feat: add session.started event that triggers when a new session is created

[berenar]

Motivation

I want to create a plugin that:

1. Runs when I start a new session
2. Checks if the AGENTS.md file is present
3. Warns the user if it's missing

I didn't find an event suited for that.

Proposed solution

I added an event session.started that triggers when a session starts.
I believe this will be useful for other plugins too.

FYI

• I added a test but I could not test a plugin that uses this event.
• I believe some types need to be updated.
• I think we should update the documentation to clearly list all events that can be used in plugins. I could update the file /packages/web/src/content/docs/plugins.mdx but maybe there's a way to keep that list updated in the docs.

[rekram1-node]

I think we should update the documentation to clearly list all events that can be used in plugins. I could update the file /packages/web/src/content/docs/plugins.mdx but maybe there's a way to keep that list updated in the docs.

We need to do some type of doc gen prolly

[rekram1-node]

for your usecase you could technically run the plugin whenever they start up opencode (rather than every new session). just make defining the warning within the plugin function rather than a hook it returns

[rekram1-node]

There is this Updated event right below, do you think having 2 events fire at same time could cause confusion here?

[berenar]

There is this Updated event right below, do you think having 2 events fire at same time could cause confusion here?

@rekram1-node Well, right now, the session is immediately updated right after it's created, so yes, it makes sense that both Created and Updated events are triggered.

However, to me, it makes more sense if createNext only triggered one Created event by replacing the Updated event with Created. But that could break any internal listeners (and users' plugins) of the Updated event that assume that's the event triggered when a session starts.

[rekram1-node]

shipping it, thanks!!

[rekram1-node]

renaming it to session.created it will be released later today probs