fix(exports): resolve .js subpath imports to real declaration files

[johnhenry]

Fixes #2701.

Problem

Subpath imports like @modelcontextprotocol/sdk/server/mcp.js have no explicit key in exports, so they fall through "./*":

"./*": { "types": "./dist/esm/*.d.ts", "import": "./dist/esm/*", "require": "./dist/cjs/*" }

The wildcard captures the entire remainder including the extension, so * = server/mcp.js and the types target becomes dist/esm/server/mcp.js.d.ts — which does not exist. The real declaration file is dist/esm/server/mcp.d.ts.

tsc is unaffected because it falls back to typesVersions ("*": ["./dist/esm/*"]), which resolves the .js → .d.ts step itself. Resolvers that implement exports but not typesVersions — notably Deno — fail with TS2307.

Because the failure is a type resolution failure, it doesn't stop at one error: once McpServer is unresolved, every zod-inferred server.tool(...) callback parameter collapses to any. A server of mine with 3 SDK imports produced 1 × TS2307 plus 19 × TS7031, all from this single root cause.

This affects the import style used throughout the README and examples, so in practice it blocks type-checking any MCP server under Deno, and blocks publishing one to JSR.

Fix

Add a "./*.js" pattern alongside the existing "./*", so the extension is excluded from the wildcard capture:

"./*.js": { "types": "./dist/esm/*.d.ts", "import": "./dist/esm/*.js", "require": "./dist/cjs/*.js" }

Node's resolution algorithm prefers the pattern with the longest prefix before *, so "./*.js" wins for .js specifiers regardless of key order, and everything else continues to fall through "./*" exactly as before. typesVersions is left alone — it already handles this case.

Verification

Against 1.30.0, before and after:

	before	after
deno check on import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"	TS2307	exit 0
node --input-type=module importing the same specifier	resolves	resolves
tsc --module nodenext --moduleResolution nodenext --strict	exit 0	exit 0

So it fixes Deno without changing Node or tsc behaviour.

Tests

test/issues/test_2701_js_subpath_exports.test.ts, following the existing test/issues/ convention. It resolves subpaths through the real exports map from package.json and asserts the types target is a genuine .d.ts, that runtime targets are unchanged, that explicit keys still take precedence, and that extensionless subpaths still work.

The four types assertions fail without the package.json change and pass with it. The runtime-target assertions pass either way, which is the intended demonstration that runtime resolution is untouched.

Full suite on this branch: 10 failed, 1643 passed. On unmodified v1.x on the same machine: 10 failed, 1629 passed — the same 10 pre-existing failures (they spawn /usr/bin/tee, which doesn't exist on NixOS), plus the 14 new passing tests. npm run lint and npm run typecheck both clean.

Based on v1.x per CONTRIBUTING, since this is a v1 packaging fix.

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