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>

alembic/versions/m3k1h7i9j0_add_activity_bus_columns.py

@@ -0,0 +1,113 @@
+"""add unified event bus columns to ap_activities
+
+Revision ID: m3k1h7i9j0
+Revises: l2j0g6h8i9
+Create Date: 2026-02-22
+
+Adds processing and visibility columns so ap_activities can serve as the
+unified event bus for both internal domain events and federation delivery.
+"""
+
+revision = "m3k1h7i9j0"
+down_revision = "l2j0g6h8i9"
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade() -> None:
+    # Add new columns with defaults so existing rows stay valid
+    op.add_column(
+        "ap_activities",
+        sa.Column("actor_uri", sa.String(512), nullable=True),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column(
+            "visibility", sa.String(20),
+            nullable=False, server_default="public",
+        ),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column(
+            "process_state", sa.String(20),
+            nullable=False, server_default="completed",
+        ),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column(
+            "process_attempts", sa.Integer(),
+            nullable=False, server_default="0",
+        ),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column(
+            "process_max_attempts", sa.Integer(),
+            nullable=False, server_default="5",
+        ),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column("process_error", sa.Text(), nullable=True),
+    )
+    op.add_column(
+        "ap_activities",
+        sa.Column(
+            "processed_at", sa.DateTime(timezone=True), nullable=True,
+        ),
+    )
+
+    # Backfill actor_uri from the related actor_profile
+    op.execute(
+        """
+        UPDATE ap_activities a
+        SET actor_uri = CONCAT(
+            'https://',
+            COALESCE(current_setting('app.ap_domain', true), 'rose-ash.com'),
+            '/users/',
+            p.preferred_username
+        )
+        FROM ap_actor_profiles p
+        WHERE a.actor_profile_id = p.id
+          AND a.actor_uri IS NULL
+        """
+    )
+
+    # Make actor_profile_id nullable (internal events have no actor profile)
+    op.alter_column(
+        "ap_activities", "actor_profile_id",
+        existing_type=sa.Integer(),
+        nullable=True,
+    )
+
+    # Index for processor polling
+    op.create_index(
+        "ix_ap_activity_process", "ap_activities", ["process_state"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_ap_activity_process", table_name="ap_activities")
+
+    # Restore actor_profile_id NOT NULL (remove any rows without it first)
+    op.execute(
+        "DELETE FROM ap_activities WHERE actor_profile_id IS NULL"
+    )
+    op.alter_column(
+        "ap_activities", "actor_profile_id",
+        existing_type=sa.Integer(),
+        nullable=False,
+    )
+
+    op.drop_column("ap_activities", "processed_at")
+    op.drop_column("ap_activities", "process_error")
+    op.drop_column("ap_activities", "process_max_attempts")
+    op.drop_column("ap_activities", "process_attempts")
+    op.drop_column("ap_activities", "process_state")
+    op.drop_column("ap_activities", "visibility")
+    op.drop_column("ap_activities", "actor_uri")

alembic/versions/n4l2i8j0k1_drop_domain_events_table.py

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+"""drop domain_events table
+
+Revision ID: n4l2i8j0k1
+Revises: m3k1h7i9j0
+Create Date: 2026-02-22
+
+The domain_events table is no longer used — all events now flow through
+ap_activities with the unified activity bus.
+"""
+
+revision = "n4l2i8j0k1"
+down_revision = "m3k1h7i9j0"
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import JSONB
+
+
+def upgrade() -> None:
+    op.drop_index("ix_domain_events_state", table_name="domain_events")
+    op.drop_index("ix_domain_events_event_type", table_name="domain_events")
+    op.drop_table("domain_events")
+
+
+def downgrade() -> None:
+    op.create_table(
+        "domain_events",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("event_type", sa.String(128), nullable=False),
+        sa.Column("aggregate_type", sa.String(64), nullable=False),
+        sa.Column("aggregate_id", sa.Integer(), nullable=False),
+        sa.Column("payload", JSONB(), nullable=True),
+        sa.Column("state", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("attempts", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("max_attempts", sa.Integer(), nullable=False, server_default="5"),
+        sa.Column("last_error", sa.Text(), nullable=True),
+        sa.Column(
+            "created_at", sa.DateTime(timezone=True),
+            nullable=False, server_default=sa.func.now(),
+        ),
+        sa.Column("processed_at", sa.DateTime(timezone=True), nullable=True),
+    )
+    op.create_index("ix_domain_events_event_type", "domain_events", ["event_type"])
+    op.create_index("ix_domain_events_state", "domain_events", ["state"])