feat: model operation outcome guarantees

crates/wip-interface/src/lib.rs

@@ -46,8 +46,10 @@
 //! `Option<T>` is supported only directly as a record field or operation
 //! parameter. It means omission, not a null value. A domain failure belongs in
 //! an application return enum/union and is returned as `Ok(value)`.
-//! [`HostError`] is reserved for host/runtime failure, so the required
-//! [`OperationResult`] convention keeps those two failure classes distinct.
+//! [`HostError`] is reserved for host/runtime failure and requires an explicit
+//! [`HostErrorKind`] plus [`EffectGuarantee`]. The required [`OperationResult`]
+//! convention therefore keeps domain failures separate from runtime failures and
+//! makes outcome uncertainty visible to Host dispatch.
 //!
 //! # Migration to canonical values
 //!
@@ -139,29 +141,107 @@ pub trait InterfaceImplementation<T>: InterfaceDefinition {
 /// `Err(HostError)` means the host or runtime could not perform the operation.
 pub type OperationResult<T> = Result<T, HostError>;
 
-/// A host/runtime failure, kept separate from the operation's application
+/// Whether an operation failure proves that no effects were committed.
+///
+/// This guarantee is consumed by Host dispatch when choosing a protocol failure:
+/// only [`NotCommitted`](Self::NotCommitted) failures may become `Internal` or
+/// `ResourceLimitExceeded`; [`Unknown`](Self::Unknown) failures must become
+/// `OperationOutcomeUnknown`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EffectGuarantee {
+    /// The operation was not invoked, or every effect was rolled back.
+    NotCommitted,
+    /// The operation may have committed effects.
+    Unknown,
+}
+
+/// Host/runtime failure category used when effects are known not to be committed.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum HostErrorKind {
+    /// The Host or backend encountered an internal failure.
+    Internal,
+    /// A cancellation, deadline, or bounded resource limit was exceeded.
+    ResourceLimitExceeded,
+}
+
+/// A typed host/runtime failure, kept separate from the operation's application
 /// return type.
+///
+/// The effect guarantee is mandatory. Host runtimes must ignore the diagnostic
+/// when producing a wire response; it is bounded here for local observability but
+/// can still contain backend-private information.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct HostError {
+    kind: HostErrorKind,
+    effect_guarantee: EffectGuarantee,
     message: String,
 }
 
 impl HostError {
-    /// Creates a host failure with a human-readable diagnostic.
+    /// Creates an internal Host failure with an explicit effect guarantee.
     #[must_use]
-    pub fn new(message: impl Into<String>) -> Self {
+    pub fn internal(message: impl Into<String>, effect_guarantee: EffectGuarantee) -> Self {
+        Self::new(HostErrorKind::Internal, effect_guarantee, message)
+    }
+
+    /// Creates a resource-limit Host failure with an explicit effect guarantee.
+    #[must_use]
+    pub fn resource_limit(message: impl Into<String>, effect_guarantee: EffectGuarantee) -> Self {
+        Self::new(
+            HostErrorKind::ResourceLimitExceeded,
+            effect_guarantee,
+            message,
+        )
+    }
+
+    fn new(
+        kind: HostErrorKind,
+        effect_guarantee: EffectGuarantee,
+        message: impl Into<String>,
+    ) -> Self {
         Self {
-            message: message.into(),
+            kind,
+            effect_guarantee,
+            message: bounded_diagnostic(message.into()),
         }
     }
 
-    /// Returns the diagnostic message.
+    /// Returns the typed Host failure category.
+    #[must_use]
+    pub fn kind(&self) -> HostErrorKind {
+        self.kind
+    }
+
+    /// Returns the operation-effect guarantee attached by the implementation.
+    #[must_use]
+    pub fn effect_guarantee(&self) -> EffectGuarantee {
+        self.effect_guarantee
+    }
+
+    /// Returns the bounded local diagnostic message.
+    ///
+    /// Host runtimes must not place this value in protocol responses because it
+    /// can contain backend paths, credentials, or other private details.
     #[must_use]
     pub fn message(&self) -> &str {
         &self.message
     }
 }
 
