feat(runtime): modularize host capabilities

- add an exact-version Capability Registry and structured descriptors
- move Clock bindings, host state, and Linker installation into its own module
- derive required capabilities from Component imports and link only requested interfaces
- cover exact-version resolution and minimal per-component capability sets

crates/wasmeld-runtime/src/bindings.rs

@@ -5,12 +5,3 @@ wasmtime::component::bindgen!({
     path: "../../wit/service",
     world: "service-component",
 });
-
-pub(crate) mod clock {
-    // Host capabilities are generated separately so adding a capability does
-    // not expand the baseline service contract for every component.
-    wasmtime::component::bindgen!({
-        path: "../../wit/clock",
-        world: "clock-host",
-    });
-}

crates/wasmeld-runtime/src/capability/clock.rs

@@ -0,0 +1,44 @@
+//! `wasmeld:clock/monotonic-clock@0.1.0` host implementation.
+
+use std::time::Instant;
+
+use wasmtime::component::Linker;
+
+use crate::{RuntimeError, runtime::HostState};
+
+wasmtime::component::bindgen!({
+    path: "../../wit/clock",
+    world: "clock-host",
+});
+
+pub(crate) const INTERFACE: &str = "wasmeld:clock/monotonic-clock@0.1.0";
+pub(crate) const PACKAGE: &str = "wasmeld:clock";
+pub(crate) const NAME: &str = "monotonic-clock";
+pub(crate) const VERSION: &str = "0.1.0";
+
+pub(crate) struct ClockState {
+    origin: Instant,
+}
+
+impl ClockState {
+    pub(crate) fn new() -> Self {
+        Self {
+            origin: Instant::now(),
+        }
+    }
+
+    pub(crate) fn now(&self) -> u64 {
+        u64::try_from(self.origin.elapsed().as_nanos()).unwrap_or(u64::MAX)
+    }
+}
+
+impl wasmeld::clock::monotonic_clock::Host for HostState {
+    fn now(&mut self) -> u64 {
+        self.capabilities.monotonic_clock_now()
+    }
+}
+
+pub(crate) fn add_to_linker(linker: &mut Linker<HostState>) -> Result<(), RuntimeError> {
+    wasmeld::clock::monotonic_clock::add_to_linker::<HostState, HostState>(linker, |state| state)
+        .map_err(|error| RuntimeError::ActorInitialization(error.to_string()))
+}

crates/wasmeld-runtime/src/capability/mod.rs

@@ -0,0 +1,29 @@
+//! Versioned host capabilities available to WebAssembly Components.
+
+mod clock;
+mod registry;
+
+pub use registry::CapabilityDescriptor;
+pub(crate) use registry::{Capability, CapabilityRegistry};
+
+/// Per-Actor state owned by enabled host capabilities.
+pub(crate) struct HostCapabilities {
+    clock: Option<clock::ClockState>,
+}
+
+impl HostCapabilities {
+    pub(crate) fn new(capabilities: &[Capability]) -> Self {
+        Self {
+            clock: capabilities
+                .contains(&Capability::MonotonicClock)
+                .then(clock::ClockState::new),
+        }
+    }
+
+    fn monotonic_clock_now(&self) -> u64 {
+        self.clock
+            .as_ref()
+            .expect("the Clock interface is linked only when its state is enabled")
+            .now()
+    }
+}

