[luc122c]

Description

Closes #141.

CloudFront's device detection headers (CloudFront-Is-*-Viewer) were only honored when the incoming User-Agent was exactly Amazon CloudFront:

if (userAgent === 'Amazon CloudFront') { ... }

Per the AWS docs, CloudFront only replaces the viewer's User-Agent with Amazon CloudFront when the header is not part of the cache/origin request policy. When User-Agent is forwarded (e.g. with an AllViewer policy), the origin sees the real browser user agent, the check fails, and the module silently ignores the CloudFront device headers in favor of user-agent parsing.

This change detects the CloudFront device headers by presence instead of keying off the user agent, so detection is configuration-independent. The headers still take precedence over user-agent parsing, and the existing mobile/tablet/desktop precedence is preserved.

Changes

• src/runtime/generateFlags.ts: detect CloudFront via the presence of any CloudFront-Is-*-Viewer header rather than the User-Agent.
• test/basic.test.ts: exercise the CloudFront headers with a real browser user agent (desktop UA for mobile/tablet/ios/android, iPhone UA for desktop) so the header precedence is actually covered, plus keep a case for the replaced Amazon CloudFront UA and a negative case with no headers.
• README.md: clarify that detection no longer requires the Amazon CloudFront user agent, and that platform/browser flags are unavailable only when CloudFront replaces the user agent.

Backward compatibility

Both configurations are covered:

• User-Agent: Amazon CloudFront + device headers (Unchanged)
• Real browser User-Agent + device headers (Now detected)
• No CloudFront headers (Falls back to user-agent parsing, as before)

Verification

pnpm dev:prepare
pnpm lint
pnpm test   # 28 passed