Unify domain_events + ap_activities into AP-shaped event bus

All cross-service events now flow through ap_activities with a unified
EventProcessor. Internal events use visibility="internal"; federation
activities use visibility="public" and get delivered by a wildcard handler.

- Add processing columns to APActivity (process_state, actor_uri, etc.)
- New emit_activity() / register_activity_handler() API
- EventProcessor polls ap_activities instead of domain_events
- Rewrite all handlers to accept APActivity
- Migrate all 7 emit_event call sites to emit_activity
- publish_activity() sets process_state=pending directly (no emit_event bridge)
- Migration to drop domain_events table

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

models/__init__.py

@@ -8,8 +8,6 @@ from .ghost_membership_entities import (
     GhostNewsletter, UserNewsletter,
     GhostTier, GhostSubscription,
 )
-from .domain_event import DomainEvent
-
 from .ghost_content import Tag, Post, Author, PostAuthor, PostTag, PostLike
 from .page_config import PageConfig
 from .order import Order, OrderItem

models/federation.py

@@ -50,14 +50,19 @@ class ActorProfile(Base):
 
 
 class APActivity(Base):
-    """An ActivityPub activity (local or remote)."""
+    """An ActivityPub activity (local or remote).
+
+    Also serves as the unified event bus: internal domain events and public
+    federation activities both live here, distinguished by ``visibility``.
+    The ``EventProcessor`` polls rows with ``process_state='pending'``.
+    """
     __tablename__ = "ap_activities"
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
     activity_id: Mapped[str] = mapped_column(String(512), unique=True, nullable=False)
     activity_type: Mapped[str] = mapped_column(String(64), nullable=False)
-    actor_profile_id: Mapped[int] = mapped_column(
-        Integer, ForeignKey("ap_actor_profiles.id", ondelete="CASCADE"), nullable=False,
+    actor_profile_id: Mapped[int | None] = mapped_column(
+        Integer, ForeignKey("ap_actor_profiles.id", ondelete="CASCADE"), nullable=True,
     )
     object_type: Mapped[str | None] = mapped_column(String(64), nullable=True)
     object_data: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
@@ -83,6 +88,27 @@ class APActivity(Base):
         DateTime(timezone=True), nullable=False, server_default=func.now(),
     )
 
+    # --- Unified event-bus columns ---
+    actor_uri: Mapped[str | None] = mapped_column(
+        String(512), nullable=True,
+    )
+    visibility: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="public", server_default="public",
+    )
+    process_state: Mapped[str] = mapped_column(
+        String(20), nullable=False, default="completed", server_default="completed",
+    )
+    process_attempts: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0, server_default="0",
+    )
+    process_max_attempts: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=5, server_default="5",
+    )
+    process_error: Mapped[str | None] = mapped_column(Text, nullable=True)
+    processed_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True,
+    )
+
     # Relationships
     actor_profile = relationship("ActorProfile", back_populates="activities")
 
@@ -90,6 +116,7 @@ class APActivity(Base):
         Index("ix_ap_activity_actor", "actor_profile_id"),
         Index("ix_ap_activity_source", "source_type", "source_id"),
         Index("ix_ap_activity_published", "published"),
+        Index("ix_ap_activity_process", "process_state"),
     )
 
     def __repr__(self) -> str: