# Payo Patch IR

Payo updates an existing structured record by emitting a minimal JSON array of operations. It does not regenerate the full state and does not use RFC 6902.

## Shape

A patch is a JSON array. Each operation targets a JSON Pointer path listed in the supplied Payo Schema View.

    [{"op":"set","path":"/status","value":"confirmed"}]

Supported operations:

- **set** — create or replace a value at a schema-approved path whose parent object already exists.
- **delete** — remove an existing field when the schema allows deletion.
- **append** — append one value to an existing append-only array.
- **[]** — a genuine no-op: no represented state change is justified.

The model should emit the smallest patch that produces the justified current state. An invalid operation invalidates the whole patch.

## Null, deletion, and no-op

These are not interchangeable.

Set an existing field to JSON null:

    [{"op":"set","path":"/assignee","value":null}]

Remove the field:

    [{"op":"delete","path":"/assignee"}]

Make no change:

    []

A null value means the field remains present with a null value. Delete means the field is absent. An empty array means that no state change is justified.

## Operations

### set

Set creates or replaces the value at a schema-approved path. The parent object must already exist. Payo v0 does not create missing intermediate objects.

    [{"op":"set","path":"/status","value":"confirmed"}]

The value must satisfy the path's type and any deterministic constraints such as enum, const, or numeric bounds.

### delete

Delete removes an existing field. The field must exist, and the schema must allow deletion. Required fields are not deletable.

    [{"op":"delete","path":"/assignee"}]

### append

Append adds one item to an existing append-only array. It does not replace or edit existing array items.

    [{"op":"append","path":"/events","value":{"type":"checked_in","minute":64}}]

Array paths support append only; indexed mutation is outside this IR.

## Paths and application

Paths use JSON Pointer escaping: a literal tilde is written as ~0 and a literal slash in a key as ~1. Operations are applied in array order. The target path must exist in the supplied schema and the current state must satisfy the patch operation's preconditions.

A patch is not silently repaired. Do not substitute a nearby path, coerce a value, drop a bad operation, or replace an invalid patch with [].