fix: Han Xin remove incorrect timing patterns, add separator bands

Han Xin Code does NOT have timing patterns (unlike QR).
Replace alternating timing with white separator bands around finders.
Match improved 71% → 75%.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: productdevbook

src/encoders/hanxin.ts

@@ -97,7 +97,7 @@ function hanxinSize(version: number): number {
  *
  * Total modules minus function patterns:
  *   - 4 finder patterns (7×7 each = 196 modules)
- *   - 4 timing strips along edges (between finders)
+ *   - Separator bands around finders
  *   - Version/format info areas
  *
  * Returns the total number of data codewords (bytes) available
@@ -110,15 +110,13 @@ function hanxinTotalCodewords(version: number): number {
   // 4 finder patterns — 7×7 each
   const finderModules = 4 * 7 * 7;
 
-  // Timing patterns along all 4 edges (between finders)
-  // Each edge has (size - 14) modules in the timing strip
-  const timingModules = 4 * (size - 14);
+  // Separator bands around finders: 4 L-shaped bands, ~8 modules each
+  const separatorModules = 4 * (8 + 7);
 
-  // Format/version info: Han Xin uses structural regions
-  // along finder edges — approximate as 36 modules per version
+  // Format/version info regions around finders
   const formatModules = Math.min(36 + version * 2, size * 4);
 
-  const usableModules = totalModules - finderModules - timingModules - formatModules;
+  const usableModules = totalModules - finderModules - separatorModules - formatModules;
 
   return Math.floor(usableModules / 8);
 }
@@ -331,12 +329,21 @@ export function encodeHanXin(text: string, options: HanXinOptions = {}): boolean
   placeFinderHX(matrix, size - 7, 0, FINDER_BL, size);
   placeFinderHX(matrix, size - 7, size - 7, FINDER_BR, size);
 
-  // Timing patterns along all 4 edges
-  for (let i = 7; i < size - 7; i++) {
-    if (matrix[0]![i] === null) matrix[0]![i] = i % 2 === 0;
-    if (matrix[i]![0] === null) matrix[i]![0] = i % 2 === 0;
-    if (matrix[size - 1]![i] === null) matrix[size - 1]![i] = i % 2 === 0;
-    if (matrix[i]![size - 1] === null) matrix[i]![size - 1] = i % 2 === 0;
+  // Han Xin has NO timing patterns — only separator bands around finders
+  // 1-module white separator around each 7x7 finder
+  for (let i = -1; i <= 7; i++) {
+    // Top-left separator
+    setSafeNull(matrix, 7, i, size);
+    setSafeNull(matrix, i, 7, size);
+    // Top-right separator
+    setSafeNull(matrix, 7, size - 8 + i, size);
+    setSafeNull(matrix, i, size - 8, size);
+    // Bottom-left separator
+    setSafeNull(matrix, size - 8, i, size);
+    setSafeNull(matrix, size - 8 + i, 7, size);
+    // Bottom-right separator
+    setSafeNull(matrix, size - 8, size - 8 + i, size);
+    setSafeNull(matrix, size - 8 + i, size - 8, size);
   }
 
   // Place data bits into available modules
@@ -360,6 +367,12 @@ export function encodeHanXin(text: string, options: HanXinOptions = {}): boolean
   return matrix.map((row) => row.map((cell) => cell === true));
 }
 
+function setSafeNull(matrix: (boolean | null)[][], r: number, c: number, size: number): void {
+  if (r >= 0 && r < size && c >= 0 && c < size && matrix[r]![c] === null) {
+    matrix[r]![c] = false;
+  }
+}
+
 function placeFinderHX(
   matrix: (boolean | null)[][],
   row: number,