fix(cli): clamp curses color 8 for 8-color terminals (Docker)

curses.init_pair(N, 8, -1) uses extended color 8 ("bright black" /
dim gray) which does not exist on 8-color terminals (COLORS == 8,
valid range 0-7).  This crashes the entire plugins UI, session
browser, and radio picker in Docker containers with:

    curses.error: init_pair() : color number is greater than COLORS-1

Replace all 5 occurrences across plugins_cmd.py, main.py, and
curses_ui.py with min(8, curses.COLORS - 1), which falls back to
COLOR_WHITE (7) on 8-color terminals.

Closes #13688

hermes_cli/curses_ui.py

@@ -71,7 +71,7 @@ def curses_checklist(
                 curses.use_default_colors()
                 curses.init_pair(1, curses.COLOR_GREEN, -1)
                 curses.init_pair(2, curses.COLOR_YELLOW, -1)
-                curses.init_pair(3, 8, -1)  # dim gray
+                curses.init_pair(3, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)  # dim gray
             cursor = 0
             scroll_offset = 0
 

hermes_cli/main.py

@@ -591,7 +591,7 @@ def _session_browse_picker(sessions: list) -> Optional[str]:
                 curses.init_pair(1, curses.COLOR_GREEN, -1)  # selected
                 curses.init_pair(2, curses.COLOR_YELLOW, -1)  # header
                 curses.init_pair(3, curses.COLOR_CYAN, -1)  # search
-                curses.init_pair(4, 8, -1)  # dim
+                curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)  # dim
 
             cursor = 0
             scroll_offset = 0

hermes_cli/plugins_cmd.py

@@ -1051,7 +1051,7 @@ def _run_composite_ui(curses, plugin_names, plugin_labels, plugin_selected,
             curses.init_pair(1, curses.COLOR_GREEN, -1)
             curses.init_pair(2, curses.COLOR_YELLOW, -1)
             curses.init_pair(3, curses.COLOR_CYAN, -1)
-            curses.init_pair(4, 8, -1)  # dim gray
+            curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)  # dim gray
         cursor = 0
         scroll_offset = 0
 
@@ -1196,7 +1196,7 @@ def _run_composite_ui(curses, plugin_names, plugin_labels, plugin_selected,
                             curses.init_pair(1, curses.COLOR_GREEN, -1)
                             curses.init_pair(2, curses.COLOR_YELLOW, -1)
                             curses.init_pair(3, curses.COLOR_CYAN, -1)
-                            curses.init_pair(4, 8, -1)
+                            curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)
                         curses.curs_set(0)
             elif key in {curses.KEY_ENTER, 10, 13}:
                 if cursor < n_plugins:
@@ -1228,7 +1228,7 @@ def _run_composite_ui(curses, plugin_names, plugin_labels, plugin_selected,
                             curses.init_pair(1, curses.COLOR_GREEN, -1)
                             curses.init_pair(2, curses.COLOR_YELLOW, -1)
                             curses.init_pair(3, curses.COLOR_CYAN, -1)
-                            curses.init_pair(4, 8, -1)
+                            curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)
                         curses.curs_set(0)
             elif key in {27, ord("q")}:
                 # Save plugin changes on exit

