> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/nemo/labs-voice-agent/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/labs-voice-agent/_mcp/server.

# nemo_voice_agent.evaluation.sync_appliers

Cross-side sync-delta applier registry (bot-side).

This module is the bot-side endpoint of the cross-side state-propagation
pipeline introduced for dual-side scenarios (telecom and any future
domain that opts into `Scenario.sync_state`).

The pipeline at a glance:

1. A write tool on bot A fires and calls `WriteScenarioTool._record_action`,
   which (in addition to appending to `shared_state["actions"]`) emits an
   `action-applied` RTVI server message.
2. The bridge picks that up, replays the action onto an in-process shadow
   copy of both DBs (using the scenario's tool map + each tool's sync
   `invoke` method), then calls `scenario.sync_state(agent_db, user_db)`.
3. `sync_state` returns a per-side `delta` dict describing the
   cross-side field changes that must land on the OTHER bot. The bridge
   dispatches each delta via the `apply_sync_delta` RTVI action.
4. The receiving bot's handler calls into `apply_sync_delta(domain, db, delta)`
   in this module to mutate its own `shared_state["db"]`.

The default applier handles "dotted path → value" deltas (e.g.
`"surroundings.payment_request": {...}`) and is sufficient for any
domain whose cross-side propagation is pure field assignment. Domains
needing more (list-by-id lookups, post-apply re-derivation hooks,
domain-specific validation) register a per-domain applier via
`@register_sync_applier(domain="...")`.

This is structurally parallel to `initialization_functions` and
`db_state_predicates` — same registry-by-domain pattern, same
opt-in shape.

## Module Contents

### Functions

| Name                                                                                        | Description                                                   |
| ------------------------------------------------------------------------------------------- | ------------------------------------------------------------- |
| [`_default_sync_applier`](#nemo_voice_agent-evaluation-sync_appliers-_default_sync_applier) | Generic dotted-path field setter.                             |
| [`apply_sync_delta`](#nemo_voice_agent-evaluation-sync_appliers-apply_sync_delta)           | Dispatch a sync delta to the registered applier for `domain`. |
| [`register_sync_applier`](#nemo_voice_agent-evaluation-sync_appliers-register_sync_applier) | Decorator: register a domain-specific applier.                |

### Data

[`SYNC_APPLIERS`](#nemo_voice_agent-evaluation-sync_appliers-SYNC_APPLIERS)

### API

```python
nemo_voice_agent.evaluation.sync_appliers._default_sync_applier(
    db: dict,
    delta: dict
) -> None
```

Generic dotted-path field setter.

Each `delta` key is a dotted path into `db`; the corresponding
value is assigned at that path. The path components are followed
verbatim — no list-index or by-id-match support. Domains needing
those (e.g. `bills[B1002].status`) must register their own
applier.

Example::

delta = \{"surroundings.payment\_request": \{"bill\_id": "B1002", ...}}

# → db\["surroundings"]\["payment\_request"] = \{"bill\_id": "B1002", ...}

**Raises:**

* `KeyError`: if an intermediate path component doesn't exist in `db`.

```python
nemo_voice_agent.evaluation.sync_appliers.apply_sync_delta(
    domain: str,
    db: dict,
    delta: dict
) -> None
```

Dispatch a sync delta to the registered applier for `domain`.

Falls back to `_default_sync_applier` (dotted-path field set) when
no per-domain applier exists. The default suffices for any future
domain whose sync deltas are pure field assignments.

**Parameters:**

**`domain`**

`Scenario.domain` value of the active scenario.

---

**`db`**

The bot's live `shared_state["db"]` (mutated in place).

---

**`delta`**

Cross-side delta from the bridge — shape is domain-defined.

---

```python
nemo_voice_agent.evaluation.sync_appliers.register_sync_applier(
    domain: str
)
```

Decorator: register a domain-specific applier.

The applier signature is `func(db: dict, delta: dict) -> None`
and must mutate `db` in place. The exact shape of `delta` is
a contract between the scenario's `sync_state` (which produces
it) and the applier (which consumes it) — the bridge transports
it verbatim.

Usage::

@register\_sync\_applier(domain="tau2\_telecom")
def apply\_telecom\_sync\_delta(db: dict, delta: dict) -> None:
...

```python
nemo_voice_agent.evaluation.sync_appliers.SYNC_APPLIERS: Dict[str, Callable[[dict, dict], None]] = {}
```