diff --git a/tests/conftest.py b/tests/conftest.py
index 349a412..28bdce4 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,7 +1,8 @@
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Iterator
 
 import pytest
 import pytest_asyncio
+import structlog
 from asgi_lifespan import LifespanManager
 from fastapi import FastAPI
 from httpx import ASGITransport, AsyncClient
@@ -10,6 +11,25 @@ from src.config import Settings
 from src.main import create_app
 
 
+@pytest.fixture(autouse=True)
+def _reset_structlog_after_test() -> Iterator[None]:
+    """Undo any real `configure_logging()` call before the next test runs.
+
+    Any test that exercises the app's lifespan (directly, or via the `client`/
+    `api_client` fixtures below and in `test_domains_api.py`) calls the real
+    `configure_logging()`, which mutates *global* structlog/stdlib state --
+    including `cache_logger_on_first_use=True`. Left in place, that setting
+    silently breaks `structlog.testing.capture_logs()` in unrelated tests
+    later in the same pytest process: a module-level
+    `logger = structlog.get_logger(__name__)` cached under the real config no
+    longer routes through `capture_logs()`'s temporary processor swap, so
+    assertions on captured events see nothing (ADR-0016: isolate per test --
+    this generalizes to global config mutations, not just data).
+    """
+    yield
+    structlog.reset_defaults()
+
+
 @pytest.fixture
 def settings() -> Settings:
     # Every external dependency points at a closed port so unit tests never
@@ -36,6 +56,24 @@ def app(settings: Settings) -> FastAPI:
     return create_app(settings)
 
 
+@pytest.fixture(autouse=True)
+def _no_real_logging_configuration(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Prevent the app lifespan from calling the real `configure_logging()`.
+
+    It sets `cache_logger_on_first_use=True` (ADR-0011), which permanently
+    monkeypatches the `.bind` method on whichever module-level
+    `logger = structlog.get_logger(__name__)` instance is used first --
+    `structlog.reset_defaults()` only resets *global* config, not that
+    per-instance mutation, so real configuration leaking into one test would
+    silently break `structlog.testing.capture_logs()` in every test that runs
+    afterward in the same process (ADR-0016: isolate per test). Tests that
+    spin up the full app via `LifespanManager` (`client`, `api_client`) are
+    testing HTTP behavior, not logging output, so they don't need it for
+    real.
+    """
+    monkeypatch.setattr("src.bootstrap.lifespan.configure_logging", lambda *a, **k: None)
+
+
 @pytest_asyncio.fixture
 async def client(app: FastAPI) -> AsyncIterator[AsyncClient]:
     async with (