crates/wasmeld-runtime/src/capability/registry.rs

@@ -0,0 +1,120 @@
+//! Exact interface lookup and Linker installation for host capabilities.
+
+use wasmtime::component::Linker;
+
+use super::clock;
+use crate::{RuntimeError, runtime::HostState};
+
+/// Stable description of one versioned WIT interface used by a Component.
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+pub struct CapabilityDescriptor {
+    interface: &'static str,
+    package: &'static str,
+    name: &'static str,
+    version: &'static str,
+}
+
+impl CapabilityDescriptor {
+    const fn new(
+        interface: &'static str,
+        package: &'static str,
+        name: &'static str,
+        version: &'static str,
+    ) -> Self {
+        Self {
+            interface,
+            package,
+            name,
+            version,
+        }
+    }
+
+    /// Returns the fully qualified and versioned WIT interface identity.
+    pub const fn interface(&self) -> &'static str {
+        self.interface
+    }
+
+    /// Returns the versioned WIT package identity without the version suffix.
+    pub const fn package(&self) -> &'static str {
+        self.package
+    }
+
+    /// Returns the WIT interface name inside the package.
+    pub const fn name(&self) -> &'static str {
+        self.name
+    }
+
+    /// Returns the exact semantic version implemented by the Runtime.
+    pub const fn version(&self) -> &'static str {
+        self.version
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+pub(crate) enum Capability {
+    MonotonicClock,
+}
+
+impl Capability {
+    pub(crate) const fn descriptor(self) -> CapabilityDescriptor {
+        match self {
+            Self::MonotonicClock => CapabilityDescriptor::new(
+                clock::INTERFACE,
+                clock::PACKAGE,
+                clock::NAME,
+                clock::VERSION,
+            ),
+        }
+    }
+
+    pub(crate) fn add_to_linker(self, linker: &mut Linker<HostState>) -> Result<(), RuntimeError> {
+        match self {
+            Self::MonotonicClock => clock::add_to_linker(linker),
+        }
+    }
+}
+
+/// Registry of the exact WIT interface versions implemented by this Runtime.
+pub(crate) struct CapabilityRegistry;
+
+impl CapabilityRegistry {
+    /// Resolves an exact Component import to a supported host capability.
+    pub(crate) fn resolve(interface: &str) -> Option<Capability> {
+        match interface {
+            clock::INTERFACE => Some(Capability::MonotonicClock),
+            _ => None,
+        }
+    }
+
+    /// Installs only the capabilities requested by one Component.
+    pub(crate) fn add_to_linker(
+        linker: &mut Linker<HostState>,
+        capabilities: &[Capability],
+    ) -> Result<(), RuntimeError> {
+        for capability in capabilities {
+            capability.add_to_linker(linker)?;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Capability, CapabilityRegistry};
+
+    #[test]
+    fn resolves_only_the_exact_supported_interface_version() {
+        assert_eq!(
+            CapabilityRegistry::resolve("wasmeld:clock/monotonic-clock@0.1.0"),
+            Some(Capability::MonotonicClock)
+        );
+        assert_eq!(
+            CapabilityRegistry::resolve("wasmeld:clock/monotonic-clock@0.2.0"),
+            None
+        );
+        assert_eq!(
+            CapabilityRegistry::resolve("wasmeld:clock/other@0.1.0"),
+            None
+        );
+    }
+}

crates/wasmeld-runtime/src/lib.rs

@@ -6,10 +6,12 @@
 //! service exports, and invokes it through one serial Actor.
 
 mod bindings;
+mod capability;
 mod error;
 mod manifest;
 mod runtime;
 
+pub use capability::CapabilityDescriptor;
 pub use error::RuntimeError;
 pub use manifest::{ResourceLimits, ServiceKey, ServiceManifest};
 pub use runtime::{ActorHandle, Runtime, RuntimeConfig, RuntimeStats};

crates/wasmeld-runtime/src/runtime.rs

@@ -30,8 +30,9 @@ use wasmtime_wasi::{
 };
 
 use crate::{
-    RuntimeError, ServiceKey, ServiceManifest,
-    bindings::{ServiceComponent, ServiceError, clock as clock_bindings},
+    CapabilityDescriptor, RuntimeError, ServiceKey, ServiceManifest,
+    bindings::{ServiceComponent, ServiceError},
+    capability::{Capability, CapabilityRegistry, HostCapabilities},
     manifest::ResourceLimits,
 };
 
@@ -40,7 +41,6 @@ const MAX_EPOCH_TICK: Duration = Duration::from_millis(10);
 const DEFAULT_MAX_WASM_STACK: usize = 512 * 1024;
 const ACTOR_RESOURCE_COUNT_LIMIT: usize = 16;
 const ACTOR_TABLE_ELEMENT_LIMIT: usize = 16 * 1024;
-const MONOTONIC_CLOCK_IMPORT: &str = "wasmeld:clock/monotonic-clock@0.1.0";
 const ALLOWED_WASI_IMPORTS: &[&str] = &[
     "wasi:cli/environment@",
     "wasi:cli/exit@",
@@ -162,12 +162,7 @@ impl Drop for EpochTicker {
 struct RegisteredService {
     manifest: ServiceManifest,
     component: Arc<Component>,
-    capabilities: Vec<HostCapability>,
-}
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-enum HostCapability {
-    MonotonicClock,
+    capabilities: Vec<Capability>,
 }
 
 impl Runtime {
@@ -327,6 +322,26 @@ impl Runtime {
         actor.invoke(input)
     }
 
+    /// Returns the exact versioned host capabilities imported by a service.
+    pub fn capabilities(
+        &self,
+        key: &ServiceKey,
+    ) -> Result<Vec<CapabilityDescriptor>, RuntimeError> {
+        let services = self
+            .inner
+            .services
+            .lock()
+            .map_err(|_| RuntimeError::LockPoisoned)?;
+        let service = services
+            .get(key)
+            .ok_or_else(|| RuntimeError::ServiceNotRegistered(key.clone()))?;
+        Ok(service
+            .capabilities
+            .iter()
+            .map(|capability| capability.descriptor())
+            .collect())
+    }
+
     /// Stops one Actor and releases its Store and Component Instance.
     pub fn stop(&self, key: &ServiceKey) -> Result<(), RuntimeError> {
         let _lifecycle = self
@@ -557,15 +572,15 @@ impl ActorStatus {
     }
 }
 
