# Error Handling Policy (Version 4)

This policy defines active V4 error taxonomy, translation boundaries, and retry semantics.

## Error Categories

| Category | Meaning | Typical Origin | User Treatment |
| :--- | :--- | :--- | :--- |
| `validation` | Input payload/selection is invalid | UI form parsing, service validators | Inline correction guidance |
| `not_found` | Target record is missing | ID lookup in service layer | Non-blocking warning or redirect |
| `conflict` | State prevents requested action | lifecycle transitions, duplicate semantic keys | Explain required precondition |
| `external` | Provider/network dependency failure | OpenRouter/provider adapter | Retry path and evidence retained |
| `timeout` | Provider call exceeded configured bound | worker/provider client timeout | Retry path and bounded messaging |
| `internal` | Unexpected local failure | unhandled service/runtime faults | Safe generic message + diagnostics capture |

## Translation Boundaries

- **Provider layer:** raise provider-scoped exceptions with provider context; do not emit UI text.
- **Service layer:** map raw exceptions into domain-aware categories and preserve causal chain.
- **UI/API layer:** convert category to user-safe message with contextual action guidance.

## Job and Page Failure Semantics

### Page-Level (`JobSource`)

- `pending` -> `transcribed` when attempt succeeds.
- `pending` -> `failed` when attempt fails terminally.
- `pending` -> `cancelled` on job cancellation before processing.

### Job-Level (`Job`)

- `transcribed` when all pages transcribe successfully.
- `partial_success` when mixed success/failure outcomes exist.
- `failed` when no page transcribes successfully.

## Retry and Retranscription Rules

1. Failed/cancelled pages may be re-queued through retranscription workflows.
2. Retry attempts must append new `ExecutionAttempt` rows; prior evidence remains immutable.
3. Selecting a better candidate must update projection pointers, not mutate historical attempt rows.

## Logging and Diagnostics Rules

1. Persist sufficient attempt error metadata (`error_category`, `error_message`, transport evidence) for post-hoc analysis.
2. Avoid leaking stack traces or local paths into user-facing message envelopes.
3. Preserve causal exception chains for internal diagnostics.

## UI Messaging Contract

- User-visible errors must be actionable, bounded, and category-consistent.
- Multi-page jobs must show partial outcomes instead of collapsing into a single opaque failure.
- Recovery actions (`retry`, `retranscribe`, `edit input`) must be offered where available.

## Cross-Reference

- [Error Handling invariant](../invariant/error_handling.md)
- [System Requirements](requirements_v4.md)
- [Data Model](schema_v4.md)