Guard domain parsing to resolve TS2532 on malformed email inputs

[Copilot]

TypeScript consumers were hitting TS2532 because email.split('@')[1] can be undefined, yet toLowerCase() was called unconditionally. This PR makes domain extraction null-safe and keeps malformed inputs on the existing false path.

• Domain extraction hardening

  • Updated detector logic to read the domain segment into an intermediate variable.
  • Added an early return when no domain segment is present.
  • Preserved behavior for valid emails by lowercasing only after the guard.

• Focused regression coverage

  • Expanded test/package.ts assertions to cover:
    • a known disposable domain (true)
    • standard non-disposable email (false)
    • malformed inputs (invalid-email, @, user@@example.com, empty string) returning false

const domainPart = email.split('@')[1];
if (!domainPart) return false;
const domain = domainPart.toLowerCase();
return disposableDomains.includes(domain);

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• pastebin.com
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node test/usage.js (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node test/usage.js detector osable-email-detector (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[deepsource-io]

DeepSource Code Review

We reviewed changes in da406b2...929330b on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

See full review on DeepSource ↗

PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
JavaScript		Apr 15, 2026 5:15p.m.	Review ↗

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 36 complexity · 0 duplication

Metric	Results
Complexity	36
Duplication	0

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[IntegerAlex]

LGTM