npm install fails with "Exit handler never called!" on every deploy attempt, consistent ~71s timing

Title: npm install fails with "Exit handler never called!" on every deploy attempt, consistent ~71s timing

Every deployment of my Next.js 14.2.35 project fails during "Installing dependencies..." with the same npm internal error, after a very consistent ~71-second delay:

npm error Exit handler never called! npm error This is an error with npm itself. Please report this error at: npm error https://github.com/npm/cli/issues Error: Command "npm install" exited with 1

This has happened identically on 4+ separate deployment attempts, each failing at almost exactly the same elapsed time (~70-71s into the install step) — not variable, as I'd expect from generic network flakiness.

What I've already ruled out:

Node.js Version: tried both 24.x and 22.x — identical failure both times
Install Command: overrode default npm install to npm ci — no change
Added NODE_OPTIONS=--dns-result-order=ipv4first to rule out IPv6 registry connectivity issues — no change
Build cache disabled on every attempt
The exact same package.json/package-lock.json installs cleanly in 24-36 seconds locally (tested with both a warm and a fully cold npm cache, on Node 22.x)
No unusual dependencies (no git/URL-based packages, all standard semver ranges), no postinstall/prepare scripts, no packageManager field, no .npmrc file, lockfileVersion 3
Checked vercel-status.com — no reported incidents

Given the dependency tree/lockfile install cleanly elsewhere and the timing is so consistent (not random), this feels like it might be specific to how this particular account/project is reaching the build infrastructure — possibly something in the iad1 (Washington D.C.) region. Has anyone hit this exact error and found a fix? Happy to share the deployment ID or more logs if useful.

Stack: Next.js 14.2.35, 119 npm packages, standard npm (not yarn/pnpm), Supabase as the backend.