Fix: Expose ActorType on MutationContext for external policy inspection

[rian-be]

Problem Statement

MutationContext.ActorType is currently internal, making it impossible for external consumers (policies, governance components) to inspect whether a mutation was initiated by a User, Service, or System. This forces consumers to rely on fragile conventions like checking string prefixes:

var isSystemActor = transaction.InitiatedBy.StartsWith("system:", StringComparison.OrdinalIgnoreCase);

---

Solution Overview

1. Expose ActorType enum as public

The enum is used by MutationContext and needs to be visible to consumers for type inspection.

2. Change MutationContext.ActorType visibility

// Before
internal ActorType ActorType { get; init; } = ActorType.Unknown;

// After
public ActorType ActorType { get; internal init; } = ActorType.Unknown;

Consumers can read the value, but only the framework can assign it.

3. Keep System() factory signature unchanged

MutationContext.System() does not set ActorId — the system actor is identified by its type, not an ID. User() and Service() continue to set ActorId as before.

---

Design Decisions

Why exclude convenience booleans (`IsSystemActor`, etc.)?

MutationContext is a data holder, not a policy engine. Adding booleans blurs responsibility and creates maintenance debt — if new actor types match the same semantics (e.g. Administrator should behave like User), the booleans become misleading. Policies should write context.ActorType is ActorType.System explicitly.

Why not add `systemId` parameter to `System()`?

ActorId has shared semantics — it identifies "who did it" regardless of actor type. System actors are identified by ActorType == ActorType.System, not by an ID. If a specific system component needs attribution, consumers can pass it via Metadata.

---

Files Changed

ActorType.cs

• Visibility changed from internal enum to public enum

MutationContext.cs

• ActorType property changed from internal to public with internal init

---

Migration

Note

No breaking changes. Existing code that uses MutationContext factory methods (System, User, Service) is unaffected. All existing callers continue to work without modification.

closes #84