fix: reject malformed host target paths

crates/wip-host/src/lib.rs

@@ -540,6 +540,8 @@ pub trait ObjectProvider {
 
     /// Fetches the canonical object projection currently published at `path`.
     fn fetch(&self, path: &str) -> Result<Object, CallError> {
+        wip_protocol::validate_path(path)
+            .map_err(|error| CallError::new(CallErrorKind::InvalidRequest, error.to_string()))?;
         self.with_object(path, PublishedObject::protocol_object)
             .ok_or_else(|| CallError::new(CallErrorKind::NotFound, "target path is not published"))
             .and_then(|object| {
@@ -552,12 +554,15 @@ pub trait ObjectProvider {
 
     /// Resolves and executes a canonical path-targeted operation request.
     ///
-    /// Failure checks follow the exact canonical precedence: path, supplied
-    /// object validator mismatch, membership, interface validator requirement
-    /// and mismatch, operation existence, object validator requirement,
-    /// arguments, then authorization. No failed precondition invokes the typed
-    /// implementation.
+    /// Structural path validation precedes provider resolution. For a valid
+    /// request, failure checks follow the exact canonical precedence: path,
+    /// supplied object validator mismatch, membership, interface validator
+    /// requirement and mismatch, operation existence, object validator
+    /// requirement, arguments, then authorization. No failed precondition
+    /// invokes the provider callback or typed implementation.
     fn call_operation(&self, request: CallRequest) -> Result<CallResult, CallError> {
+        wip_protocol::validate_path(&request.target.path)
+            .map_err(|error| CallError::new(CallErrorKind::InvalidRequest, error.to_string()))?;
         let path = request.target.path.clone();
         self.with_object(&path, |publication| {
             publication.dispatch_resolved(request, |object, interface, operation| {
@@ -592,6 +597,8 @@ impl Error for PublicationError {}
 /// Stable host dispatch failure kind.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CallErrorKind {
+    /// The request is structurally invalid.
+    InvalidRequest,
     /// The target path is not currently published.
     NotFound,
     /// The selected interface is not exposed by the current object.
@@ -671,6 +678,7 @@ impl CallError {
     #[must_use]
     pub fn protocol_error(&self) -> ProtocolError {
         let code = match self.kind {
+            CallErrorKind::InvalidRequest => ProtocolErrorCode::InvalidRequest,
             CallErrorKind::NotFound => ProtocolErrorCode::NotFound,
             CallErrorKind::InterfaceMismatch => ProtocolErrorCode::InterfaceMismatch,
             CallErrorKind::OperationNotFound => ProtocolErrorCode::OperationNotFound,

crates/wip-host/tests/host.rs

@@ -440,6 +440,37 @@ fn path_dispatch_is_interface_qualified_and_resolves_once_per_call() {
 fn call_failures_follow_canonical_precedence_without_execution() {
     let (_, provider, hidden) = registry_and_provider();
 
+    let resolutions = provider.resolutions.get();
+    for invalid_path in [
+        "relative",
+        "/trailing/",
+        "/double//segment",
+        "/dot/./segment",
+        "/parent/../segment",
+    ] {
+        assert_failure(
+            provider
+                .call_operation(request(
+                    invalid_path,
+                    Some(b"stale"),
+                    hidden.reference(),
+                    Some(b"stale"),
+                    "missing",
+                    BTreeMap::new(),
+                ))
+                .unwrap_err(),
+            CallErrorKind::InvalidRequest,
+            ProtocolErrorCode::InvalidRequest,
+        );
+    }
+    assert_eq!(provider.resolutions.get(), resolutions);
+    assert_failure(
+        provider.fetch("/invalid/").unwrap_err(),
+        CallErrorKind::InvalidRequest,
+        ProtocolErrorCode::InvalidRequest,
+    );
+    assert_eq!(provider.resolutions.get(), resolutions);
+
     assert_failure(
         provider
             .call_operation(request(