docs: expand events actor and debugging guidance

docs/events.md

@@ -3,12 +3,46 @@
 
 Datasette includes a mechanism for tracking events that occur while the software is running. This is primarily intended to be used by plugins, which can both trigger events and listen for events.
 
-The core Datasette application triggers events when certain things happen. This page describes those events.
+The core Datasette application triggers events for actions such as signing in or changing data. Each event is a dataclass with a `name`, a `created` timestamp, an `actor` and fields describing the action. This page describes the built-in event classes.
 
 Note that these events will *not* fire for changes made to a SQLite database by a process other than Datasette itself.
 
 Plugins can listen for events using the {ref}`plugin_hook_track_event` plugin hook, which will be called with instances of the following classes - or additional classes {ref}`registered by other plugins <plugin_hook_register_events>`.
 
+## Event actors
+
+The `actor=` argument identifies the authenticated user or API client responsible for the event. It uses the same JSON-compatible dictionary as {ref}`request.actor <authentication_actor>`, and should normally include a unique `"id"` string. Pass `actor=None` for an anonymous request or an action that was not initiated by an authenticated actor.
+
+`actor` is a required field on the event object, not an argument to `datasette.track_event()`. A plugin that tracks an event associated with the current request can use:
+
+```python
+from datasette.events import InsertRowsEvent
+
+
+await datasette.track_event(
+    InsertRowsEvent(
+        actor=request.actor,
+        database="data",
+        table="items",
+        num_rows=1,
+        ignore=False,
+        replace=False,
+    )
+)
+```
+
+The actor dictionary is passed to `track_event` hooks as part of the event. Plugins that record events should treat it as authentication metadata and avoid adding secrets or credentials to it.
+
+## Debugging events
+
+The [datasette-debug-events](https://github.com/datasette/datasette-debug-events) plugin prints every event to standard error. Install it in the same environment as Datasette:
+
+```bash
+datasette install datasette-debug-events
+```
+
+Once installed, run Datasette from a terminal and perform the action you want to inspect. The corresponding events, including their actors and properties, will be displayed in that terminal.
+
 ```{eval-rst}
 .. automodule:: datasette.events
     :members: