fix: stop shipping declaration source maps that reference unshipped src/

[claude]

Requested by Felix Weinberger · Slack thread

Before / After

Before: every published v2 package (verified on @modelcontextprotocol/{core,client,server}@2.0.0-beta.4) ships dist/**/*.d.mts.map / *.d.cts.map declaration maps whose sources point at ../src/*.ts — and, for the packages that bundle it, at ../../core-internal/src/*.ts, a private: true workspace package that is never published. Since the tarballs contain only dist/ ("files": ["dist"]) and the maps carry no usable sourcesContent, none of those references can resolve on a consumer's machine: declaration-map-aware tooling (e.g. TypeScript's "Go to Source Definition") loads the map and lands nowhere, ~0.9 MB of dead-weight maps ship per install, and the maps leak internal monorepo paths.

After: the packages ship no declaration maps and the .d.mts/.d.cts files carry no //# sourceMappingURL= reference — editors fall back to the normal .d.ts navigation instead of chasing a map that cannot resolve. The runtime JS source maps (.mjs.map/.cjs.map), which do embed sourcesContent and resolve fine, are unchanged.

Verified by pnpm pack-ing all nine published packages (core, client, server, server-legacy, codemod, express, fastify, hono, node): 0 .d.*ts.map files in any tarball, 0 declaration files referencing a map, and every sources entry of every remaining shipped .map has embedded sourcesContent (no ../src or core-internal references left).

How

• packages/{core,client,server,server-legacy,codemod}/tsdown.config.ts, packages/middleware/{express,fastify,hono,node}/tsdown.config.ts: set dts.sourcemap: false, which turns off declarationMap for the dts pass and drops the .d.*ts.map assets from the bundle.
• common/tsdown/stripDtsSourceMappingUrl.mjs (+ .d.mts for typecheck): a shared inputOptions hook that strips the trailing //# sourceMappingURL= comment rolldown still appends to the (now map-less) declaration chunks. It is wired through inputOptions rather than plugins because tsdown does not forward user plugins to the extra CJS dts pass that emits the .d.cts files. Plain .mjs so tsdown's native config loader can import it on every supported Node version (Node 20 cannot natively import .ts).
• .changeset/no-dangling-declaration-maps.md: patch bump for all nine published packages.

Rejected alternatives: embedding sources is not possible — tsc has no inlineSources equivalent for declaration maps (microsoft/TypeScript#38966), which is exactly why the JS maps are fine on main while the declaration maps dangle. Shipping src/ would fix each package's own ../src references but not the ../../core-internal/src ones (private, unpublished, and bundled), would grow every tarball, and would still expose internal layout. Dropping the maps is the only option that leaves nothing unresolvable.

For the record: the .js.map side of #2233 as originally reported against v1.x does not affect main — the tsdown/rolldown build already embeds sourcesContent into the runtime JS maps. The declaration maps were the remaining unresolvable piece on main, as flagged in the #2233 thread and reported in detail in #2491 (this implements its option 2).

Verification run: pnpm -r build, pnpm typecheck:all, node scripts/smoke-dist-types.mjs (clean with skipLibCheck: false), tests for all nine affected packages, and lint/prettier — all passing.

Fixes #2233
Fixes #2491

🤖 Generated with Claude Code

https://claude.ai/code/session_016gag9FFr6udcsF8qvMvMV8

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Generated by Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 75313b5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@modelcontextprotocol/core	Patch
@modelcontextprotocol/client	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/server-legacy	Patch
@modelcontextprotocol/codemod	Patch
@modelcontextprotocol/express	Patch
@modelcontextprotocol/fastify	Patch
@modelcontextprotocol/hono	Patch
@modelcontextprotocol/node	Patch
@modelcontextprotocol/core-internal	Patch

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commit: 75313b5