From 9aae0161d88d7093ec9901546ffffc6e4d80561b Mon Sep 17 00:00:00 2001
From: brunota20 <brunot.anjos@gmail.com>
Date: Mon, 15 Jun 2026 10:40:00 -0300
Subject: [PATCH] feat(ethflow-watcher): workspace + skeleton (BLEU-831)
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Mirror of the twap-monitor skeleton (BLEU-825) for the EthFlow
path. Adds modules/ethflow-watcher/ as a workspace member, with
[lib] crate-type = ["cdylib"] for WASM Component output, and the
same dep set (cowprotocol no-default-features, alloy-primitives,
alloy-sol-types, wit-bindgen) pre-pulled so BLEU-832 (event
decode) and BLEU-833 (EIP-1271 submit + retry) can layer in
without churning Cargo.toml.

src/lib.rs binds against shepherd:cow/shepherd, init logs once,
on_event logs Event::Logs as a placeholder until BLEU-832 decodes
the CoWSwapEthFlow OrderPlacement payload.

cargo build --target wasm32-wasip2 --release -p ethflow-watcher
emits a 67 KB .wasm (within ~3 KB of twap-monitor's skeleton —
identical world + deps, identical link footprint). Engine load is
gated on module.toml (BLEU-834).
---
 Cargo.toml                         |  1 +
 modules/ethflow-watcher/Cargo.toml | 15 +++++++++++++
 modules/ethflow-watcher/src/lib.rs | 35 ++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 modules/ethflow-watcher/Cargo.toml
 create mode 100644 modules/ethflow-watcher/src/lib.rs

diff --git a/Cargo.toml b/Cargo.toml
index ed79b10..9346ac7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "crates/nexum-engine",
+    "modules/ethflow-watcher",
     "modules/example",
 ]
 resolver = "2"
diff --git a/modules/ethflow-watcher/Cargo.toml b/modules/ethflow-watcher/Cargo.toml
new file mode 100644
index 0000000..5d9fa3d
--- /dev/null
+++ b/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"] }
diff --git a/modules/ethflow-watcher/src/lib.rs b/modules/ethflow-watcher/src/lib.rs
new file mode 100644
index 0000000..4442708
--- /dev/null
+++ b/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);