test: 修复三处跳过守卫，它们只在真实资源到位时才暴露

这三个测试都犯了同一个错误：**守卫检查的资源，和实际读取的资源不是同
一个**。在 `samples/d2` 缺席时它们一律静默跳过，看起来是绿的；真实 MPQ
一旦放进来，守卫放行，然后立刻炸在一个完全无关的缺失文件上。

- `tests/dcc.test.ts`
  守卫看 `samples/d2`，扫描目标却硬编码成 `samples/fixtures`——那里没有
  `d2char.mpq`。于是这个套件**从来没有真正跑过**：没资源时跳过，有资源时
  `TypeError: Cannot read properties of null (reading 'listFiles')`。
  目标改为 `samples/d2`；打开归档失败时由"打日志后继续"改为 `throw`
  并带上归档名，避免把"文件缺失"伪装成 100 行之外的空指针；
  `let characters: any` 收紧为 `MpqArchive | null`。

- `tests/widths.test.ts`
  守卫看 `samples/d2`，真实输入却是一个空成员名和
  `scripts/browser/checks/map-widths.txt`——后者在仓库里从未存在过。
  改为按实际输入判断。顺带补 `: string` 标注，否则空字符串字面量会被
  收窄成 `never`。

- `tests/formats-malformed.test.ts`
  守卫看 `samples/d2` 目录是否存在，却去读其中一个散落的 `.cof`。但
  `samples/d2/` 放的是 MPQ **归档**，不是解包后的目录树，目录存在完全
  不能说明那个文件存在。改为直接判断该文件路径。

修复后，在真实 MPQ 就位的情况下：
21 passed | 1 skipped (22 files)，421 passed | 2 skipped (423)，tsc 0 error。
其中 `dcc.test.ts` 从"0 个测试"变成真正执行。

tests/dcc.test.ts

@@ -136,7 +136,11 @@ interface DccResult {
   readonly dcc: DccFile
 }
 
-const args = ['samples/fixtures']
+// This sweep needs the original character/object archives, so it must target
+// the real drop — `samples/fixtures` has no `d2char.mpq`. Keep this in step
+// with `isSkip` above: guarding on one directory while reading another is what
+// previously made this suite silently unrunnable.
+const args = ['samples/d2']
 const dir = args.find((a) => !a.startsWith('--')) ?? 'samples/d2'
 const quick = args.includes('--quick')
 
@@ -610,12 +614,14 @@ async function sweepSorceress(archive: MpqArchive, names: readonly string[]): Pr
 console.log(`== cof + dcc verification over ${dir}${quick ? ' (quick)' : ''} ==`)
 
 const characterPath = `${dir}/${CHARACTER_ARCHIVE}`
-let characters: any = null;
+let characters: MpqArchive | null = null;
 try {
   characters = await MpqArchive.open(await fileSource(characterPath))
 } catch (err) {
-  console.log(`cannot open ${characterPath}: ${messageOf(err)}`)
-  // disabled exit: 2)
+  // Do not fall through: the old code logged here and then dereferenced
+  // `characters`, turning "archive missing" into an opaque TypeError 100 lines
+  // away from the cause.
+  throw new Error(`cannot open ${characterPath}: ${messageOf(err)}`)
 }
 const characterNames = (await characters.listFiles()).map(normalize)
 console.log(`${CHARACTER_ARCHIVE}: ${String(characterNames.length)} members listed`)

tests/formats-malformed.test.ts

@@ -132,9 +132,14 @@ describe('Malformed binary formats fail loudly', () => {
   });
 
   describe('cof', () => {
-    const hasD2Drop = fs.existsSync(path.join(__dirname, '../samples/d2'));
-    test.skipIf(!hasD2Drop)('valid decodes successfully on real asset', () => {
-      const validCof = fs.readFileSync(path.join(__dirname, '../samples/d2/data/global/chars/so/co/sowaxlbh.cof'));
+    // `samples/d2/` holds the original MPQ *archives*, not an extracted tree,
+    // so the presence of that directory says nothing about whether this loose
+    // .cof exists. Guard on the file we actually open, otherwise dropping in
+    // real assets turns a silent skip into a hard ENOENT.
+    const realCofPath = path.join(__dirname, '../samples/d2/data/global/chars/so/co/sowaxlbh.cof');
+    const hasRealCof = fs.existsSync(realCofPath);
+    test.skipIf(!hasRealCof)('valid decodes successfully on real asset', () => {
+      const validCof = fs.readFileSync(realCofPath);
       const out = decodeCof(validCof);
       expect(out.numberOfLayers).toBe(16);
     });

tests/widths.test.ts

@@ -16,7 +16,15 @@ import { readFile } from 'node:fs/promises'
 import { MpqArchive } from '../src/mpq/archive.ts'
 import { fileSource } from '../src/mpq/file-source.ts'
 import { decodeSpriteFile } from '../src/formats/cel.ts'
-const isSkip = true && !fs.existsSync('samples/d2');
+const WIDTHS_ARCHIVE: string = 'samples/fixtures'
+const WIDTHS_MEMBER: string = ''
+const WIDTHS_PATH: string = 'scripts/browser/checks/map-widths.txt'
+// This check needs a per-frame widths sidecar and a named member. Neither has
+// ever been present in the repo, and neither is supplied by `samples/d2` — so
+// guarding on that directory (as this file used to) meant the suite stayed
+// silently skipped until real assets appeared, then failed on an unrelated
+// missing file. Guard on the inputs actually opened below.
+const isSkip = WIDTHS_MEMBER === '' || !fs.existsSync(WIDTHS_PATH);
 const _results: any[] = [];
 let suiteCompleted = false;
 let problems: string[] = [];
@@ -31,7 +39,7 @@ function check(nameOrOk: any, okOrMessage: any, detail?: string) {
 }
 if (!isSkip) {
 
-const [path, member, widthsPath] = ['samples/fixtures', '', 'scripts/browser/checks/map-widths.txt']
+const [path, member, widthsPath] = [WIDTHS_ARCHIVE, WIDTHS_MEMBER, WIDTHS_PATH]
 if (path === undefined || member === undefined || widthsPath === undefined) {
   console.error('usage: node scripts/verify-widths.ts <archive> <member> <widths-file>')
   // disabled exit: 2)