B1: add Dalamud-free CjkFallbackRange helper + coverage tests

HellionChat/CjkFallbackRange.cs

@@ -0,0 +1,31 @@
+namespace HellionChat;
+
+// Reduced CJK fallback coverage for the v1.5.3 NotoSansCjk fallback merge (B1).
+// Before B1 the fallback merged over the full `Ranges` array (Default + endonyms),
+// duplicating the Latin/Default work already done by the global/Japanese fonts.
+// This is the trimmed remainder the fallback is actually the sole source for:
+//   - Hangul Syllables (AC00-D7A3): no other merged font ships Korean glyphs.
+//   - The full CJK Unified Ideographs (Han) block: at UseHellionFont=true the global
+//     font is Inter-Light (no CJK), so the fallback is the SOLE Han source. The JpRange
+//     overlap is harmless (MergeMode: the Japanese font wins for shared kanji).
+// Deliberately excluded: ONLY the ASCII/Latin Default block (0x20-0xFF), which the
+// global font already owns -- that doubled Latin merge is the B1 waste being removed.
+// Kept as plain start/end pairs so it is unit-testable without the unsafe ImGui
+// glyph-range builder (mirrors FontSizeResolver's split-for-test rationale).
+internal static class CjkFallbackRange
+{
+    // Hangul Syllables block + the FULL CJK Unified Ideographs (Han) block. The full
+    // Han window is REQUIRED, not optional: at UseHellionFont=true the global font is
+    // Inter-Light (no CJK), so this fallback is the SOLE source for Han + Hangul. The
+    // overlap with JpRange (kanji the Japanese font also ships) is harmless under ImGui
+    // MergeMode -- the earlier-merged Japanese font wins for shared codepoints, the
+    // fallback only fills holes (简 0x7B80, 中 0x4E2D, 国 0x56FD). The dedup win is
+    // NOT re-merging the ASCII/Latin Default block, which the global font already owns.
+    internal static readonly ushort[] Pairs =
+    [
+        0xAC00,
+        0xD7A3, // Hangul Syllables
+        0x4E00,
+        0x9FFF, // CJK Unified Ideographs (full Han) -- sole source at UseHellionFont
+    ];
+}