test(cli): cover light-mode detection + SkinConfig.get_color remap

Adds 16 unit tests covering the light/dark terminal detection path
introduced in the previous commit:

- Env override priority (HERMES_LIGHT, HERMES_TUI_LIGHT,
  HERMES_TUI_THEME, HERMES_TUI_BACKGROUND, COLORFGBG)
- Detection cache stickiness
- _maybe_remap_for_light_mode() no-op in dark mode
- Known dark-mode color remap (#FFF8DC -> #1A1A1A etc)
- Case-insensitive lookup
- Unknown color passthrough
- Status-bar paired colors (#C0C0C0, #888888, #555555, #8B8682) are
  intentionally NOT remapped — regression guard for the patch-11 fix,
  since remapping them would produce dark-on-dark on the status bar's
  navy bg
- SkinConfig.get_color() wrapper is installed and idempotent
- SkinConfig.get_color() does remap in light mode and passes through
  in dark mode

We don't try to fake an OSC 11 reply — that path is exercised
end-to-end in real Terminal.app; the env-override path covers the
algorithmic logic.

tests/cli/test_cli_light_mode.py

@@ -0,0 +1,154 @@
+"""Tests for the light-mode terminal detection + color remap in cli.py.
+
+Covers the env-override path and the SkinConfig.get_color() wrapper that
+the resize / light-mode salvage installs at module import time.  We don't
+try to fake an OSC 11 reply — the env-override branch short-circuits
+before the terminal query, which is the path most users hit.
+"""
+
+from __future__ import annotations
+
+import importlib
+
+import pytest
+
+
+@pytest.fixture
+def cli_mod(monkeypatch):
+    """Import cli with the light-mode cache cleared each test."""
+    import cli as _cli
+
+    # The module-level _install_skin_light_mode_hook() and import-time
+    # _detect_light_mode() prime ran once at first import.  We just reset
+    # the detection cache so the per-test env override takes effect.
+    monkeypatch.setattr(_cli, "_LIGHT_MODE_CACHE", None)
+    return _cli
+
+
+class TestLightModeDetection:
+    def test_hermes_light_env_true_forces_light(self, cli_mod, monkeypatch):
+        monkeypatch.setenv("HERMES_LIGHT", "1")
+        assert cli_mod._detect_light_mode() is True
+
+    def test_hermes_light_env_false_forces_dark(self, cli_mod, monkeypatch):
+        monkeypatch.setenv("HERMES_LIGHT", "0")
+        # Also blank out other signals so nothing else flips it light.
+        monkeypatch.delenv("HERMES_TUI_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_THEME", raising=False)
+        monkeypatch.delenv("HERMES_TUI_BACKGROUND", raising=False)
+        monkeypatch.delenv("COLORFGBG", raising=False)
+        assert cli_mod._detect_light_mode() is False
+
+    def test_theme_hint_light(self, cli_mod, monkeypatch):
+        monkeypatch.delenv("HERMES_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_LIGHT", raising=False)
+        monkeypatch.setenv("HERMES_TUI_THEME", "light")
+        assert cli_mod._detect_light_mode() is True
+
+    def test_background_hex_hint_light(self, cli_mod, monkeypatch):
+        monkeypatch.delenv("HERMES_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_THEME", raising=False)
+        monkeypatch.setenv("HERMES_TUI_BACKGROUND", "#FFFFFF")
+        assert cli_mod._detect_light_mode() is True
+
+    def test_background_hex_hint_dark(self, cli_mod, monkeypatch):
+        monkeypatch.delenv("HERMES_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_THEME", raising=False)
+        monkeypatch.setenv("HERMES_TUI_BACKGROUND", "#1a1a2e")
+        monkeypatch.delenv("COLORFGBG", raising=False)
+        assert cli_mod._detect_light_mode() is False
+
+    def test_colorfgbg_light_bg_slot(self, cli_mod, monkeypatch):
+        monkeypatch.delenv("HERMES_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_LIGHT", raising=False)
+        monkeypatch.delenv("HERMES_TUI_THEME", raising=False)
+        monkeypatch.delenv("HERMES_TUI_BACKGROUND", raising=False)
