Replace platform-specific optionalDependencies with bun devDependency

[gh0stonio]

Note: See #516 for a lower-impact alternative that keeps optionalDependencies and strips them at publish time via prepack/postpack. A bit more hacky but doesn't change the contributor setup at all.

Summary

Fixes #222

Replaces the 17 platform-specific optionalDependencies (@oven/bun-*, @rollup/rollup-*) with a single bun devDependency, and removes setup-bun.mjs entirely.

Builds on the investigation from #451, thanks @ochafik!

Context

At Datadog we're building on MCP Apps and this optionalDependencies bloat (~400MB of platform binaries) is blocking our CI pipelines, which motivated picking this up.

Problem

The repo listed 11 @oven/bun-* and 6 @rollup/rollup-* platform-specific packages in optionalDependencies. npm's optionalDependencies are installed for all consumers (they're "optional" in that npm doesn't fail if installation fails, not that they're skipped). This caused ~400MB of unnecessary downloads for anyone installing the SDK.

Why the previous approaches don't work

• Moving to devDependencies (Move Bun and Rollup binaries to devDependencies and skip setup when installed as dependency #451): these packages declare os/cpu constraints — npm silently skips mismatches in optionalDependencies but fails hard in devDependencies (npm ci on macOS ARM errors on @oven/bun-linux-x64)
• Removing them entirely: contributors need bun available before prepare runs for the build step

Approach

Instead of working around the problem, fix the root cause — the dependencies were declared at the wrong level:

@rollup/rollup-* — remove them

The SDK build uses bun (build.bun.ts), not rollup. These entries were added in 556a857f as a workaround for an npm bug where rollup's nested optionalDependencies weren't being fetched for the example workspaces (which use vite).

Verified that @rollup/rollup-darwin-arm64 now resolves correctly via vite without the top-level entries (tested with npm 10.9.2). If the bug resurfaces on older npm versions, contributors would see example build failures — the fix is simply to update npm. This only affects example workspace builds, not the SDK itself.

@oven/bun-* — replace with "bun": "^1.2.21" in devDependencies

The bun npm meta-package handles platform detection internally (via its own scoped optionalDependencies) and registers the binary in node_modules/.bin/bun automatically. As a devDependency, it's only installed for contributors, never for consumers.

Remove setup-bun.mjs

This script existed because the raw @oven/bun-* platform packages don't have a bin field — they just contain the binary file. The script had to manually detect the platform, find the right package in node_modules/@oven/bun-*, and symlink the binary to .bin/bun. With the bun meta-package, all of that is handled automatically by npm. The script is no longer needed.

Remove postinstall, simplify prepare

Based on this comment #451 (review) from @jonathanhefner.

• postinstall (node scripts/setup-bun.mjs || ...) was redundant with prepare which already ran the same script, and setup-bun.mjs wasn't even shipped in the published package ("files": ["dist"])
• prepare simplified from "node scripts/setup-bun.mjs && npm run build && husky" to "npm run build && husky"

Test plan

Verified from a clean state (rm -rf node_modules && npm ci):

• npm ci succeeds
• npm run build / npm run build:all succeed
• npm test passes (85/85)
• npm run test:e2e passes
• npm run prettier passes
• typedoc passes
• npm pack produces a tarball with no optionalDependencies
• @rollup/rollup-darwin-arm64 resolves correctly via vite without top-level entries (npm 10.9.2)
• Consumer install from tarball: 92 packages / 26MB, zero @oven/bun-* or @rollup/rollup-*

[ochafik]

Thanks @gh0stonio !!