diff --git a/packages/db-dtypes/docs/conf.py b/packages/db-dtypes/docs/conf.py
index 672dafff8ba7..2c755cbc5cbe 100644
--- a/packages/db-dtypes/docs/conf.py
+++ b/packages/db-dtypes/docs/conf.py
@@ -359,7 +359,6 @@
 
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
-    "python": ("https://python.readthedocs.org/en/latest/", None),
     "google-auth": ("https://googleapis.dev/python/google-auth/latest/", None),
     "google.api_core": (
         "https://googleapis.dev/python/google-api-core/latest/",
@@ -371,6 +370,21 @@
     "pandas": ("https://pandas.pydata.org/pandas-docs/stable/", None),
 }
 
+# Check reachability of the Python standard library inventory before attaching it.
+# Because Sphinx is run with `-W` (warnings as errors) in CI, an external network
+# failure or upstream outage on docs.python.org would otherwise treat the missing
+# inventory as a fatal error and fail the build.
+try:
+    import urllib.request
+
+    with urllib.request.urlopen("https://docs.python.org/3/objects.inv", timeout=2):
+        intersphinx_mapping["python"] = (
+            "https://python.readthedocs.org/en/latest/",
+            None,
+        )
+except Exception:
+    pass
+
 
 # Napoleon settings
 napoleon_google_docstring = True
diff --git a/packages/db-dtypes/testing/constraints-3.14.txt b/packages/db-dtypes/testing/constraints-3.14.txt
index e69de29bb2d1..72e1e5759b6f 100644
--- a/packages/db-dtypes/testing/constraints-3.14.txt
+++ b/packages/db-dtypes/testing/constraints-3.14.txt
@@ -0,0 +1,10 @@
+# When testing with `pandas >= 3.1.0` (currently in pre-release as `pandas==3.1.0rc0`),
+# the `db-dtypes` compliance test suite (`tests/compliance`) fails due to upstream
+# changes in pandas internal utilities and ExtensionArray interface contracts.
+# To prevent presubmit PR CI from failing unexpectedly on developer branches, a
+# temporary ceiling constraint (`pandas < 3.1.0dev0`) was added.
+#
+# Forward-looking tests against upcoming, unreleased versions of pandas and other
+# dependencies continue to run in our dedicated pre-release test suite.
+
+pandas < 3.1.0dev0
diff --git a/packages/db-dtypes/tests/unit/test_dtypes.py b/packages/db-dtypes/tests/unit/test_dtypes.py
index b4039c595828..c3283929101a 100644
--- a/packages/db-dtypes/tests/unit/test_dtypes.py
+++ b/packages/db-dtypes/tests/unit/test_dtypes.py
@@ -534,7 +534,15 @@ def exercise_any():
         try:
             return a.any()
         except TypeError as e:
-            if "does not support operation" in str(e) or "not supported" in str(e):
+            # Truth reduction ('any'/'all') is disallowed on datetime64 arrays (pandas GH#34479).
+            # Known messages across pandas versions:
+            #   - pandas < 3.0:  "datetime64 type does not support operation 'any'"
+            #   - pandas >= 3.0: "'any' with datetime64 dtypes is not supported"
+            #   - test mock:     "does not support operation"
+            msg = str(e)
+            if "does not support operation" in msg or (
+                "datetime64" in msg and "is not supported" in msg
+            ):
                 return
             raise e
 
@@ -571,7 +579,15 @@ def exercise_all():
         try:
             return a.all()
         except TypeError as e:
-            if "does not support operation" in str(e) or "not supported" in str(e):
+            # Truth reduction ('any'/'all') is disallowed on datetime64 arrays (pandas GH#34479).
+            # Known messages across pandas versions:
+            #   - pandas < 3.0:  "datetime64 type does not support operation 'all'"
+            #   - pandas >= 3.0: "'all' with datetime64 dtypes is not supported"
+            #   - test mock:     "does not support operation"
+            msg = str(e)
+            if "does not support operation" in msg or (
+                "datetime64" in msg and "is not supported" in msg
+            ):
                 return
             raise e
 
diff --git a/packages/gcp-sphinx-docfx-yaml/noxfile.py b/packages/gcp-sphinx-docfx-yaml/noxfile.py
index c07b64581285..59a5741a796c 100644
--- a/packages/gcp-sphinx-docfx-yaml/noxfile.py
+++ b/packages/gcp-sphinx-docfx-yaml/noxfile.py
@@ -171,7 +171,9 @@ def lint_setup_py(session):
     session.run("flake8", "setup.py")
 
 
-@nox.session(python=UNIT_TEST_PYTHON_VERSIONS)
+# Use virtualenv backend to prevent modern uv build isolation from failing on
+# legacy sdist dependencies (unify/untokenize)
+@nox.session(python=UNIT_TEST_PYTHON_VERSIONS, venv_backend="virtualenv")
 def unit(session):
     """Run unit tests."""
     # Re-enable 3.11, 3.12, and 3.13 after environment verification.