diff --git a/.claude/hooks/session-start.sh b/.claude/hooks/session-start.sh
index e726795..ead61e0 100755
--- a/.claude/hooks/session-start.sh
+++ b/.claude/hooks/session-start.sh
@@ -29,7 +29,13 @@ python -m pip install --upgrade --ignore-installed setuptools wheel || true
 # Editable install with the same extras CI uses. Editable + plain `install`
 # (not `ci`-style clean installs) so the resolved deps are cached in the
 # container image for later sessions.
-pip install -e ".[pyscf,ase,dev,xtb]"
+#
+# `python -m pip`, not bare `pip`: in the cloud image `pip` is /usr/bin/pip
+# (the distro Python) while `python` is /usr/local/bin/python. The setuptools
+# upgrade above targets `python`, so a bare `pip` install used the distro
+# setuptools and failed to build pyscf-properties, which left the session
+# with nothing installed.
+python -m pip install -e ".[pyscf,ase,dev,xtb]"
 
 echo "QuantUI cloud env ready: package + [pyscf,ase,dev,xtb] installed." >&2
 
diff --git a/quantui/app.py b/quantui/app.py
index 67a8757..ad47e2d 100644
--- a/quantui/app.py
+++ b/quantui/app.py
@@ -3564,8 +3564,16 @@ def _apply_plotly_theme(self, fig) -> None:
             plot_bgcolor="rgba(0,0,0,0)",
             paper_bgcolor="rgba(0,0,0,0)",
             font=dict(color=tc["font_color"]),
-            xaxis=dict(gridcolor=tc["grid_color"]),
-            yaxis=dict(gridcolor=tc["grid_color"]),
+            xaxis=dict(
+                gridcolor=tc["grid_color"],
+                linecolor=tc["axis_line_color"],
+                zerolinecolor=tc["axis_line_color"],
+            ),
+            yaxis=dict(
+                gridcolor=tc["grid_color"],
+                linecolor=tc["axis_line_color"],
+                zerolinecolor=tc["axis_line_color"],
+            ),
         )
 
     def _set_html_output(self, out: widgets.Output, html: str) -> None:
diff --git a/quantui/theme.py b/quantui/theme.py
index c295f5e..bd6cdde 100644
--- a/quantui/theme.py
+++ b/quantui/theme.py
@@ -646,6 +646,10 @@ def plotly_colors(palette_id: str) -> dict:
         "paper_bgcolor": palette.page_bg,
         "font_color": palette.text_strong,
         "grid_color": palette.border,
+        # Axis and zero lines: one step stronger than the grid, so they stay
+        # visible on dark palettes (the plotly_white default is a pale
+        # blue-gray meant for white backgrounds).
+        "axis_line_color": palette.border_strong,
         "scene_bgcolor": "#000000" if palette.is_dark else "#ffffff",
     }
 
diff --git a/tests/test_theme_contrast.py b/tests/test_theme_contrast.py
index 3a22160..f57aac9 100644
--- a/tests/test_theme_contrast.py
+++ b/tests/test_theme_contrast.py
@@ -86,6 +86,9 @@ def test_plotly_colours_track_palette(self, palette_id):
         palette = theme.get_palette(palette_id)
         assert colours["plot_bgcolor"] == palette.bg_panel
         assert colours["paper_bgcolor"] == palette.page_bg
+        # Axis/zero lines follow the palette too (M-THEME), not the
+        # plotly_white template's pale default.
+        assert colours["axis_line_color"] == palette.border_strong
 
 
 class TestBordersMeetContrastBar: