_fbc cookies written by Meta are not parsed: SDK regex rejects '-'/'_' and the newer 5-segment format

[loevgaard]

Problem

CookieBasedFbcContext (src/Context/Fbc/CookieBasedFbcContext.php:26) parses the _fbc cookie with Setono\MetaConversionsApi\ValueObject\Fbc::fromString() from the SDK, which requires

/^fb\.([012])\.(\d{13})\.([a-zA-Z0-9]+)$/

and the bundle silently returns null when it throws.

Two classes of legitimate cookies do not match:

1. Click ids containing - or _. Real fbclid values are base64url and regularly contain both characters. QueryBasedFbcContext + StoreFbcSubscriber store fb.1.<ts>.IwAR1a-b_c in the cookie; on the next request fromString() throws, the exception is swallowed, and fbc is null. The cookie is written but never read back.
2. Meta's current five-segment format. Meta's official parameter builder (facebook/capi-param-builder-php, installed transitively through facebook/php-business-sdk) writes _fbc as fb.<idx>.<ts>.<fbclid>.<appendix> where the appendix is a 2- or 8-character token (see php/capi-param-builder/src/ParamBuilder.php around lines 261-267 and model/Constants.php: APPENDIX_LENGTH_V1 = 2, APPENDIX_LENGTH_V2 = 8). The browser pixel has been moving to the same format. The SDK regex requires exactly four segments, so such a cookie yields fbc = null, and server-side events lose click attribution precisely when the browser pixel is active.

Please verify the second point against what fbevents.js writes in a current browser before changing anything; the parameter builder source is the reference used here.

Impact

Lost click attribution on server-side events. It is silent: no log, no exception, just a missing parameter and a lower Event Match Quality in Events Manager.

Suggested fix

The regex lives in setono/meta-conversions-api-php-sdk:

• SDK: relax the click id charset to [A-Za-z0-9_-]+ and accept an optional trailing \.[A-Za-z0-9_-]{2,8} segment, preserving it in value() so an existing cookie is not rewritten in a different shape.
• Bundle: bump the SDK constraint once released, add regression tests for both cookie shapes, and log at debug level when a cookie value cannot be parsed so the situation is at least visible.

Related: #19.

Tests

Unit tests for CookieBasedFbcContext: four-segment cookie, cookie with -/_, five-segment cookie, garbage cookie, no cookie, no request.