Declare @x402/fetch as an optional peer dependency (undeclared dynamic import breaks bundlers/tracers)

[ryantbrown]

Problem

The SDK lazily imports @x402/fetch for the optional payments feature, but the package is not declared anywhere in package.json:

• src/wrapper/x402.ts — const { x402HTTPClient } = await import("@x402/fetch"); (plus a type import)
• src/wrapper/Client.ts — const { wrapFetchWithPayment } = await import("@x402/fetch");
• package.json — dependencies: { "ws": "..." } only; no peerDependencies, no optionalDependencies

That makes @x402/fetch a phantom optional dependency. It works in plain Node only if the consumer coincidentally has the package installed, and it breaks any toolchain that statically analyzes the import:

• Bundlers (rollup/rolldown/vite/esbuild) fail with unresolvable-import errors unless every consumer manually externalizes @x402/fetch.
• File tracers / snapshot builders (@vercel/nft, and build systems that materialize dependency closures, e.g. eve 0.24+) fail hard because a configured external must be resolvable on disk: Cannot resolve external package "@x402/fetch".
• Isolated installers (bun isolated linker, pnpm) guarantee phantom resolution never works, so the runtime fallback path can't save it either.

We hit this as a hard production build failure and now carry two workarounds in our monorepo: externalizing @x402/fetch in three bundler configs and installing it as a direct dependency of the consuming app purely so build tooling can resolve an import that never executes.

Suggested fix

Declare the dependency so tooling and consumers can see it:

{
  "peerDependencies": {
    "@x402/fetch": "^2"
  },
  "peerDependenciesMeta": {
    "@x402/fetch": { "optional": true }
  }
}

This keeps the feature opt-in (consumers install @x402/fetch only if they use payments), lets bundlers and tracers understand the import instead of erroring, and documents the requirement instead of leaving it to runtime discovery.

Observed on agentmail@0.5.14/0.5.15 and current main.