+const MAX_DIAGNOSTIC_BYTES: usize = 512;
+
+fn bounded_diagnostic(mut message: String) -> String {
+    if message.len() <= MAX_DIAGNOSTIC_BYTES {
+        return message;
+    }
+    let mut end = MAX_DIAGNOSTIC_BYTES;
+    while !message.is_char_boundary(end) {
+        end -= 1;
+    }
+    message.truncate(end);
+    message
+}
+
 impl Display for HostError {
     fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
         formatter.write_str(&self.message)
@@ -241,12 +321,59 @@ pub enum DispatchError {
     Decode(CodecError),
     /// The implementation reported a host/runtime failure.
     Host(HostError),
+    /// The implementation panicked after invocation began.
+    ///
+    /// Panic payloads are deliberately discarded because they can contain
+    /// backend-private diagnostics.
+    Panic,
     /// The Rust result could not be encoded.
     Encode(CodecError),
     /// The encoded result did not match the generated declaration.
     InvalidResult(wip_protocol::ValidationError),
 }
 
+/// Whether generated dispatch failed before or after typed implementation
+/// invocation began.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DispatchPhase {
+    /// Typed implementation code was not invoked.
+    BeforeInvocation,
+    /// Typed implementation invocation began, so effects require an explicit
+    /// non-commit or rollback guarantee.
+    AfterInvocation,
+}
+
+impl DispatchError {
+    /// Returns the execution phase in which this dispatch failure occurred.
+    #[must_use]
+    pub fn phase(&self) -> DispatchPhase {
+        match self {
+            Self::UnknownOperation(_) | Self::InvalidArguments(_) | Self::Decode(_) => {
+                DispatchPhase::BeforeInvocation
+            }
+            Self::Host(_) | Self::Panic | Self::Encode(_) | Self::InvalidResult(_) => {
+                DispatchPhase::AfterInvocation
+            }
+        }
+    }
+
+    /// Returns a post-invocation effect guarantee when the implementation
+    /// supplied one.
+    ///
+    /// Panic, encode, and result-validation failures default to `Unknown` until
+    /// a provider confirms rollback. Pre-invocation failures return `None`.
+    #[must_use]
+    pub fn effect_guarantee(&self) -> Option<EffectGuarantee> {
+        match self {
+            Self::UnknownOperation(_) | Self::InvalidArguments(_) | Self::Decode(_) => None,
+            Self::Host(error) => Some(error.effect_guarantee()),
+            Self::Panic | Self::Encode(_) | Self::InvalidResult(_) => {
+                Some(EffectGuarantee::Unknown)
+            }
+        }
+    }
+}
+
 impl Display for DispatchError {
     fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
         match self {
@@ -256,6 +383,7 @@ impl Display for DispatchError {
             Self::InvalidArguments(error) => write!(formatter, "invalid arguments: {error}"),
             Self::Decode(error) => write!(formatter, "argument decoding failed: {error}"),
             Self::Host(error) => write!(formatter, "host operation failed: {error}"),
+            Self::Panic => formatter.write_str("operation implementation panicked"),
             Self::Encode(error) => write!(formatter, "result encoding failed: {error}"),
             Self::InvalidResult(error) => write!(formatter, "invalid operation result: {error}"),
         }
@@ -265,7 +393,7 @@ impl Display for DispatchError {
 impl Error for DispatchError {
     fn source(&self) -> Option<&(dyn Error + 'static)> {
         match self {
-            Self::UnknownOperation(_) => None,
+            Self::UnknownOperation(_) | Self::Panic => None,
             Self::InvalidArguments(error) | Self::InvalidResult(error) => Some(error),
             Self::Decode(error) | Self::Encode(error) => Some(error),
             Self::Host(error) => Some(error),

crates/wip-interface/tests/interface.rs

@@ -1,7 +1,10 @@
 use std::collections::BTreeMap;
 
 use wip_interface::wip_protocol::{INTERFACE_FORMAT_V1, TypeExpr, Value};
-use wip_interface::{DispatchError, HostError, OperationResult, WipType, interface};
+use wip_interface::{
+    DispatchError, DispatchPhase, EffectGuarantee, HostError, HostErrorKind, OperationResult,
+    WipType, interface,
+};
 
