docs: record the intent architecture (venue adapters, egress guard)

.github/workflows/ci.yml

@@ -87,8 +87,8 @@ jobs:
         run: |
           cargo build --release --target wasm32-wasip2 --locked \
             -p example -p twap-monitor -p ethflow-watcher -p price-alert \
-            -p balance-tracker -p stop-loss -p http-probe \
-            -p clock-reader -p flaky-bomb -p fuel-bomb \
+            -p balance-tracker -p stop-loss -p http-probe -p echo-venue \
+            -p echo-client -p clock-reader -p flaky-bomb -p fuel-bomb \
             -p memory-bomb -p panic-bomb
           {
             echo "### module .wasm sizes"

.gitignore

@@ -32,6 +32,9 @@ skills-lock.json
 
 # Engine runtime state (default state_dir from engine.toml).
 data/
+# Shipped crate data slices are source, not runtime state: keep them.
+!crates/*/data/
+!crates/*/data/**
 
 # E2E automation: rendered configs with embedded RPC keys + script state
 # never get committed.

Cargo.toml

@@ -1,16 +1,22 @@
 [workspace]
 members = [
+    "crates/cow-venue",
     "crates/nexum-cli",
+    "crates/nexum-macros",
     "crates/nexum-runtime",
     "crates/nexum-sdk",
     "crates/nexum-sdk-test",
+    "crates/nexum-venue-sdk",
+    "crates/nexum-venue-test",
     "crates/shepherd-backtest",
     "crates/shepherd-cow-host",
     "crates/shepherd-sdk",
     "crates/shepherd-sdk-test",
     "modules/ethflow-watcher",
     "modules/example",
     "modules/examples/balance-tracker",
+    "modules/examples/echo-client",
+    "modules/examples/echo-venue",
     "modules/examples/http-probe",
     "modules/examples/price-alert",
     "modules/examples/stop-loss",
@@ -51,6 +57,12 @@ futures = "0.3"
 serde = { version = "1", features = ["derive"] }
 serde_json = { version = "1", default-features = false, features = ["alloc"] }
 
+# Borsh wire codec behind the venue SDK's versioned `IntentBody` bodies.
+# The venue SDK re-exports the runtime crate for its derive's generated
+# code; `derive` is on so venue payload types can `#[derive(BorshSerialize,
+# BorshDeserialize)]` through the same dependency.
+borsh = { version = "1", features = ["derive"] }
+
 # Observability.
 tracing = "0.1"
 # `tracing-core` alone (no subscriber registry) backs the guest-side
@@ -115,6 +127,13 @@ http-body = "1"
 http-body-util = "0.1"
 bytes = "1"
 
+# Proc-macro toolkit backing `nexum-macros`. Host-side only: the
+# proc-macro crate always builds for the host, even when the module
+# consuming it targets wasm.
+proc-macro2 = "1"
+quote = "1"
+syn = { version = "2", features = ["full"] }
+
 # `wit-bindgen` is consumed by every guest module crate (example +
 # every strategy + every fixture). Hoisted so a single bump moves
 # them in lock-step.