fix: reject missing Git blobs before consulting indexed facts

Author: Bill Leoutsakos

scripts/design-diff/git.ts

@@ -62,8 +62,11 @@ export class GitReader {
       const tab = record.indexOf('\t')
       const [mode, type, oid, size] = record.slice(0, tab).trim().split(/\s+/)
       if (type !== 'blob') continue
+      const bytes = Number(size)
+      // Git can exit successfully with size BAD for a missing blob. Cached facts must not hide it.
+      if (!Number.isSafeInteger(bytes) || bytes < 0) throw new Error('Unreadable Git blob metadata')
       const path = record.slice(tab + 1)
-      entries.set(path, { path, mode, oid, size: Number(size) })
+      entries.set(path, { path, mode, oid, size: bytes })
     }
     return entries
   }

scripts/design-diff/tests/git.test.ts

@@ -77,3 +77,20 @@ it('fails explicitly for unreadable revisions and missing history', async () =>
     rmSync(shallow, { recursive: true, force: true })
   }
 })
+
+it('rejects missing source blobs even when Git returns successful tree metadata', async () => {
+  const repo = new FixtureRepo()
+  try {
+    const file = 'apps/sim/control.tsx'
+    const base = repo.commit({ [file]: 'export const Control=()=> <button className="p-2"/>' })
+    const head = repo.commit({ 'README.md': 'Nonvisual edit' })
+    const blob = repo.git('rev-parse', `${base}:${file}`)
+    rmSync(path.join(repo.cwd, '.git/objects', blob.slice(0, 2), blob.slice(2)))
+    expect(() => new GitReader(repo.cwd).tree(base)).toThrow('Unreadable Git blob metadata')
+    await expect(analyze(repo.cwd, base, head, config)).rejects.toThrow(
+      'Unreadable Git blob metadata'
+    )
+  } finally {
+    repo.close()
+  }
+})

scripts/design-diff/tests/index-runtime.ts

@@ -221,6 +221,12 @@ try {
       )
     )
     assert.equal((await cached()).report, await fresh())
+  } else if (mode === 'missing-source') {
+    await cached()
+    const blob = repo.git('rev-parse', `${base}:${file}`)
+    rmSync(path.join(repo.cwd, '.git/objects', blob.slice(0, 2), blob.slice(2)))
+    await assert.rejects(cached(), /Unreadable Git blob metadata/)
+    await assert.rejects(fresh(), /Unreadable Git blob metadata/)
   } else if (mode === 'themes') {
     const theme = 'apps/sim/app/globals.css'
     const themedBase = repo.commit({

scripts/design-diff/tests/index.test.ts

@@ -13,6 +13,7 @@ it.each([
   'themes',
   'sentinels',
   'restart',
+  'missing-source',
 ])(
   'maintains indexed correctness: %s',
   (mode) => {