-struct HostState {
+pub(crate) struct HostState {
     store_limits: StoreLimits,
     wasi: WasiCtx,
     wasi_table: ResourceTable,
-    clock_origin: Instant,
+    pub(crate) capabilities: HostCapabilities,
 }
 
 impl HostState {
-    fn new(limits: &ResourceLimits) -> Self {
+    fn new(limits: &ResourceLimits, capabilities: &[Capability]) -> Self {
         let store_limits = StoreLimitsBuilder::new()
             .memory_size(limits.memory_bytes)
             .table_elements(ACTOR_TABLE_ELEMENT_LIMIT)
@@ -585,7 +600,7 @@ impl HostState {
             store_limits,
             wasi: wasi.build(),
             wasi_table: ResourceTable::new(),
-            clock_origin: Instant::now(),
+            capabilities: HostCapabilities::new(capabilities),
         }
     }
 }
@@ -594,12 +609,6 @@ impl HasData for HostState {
     type Data<'a> = &'a mut HostState;
 }
 
-impl clock_bindings::wasmeld::clock::monotonic_clock::Host for HostState {
-    fn now(&mut self) -> u64 {
-        u64::try_from(self.clock_origin.elapsed().as_nanos()).unwrap_or(u64::MAX)
-    }
-}
-
 impl WasiView for HostState {
     fn ctx(&mut self) -> WasiCtxView<'_> {
         WasiCtxView {
@@ -639,12 +648,12 @@ impl ActorWorker {
             });
         }
 
-        let mut store = Store::new(&engine, HostState::new(&limits));
+        let mut store = Store::new(&engine, HostState::new(&limits, &service.capabilities));
         store.limiter(|state| &mut state.store_limits);
 
         let mut linker = Linker::new(&engine);
         add_restricted_wasi(&mut linker)?;
-        add_host_capabilities(&mut linker, &service.capabilities)?;
+        CapabilityRegistry::add_to_linker(&mut linker, &service.capabilities)?;
 
         let epoch_ticks = ticks_for(limits.deadline(), epoch_tick);
         configure_call_budget(&mut store, &limits, epoch_ticks)?;
@@ -758,33 +767,16 @@ fn link_wasi(result: wasmtime::Result<()>) -> Result<(), RuntimeError> {
     result.map_err(|error| RuntimeError::ActorInitialization(error.to_string()))
 }
 
-fn add_host_capabilities(
-    linker: &mut Linker<HostState>,
-    capabilities: &[HostCapability],
-) -> Result<(), RuntimeError> {
-    for capability in capabilities {
-        match capability {
-            HostCapability::MonotonicClock => link_wasi(
-                clock_bindings::wasmeld::clock::monotonic_clock::add_to_linker::<
-                    HostState,
-                    HostState,
-                >(linker, |state| state),
-            )?,
-        }
-    }
-    Ok(())
-}
-
 fn validate_component_imports(
     component: &Component,
     engine: &Engine,
-) -> Result<Vec<HostCapability>, RuntimeError> {
+) -> Result<Vec<Capability>, RuntimeError> {
     // Import validation is deny-by-default. A host function is linked only
     // after its exact WIT identity or WASI family has passed this allowlist.
     let mut capabilities = Vec::new();
     for (name, _) in component.component_type().imports(engine) {
-        if name == MONOTONIC_CLOCK_IMPORT {
-            capabilities.push(HostCapability::MonotonicClock);
+        if let Some(capability) = CapabilityRegistry::resolve(name) {
+            capabilities.push(capability);
         } else if !ALLOWED_WASI_IMPORTS
             .iter()
             .any(|allowed| name.starts_with(allowed))
@@ -793,6 +785,8 @@ fn validate_component_imports(
         }
     }
 
+    capabilities.sort_unstable();
+    capabilities.dedup();
     Ok(capabilities)
 }
 

crates/wasmeld-runtime/tests/runtime_components.rs

@@ -16,6 +16,7 @@ fn echo_component_round_trips_bytes() {
     let runtime = Runtime::new(RuntimeConfig::default()).expect("runtime should start");
     let (key, actor) = start_component(&runtime, "echo", "echo_component.wasm");
 
+    assert!(runtime.capabilities(&key).unwrap().is_empty());
     assert_eq!(actor.invoke(b"hello wasm".to_vec()).unwrap(), b"hello wasm");
 
     runtime.stop(&key).unwrap();
@@ -171,6 +172,13 @@ fn explicit_clock_capability_is_linked() {
     let runtime = Runtime::new(RuntimeConfig::default()).expect("runtime should start");
     let (key, actor) = start_component(&runtime, "clock-probe", "clock_probe_component.wasm");
 
+    let capabilities = runtime.capabilities(&key).unwrap();
+    assert_eq!(capabilities.len(), 1);
+    assert_eq!(
+        capabilities[0].interface(),
+        "wasmeld:clock/monotonic-clock@0.1.0"
+    );
+
     let first = actor.invoke(b"first".to_vec()).unwrap();
     let second = actor.invoke(b"second".to_vec()).unwrap();
     assert_eq!(&first[8..], b"first");