docs(wit): document capability and component contracts

components/fault/src/lib.rs

@@ -1,4 +1,10 @@
+//! Deliberately trapping Component used to verify Actor fault isolation.
+//!
+//! Sending the exact bytes `fault` triggers a panic. This crate is a test
+//! fixture and must not be deployed as an application service.
+
 mod bindings {
+    // Compile the versioned WIT world into canonical ABI Rust bindings.
     wit_bindgen::generate!({
         path: "wit",
         world: "fault-component",
@@ -13,6 +19,8 @@ impl bindings::Guest for Fault {
     }
 
     fn invoke(input: Vec<u8>) -> Result<Vec<u8>, bindings::ServiceError> {
+        // A panic becomes a Wasm trap so Runtime tests can assert that one
+        // faulted Actor does not corrupt other service instances.
         assert_ne!(input, b"fault", "intentional test fault");
         Ok(input)
     }