Require a name and a domain in email addresses

[sergical]

isEmail now needs some text before the @, a domain with a dot after it, and no spaces. Before, any string with an @ passed, so "@" and "name@" were treated as valid addresses.

Created with Claude Code

[github-actions]

Verdict: Approve with minor suggestions — the regex is a solid improvement over the old includes("@") check, but has a couple of known edge-case gaps and could use documentation.

Correctness

• No failing tests (run_tests found no related tests to run for this fixture).
• Improvement: correctly rejects strings with multiple @ symbols, missing domain dots, and leading/trailing whitespace around the whole string — all of which the old includes("@") check incorrectly accepted.
• Edge case / behavior change to be aware of: addresses without a dot in the domain (e.g. user@localhost) now return false, whereas they used to pass. If any caller or test relies on such addresses being accepted, this is a breaking change worth calling out in the PR description.
• Superficial validation gap: the regex only requires some dot after @, it doesn't prevent malformed patterns like consecutive dots or a trailing dot in the domain (e.g. [email protected], [email protected]. would still match). Not a regression, but worth knowing this isn't full RFC validation.
• Unicode/IDN domains are still accepted by [^\s@]+ (consistent with previous lenient behavior, not a new issue).

Style

• The regex is opaque inline; consider extracting it to a named module-level constant (e.g. const EMAIL_PATTERN = ...) both for readability and to avoid re-constructing the literal on every call (minor; JS regex literals are typically cached by engines, but naming still aids clarity).
• Add a short comment noting this is a basic format check, not full RFC 5322 validation, so readers don't assume stronger guarantees than it provides.
• Optional: consider a doc comment on isEmail clarifying its intentionally lightweight scope.

Overall a reasonable, low-risk tightening of validation logic; the above are non-blocking suggestions.