diff --git a/.gitignore b/.gitignore
index d816355..4ef1c6e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,3 +25,5 @@ config.*.yaml
 venv
 .venv
 dist
+
+.claude
diff --git a/tests/api/conftest.py b/tests/api/conftest.py
index eef0b32..e76b0ac 100644
--- a/tests/api/conftest.py
+++ b/tests/api/conftest.py
@@ -31,9 +31,15 @@ async def app(db_backend_config: DatabaseConfig) -> AsyncGenerator[FastAPI, None
     # create tables in the test database
     async with app.state.db_engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)
-    yield app
-    async with app.state.db_engine.begin() as conn:
-        await conn.run_sync(Base.metadata.drop_all)
+    try:
+        yield app
+
+        async with app.state.db_engine.begin() as conn:
+            await conn.run_sync(Base.metadata.drop_all)
+    finally:
+        # See tests/scheduler/conftest.py: the database is shared, so the
+        # engine has to be disposed even when the teardown above fails.
+        await app.state.db_engine.dispose()
 
 
 @pytest_asyncio.fixture
diff --git a/tests/scheduler/conftest.py b/tests/scheduler/conftest.py
index 12b83f2..f681d80 100644
--- a/tests/scheduler/conftest.py
+++ b/tests/scheduler/conftest.py
@@ -1,24 +1,29 @@
 """Pytest fixture and configurations"""
 
 import pytest_asyncio
-from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.ext.asyncio import async_sessionmaker
 
-from warden.lib.db.database import Base, build_db_url
+from warden.lib.db.database import Base, build_engine
 
 
 @pytest_asyncio.fixture(scope="function")
 async def db_engine(config_db):
-    engine = create_async_engine(build_db_url(config_db.database))
+    engine = build_engine(config_db.database)
 
     async with engine.begin() as conn:
         # Create all tables once
         await conn.run_sync(Base.metadata.create_all)
-    yield engine
-
-    async with engine.begin() as conn:
-        # Delete tables
-        await conn.run_sync(Base.metadata.drop_all)
-    await engine.dispose()
+    try:
+        yield engine
+
+        async with engine.begin() as conn:
+            # Delete tables
+            await conn.run_sync(Base.metadata.drop_all)
+    finally:
+        # Always dispose: every backend shares one database across the test
+        # session, so an engine left open on a failing teardown leaks its
+        # connections - and their transactions - into every later test.
+        await engine.dispose()
 
 
 @pytest_asyncio.fixture(scope="function")
diff --git a/warden/api/routes/dependencies/db.py b/warden/api/routes/dependencies/db.py
index 6af1224..4ccf6b8 100644
--- a/warden/api/routes/dependencies/db.py
+++ b/warden/api/routes/dependencies/db.py
@@ -1,15 +1,15 @@
 from typing import Annotated, AsyncGenerator
 
 from fastapi import Depends, FastAPI, Request
-from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 
 from warden.lib.config import DatabaseConfig
-from warden.lib.db.database import build_db_url
+from warden.lib.db.database import build_engine
 
 
 def init_db(app: FastAPI, db_config: DatabaseConfig):
     """Initialize the async engine and session factory with the given DB URL."""
-    engine = create_async_engine(build_db_url(db_config), echo=db_config.echo)
+    engine = build_engine(db_config)
 
     # TODO: ensure isolation between concurrent requests
     session_factory = async_sessionmaker(bind=engine, expire_on_commit=False)
diff --git a/warden/lib/db/database.py b/warden/lib/db/database.py
index 496d60c..f33cd87 100644
--- a/warden/lib/db/database.py
+++ b/warden/lib/db/database.py
@@ -1,6 +1,7 @@
 """Warden db utils"""
 
 from sqlalchemy.engine.url import URL
+from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
 from sqlalchemy.orm import declarative_base
 
 from warden.lib.config import DatabaseConfig
@@ -35,3 +36,11 @@ def build_db_url(cfg: DatabaseConfig) -> str:
         ).render_as_string(hide_password=False)
 
     raise ValueError(f"Unsupported backend: {cfg.backend}")
+
+
+def build_engine(cfg: DatabaseConfig) -> AsyncEngine:
+    """Build the async engine for `cfg`."""
+
+    engine = create_async_engine(build_db_url(cfg), echo=cfg.echo)
+
+    return engine
diff --git a/warden/scheduler/main.py b/warden/scheduler/main.py
index c48a989..7b2f1f4 100644
--- a/warden/scheduler/main.py
+++ b/warden/scheduler/main.py
@@ -9,11 +9,10 @@
 from sqlalchemy.ext.asyncio import (
     AsyncEngine,
     async_sessionmaker,
-    create_async_engine,
 )
 
 from warden.lib.config import Config
-from warden.lib.db.database import build_db_url
+from warden.lib.db.database import build_engine
 from warden.lib.models import Job
 from warden.scheduler.cancellation_worker import cancellation_worker
 from warden.scheduler.db import job_update_commiter
@@ -144,7 +143,7 @@ async def main_async(conf: Config | None = None):
         conf = Config()
 
     logging.config.dictConfig(config=conf.logging)
-    engine = create_async_engine(build_db_url(conf.database), echo=conf.database.echo)
+    engine = build_engine(conf.database)
     loop = asyncio.get_running_loop()
     stop_event = asyncio.Event()