tests/hermes_cli/test_curses_color_compat.py

@@ -0,0 +1,131 @@
+"""Tests for curses color compatibility on low-color terminals (Docker).
+
+Regression test for #13688: ``hermes plugins`` crashes with
+``curses.error: init_pair() : color number is greater than COLORS-1``
+in Docker containers where curses.COLORS == 8 (only colors 0-7 exist).
+
+The bug was ``curses.init_pair(4, 8, -1)`` using raw color 8 ("bright
+black" / dim gray) which does not exist on 8-color terminals.  The fix
+clamps with ``min(8, curses.COLORS - 1)``.
+"""
+
+import curses
+import re
+from pathlib import Path
+from unittest.mock import patch, MagicMock, call
+
+import pytest
+
+
+# Path to the source files under test
+_SRC_ROOT = Path(__file__).parent.parent.parent / "hermes_cli"
+
+
+class TestInitPairClampingBehavior:
+    """Simulate curses color initialization on low-color terminals.
+
+    Patches curses.COLORS to 8 (Docker default) and verifies that
+    init_pair is never called with a color >= COLORS.
+    """
+
+    def _collect_init_pair_calls(self, draw_fn, colors_value):
+        """Run a curses draw function with a mock stdscr and patched COLORS.
+
+        Returns list of (pair_number, fg, bg) tuples from init_pair calls.
+        """
+        calls = []
+        real_init_pair = curses.init_pair
+
+        def tracking_init_pair(pair, fg, bg):
+            calls.append((pair, fg, bg))
+
+        mock_stdscr = MagicMock()
+        mock_stdscr.getmaxyx.return_value = (24, 80)
+        mock_stdscr.getch.return_value = 27  # ESC to exit
+
+        with patch("curses.COLORS", colors_value, create=True), \
+             patch("curses.init_pair", side_effect=tracking_init_pair), \
+             patch("curses.has_colors", return_value=True), \
+             patch("curses.start_color"), \
+             patch("curses.use_default_colors"), \
+             patch("curses.curs_set"):
+            try:
+                draw_fn(mock_stdscr)
+            except (SystemExit, StopIteration, Exception):
+                pass  # draw functions loop until keypress
+
+        return calls
+
+    def test_8_color_terminal_no_color_exceeds_limit(self):
+        """On an 8-color terminal (Docker), no init_pair fg color >= 8."""
+        # Simulate the color init pattern from plugins_cmd.py
+        def _simulated_color_init(stdscr):
+            if curses.has_colors():
+                curses.start_color()
+                curses.use_default_colors()
+                curses.init_pair(1, curses.COLOR_GREEN, -1)
+                curses.init_pair(2, curses.COLOR_YELLOW, -1)
+                curses.init_pair(3, curses.COLOR_CYAN, -1)
+                curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)
+
+        calls = self._collect_init_pair_calls(_simulated_color_init, 8)
+        for pair, fg, bg in calls:
+            assert fg < 8, (
+                f"init_pair({pair}, {fg}, {bg}) uses color {fg} which "
+                f"does not exist on an 8-color terminal (valid: 0-7)"
+            )
+
+    def test_256_color_terminal_uses_color_8(self):
+        """On a 256-color terminal, color 8 (dim gray) should be used."""
+        def _simulated_color_init(stdscr):
+            if curses.has_colors():
+                curses.start_color()
+                curses.use_default_colors()
+                curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)
+
+        calls = self._collect_init_pair_calls(_simulated_color_init, 256)
+        assert any(fg == 8 for _, fg, _ in calls), (
+            "On 256-color terminals, color 8 (dim gray) should be used"
+        )
+
+    def test_16_color_terminal_uses_color_8(self):
+        """On a 16-color terminal, color 8 should be available."""
+        def _simulated_color_init(stdscr):
+            if curses.has_colors():
+                curses.start_color()
+                curses.use_default_colors()
+                curses.init_pair(4, 8 if curses.COLORS > 8 else curses.COLOR_WHITE, -1)
+
+        calls = self._collect_init_pair_calls(_simulated_color_init, 16)
+        assert any(fg == 8 for _, fg, _ in calls)
+
+
+class TestSourceCodeGuardrails:
+    """Regression guardrails: raw color 8 must not reappear in source.
+
+    These complement the behavioral tests above — they catch regressions
+    introduced by copy-paste of the old pattern.
+    """
+
+    _RAW_COLOR_8_PATTERN = re.compile(r'init_pair\(\d+,\s*8\s*,')
+
+    def test_no_raw_color_8_in_plugins_cmd(self):
+        source = (_SRC_ROOT / "plugins_cmd.py").read_text()
+        matches = self._RAW_COLOR_8_PATTERN.findall(source)
+        assert not matches, (
+            f"plugins_cmd.py contains unclamped color 8: {matches}"
+        )
+
+    def test_no_raw_color_8_in_main(self):
+        source = (_SRC_ROOT / "main.py").read_text()
+        matches = self._RAW_COLOR_8_PATTERN.findall(source)
+        assert not matches, (
+            f"main.py contains unclamped color 8: {matches}"
+        )
+
+    def test_no_raw_color_8_in_curses_ui(self):
+        source = (_SRC_ROOT / "curses_ui.py").read_text()
+        matches = self._RAW_COLOR_8_PATTERN.findall(source)
+        assert not matches, (
+            f"curses_ui.py contains unclamped color 8: {matches}"
+        )