Add server-side Collection API service (ServerSideEventSender)

Problem/Motivation

The PA module currently only tracks page views via the client-side JS SDK. There are scenarios where the JS SDK never executes — server-side redirects (301/302), API endpoints, cron jobs — and events for these are lost entirely.

The PA Collection API supports server-side HTTP event submission, but there is no reusable service in the module to leverage it.

Proposed resolution

Add a new ServerSideEventSender service that POSTs events to the PA Collection API using the site ID and collect domain already configured in pianoanalytics.settings.

The service:

• POSTs JSON to https://{collect_domain}/event?s={site}&idclient={visitor_id} with Content-Type: text/plain (per PA Collection API spec)
• Auto-enriches event properties with device_timestamp_utc and event_collection_platform: api
• Forwards browser context headers (User-Agent, Referer, X-Forwarded-For) so PA can perform device and geo analysis on server-side events
• Provides resolveVisitorId(Request) to extract the visitor ID from PA cookies (_pcid, pa_vid, atuserid) with fallback to a sha256 hash of the client IP
• Provides extractBrowserHeaders(Request) to extract the relevant headers from a Symfony request
• Uses a 2-second timeout and catches all exceptions — callers are never broken by PA failures
• Errors are logged to the pianoanalytics logger channel

New files

• pianoanalytics.services.yml — declares the pianoanalytics logger channel and the autowired ServerSideEventSender service
• src/ServerSideEventSender.php — the service class
• tests/src/Kernel/ServerSideEventSenderTest.php — 6 kernel tests covering request construction, Content-Type, auto-enriched properties, browser header forwarding, missing config guard, HTTP error handling, cookie-based visitor ID resolution, and header extraction

API usage example

$sender = \Drupal::service(ServerSideEventSender::class);
$visitor_id = ServerSideEventSender::resolveVisitorId($request);
$headers = ServerSideEventSender::extractBrowserHeaders($request);

$sender->sendEvent('page.display', [
  'page' => '/my-page',
  'page_chapter1' => 'section',
], $visitor_id, $headers);

Remaining tasks

• Review
• Test