feat: govern accessible appearance overrides

tests/test_appearance.py

@@ -1,6 +1,35 @@
 from __future__ import annotations
 
-from govoplan_core.core.appearance import resolve_effective_appearance, update_appearance_settings
+import pytest
+
+from govoplan_core.core.appearance import (
+    normalize_appearance_overrides,
+    resolve_effective_appearance,
+    update_appearance_custom_overrides_policy,
+    update_appearance_settings,
+)
+
+
+def _overrides() -> dict[str, object]:
+    return {
+        "schema_version": "1",
+        "light": {
+            "accent": "#245f91", "accent_foreground": "#ffffff",
+            "surface": "#ffffff", "surface_foreground": "#303135",
+            "success": "#d8eee8", "success_foreground": "#315f55",
+            "info": "#dce9f3", "info_foreground": "#294a61",
+            "warning": "#ffe1a3", "warning_foreground": "#593700",
+            "danger": "#f8d1cc", "danger_foreground": "#873c35",
+        },
+        "dark": {
+            "accent": "#7ea6c5", "accent_foreground": "#242424",
+            "surface": "#262724", "surface_foreground": "#f1f1f1",
+            "success": "#24473f", "success_foreground": "#d8eee8",
+            "info": "#243d4e", "info_foreground": "#dce9f3",
+            "warning": "#5a431f", "warning_foreground": "#ffe1a3",
+            "danger": "#4f2d2a", "danger_foreground": "#f8d1cc",
+        },
+    }
 
 
 def test_appearance_precedence_and_inheritance() -> None:
@@ -32,6 +61,8 @@ def test_system_lock_wins_and_invalid_values_fail_safe() -> None:
         "system_default_palette": "civic_blue",
         "tenant_default_palette": "forest",
         "inherited_palette": "civic_blue",
+        "custom_overrides": None,
+        "custom_overrides_allowed": False,
     }
     fallback = resolve_effective_appearance(
         system_settings={"appearance": {"default_palette": "unsafe"}},
@@ -52,3 +83,45 @@ def test_appearance_settings_reset_without_touching_neighbors() -> None:
     assert update_appearance_settings(configured, default_palette=None, palette_locked=False) == {
         "neighbor": {"kept": True}
     }
+
+
+def test_custom_overrides_require_system_and_tenant_policy_and_validate_both_modes() -> None:
+    document = _overrides()
+    normalized = normalize_appearance_overrides(document)
+    assert normalized == document
+    decision = resolve_effective_appearance(
+        system_settings={"appearance": {"allow_custom_overrides": True}},
+        tenant_settings={"appearance": {"allow_custom_overrides": True}},
+        user_settings={"ui": {"appearance_overrides": document}},
+    )
+    assert decision.custom_overrides_allowed is True
+    assert decision.custom_overrides == document
+
+    blocked = resolve_effective_appearance(
+        system_settings={"appearance": {"allow_custom_overrides": True}},
+        tenant_settings={"appearance": {"allow_custom_overrides": False}},
+        user_settings={"ui": {"appearance_overrides": document}},
+    )
+    assert blocked.custom_overrides_allowed is False
+    assert blocked.custom_overrides is None
+
+    invalid = _overrides()
+    invalid["dark"]["danger"] = invalid["dark"]["warning"]  # type: ignore[index]
+    with pytest.raises(ValueError, match="visibly distinct"):
+        normalize_appearance_overrides(invalid)
+
+    low_contrast = _overrides()
+    low_contrast["light"]["accent_foreground"] = "#245f91"  # type: ignore[index]
+    with pytest.raises(ValueError, match="WCAG AA"):
+        normalize_appearance_overrides(low_contrast)
+
+
+def test_custom_override_policy_update_preserves_neighboring_appearance_settings() -> None:
+    configured = update_appearance_custom_overrides_policy(
+        {"appearance": {"default_palette": "forest"}},
+        allowed=True,
+    )
+    assert configured == {"appearance": {"default_palette": "forest", "allow_custom_overrides": True}}
+    assert update_appearance_custom_overrides_policy(configured, allowed=None) == {
+        "appearance": {"default_palette": "forest"}
+    }