexum-host", "../../wit/shepherd-cow"],
+    world: "shepherd:cow/shepherd",
+    generate_all,
+});
+
+use nexum::host::{logging, types};
+
+struct EthFlowWatcher;
+
+impl Guest for EthFlowWatcher {
+    fn init(_config: Vec<(String, String)>) -> Result<(), HostError> {
+        logging::log(logging::Level::Info, "ethflow-watcher init");
+        Ok(())
+    }
+
+    fn on_event(event: types::Event) -> Result<(), HostError> {
+        // CoWSwapEthFlow `OrderPlacement` decode lands in BLEU-832; the
+        // EIP-1271 submission path lands in BLEU-833. Block / Tick /
+        // Message are not used by this module.
+        if let types::Event::Logs(logs) = event {
+            logging::log(
+                logging::Level::Info,
+                &format!("ethflow received {} logs (decode in BLEU-832)", logs.len()),
+            );
+        }
+        Ok(())
+    }
+}
+
+export!(EthFlowWatcher);