resolvePath should strip trailing slashes from node: builtin specifiers

[ashtonjurgens]

Environment

I've seen this bug in both node and deno

node v25.8.1

deno 2.8.2 (stable, release, aarch64-apple-darwin)
v8 14.9.207.2-rusty
typescript 6.0.3

Reproduction

See description...

Describe the bug

Summary

resolvePath currently preserves trailing slashes when a specifier resolves to a node: builtin.

That is a problem because normal package imports may legally use a trailing slash, but node: builtin specifiers must not.

For example, Node accepts:

await import("punycode/")

but rejects:

await import("node:punycode/")

with:

Error [ERR_UNKNOWN_BUILTIN_MODULE]: No such built-in module: node:punycode/

Real-world case
This showed up with punycode, which exists both as an npm package and as a Node builtin.
A dependency imported punycode/, and unenv converted that to the builtin form. The trailing slash was preserved, so the final specifier became node:punycode/, which is invalid in Node.
Reproduction

const { env } = defineEnv({
  nodeCompat: false,
  resolve: true,
  overrides: {
    alias: {
      punycode: "node:punycode",
      foo: "punycode/",
    },
  },
});

env.alias.foo;

Current result:

"node:punycode/"

Expected result:

"node:punycode"

Expected behavior
When resolvePath resolves a specifier to a builtin module, it should normalize a trailing slash away before returning the node: form.
This normalization should only apply to builtins. Regular non-builtin imports like my-module/ should remain unchanged.

Additional context

No response

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