feat: bound news AI concurrency with immediate task refill

backend/alembic/versions/20261101_e5f701234567_news_concurrency.py

@@ -0,0 +1,28 @@
+"""Add the news pipeline concurrency limit and durable item states."""
+from alembic import op
+import sqlalchemy as sa
+
+revision = 'e5f701234567'
+down_revision = 'd4e6f8012345'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column('risk_settings', sa.Column('max_concurrency', sa.Integer(), server_default='5', nullable=False))
+    op.create_check_constraint('risk_concurrency_positive', 'risk_settings', 'max_concurrency > 0')
+    op.execute("""UPDATE news_ai_reprocess_jobs j SET items = (
+        SELECT COALESCE(jsonb_agg(item || jsonb_build_object('state', CASE
+            WHEN ordinal > j.position THEN 'pending'
+            WHEN EXISTS (SELECT 1 FROM jsonb_array_elements(j.failures) f
+                WHERE f->>'stage' = 'grouping' AND f->>'id' = item->>'id') THEN 'failed'
+            ELSE 'done' END) ORDER BY ordinal), '[]'::jsonb)
+        FROM jsonb_array_elements(j.items) WITH ORDINALITY AS entries(item, ordinal))""")
+
+
+def downgrade():
+    op.execute("""UPDATE news_ai_reprocess_jobs SET items = (
+        SELECT COALESCE(jsonb_agg(item - 'state' ORDER BY CASE WHEN item->>'state' IN ('done', 'failed') THEN 0 ELSE 1 END, ordinal), '[]'::jsonb)
+        FROM jsonb_array_elements(items) WITH ORDINALITY AS entries(item, ordinal))""")
+    op.drop_constraint('risk_concurrency_positive', 'risk_settings', type_='check')
+    op.drop_column('risk_settings', 'max_concurrency')