feat(messenger): add getRegisteredActionTypes accessor

[sirtimid]

Explanation

Adds a public, read-only accessor Messenger.getRegisteredActionTypes() that returns the action types a messenger can call() directly — actions registered on it plus actions delegated into it from a child messenger. It returns [...this.#actions.keys()].

There is no public way to enumerate a messenger's callable actions today.

Why string[] and not Action['type'][]

The first instinct is to type the return as the messenger's action-type union for nicer caller types. That's not safe here: it would make Action appear in a covariant (return) position — the first such member on the class. Every existing Action-dependent method (call, registerActionHandler) deliberately keeps Action behind a bounded generic to avoid this. A covariant Action member breaks assigning a messenger to a narrower-typed one (e.g. passing a controller's full messenger to a service typed against only a subset of its actions) — a pattern consumers rely on (@metamask/perps-controller does exactly this and fails to compile with the union return). No union-derived return type avoids this; only a constant return type does. string[] is sufficient for the consumer below, which just lists/prints the types.

Why

@metamask/wallet-cli is gaining an mm daemon list command to enumerate the actions on the wallet's root messenger (sibling to the existing mm daemon call <Controller>:<method>). That needs a public accessor on the messenger, which this PR adds. The command itself is a separate wallet-cli follow-up.

Notes for reviewers

• Non-breaking and purely additive — new read-only method, no behavior change. Verified with a full monorepo build.
• Method name is open to bikeshedding.

🤖 Generated with Claude Code

---

Note

Low Risk
Purely additive read-only introspection with no changes to registration, delegation, or call behavior.

Overview
Adds a read-only Messenger.getRegisteredActionTypes() API that lists every action type the instance can invoke via call()—handlers on that messenger plus actions delegated into it, and not actions delegated away.

The implementation snapshots keys from the internal #actions map (same source getAction / call use), so unregistering or revoking delegation updates the list. Tests cover empty messengers, register/unregister, and delegated-in actions; the unreleased changelog documents the method for tooling such as wallet CLI action listing.

^{Reviewed by Cursor Bugbot for commit c14f260. Bugbot is set up for automated code reviews on this repo. Configure here.}