No conflicting duplicate package versions

Duplicate versions of shared packages in the lock file trigger the infamous "Invalid hook call" error for React and produce silent type mismatches, doubled bundle size, and non-deterministic runtime behavior when two copies of the same module hold separate module-level state. When react, react-dom, graphql, or @types/* resolve to multiple versions, instanceof checks fail across module boundaries, context providers stop propagating to consumers imported from the other copy, and production bugs surface only on specific code paths. This directly undermines dependency-coherence hygiene and turns routine upgrades into days-long debugging sessions.

Run npm ls <package> (or pnpm why <package> / yarn why <package>) to locate the offending duplicate, then npm dedupe to collapse compatible ranges. When an upstream dependency pins an older version, force a single resolution via the overrides field in package.json and verify the dependent package still works:

{
  "overrides": {
    "react": "^18.0.0",
    "react-dom": "^18.0.0"
  }
}

Also remove any package listed in both dependencies and devDependencies.

• ID: no-duplicate-deps

• Severity: low

• What to look for: Examine the lock file (package-lock.json, pnpm-lock.yaml, yarn.lock) for instances where the same package appears at multiple versions. This happens when two dependencies require incompatible versions of a shared sub-dependency. Common culprits: react (multiple versions cause runtime crashes), graphql, @types/* packages. Also check package.json directly for packages listed in both dependencies and devDependencies.

• Pass criteria: Count all packages that appear at multiple versions in the lock file. No critical shared packages (especially react, react-dom, framework packages) appear at multiple versions. No more than 3 total duplicate packages across the lock file. Report the count: "Found X packages at multiple versions in lock file."

• Fail criteria: react or react-dom appears at multiple versions in the lock file, OR a package appears in both dependencies and devDependencies in package.json.

• Skip (N/A) when: No lock file present (this is caught by the lockfile-present check in Code Hygiene). Signal: no lock file detected.

• Detail on fail: "react appears at two versions in package-lock.json: 18.3.1 (direct) and 17.0.2 (via a dependency). This can cause runtime 'multiple React instances' errors." or "@types/node listed in both dependencies and devDependencies with conflicting versions."

• Remediation: Duplicate React versions in particular cause the "Invalid hook call" error and similar mysterious runtime failures. To identify and resolve:

  # For npm — check for duplicate packages
  npm ls react
  # Look for entries with deduped or multiple versions listed
  
  # Force deduplication
  npm dedupe
  

  If the duplicate is caused by an upstream package requiring an old version, you can override it in package.json:

  "overrides": {
    "react": "^18.0.0"
  }
  

  Use overrides carefully — verify the dependent package actually works with the forced version.