perf(persistence): remove unused resource URL indexes

- Keep only primary-key and URL-hash unique indexes
- Fold index cleanup into migration 0041
- Verify SQLite and PostgreSQL migration behavior

ARCHITECTURE.md

@@ -275,7 +275,7 @@ Persistence is centered on `pkg/persistence/mgr.py`.
 - SQLite is the default database; PostgreSQL is supported.
 - Models live under `pkg/entity/persistence/`.
 - `pkg/persistence/media.py::MediaReferenceText` validates bound conversation payloads on ORM/Core writes while preserving the existing TEXT schema and string API. It rejects recognized structured inline images: retained images go through `MediaCache.externalize_chain_dump()` before serialization, while metadata-only snapshots and transcripts use `redact_inline_images()`. Reads and comparisons preserve historical values for incremental cleanup. Runtime/adapter messages, arbitrary diagnostic text, and opaque strings are outside this contract.
-- `pkg/persistence/resource_urls.py` interns structured resource URL fields in retained messages, history and monitoring at the typed SQL boundary, in the source transaction. `MediaReferenceJSON` preserves native JSON monitoring details. Payloads store opaque references to the global `resource_urls` catalog; typed SQL reads and comparisons expand them to current URLs, preserving API shapes and source-record authorization. Configuration URLs and URLs in free text are excluded. The URL hash has a unique index; canonical IDs and check timestamps are indexed. Successful refreshes overwrite the current URL and persist the check time even when standard `get_msg` returns the same URL. Converging URLs retain only ID redirects, with no old URL. PostgreSQL row locks and SQLite's immediate write transaction serialize concurrent refreshes; SQLite holds its write lock during the upstream call. Bounded in-memory aliases let reused Runner payloads resolve old URLs without retaining those URLs in the database. Migration `0041_resource_urls` normalizes existing payloads using their source creation timestamps before producers start; downgrade expands references before dropping the catalog.
+- `pkg/persistence/resource_urls.py` interns structured resource URL fields in retained messages, history and monitoring at the typed SQL boundary, in the source transaction. `MediaReferenceJSON` preserves native JSON monitoring details. Payloads store opaque references to the global `resource_urls` catalog; typed SQL reads and comparisons expand them to current URLs, preserving API shapes and source-record authorization. Configuration URLs and URLs in free text are excluded. Catalog lookups use only the primary-key and URL-hash unique indexes. Successful refreshes overwrite the current URL and persist the check time even when standard `get_msg` returns the same URL. Converging URLs retain only ID redirects, with no old URL. PostgreSQL row locks and SQLite's immediate write transaction serialize concurrent refreshes; SQLite holds its write lock during the upstream call. Bounded in-memory aliases let reused Runner payloads resolve old URLs without retaining those URLs in the database. Migration `0041_resource_urls` normalizes existing payloads using their source creation timestamps before producers start; downgrade expands references before dropping the catalog.
 - Timezone-less SQL `DateTime` columns store UTC-naive values on both backends. Normalize aware values with `pkg/persistence/datetime_utils.py::as_naive_utc` at the bind boundary, including deadlines, leases, event times, and query/retention cutoffs; do not merely strip an offset. Existing naive rows represent UTC. Restore UTC awareness for application comparisons and epoch serialization. Runner ledger/event/transcript stores follow this existing schema contract without a data migration or changes to journal/tenant authorization.
 - Fresh schemas are created from current metadata, then Alembic migrations run to head. LangBot 4.x does not upgrade 3.x databases.
 - New schema changes use Alembic under `pkg/persistence/alembic/versions/`; there is no legacy migration chain in 4.x.

src/langbot/pkg/entity/persistence/resource_url.py

@@ -11,7 +11,7 @@ class ResourceURL(Base):
     id = sa.Column(sa.String(36), primary_key=True)
     url = sa.Column(sa.Text, nullable=True)
     url_hash = sa.Column(sa.String(64), nullable=True, unique=True)
-    canonical_id = sa.Column(sa.String(36), sa.ForeignKey('resource_urls.id'), nullable=True, index=True)
+    canonical_id = sa.Column(sa.String(36), sa.ForeignKey('resource_urls.id'), nullable=True)
     created_at = sa.Column(sa.DateTime, nullable=False)
     last_checked_at = sa.Column(sa.DateTime, nullable=True)
     updated_at = sa.Column(sa.DateTime, nullable=False)
@@ -22,5 +22,4 @@ class ResourceURL(Base):
             'OR (canonical_id IS NOT NULL AND url IS NULL AND url_hash IS NULL)',
             name='ck_resource_url_canonical',
         ),
-        sa.Index('ix_resource_urls_last_checked', 'last_checked_at'),
     )

src/langbot/pkg/persistence/alembic/versions/0041_resource_urls.py

@@ -20,6 +20,8 @@ def upgrade():
 
     connection = op.get_bind()
     ResourceURL.__table__.create(connection, checkfirst=True)
+    op.drop_index('ix_resource_urls_canonical_id', table_name='resource_urls', if_exists=True)
+    op.drop_index('ix_resource_urls_last_checked', table_name='resource_urls', if_exists=True)
     install(connection.engine)
     if connection.dialect.name == 'postgresql':
         create_postgres_expansion(connection)

tests/unit_tests/persistence/test_resource_urls.py

@@ -321,6 +321,39 @@ async def test_napcat_uses_key_ttl_instead_of_the_standard_interval(database):
         assert 'rkey=key2' in await db.scalar(sa.select(EventLog.input_json))
 
 
+@pytest.mark.asyncio
+async def test_index_migration_preserves_primary_key_unique_hash_and_payload(database):
+    migration = importlib.import_module('langbot.pkg.persistence.alembic.versions.0041_resource_urls')
+    removed = {'ix_resource_urls_canonical_id', 'ix_resource_urls_last_checked'}
+
+    def indexes(sync):
+        return {index['name'] for index in sa.inspect(sync).get_indexes('resource_urls')}
+
+    def upgrade(sync):
+        with Operations.context(MigrationContext.configure(sync)):
+            migration.upgrade()
+
+    def create_legacy_indexes(sync):
+        operations = Operations(MigrationContext.configure(sync))
+        operations.create_index('ix_resource_urls_canonical_id', 'resource_urls', ['canonical_id'])
+        operations.create_index('ix_resource_urls_last_checked', 'resource_urls', ['last_checked_at'])
+
+    async with database.begin() as db:
+        await append(db, 'a')
+        assert removed.isdisjoint(await db.run_sync(indexes))
+        # Recreate the schema deployed before the indexes were removed.
+        await db.run_sync(create_legacy_indexes)
+        assert removed <= await db.run_sync(indexes)
+        await db.run_sync(upgrade)
+        await db.run_sync(upgrade)
+        assert removed.isdisjoint(await db.run_sync(indexes))
+        primary_key = await db.run_sync(lambda sync: sa.inspect(sync).get_pk_constraint('resource_urls'))
+        assert primary_key['constrained_columns'] == ['id']
+        constraints = await db.run_sync(lambda sync: sa.inspect(sync).get_unique_constraints('resource_urls'))
+        assert any(constraint['column_names'] == ['url_hash'] for constraint in constraints)
+        assert OLD in await db.scalar(sa.select(EventLog.input_json))
+
+
 @pytest.mark.asyncio
 async def test_migration_preserves_source_creation_and_downgrade(database):
     migration = importlib.import_module('langbot.pkg.persistence.alembic.versions.0041_resource_urls')