In browser builds, if a plugin returns the result of this.resolve(..., { skipSelf: true }) from resolveId, an import that should be disabled via browser: false is instead resolved to the package directory and later fails to load.

Reproduction link or steps

Minimal repro:

package.json

{
  "private": true,
  "type": "module",
  "scripts": {
    "build": "rolldown -c rolldown.config.mjs"
  },
  "devDependencies": {
    "rolldown": "1.0.0-rc.12"
  }
}

src/main.js

import "../demo/index.js";

demo/package.json

{
  "name": "demo",
  "type": "module",
  "browser": {
    "buffer": false
  }
}

demo/index.js

import "buffer";

rolldown.config.mjs

export default {
  input: "./src/main.js",
  platform: "browser",
  plugins: [
    {
      name: "probe",
      async resolveId(id, importer, options) {
        if (options?.isEntry || !id || id.startsWith(".") || id.startsWith("/")) {
          return null;
        }

        const resolved = await this.resolve(id, importer, {
          ...options,
          skipSelf: true,
        });

        console.log(id, resolved);
        return resolved ?? null;
      },
    },
  ],
};

Run:

npm install
npm run build

Control:

• If return resolved ?? null is changed to return null, the build succeeds.

What is expected?

Returning the result of this.resolve() from resolveId should preserve browser: false handling.

In this repro, import "buffer" inside demo/index.js should remain disabled/ignored for the browser build rather than being turned into a loadable module path.

What is actually happening?

The build fails with:

[UNLOADABLE_DEPENDENCY] Error: Could not load demo
demo/index.js:1:8
import "buffer";
       ^^^^^^^^
Is a directory (os error 21)

The logged resolution for buffer points at the package directory instead of preserving the browser: false result. Rolldown later tries to load that directory as a module and fails with Is a directory.

System Info

System:
  OS: macOS 26.4
  CPU: (12) arm64 Apple M4 Pro
  Memory: 1020.94 MB / 24.00 GB
  Shell: 4.6.0 - /opt/homebrew/bin/fish
Binaries:
  Node: 24.14.1 - /Users/akolberg/.local/share/mise/installs/node/24.14.1/bin/node
  Yarn: 4.13.0 - /Users/akolberg/.local/share/mise/installs/yarn/4.13.0/bin/yarn
  npm: 11.11.0 - /Users/akolberg/.local/share/mise/installs/node/24.14.1/bin/npm
  pnpm: 10.29.3 - /Users/akolberg/.local/share/mise/installs/pnpm/10.29.3/pnpm
  bun: 1.3.9 - /Users/akolberg/.local/share/mise/installs/bun/1.3.9/bin/bun
  Deno: 2.7.11 - /opt/homebrew/bin/deno
Browsers:
  Chrome: 147.0.7727.56
  Firefox: 149.0.2
  Safari: 26.4
npmPackages:
  rolldown: 1.0.0-rc.12 => 1.0.0-rc.12