Enum BackendError 

pub enum BackendError {
    InvalidRequest {
        message: String,
    },
    ExecutionFailed {
        message: String,
    },
    Unavailable {
        message: String,
    },
    BudgetExceeded {
        resource: String,
        limit: String,
    },
    ContractFailed {
        contract: String,
        message: String,
    },
    UnsupportedCapability {
        capability: BackendCapability,
    },
    AdapterError {
        message: String,
    },
    RecallError {
        message: String,
    },
    Timeout {
        deadline_ms: u64,
        elapsed_ms: u64,
    },
    CircuitOpen {
        backend: String,
        retry_after_ms: Option<u64>,
    },
    Retried {
        message: String,
        attempts: usize,
        was_transient: bool,
    },
    Other {
        message: String,
    },
}

Error type for backend operations.

This is capability-agnostic - implementations can wrap their specific errors.

Retryable Errors

Some errors are transient and can be retried:

• Timeout - operation exceeded deadline but might succeed on retry
• Unavailable - backend temporarily unavailable
• ExecutionFailed - if caused by transient infrastructure issues

Use is_retryable() to check if an error should trigger retry logic.

Variants

InvalidRequest

Request validation failed (NOT retryable - fix the request)

Fields

message: String

ExecutionFailed

Backend execution failed (may be retryable depending on cause)

Fields

message: String

Unavailable

Backend is unavailable (retryable - try again later)

Fields

message: String

BudgetExceeded

Budget exceeded (NOT retryable - increase budget or reduce request)

Fields

resource: String

limit: String

ContractFailed

Contract validation failed (NOT retryable - output doesn’t match contract)

Fields

contract: String

message: String

UnsupportedCapability

Capability not supported (NOT retryable - use different backend)

Fields

capability: BackendCapability

AdapterError

Adapter not found or incompatible (NOT retryable - fix configuration)

Fields

message: String

RecallError

Recall operation failed (may be retryable)

Fields

message: String

Timeout

Operation timed out (retryable - might succeed with more time)

Fields

deadline_ms: u64

Configured deadline in milliseconds

elapsed_ms: u64

Actual elapsed time in milliseconds

CircuitOpen

Circuit breaker is open (NOT retryable until circuit closes)

Fields

backend: String

Name of the backend with open circuit

retry_after_ms: Option<u64>

When the circuit will transition to half-open (Unix timestamp ms)

Retried

Retryable wrapper - indicates retry was attempted

Fields

message: String

The final error after all retries exhausted

attempts: usize

Number of attempts made

was_transient: bool

Whether the underlying error was transient

Other

Generic error with context

Fields

message: String

Implementations

impl BackendError

pub fn is_retryable(&self) -> bool

Check if this error is retryable.

Retryable errors are transient and might succeed on retry:

• Timeout
• Unavailable
• Some ExecutionFailed (network issues, rate limits)

Non-retryable errors require intervention:

• InvalidRequest (fix the request)
• BudgetExceeded (increase budget)
• ContractFailed (output doesn’t match)
• UnsupportedCapability (use different backend)
• CircuitOpen (wait for circuit to close)

pub fn is_overload(&self) -> bool

Check if this error indicates the backend is overloaded.

Used by circuit breakers to track failure patterns.

Trait Implementations

impl Clone for BackendError

fn clone(&self) -> BackendError

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for BackendError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for BackendError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for BackendError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for BackendError

fn eq(&self, other: &BackendError) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for BackendError

impl StructuralPartialEq for BackendError