dev/todo: Note the webpack to Turbopack dev migration

Amp-Thread-ID: https://ampcode.com/threads/T-01a0ad75-46cf-77ed-889b-438e2521bc89
Co-authored-by: Amp <amp@ampcode.com>

Author: marcleblanc2

dev/TODO.md

@@ -4,11 +4,12 @@
   React Compiler ESLint rules `react-hooks/refs`, `react-hooks/set-state-in-effect`
   and `react-hooks/static-components` can go back to `error` in `eslint.config.mjs`
   (31 of the 39 warnings from `pnpm run lint` are in that directory)
-- `pnpm run dev` (`next dev --webpack`) fails to serve pages on main since the
-  Next 16 upgrade: `ReferenceError: require is not defined` from
-  `next/src/build/webpack/loaders/postcss-loader`. Fix it, or move dev to
-  Turbopack by running `contentlayer2 dev` alongside `next dev` and dropping
-  the `next-contentlayer2` plugin from `next.config.js` entirely
+- Move `pnpm run dev` from webpack to Turbopack, like `pnpm run build`. The only
+  thing keeping it on webpack is the `next-contentlayer2` plugin, which
+  regenerates `.contentlayer` when an `.mdx` file changes; Turbopack has no
+  plugin hook for that. Needs a way to start contentlayer's watcher
+  (`contentlayer2 dev`) automatically when `next dev` starts, then the plugin
+  and the `PHASE_DEVELOPMENT_SERVER` branch in `next.config.js` can go
 - Faster Vercel static generation: the 505 `/api/og` images are ~40% of the
   "Generating static pages" time (locally 6.6s with them, 3.6s without).
   Options: hoist the font and logo reads in `src/app/api/og/[...path]/route.tsx`