Summary

Fix pnpm why --exclude-peers so reverse dependency trees exclude peer dependency
edges.

pnpm why now builds a reverse dependency tree. The reverse graph was not
carrying whether an edge came from a peer dependency, and the CLI handler was not
passing excludePeerDependencies through to the dependents tree builder. As a
result, pnpm why --prod --exclude-peers could still show a package that was
only present as a resolved peer.

Changes

• Pass excludePeerDependencies from the why command to whyForPackages and
  buildDependentsTree.
• Preserve peer-edge information when building the reverse graph.
• Skip peer edges while walking reverse dependents when peers are excluded.
• Add regression coverage for peer-only and mixed direct+peer dependency paths.

Repro

Public repro repository: https://github.com/DrBearZay/pnpm-why-exclude-peers-repro

Minimal repository contents:

.
├── package.json
├── pnpm-lock.yaml
└── pnpm-workspace.yaml

{
  "name": "pnpm-why-exclude-peers-repro",
  "version": "1.0.0",
  "private": true,
  "packageManager": "pnpm@11.9.0",
  "dependencies": {
    "@electron-toolkit/utils": "4.0.0"
  },
  "devDependencies": {
    "electron": "39.7.0"
  }
}

@electron-toolkit/utils@4.0.0 declares electron as a peer dependency. The
root project provides electron@39.7.0 only from devDependencies.

The lockfile records that peer-resolved package instance like this:

'@electron-toolkit/utils@4.0.0':
  peerDependencies:
    electron: '>=13.0.0'

'@electron-toolkit/utils@4.0.0(electron@39.7.0)':
  dependencies:
    electron: 39.7.0

Since electron is only reached as a resolved peer from a production dependency,
--exclude-peers should remove it from the result.

Actual output

$ corepack pnpm@10.9.0 why electron --prod --exclude-peers

$ corepack pnpm@10.9.0 list electron --prod --depth Infinity --exclude-peers

$ corepack pnpm@11.9.0 why electron --prod --exclude-peers
electron@39.7.0
└─┬ @electron-toolkit/utils@4.0.0
  └── pnpm-why-exclude-peers-repro@1.0.0 (dependencies)

Found 1 version of electron

$ corepack pnpm@11.9.0 list electron --prod --depth Infinity --exclude-peers

pnpm@11.9.0 list --exclude-peers agrees with pnpm@10.9.0 and prints
nothing. Only pnpm@11.9.0 why --exclude-peers reports electron, so the
regression appears to be in the reverse-tree why path.

Verification

corepack pnpm@11.9.0 --filter @pnpm/deps.inspection.tree-builder compile
corepack pnpm@11.9.0 --filter @pnpm/deps.inspection.list compile
corepack pnpm@11.9.0 --filter @pnpm/deps.inspection.commands compile
corepack pnpm@11.9.0 --filter @pnpm/deps.inspection.tree-builder test -- buildDependentsTree.test.ts
node /private/tmp/verify-pnpm-why-peer.mjs