Mint: migration to clean up overly large witnesses (#817)

* add migration to clean up overly large witnesses

* bump to 0.18.1

tests/mint/test_mint_migrations.py

@@ -0,0 +1,74 @@
+import pytest
+
+from cashu.core.db import Database
+from cashu.core.migrations import migrate_databases
+from cashu.mint import migrations as mint_migrations
+
+
+@pytest.mark.asyncio
+async def test_m029_witness_cleanup():
+    db = Database("mint", "./test_data/mig_witness_cleanup")
+
+    # Ensure schema is at latest so tables exist
+    await migrate_databases(db, mint_migrations)
+
+    long_witness = "a" * 1025
+    short_witness = "b" * 10
+
+    async with db.connect() as conn:
+        # Insert into proofs_used
+        await conn.execute(
+            f"""
+            INSERT INTO {db.table_with_schema('proofs_used')} (amount, id, c, secret, y, witness, created, melt_quote)
+            VALUES (1, 'kid', 'c_used_long', 's_used_long', 'y_used_long', :w, {db.timestamp_now}, NULL)
+            """,
+            {"w": long_witness},
+        )
+        await conn.execute(
+            f"""
+            INSERT INTO {db.table_with_schema('proofs_used')} (amount, id, c, secret, y, witness, created, melt_quote)
+            VALUES (1, 'kid', 'c_used_short', 's_used_short', 'y_used_short', :w, {db.timestamp_now}, NULL)
+            """,
+            {"w": short_witness},
+        )
+
+        # Insert into proofs_pending
+        await conn.execute(
+            f"""
+            INSERT INTO {db.table_with_schema('proofs_pending')} (amount, id, c, secret, y, witness, created, melt_quote)
+            VALUES (1, 'kid', 'c_pend_long', 's_pend_long', 'y_pend_long', :w, {db.timestamp_now}, NULL)
+            """,
+            {"w": long_witness},
+        )
+        await conn.execute(
+            f"""
+            INSERT INTO {db.table_with_schema('proofs_pending')} (amount, id, c, secret, y, witness, created, melt_quote)
+            VALUES (1, 'kid', 'c_pend_short', 's_pend_short', 'y_pend_short', :w, {db.timestamp_now}, NULL)
+            """,
+            {"w": short_witness},
+        )
+
+    # Run the migration under test directly
+    await mint_migrations.m029_remove_overlong_witness_values(db)
+
+    # Validate cleanup
+    async with db.connect() as conn:
+        row = await conn.fetchone(
+            f"SELECT witness FROM {db.table_with_schema('proofs_used')} WHERE secret = 's_used_long'"
+        )
+        assert row["witness"] is None
+
+        row = await conn.fetchone(
+            f"SELECT witness FROM {db.table_with_schema('proofs_used')} WHERE secret = 's_used_short'"
+        )
+        assert row["witness"] == short_witness
+
+        row = await conn.fetchone(
+            f"SELECT witness FROM {db.table_with_schema('proofs_pending')} WHERE secret = 's_pend_long'"
+        )
+        assert row["witness"] is None
+
+        row = await conn.fetchone(
+            f"SELECT witness FROM {db.table_with_schema('proofs_pending')} WHERE secret = 's_pend_short'"
+        )
+        assert row["witness"] == short_witness