+        monkeypatch.setenv("COLORFGBG", "0;15")  # bg slot 15 = light
+        assert cli_mod._detect_light_mode() is True
+
+    def test_cache_is_sticky(self, cli_mod, monkeypatch):
+        monkeypatch.setenv("HERMES_LIGHT", "1")
+        assert cli_mod._detect_light_mode() is True
+        # Even if the env flips, the cached result wins until reset.
+        monkeypatch.setenv("HERMES_LIGHT", "0")
+        assert cli_mod._detect_light_mode() is True
+
+
+class TestLightModeRemap:
+    def test_remap_no_op_in_dark_mode(self, cli_mod, monkeypatch):
+        monkeypatch.setenv("HERMES_LIGHT", "0")
+        # Cache is None from the fixture; first call sticks at False.
+        assert cli_mod._maybe_remap_for_light_mode("#FFF8DC") == "#FFF8DC"
+
+    def test_remap_known_dark_color(self, cli_mod, monkeypatch):
+        monkeypatch.setenv("HERMES_LIGHT", "1")
+        # Force the detect cache to True for this test.
+        cli_mod._LIGHT_MODE_CACHE = True
+        assert cli_mod._maybe_remap_for_light_mode("#FFF8DC") == "#1A1A1A"
+        assert cli_mod._maybe_remap_for_light_mode("#FFD700") == "#9A6B00"
+
+    def test_remap_case_insensitive(self, cli_mod, monkeypatch):
+        cli_mod._LIGHT_MODE_CACHE = True
+        # Lowercase input should still remap.
+        assert cli_mod._maybe_remap_for_light_mode("#fff8dc") == "#1A1A1A"
+
+    def test_remap_unknown_color_passthrough(self, cli_mod, monkeypatch):
+        cli_mod._LIGHT_MODE_CACHE = True
+        # A color not in the remap table is returned unchanged.
+        assert cli_mod._maybe_remap_for_light_mode("#ABCDEF") == "#ABCDEF"
+
+    def test_remap_skips_statusbar_paired_colors(self, cli_mod, monkeypatch):
+        """Colors that live on a dark bg (status bar fg) MUST NOT be
+        remapped — otherwise they go dark-on-dark and disappear.
+
+        Regression guard for the patch-11 fix (intentional table omission).
+        """
+        cli_mod._LIGHT_MODE_CACHE = True
+        for fg in ("#C0C0C0", "#888888", "#555555", "#8B8682"):
+            assert cli_mod._maybe_remap_for_light_mode(fg) == fg, (
+                f"{fg} is a status-bar fg paired with dark bg; remapping it "
+                "would produce dark-on-dark"
+            )
+
+
+class TestSkinConfigHook:
+    """The salvage wraps SkinConfig.get_color at module import time so
+    every skin color read goes through the light-mode remap.  Verify
+    the hook installed and functions correctly.
+    """
+
+    def test_hook_installed(self, cli_mod):
+        from hermes_cli.skin_engine import SkinConfig
+
+        assert getattr(SkinConfig, "_hermes_light_mode_hook_installed", False) is True
+
+    def test_hook_is_idempotent(self, cli_mod):
+        # Calling the installer twice must not double-wrap (the marker
+        # attribute is the guard).
+        from hermes_cli.skin_engine import SkinConfig
+
+        before = SkinConfig.get_color
+        cli_mod._install_skin_light_mode_hook()
+        after = SkinConfig.get_color
+        assert before is after
+
+    def test_skin_color_remaps_through_wrapper_in_light_mode(self, cli_mod, monkeypatch):
+        from hermes_cli.skin_engine import SkinConfig
+
+        cli_mod._LIGHT_MODE_CACHE = True
+        skin = SkinConfig(
+            name="test",
+            colors={"banner_text": "#FFF8DC", "response_border": "#FFD700"},
+        )
+        # The wrapper kicks in at get_color, not at construction time.
+        assert skin.get_color("banner_text") == "#1A1A1A"
+        assert skin.get_color("response_border") == "#9A6B00"
+
+    def test_skin_color_passthrough_in_dark_mode(self, cli_mod, monkeypatch):
+        from hermes_cli.skin_engine import SkinConfig
+
+        cli_mod._LIGHT_MODE_CACHE = False
+        skin = SkinConfig(name="test", colors={"banner_text": "#FFF8DC"})
+        assert skin.get_color("banner_text") == "#FFF8DC"