[BUG] Workspace Bin Hoisting Collision causes incorrect binary execution via npm exec

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

When two workspaces each depend on a different package that exports a binary with the exact same name, Arborist hoists both dependencies to the root node_modules/. However, because bin-links uses a "first-wins" mechanism, only one shim gets created in root/node_modules/.bin/.

As a result, when running npm exec -w <loser-workspace> -- <bin>, libnpmexec falls back to the root .bin folder and inadvertently executes the wrong binary (the one belonging to the other workspace's dependency) because a local .bin folder was never created for the workspace.

Expected Behavior

npm exec -w <workspace> should completely isolate identical binary names in a monorepo and always execute the binary that belongs to the target workspace's dependency tree, regardless of hoisting rules at the root.

Steps To Reproduce

1. Create a monorepo with two workspaces: workspace-a and workspace-b.
2. Install dep-1 (which exports a bin named my-cli) into workspace-a.
3. Install dep-2 (which also exports a bin named my-cli) into workspace-b.
4. Observe that both dependencies hoist to the root. Only one of them (e.g., dep-1) gets its my-cli shim created in root/node_modules/.bin/.
5. Run npm exec -w workspace-b -- my-cli (the one that "lost" the race).
6. See that dep-1's script is executed instead of dep-2's script.

Environment

• npm: 12.0.0-pre.2
• Node.js: v23.11.1
• OS Name: macOS 15.7.7
• System Model Name: MacBookPro18,1
• npm config:

; "user" config from /Users/arjun/.npmrc

//registry.npmjs.org/:_authToken = (protected)

; "project" config from /Users/arjun/Desktop/npm/.npmrc

package-lock = true

; node bin location = /Users/arjun/.nvm/versions/node/v23.11.1/bin/node
; node version = v23.11.1
; npm local prefix = /Users/arjun/Desktop/npm
; npm version = 12.0.0-pre.2
; cwd = /Users/arjun/Desktop/npm
; HOME = /Users/arjun
; Run `npm config ls -l` to show all defaults.

Start by reproducing the workspace setup described in the issue and inspect how bin-links creates root and workspace .bin shims. Trace the npm exec workspace path through libnpmexec, especially its fallback to the root .bin folder. Done means npm exec -w workspace-b -- my-cli runs dep-2's binary when dep-1 and dep-2 export the same name.