[BUG] Inconsistent behavior of `--omit=optional` in `npm i` and `npm ls`

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

This is not just a request to bump a dependency for a CVE

• This is not solely a request to bump a dependency for a CVE

Current Behavior

npm ls --omit=optional --all continues to include optional dependencies in its output.

However, npm ls --omit=dev --all excludes all development-only dependencies.

Additionally, npm i --omit=optional excludes all optional dependencies from being installed (docs).

Expected Behavior

When --omit=optional is supplied to npm ls, optional dependency entries should be excluded from the reported dependency tree, just like --omit=dev consistently excludes development-only dependency roots from the output and npm i --omit=optional does not install optional dependencies.

Steps To Reproduce

1. Create a project with a package.json like this:

{
  "name": "npm-omit-optional-reproduction",
  "private": true,
  "version": "1.0.0",
  "dependencies": {
    "@stencil/core": "4.39.0"
  }
}

2. Install dependencies:

npm install

3. Then run:

npm ls --omit=optional --alll

The output includes optional dependencies:

└─┬ @stencil/core@4.39.0
  ├── @rollup/rollup-darwin-arm64@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-darwin-x64@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-linux-arm64-gnu@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-linux-arm64-musl@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-linux-x64-gnu@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-linux-x64-musl@4.34.9
  ├── UNMET OPTIONAL DEPENDENCY @rollup/rollup-win32-arm64-msvc@4.34.9
  └── UNMET OPTIONAL DEPENDENCY @rollup/rollup-win32-x64-msvc@4.34.9

The same behavior is visible in JSON output:

npm ls --json --all --omit=optional

4. Then run a clean re-install with the --omit=optional flag set:

npm ci --omit=optional

5. Finally execute ls (--omit=all is not needed):

npm ls --omit=optional --all

The output doesn't include any optional dependency:

└──  @stencil/core@4.39.0

Environment

• npm: 12.0.1
• Node.js: v24.18.0
• OS Name: macOS arm64
• System Model Name:
• npm config:

; copy and paste output from `npm config ls` here

Start with the package.json reproduction and compare npm ls --json --all --omit=optional before and after npm ci --omit=optional. Trace the npm ls handling of the --omit=optional flag, then verify that optional entries are absent from both regular and JSON dependency-tree output while --omit=dev behavior remains unchanged.