## on_session_end()

Register a handler that fires when a call session ends. Use this to save call data, trigger post-call workflows, or log outcomes.

The `BotSessionEnded` event carries a `termination_reason` field that tells you why the session ended:

| Value             | Meaning                                               |
|-------------------|-------------------------------------------------------|
| `"user-hangup"` | The caller hung up.                                   |
| `"bot-hangup"`  | The agent ended the call (e.g. via `call.hangup()`).|
| `"bot-failure"` | The session ended due to an internal error.          |
| `"bot-transfer"`| The call was transferred to another destination.      |
| `"voicemail"`   | The outbound call reached voicemail.                  |

### Signature

```python
@agent.on_session_end
def on_session_end(call: guava.Call, event: BotSessionEnded) -> None:
    ...
```

```typescript
agent.onSessionEnd(async (call: guava.Call, event: BotSessionEnded) => void);
```

### Example

```python
import logging
from guava.events import BotSessionEnded

logger = logging.getLogger(__name__)

@agent.on_session_end
def on_session_end(call: guava.Call, event: BotSessionEnded):
    logger.info("session ended: reason=%s", event.termination_reason)
    if event.termination_reason == "user-hangup":
        # caller hung up — save any collected data
        ...
    elif event.termination_reason == "bot-transfer":
        # call was transferred to a human agent
        ...
```

```typescript
import * as guava from "@guava-ai/guava-sdk";
import type { BotSessionEnded } from "@guava-ai/guava-sdk";

agent.onSessionEnd(async (_call: guava.Call, event: BotSessionEnded) => {
  console.log("session ended:", event.termination_reason);
  if (event.termination_reason === "user-hangup") {
    // caller hung up — save any collected data
  } else if (event.termination_reason === "bot-transfer") {
    // call was transferred to a human agent
  }
});
```