diff --git a/pkg-py/tests/playwright/conftest.py b/pkg-py/tests/playwright/conftest.py
index 961af01f..3a2db45d 100644
--- a/pkg-py/tests/playwright/conftest.py
+++ b/pkg-py/tests/playwright/conftest.py
@@ -359,9 +359,20 @@ def _stop_streamlit_server(process: subprocess.Popen) -> None:
             process.kill()
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture
 def app_04_streamlit() -> Generator[str, None, None]:
-    """Start the 04-streamlit-app.py Streamlit server for testing."""
+    """
+    Start the 04-streamlit-app.py Streamlit server for testing.
+
+    Function-scoped (a fresh subprocess per test), unlike the Shiny/Gradio/Dash
+    app fixtures in this file. A single Streamlit server was observed to stop
+    re-running its script for new browser sessions after the first test's
+    session completed successfully -- the static page shell still loads, but
+    no reactive content (e.g. the chat greeting) ever streams in, with no
+    error on either side, and the condition persists for the rest of the
+    server's life (a fresh browser context/page doesn't recover it; only a
+    new server process does).
+    """
     app_path = str(EXAMPLES_DIR / "04-streamlit-app.py")
 
     def start_factory():
@@ -381,9 +392,9 @@ def streamlit_cleanup(process, _):
         _stop_streamlit_server(process)
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture
 def app_09_streamlit_custom() -> Generator[str, None, None]:
-    """Start the 09-streamlit-custom-app.py Streamlit server for testing."""
+    """Start the 09-streamlit-custom-app.py Streamlit server for testing. Function-scoped; see app_04_streamlit()."""
     app_path = str(EXAMPLES_DIR / "09-streamlit-custom-app.py")
 
     def start_factory():
diff --git a/pyproject.toml b/pyproject.toml
index bec6902f..cddceb52 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -43,7 +43,7 @@ classifiers = [
 [project.optional-dependencies]
 # For SQLAlchemySource and sample data, one of polars or pandas is required
 pandas = ["pandas"]
-polars = ["polars", "pyarrow"] # duckdb requires pyarrow for polars DataFrame registration
+polars = ["polars", "pyarrow<25.0.0"] # duckdb requires pyarrow for polars DataFrame registration; pyarrow>=25.0.0 segfaults when its native conversion code runs on more than ~2 OS threads over a process's lifetime (e.g. Streamlit reruns each script on a fresh thread) -- see #268
 ibis = ["ibis-framework>=9.0.0", "pandas"]  # pandas required for ibis .execute() to return DataFrames
 pins = ["pins>=0.9.1"]
 # Web framework extras
@@ -101,7 +101,7 @@ dev = [
     "tox-uv>=1.11.4",
     "pytest>=8.4.0",
     "polars>=1.0.0",
-    "pyarrow>=14.0.0",
+    "pyarrow<25.0.0", # see comment on the `polars` extra above
     "ibis-framework[duckdb]>=9.0.0",
     "ggsql>=0.3.2",
     "altair>=6.0",