fix(migrations): clarify sequence widening handling in PostgreSQL bigint migration

- Added comments to explain that altering column types does not change SERIAL sequence types.
- Noted that sequence widening is managed by a previous migration.

Author: x0sina

app/db/migrations/versions/4f15c0789493_use_bigint_for_id_column.py

@@ -88,6 +88,8 @@ def _upgrade_mysql() -> None:
 def _upgrade_postgresql() -> None:
     """PostgreSQL: Direct column alteration (automatically cascades to FKs)"""
     _alter_columns_to_bigint()
+    # ALTER COLUMN ... TYPE BIGINT does not change SERIAL sequence types.
+    # Sequence widening is handled by 8e2f1a9c4b70.
 
 
 def _is_bigint_type(sqlalchemy_type) -> bool:

app/db/migrations/versions/8e2f1a9c4b70_widen_postgres_integer_sequences.py

@@ -0,0 +1,79 @@
+"""widen leftover PostgreSQL INTEGER sequences to BIGINT
+
+Revision ID: 8e2f1a9c4b70
+Revises: 7c4bd5128e62
+Create Date: 2026-09-08 11:30:00.000000
+
+ALTER COLUMN ... TYPE BIGINT does not change SERIAL/IDENTITY sequence types.
+PostgreSQL INSERT ... ON CONFLICT still calls nextval(), so high-churn tables
+like node_user_usages exhaust INTEGER sequences at 2147483647.
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "8e2f1a9c4b70"
+down_revision = "7c4bd5128e62"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    if bind.dialect.name != "postgresql":
+        return
+
+    # Idempotent: only sequences still typed as integer are touched.
+    # Columns already BIGINT skip the table rewrite; only the sequence type changes.
+    op.execute(
+        sa.text(
+            """
+            DO $$
+            DECLARE
+                rec RECORD;
+            BEGIN
+                FOR rec IN
+                    SELECT
+                        n.nspname AS schema_name,
+                        s.relname AS sequence_name,
+                        t.relname AS table_name,
+                        a.attname AS column_name,
+                        format_type(a.atttypid, a.atttypmod) AS column_type
+                    FROM pg_class s
+                    JOIN pg_namespace n ON n.oid = s.relnamespace
+                    JOIN pg_depend d ON d.objid = s.oid AND d.deptype IN ('a', 'i')
+                    JOIN pg_class t ON t.oid = d.refobjid
+                    JOIN pg_attribute a ON a.attrelid = t.oid AND a.attnum = d.refobjsubid
+                    JOIN pg_sequence seq ON seq.seqrelid = s.oid
+                    WHERE s.relkind = 'S'
+                      AND n.nspname = current_schema()
+                      AND seq.seqtypid = 'integer'::regtype
+                      AND a.attnum > 0
+                      AND NOT a.attisdropped
+                LOOP
+                    IF rec.column_type NOT IN ('bigint', 'int8') THEN
+                        EXECUTE format(
+                            'ALTER TABLE %I.%I ALTER COLUMN %I TYPE BIGINT',
+                            rec.schema_name,
+                            rec.table_name,
+                            rec.column_name
+                        );
+                    END IF;
+
+                    EXECUTE format(
+                        'ALTER SEQUENCE %I.%I AS bigint',
+                        rec.schema_name,
+                        rec.sequence_name
+                    );
+                END LOOP;
+            END
+            $$;
+            """
+        )
+    )
+
+
+def downgrade() -> None:
+    # Values may already exceed INTEGER range; shrinking sequences is unsafe.
+    pass