fix(dev): stop @shopify/hydrogen watch from racing example bundlers

[div-cowboy]

Problem

Running pnpm dev (and pnpm dev:next / pnpm dev:rr) prints a wall of transient errors at startup:

Module not found: Can't resolve '@shopify/hydrogen'
  ./examples/nextjs/proxy.ts
  ./examples/nextjs/lib/cart-handlers.ts
  ...

The app still serves once startup settles, but it looks broken and is alarming.

Cause

Those scripts schedule both @shopify/hydrogen#build (one-shot) and @shopify/hydrogen#dev (tsdown --watch). The watch rewrites dist/ on startup while the example bundlers (Turbopack, Vite) are reading it, so they momentarily resolve partial/empty module files → "Module not found".

I confirmed:

• It's transient — dist/ files never disappear (high-frequency polling shows 0 missing); it's mid-write partial reads.
• The watch alone causes it even when @shopify/hydrogen#build is a turbo cache hit, so serializing build→dev wouldn't fix it. The concurrent watch has to be removed from the examples' dev path.

Fix

Scope the dev scripts to the examples. Turbo still builds @shopify/hydrogen once via dependsOn: ["^build"], but no longer runs its watch alongside the examples:

- "dev": "turbo run dev",
+ "dev": "turbo run dev --filter='./examples/*'",
- "dev:rr": "turbo run dev --filter=@shopify/hydrogen-example-react-router...",
- "dev:next": "turbo run dev --filter=@shopify/hydrogen-example-nextjs...",
+ "dev:rr": "turbo run dev --filter=@shopify/hydrogen-example-react-router",
+ "dev:next": "turbo run dev --filter=@shopify/hydrogen-example-nextjs",

dev:pkgs still watches ./packages/* for SDK development — run it alongside an example only when actively editing the SDK. This also makes pnpm dev match its README description ("every example's dev server in parallel").

Trade-off

Editing @shopify/hydrogen source no longer hot-rebuilds into a running example under pnpm dev (use pnpm dev:pkgs for that). A future improvement could restore concurrent SDK-watch + examples by making the SDK build write dist/ atomically (temp + rename) so bundlers never observe a partial file.

Verification

Cold (packages/hydrogen/dist removed, .next and turbo cache cleared):

pnpm dev:next
→ 0 module-not-found errors (was 22)
→ @shopify/hydrogen#build runs; @shopify/hydrogen#dev (watch) does not

Turbo dry-run confirms @shopify/hydrogen#build is still scheduled and @shopify/hydrogen#dev is dropped.

🤖 Generated with Claude Code

[div-cowboy]

I have signed the CLA!

[div-cowboy]

Superseded by #3825. That PR fixes the same pnpm dev "Module not found" race at its root — @shopify/hydrogen's tsdown --watch was cleaning dist/ on startup while example bundlers read it — by skipping the clean in watch mode. That keeps the SDK watch (and hot reload) running, whereas this PR removed the watch from the dev scripts and lost hot reload. Folding both the render fix and the race fix into #3825 so a fresh clone works in one PR.