# Error Handling

Kitaru exposes a typed exception hierarchy so you can distinguish usage, context, state, runtime, backend, and execution failures.

## Core exception types

```python
import kitaru

try:
    result = my_flow.run(...).get()
except kitaru.KitaruUserCodeError as exc:
    # user checkpoint/flow code raised
    print(exc.exec_id, exc.status, exc.failure_origin)
except kitaru.KitaruDivergenceError:
    # replay divergence surfaced from backend contract
    ...
except kitaru.KitaruExecutionError:
    # other execution-level failure
    ...
```

## Wait-input validation failures

`client.executions.input(...)` raises `kitaru.KitaruWaitValidationError` when supplied input does not satisfy the wait schema.

```python
try:
    client.executions.input(exec_id, wait="approve_deploy", value="yes")
except kitaru.KitaruWaitValidationError as exc:
    print(exc)
```

When validation fails, the execution remains in `waiting`.

## Failure journaling in the client

`KitaruClient` surfaces structured failure details:

* `execution.failure`: failure summary for failed executions
* `checkpoint.failure`: final checkpoint failure (if terminal attempt failed)
* `checkpoint.attempts`: full retry attempt history, including failed attempts

```python
client = kitaru.KitaruClient()
execution = client.executions.get(exec_id)

if execution.failure:
    print(execution.failure.origin, execution.failure.message)

for checkpoint in execution.checkpoints:
    for attempt in checkpoint.attempts:
        print(attempt.attempt_id, attempt.status)
        if attempt.failure:
            print("  ", attempt.failure.exception_type, attempt.failure.message)
```

## Replay divergence behavior

`client.executions.replay(...)` may fail immediately with `kitaru.KitaruDivergenceError` when the backend detects an incompatible durable call sequence.

Even when replay submission succeeds, divergence can still surface later on the replayed execution as normal execution failure metadata:

```python
replayed = client.executions.replay(exec_id, from_="write_draft")
latest = replayed.refresh()

if latest.failure and latest.failure.origin == kitaru.FailureOrigin.DIVERGENCE:
    print("Replay divergence:", latest.failure.message)
```


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