diff --git a/backend/fluksio/flow/logs.py b/backend/fluksio/flow/logs.py
index 9cb60bf..e8f1957 100644
--- a/backend/fluksio/flow/logs.py
+++ b/backend/fluksio/flow/logs.py
@@ -36,17 +36,19 @@ class _Tee(io.TextIOBase):
             sink(text)
         try:
             return self._real.write(text)
-        except OSError:
+        except (OSError, ValueError):
             # A dead stdout — `fluksio serve` runs the engine as a child of the
             # dashboard, which holds the far end of that pipe — must not fail
             # the node whose output was being teed. The capture above has it,
-            # and there is nowhere left to report the loss to anyway.
+            # and there is nowhere left to report the loss to anyway. A closed
+            # one (ValueError) is the same at interpreter exit, when whatever
+            # was wrapped — pytest's capture, say — has been closed first.
             return len(text)
 
     def flush(self) -> None:
         try:
             self._real.flush()
-        except OSError:
+        except (OSError, ValueError):
             pass
 
     def isatty(self) -> bool:
diff --git a/backend/tests/flow/test_connector.py b/backend/tests/flow/test_connector.py
index 4abde58..258ceb6 100644
--- a/backend/tests/flow/test_connector.py
+++ b/backend/tests/flow/test_connector.py
@@ -1,6 +1,7 @@
 """The connector contract: polling, deduplication, health and discovery."""
 
 import asyncio
+from collections.abc import Callable
 from types import SimpleNamespace
 from typing import Any
 
@@ -48,12 +49,28 @@ def a_sensor(readings: list[Any], **params: Any) -> Sensor:
     return node
 
 
-def run_briefly(node: ConnectorNode, seconds: float = 0.12, app: Any = None) -> None:
-    """Start the poll loop, let it tick a few times, stop it."""
+def run_briefly(
+    node: ConnectorNode,
+    seconds: float = 0.12,
+    app: Any = None,
+    until: Callable[[], bool] | None = None,
+) -> None:
+    """Start the poll loop, let it tick a few times, stop it.
+
+    With ``until``, stop once that holds instead, giving up after 5 s: a fixed
+    pause is too short when the machine is busy. The caller's asserts then say
+    what never happened.
+    """
 
     async def cycle() -> None:
         await node.start(app)
-        await asyncio.sleep(seconds)
+        if until is None:
+            await asyncio.sleep(seconds)
+        else:
+            for _ in range(500):
+                if until():
+                    break
+                await asyncio.sleep(0.01)
         await node.stop()
 
     asyncio.run(cycle())
@@ -97,7 +114,8 @@ def test_a_failing_poll_reports_down_and_keeps_going():
     node._on_health = lambda _node, status, detail: health.append((status, detail))
     Pipeline(nodes=[node])
 
-    run_briefly(node)
+    # The first poll fails, so an "ok" after it is the recovery.
+    run_briefly(node, until=lambda: len(health) > 1 and health[-1][0] == "ok")
 
     assert ("down", "RuntimeError: device unplugged") in health
     # It recovered rather than giving up.
diff --git a/backend/tests/test_cli.py b/backend/tests/test_cli.py
index 61cb816..355d218 100644
--- a/backend/tests/test_cli.py
+++ b/backend/tests/test_cli.py
@@ -636,6 +636,8 @@ def test_two_files_of_one_name_are_refused(tmp_path) -> None:
     where it sits; this is the spelling that still gets there — two files
     named on the command line, each rooted at its own directory.
     """
+    import sys
+
     import pytest
 
     from fluksio.sdk import SyncError
@@ -647,9 +649,14 @@ def test_two_files_of_one_name_are_refused(tmp_path) -> None:
 
     first = tmp_path / "s1" / "study.py"
     second = tmp_path / "s2" / "study.py"
-    _import(*_module_of(first), first)
-    with pytest.raises(SyncError, match="both import as 'study'"):
-        _import(*_module_of(second), second)
+    roots = {str(tmp_path / "s1"), str(tmp_path / "s2")}
+    try:
+        _import(*_module_of(first), first)
+        with pytest.raises(SyncError, match="both import as 'study'"):
+            _import(*_module_of(second), second)
+    finally:
+        sys.modules.pop("study", None)
+        sys.path[:] = [entry for entry in sys.path if entry not in roots]
 
 
 def test_how_long_ago_reads_like_a_duration() -> None: