feat(runtime): add resident Wasmtime actor runtime

- define versioned service and clock WIT contracts
- enforce import allowlists, fuel, epoch, memory, I/O, and mailbox limits
- keep one Store and Component Instance resident per serial Actor
- add echo, counter, fault, spin, and capability probe components
- cover lifecycle, concurrency, sandbox, and fault recovery behavior

components/spin/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "spin-component"
+version = "0.1.0"
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+
+[package.metadata.wasmeld]
+id = "spin"
+world = "component:spin/spin-component@0.1.0"
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+wit-bindgen.workspace = true

components/spin/src/lib.rs

@@ -0,0 +1,43 @@
+mod bindings {
+    wit_bindgen::generate!({
+        path: "wit",
+        world: "spin-component",
+    });
+}
+
+static mut SPIN_STATE: u64 = 0;
+
+struct Spin;
+
+impl bindings::Guest for Spin {
+    fn init(config: Vec<u8>) -> Result<(), bindings::ServiceError> {
+        if config == b"spin" {
+            burn(u64::MAX);
+        }
+
+        Ok(())
+    }
+
+    fn invoke(input: Vec<u8>) -> Result<Vec<u8>, bindings::ServiceError> {
+        let steps = input
+            .get(..size_of::<u64>())
+            .and_then(|bytes| bytes.try_into().ok())
+            .map(u64::from_le_bytes)
+            .unwrap_or_default();
+
+        burn(steps);
+        Ok(Vec::new())
+    }
+}
+
+// The volatile write makes every loop iteration observable to the optimizer.
+fn burn(steps: u64) {
+    let mut state = unsafe { core::ptr::read_volatile(&raw const SPIN_STATE) };
+
+    for _ in 0..steps {
+        state = state.rotate_left(7).wrapping_add(0x9e37_79b9_7f4a_7c15);
+        unsafe { core::ptr::write_volatile(&raw mut SPIN_STATE, state) };
+    }
+}
+
+bindings::export!(Spin with_types_in bindings);

components/spin/wasmeld.toml

@@ -0,0 +1,7 @@
+schema_version = 1
+
+[dependencies]
+"wasmeld:service" = "0.1.0"
+
+[replace."wasmeld:service"]
+path = "../../wit/service"

components/spin/wit.lock

@@ -0,0 +1,8 @@
+schema_version = 1
+
+[[package]]
+name = "wasmeld:service"
+version = "0.1.0"
+source = "path+../../wit/service"
+sha256 = "d5497307bbcd1e159f7707f385b488a6f2e26362d5256d5bc1080ac603a51305"
+replaced = true

components/spin/wit/world.wit

@@ -0,0 +1,5 @@
+package component:spin@0.1.0;
+
+world spin-component {
+  include wasmeld:service/service-component@0.1.0;
+}