chore: establish YCode replication baseline and TODO

scripts/artifact-diff-regression.ts

@@ -0,0 +1,97 @@
+import assert from 'node:assert/strict'
+import {
+  diffSidesFromCurrentFile,
+  diffSidesFromUnifiedDiff,
+  parseDiffContent,
+  resolveCachedDiffSides
+} from '../src/renderer/src/workbuddy/artifacts/diff-content'
+
+const diff = [
+  'diff --git a/file.txt b/file.txt',
+  'index 1234567..abcdef0 100644',
+  '--- a/file.txt',
+  '+++ b/file.txt',
+  '@@ -1,3 +1,3 @@',
+  ' before',
+  '-old value',
+  '+new value',
+  ' after'
+].join('\n')
+
+assert.deepEqual(parseDiffContent(diff), {
+  original: 'before\nold value\nafter',
+  modified: 'before\nnew value\nafter'
+})
+assert.deepEqual(parseDiffContent(undefined), { original: '', modified: '' })
+
+assert.equal(resolveCachedDiffSides(undefined, diff), undefined)
+assert.deepEqual(diffSidesFromCurrentFile('current file', 'added'), { original: '', modified: 'current file' })
+assert.deepEqual(diffSidesFromCurrentFile('removed file', 'deleted'), { original: 'removed file', modified: '' })
+assert.deepEqual(resolveCachedDiffSides('current file', undefined, 'added'), { original: '', modified: 'current file' })
+assert.deepEqual(resolveCachedDiffSides('removed file', undefined, 'deleted'), { original: 'removed file', modified: '' })
+
+const cached = diffSidesFromUnifiedDiff('before\nnew value\nafter', diff)
+assert.deepEqual(cached, {
+  original: 'before\nold value\nafter',
+  modified: 'before\nnew value\nafter',
+  exactDiff: diff
+})
+assert.deepEqual(resolveCachedDiffSides('before\nnew value\nafter', diff), cached)
+
+const bareHunk = '@@ -1 +1 @@\n-old\n+new'
+assert.deepEqual(diffSidesFromUnifiedDiff('new', bareHunk), {
+  original: 'old',
+  modified: 'new',
+  exactDiff: bareHunk
+})
+const shiftedHunk = '@@ -1 +1 @@\n-old\n+new'
+assert.deepEqual(diffSidesFromUnifiedDiff('prefix\nnew\nsuffix', shiftedHunk), {
+  original: 'prefix\nold\nsuffix',
+  modified: 'prefix\nnew\nsuffix',
+  exactDiff: shiftedHunk
+})
+
+const multipleHunks = [
+  '--- a/file.txt',
+  '+++ b/file.txt',
+  '@@ -2,3 +2,3 @@',
+  ' b',
+  '-c',
+  '+C',
+  ' d',
+  '@@ -6,2 +6,2 @@',
+  ' f',
+  '-g',
+  '+G'
+].join('\n')
+assert.equal(
+  diffSidesFromUnifiedDiff('a\nb\nC\nd\ne\nf\nG', multipleHunks).original,
+  'a\nb\nc\nd\ne\nf\ng'
+)
+assert.equal(
+  diffSidesFromUnifiedDiff('before\r\nnew value\r\nafter\r\n', diff).original,
+  'before\r\nold value\r\nafter\r\n'
+)
+
+const noFinalNewline = [
+  '--- a/file.txt',
+  '+++ b/file.txt',
+  '@@ -1 +1 @@',
+  '-old',
+  '\\ No newline at end of file',
+  '+new',
+  '\\ No newline at end of file'
+].join('\n')
+assert.deepEqual(diffSidesFromUnifiedDiff('new', noFinalNewline), {
+  original: 'old',
+  modified: 'new',
+  exactDiff: noFinalNewline
+})
+
+const mismatchedCache = diffSidesFromUnifiedDiff('unrelated cached content', diff)
+assert.deepEqual(mismatchedCache, {
+  original: 'before\nold value\nafter',
+  modified: 'unrelated cached content'
+})
+
+console.log('Artifact diff recovery regression checks passed')