fix(pr-review-canvas): preserve header-like source lines inside hunks

cursor-team-kit/skills/pr-review-canvas/renderer.js

@@ -114,11 +114,14 @@ function renderDiff(target, diffInput) {
   }
 
   var dels = [], adds = [], parsed = [];
-  var oL = 0, nL = 0, pD = false, pA = false;
+  var oL = 0, nL = 0, pD = false, pA = false, inHunk = false;
   for (var pi = 0; pi < wsOut.length; pi++) {
     var line = wsOut[pi];
-    if (line.startsWith('--- ') || line.startsWith('+++ ') || line.startsWith('diff ')) continue;
+    if (line.startsWith('diff ')) { inHunk = false; continue; }
+    // Within a hunk these prefixes are source text, e.g. -- count; / ++ count;.
+    if (!inHunk && (line.startsWith('--- ') || line.startsWith('+++ '))) continue;
     if (line.startsWith('@@')) {
+      inHunk = true;
       var hm = line.match(/@@ -(\d+)(?:,\d+)? \+(\d+)/);
       if (hm) { oL = parseInt(hm[1]); nL = parseInt(hm[2]); }
       parsed.push({ type: 'hunk', text: line }); pD = false; pA = false; continue;

cursor-team-kit/skills/pr-review-canvas/tests/header-content.test.cjs

@@ -0,0 +1,48 @@
+const assert = require('node:assert/strict');
+const { execFileSync } = require('node:child_process');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const test = require('node:test');
+const vm = require('node:vm');
+
+function render(patch, fullDiff = false) {
+  const context = { document: { addEventListener() {} } };
+  vm.createContext(context);
+  vm.runInContext(fs.readFileSync(path.join(__dirname, '../renderer.js'), 'utf8'), context);
+  const target = { innerHTML: '' };
+  // GitHub's files API exposes the hunk portion of git diff as `patch`.
+  context.renderDiff(target, fullDiff ? patch : patch.slice(patch.indexOf('@@')));
+  return target.innerHTML;
+}
+
+function patchFor(before, after) {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'canvas-newline-'));
+  try {
+    fs.writeFileSync(path.join(dir, 'before'), before);
+    fs.writeFileSync(path.join(dir, 'after'), after);
+    try {
+      return execFileSync('git', ['diff', '--no-index', '--no-color', '--', 'before', 'after'], { cwd: dir, encoding: 'utf8' });
+    } catch (error) {
+      if (error.status !== 1) throw error;
+      return error.stdout;
+    }
+  } finally {
+    fs.rmSync(dir, { recursive: true });
+  }
+}
+
+for (const fullDiff of [false, true]) {
+  test(`preserve increment/decrement code in ${fullDiff ? 'full diff' : 'API patch'}`, () => {
+    const html = render(patchFor('-- count;\n', '++ count;\n'), fullDiff);
+    assert.match(html, /class="diff-del"><td class="diff-ln">1<\/td><td class="diff-ln"><\/td><td class="diff-code">-- count;<\/td>/);
+    assert.match(html, /class="diff-add"><td class="diff-ln"><\/td><td class="diff-ln">1<\/td><td class="diff-code">\+\+ count;<\/td>/);
+    assert.doesNotMatch(html, /diff-code">[+-]{2} [ab]\/(?:before|after)/);
+  });
+}
+
+test('ordinary changed lines remain visible', () => {
+  const html = render(patchFor('old\n', 'new\n'));
+  assert.match(html, /diff-code">old<\/td>/);
+  assert.match(html, /diff-code">new<\/td>/);
+});