Error Handling

iii has two broad error classes: SDK/local errors and engine/remote invocation errors. Agents should branch on the error code instead of matching only message strings.

Error Codes

Branch on exact code strings, but keep engine wire codes separate from SDK-local codes.

Code	Emitted by	Meaning	Typical handling
`function_not_found`	Engine and SDK local dispatch	No registered function is available under that ID	Check function ID, worker install/startup, discovery, and trigger type hints
`invocation_error`	Engine invocation/router path	Engine failed to route, record, or complete the invocation	Inspect engine logs, protocol state, and worker connectivity
`invocation_stopped`	Engine invocation handler	Invocation was cancelled or stopped by the engine/runtime	Treat as failed work; decide whether caller should retry
`FORBIDDEN`	RBAC / worker-gated engine functions	RBAC denied the action	Do not retry blindly; inspect policy, auth context, and allowed functions
`timeout`	A target worker's handler, forwarded verbatim by the engine	Not produced by the engine or the Node/Python SDKs (they emit `TIMEOUT`); appears only if the worker you called returns it	Treat as a timeout if you know the target worker emits it; otherwise branch on `TIMEOUT`
`function_not_invokable`	SDK local dispatch	Registration exists but cannot be invoked as a normal local function	Inspect registration/invocation type
`invocation_failed`	SDK worker handler wrappers	Local worker handler, HTTP-invoked function wrapper, or SDK-side handler path failed	Inspect handler logs, stacktrace, and payload validation
`TIMEOUT`	Node/Python SDK caller timeout	Client waited longer than `trigger()` timeout	Increase timeout only if the workload is expected to run long; otherwise optimize or enqueue

Handler vs Engine Errors

Handler errors originate in user function code, SDK local dispatch, or HTTP-invoked endpoints.
Engine errors originate in routing, invocation state, RBAC, protocol handling, or worker-reported wire errors.
Queue retries only apply to enqueued work. Synchronous failures are returned directly to the caller.
Void dispatch does not return handler results, so use logs/observability for failures.

Retryability

Retry transient TIMEOUT (or a lowercase timeout returned by a target worker), transport, or worker reconnect failures only when the operation is idempotent.
Do not retry FORBIDDEN without changing auth/policy.
Do not retry function_not_found by calling the same ID repeatedly; discover functions or install/start the missing worker.
For reliable background work, use TriggerAction.Enqueue({ queue }) and queue retry/DLQ policy.

SDK Surfaces

Node

import { InvocationError } from 'iii-sdk'

try {
  await iii.trigger({ function_id: 'orders::charge', payload })
} catch (error) {
  if (error instanceof InvocationError && error.code === 'FORBIDDEN') {
    throw new Error('Policy denied orders::charge')
  }
  throw error
}

Python

from iii import InvocationError

try:
    result = iii.trigger({"function_id": "orders::charge", "payload": payload})
except InvocationError as exc:
    if exc.code == "FORBIDDEN":
        raise RuntimeError("Policy denied orders::charge")
    if exc.code in ("TIMEOUT", "timeout"):  # SDK caller timeout, or a lowercase code returned by the target worker
        raise RuntimeError("orders::charge timed out")
    raise RuntimeError(f"{exc.code}: {exc.message}")

Rust

match iii.trigger(request).await {
    Ok(value) => value,
    Err(iii_sdk::Error::Timeout) => {
        return Err("orders::charge timed out".into());
    }
    Err(iii_sdk::Error::Remote { code, message, .. }) if code == "FORBIDDEN" => {
        return Err(format!("policy denied: {message}").into());
    }
    Err(err) => return Err(err.into()),
}

Browser

Browser trigger calls reject with JavaScript errors. Preserve the engine-provided code/message when present and show policy failures as permission errors in UI.

Pattern Boundaries

For invocation modes and enqueue decisions, prefer iii-core-primitives.
For SDK-specific exception classes and syntax, prefer iii-sdk-reference.
For workflow-level retry and DLQ design, prefer iii-architecture-patterns.
For RBAC policy design see the rbac-proxy worker; for logs and traces around worker failures, use the matching worker page on https://workers.iii.dev/.

When to Use

Use this skill when the task mentions iii errors, exception handling, failed invocations, timeouts, forbidden calls, retry behavior, or SDK error classes.

Boundaries

Do not retry non-idempotent work automatically unless it is enqueued under queue policy.
Do not treat RBAC denial as a missing worker.
Do not generate removed service APIs or adapter-extension APIs.

iii-error-handling