[BUG] npm install livelocks (100% CPU, infinite CanPlaceDep/canPlacePeers cycle) on dependency graph with cyclic peerDependencies

Current Behavior

npm install @deepseek-ai/dsh in a fresh directory never completes. The process spins at ~100% CPU indefinitely (verified for 5+ minutes; log output freezes) during dependency tree resolution. npm install -g of the same package completes normally in ~30s.

Expected Behavior

The install completes, or fails with an ERESOLVE error, instead of livelocking.

Steps To Reproduce

mkdir repro && cd repro
npm init -y
npm install @deepseek-ai/dsh
# hangs forever at ~100% CPU, no further output

With --loglevel silly, the last output is a stream of placeDep ROOT @deepseek-ai/... OK for: @deepseek-ai/... lines, then output freezes while CPU stays pegged.

Diagnosis

I attached the inspector (kill -USR1) and sampled the main thread three times via CDP Debugger.pause. All samples show the same repeating stack pattern in arborist (line numbers from @npmcli/arborist 10.0.2 shipped with npm 12.0.2):

getBundler              node.js:528
getBundler              node.js:556   (repeated ~7x)
get inDepBundle         node.js:577
satisfiedBy             can-place-dep.js:113
satisfies               node.js:1166
CanPlaceDep             can-place-dep.js:116
canPlacePeers           can-place-dep.js:390
checkCanPlaceNoCurrent  can-place-dep.js:344
checkCanPlace           can-place-dep.js:161
CanPlaceDep             can-place-dep.js:118
canPlacePeers           can-place-dep.js:390
...

The cycle CanPlaceDep constructor → checkCanPlace() → canPlacePeers() → new CanPlaceDep(...) never terminates for this dependency graph. The package has ~50 @deepseek-ai/* scoped packages that declare each other as peerDependencies, including cycles (e.g. dsh-agent peers on dsh-llm, dsh-tools peers on both dsh-agent and dsh-llm, dsh-client-runtime peers on many of them). The peerPath.includes(peerEdge.to) guard in canPlacePeers (can-place-dep.js:382) appears insufficient to terminate in this case.

Additional data points:

• Reproduced with the default registry and with https://registry.npmjs.org (not registry-related).
• Reproduced with npm 11.16.0 and npm 12.0.2, and with --install-strategy=nested.
• npm install -g of the same package works fine (different placement path).
• --legacy-peer-deps completes, but predictably produces a tree that omits the peer dependencies, so the installed CLI cannot load its modules.

Environment

• npm: 12.0.2 (also reproduced on 11.16.0)
• Node: v26.0.0
• OS: macOS 15.7.7 (x86_64)
• Package: @deepseek-ai/dsh@0.1.1-rc.2 (public, 453 transitive deps)

Reproduce with the provided npm install @deepseek-ai/dsh command, then inspect @npmcli/arborist's can-place-dep.js around canPlacePeers, checkCanPlace, and the peerPath.includes guard, along with the referenced node.js helpers. Trace the cyclic peer-dependency path and add coverage for this graph; done means installation terminates with a completed tree or an ERESOLVE error instead of spinning indefinitely.