 /// Publication request.
 #[derive(Debug, Clone, PartialEq, WipType)]
@@ -66,7 +69,10 @@ impl Catalog for AcceptingCatalog {
     }
 
     fn host_value(&self) -> OperationResult<String> {
-        Err(HostError::new("backend unavailable"))
+        Err(HostError::internal(
+            "backend unavailable",
+            EffectGuarantee::Unknown,
+        ))
     }
 }
 
@@ -90,6 +96,26 @@ impl Catalog for RejectingCatalog {
     }
 }
 
+struct PanickingCatalog;
+
+impl Catalog for PanickingCatalog {
+    fn publish(
+        &self,
+        _request: PublishRequest,
+        _note: Option<String>,
+    ) -> OperationResult<PublishOutcome> {
+        panic!("private panic payload")
+    }
+
+    fn ping(&self) -> OperationResult<()> {
+        panic!("private panic payload")
+    }
+
+    fn host_value(&self) -> OperationResult<String> {
+        panic!("private panic payload")
+    }
+}
+
 fn publish_arguments(with_note: bool) -> BTreeMap<String, Value> {
     let mut arguments = BTreeMap::from([(
         "request".into(),
@@ -203,16 +229,41 @@ fn typed_dispatch_validates_decodes_invokes_encodes_and_validates() {
     let invalid =
         CatalogDefinition::dispatch(&AcceptingCatalog, "publish", BTreeMap::new()).unwrap_err();
     assert!(matches!(invalid, DispatchError::InvalidArguments(_)));
+    assert_eq!(invalid.phase(), DispatchPhase::BeforeInvocation);
+    assert_eq!(invalid.effect_guarantee(), None);
 
     let host =
         CatalogDefinition::dispatch(&AcceptingCatalog, "host_value", BTreeMap::new()).unwrap_err();
-    assert!(matches!(host, DispatchError::Host(error) if error.message() == "backend unavailable"));
+    assert!(
+        matches!(&host, DispatchError::Host(error) if error.message() == "backend unavailable")
+    );
+    assert_eq!(host.phase(), DispatchPhase::AfterInvocation);
+    assert_eq!(host.effect_guarantee(), Some(EffectGuarantee::Unknown));
+
+    let panic =
+        CatalogDefinition::dispatch(&PanickingCatalog, "host_value", BTreeMap::new()).unwrap_err();
+    assert!(matches!(panic, DispatchError::Panic));
+    assert_eq!(panic.phase(), DispatchPhase::AfterInvocation);
+    assert_eq!(panic.effect_guarantee(), Some(EffectGuarantee::Unknown));
+    assert!(!panic.to_string().contains("private panic payload"));
 
     let unknown =
         CatalogDefinition::dispatch(&AcceptingCatalog, "missing", BTreeMap::new()).unwrap_err();
     assert!(matches!(unknown, DispatchError::UnknownOperation(name) if name == "missing"));
 }
 
+#[test]
+fn host_errors_require_a_typed_kind_and_effect_guarantee() {
+    let internal = HostError::internal("x".repeat(4_096), EffectGuarantee::NotCommitted);
+    assert_eq!(internal.kind(), HostErrorKind::Internal);
+    assert_eq!(internal.effect_guarantee(), EffectGuarantee::NotCommitted);
+    assert!(internal.message().len() <= 512);
+
+    let resource = HostError::resource_limit("deadline", EffectGuarantee::Unknown);
+    assert_eq!(resource.kind(), HostErrorKind::ResourceLimitExceeded);
+    assert_eq!(resource.effect_guarantee(), EffectGuarantee::Unknown);
+}
+
 /// Operations whose distinct source names normalize to the same PascalCase.
 #[interface]
 pub trait DistinctOperations {