These changes helped me find the definitive source of the problem in
Vite 5.0.0-beta.8:

- "fix!: return 404 for resources requests outside the base path"
  vitejs/vite@40fd2d9
  vitejs/vite#5657
  vitejs/vite#5656
  https://vitejs.dev/guide/migration.html#advanced

- Related:
  vuejs/vitepress#3239
  sveltejs/kit#2958

Of course, this is effectively a bug fix for Vite, pointing at a bug in
Vitest. Vite is now more strict about enforcing the Public Base Path,
and Vitest needs to propagate config.base somehow:

- https://vitejs.dev/config/shared-options.html#base
- https://vitejs.dev/guide/build.html#public-base-path

I'll explain the workaround in the next commit. What follows describes
how my methodology to pinpoint the problem evolved and concluded.

---

Adding the vite/packages/vite as a "file:" dependency and adding its
directory as part of the workspace proved challenging. The TypeScript
compiler (`tsc`) kept erroring out on the `tsc --emitDeclarationOnly
--outDir temp/node -p src/node` step of the build.

It took a few tries to realize that I needed to remove vite/node_modules
before every "pnpm build" in vite/. Somehow some stale artifacts were
poisoning subsequent runs.

That left the problem of running `pnpm i` in this project, which would
still try to rebuild vite/packages/vite and choke on the TypeScript.

After skimming vite/README.md, I realized I could try adding
vite/packages/vite as a "link:" dependency instead of a "file:"
dependency. I also learned I could use pnpm.overrides in package.json to
ensure other packages used this local version. I kept vitest/packages/*
in the workspace to make sure they used this linked version of
vite/packages/vite.

After that, I could now reliably build the two local packages, and have
the local vitest use the local vite.

Each time in the ../vite repository, I would:

```sh
rm -rf packages/vite/node_modules
git reset --hard <tag or commit>
pnpm i --frozen-lockfile
pnpm build
```

Then I'd go back to this repository and:

```sh
pnpm i
pnpm test
```

And here's the results of my bisection (I didn't actually use `git
bisect`, but followed the same essential process):

```text
v5.0.0-beta.12 FAIL
v5.0.0-beta.6  OK
v5.0.0-beta.9  FAIL
v5.0.0-beta.7  OK
v5.0.0-beta.8  FAIL
```text

Once I had my culprit, I went back into ../vite and ran:

```sh
gitk v5.0.0-beta.7..v5.0.0-beta.8
```

And once I did that, I could see the the commit immediately after
v5.0.0-beta.7 affected base path handling. So I repeated the process,
setting `<tag or commit>` in ../vite to
40fd2d9bf4073420e6c334f48dc3b63558b688ce. Indeed, this build failed,
confirming that commit as the culprit.