Prioritize realtime news and make historical backfill resumable

backend/alembic/versions/20261106_dd4567890123_priority_queue.py

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+"""Persist realtime boundaries and enforce one active call per subject."""
+from alembic import op
+import sqlalchemy as sa
+
+revision = 'dd4567890123'
+down_revision = 'dc3456789012'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column('news_research_settings', sa.Column('realtime_from', sa.DateTime(timezone=True)))
+    op.add_column('news_research_events', sa.Column('realtime_pending', sa.Boolean(), nullable=False, server_default=sa.false()))
+    op.create_index('uq_news_attempt_active', 'news_research_attempts', ['package_id'], unique=True,
+                    postgresql_where=sa.text("state = 'processing'"))
+    op.create_index('uq_news_version_active', 'news_research_versions', ['event_id'], unique=True,
+                    postgresql_where=sa.text("state = 'processing'"))
+
+
+def downgrade():
+    op.drop_index('uq_news_version_active', table_name='news_research_versions')
+    op.drop_index('uq_news_attempt_active', table_name='news_research_attempts')
+    op.drop_column('news_research_events', 'realtime_pending')
+    op.drop_column('news_research_settings', 'realtime_from')