Pin session cookie name, stop deriving it from APP_NAME

config/session.php

@@ -0,0 +1,19 @@
+<?php
+
+// App-level config files are merged over Laravel's framework defaults key by
+// key (see Illuminate\Foundation\Bootstrap\LoadConfiguration), so only the
+// keys that need to differ from the default belong here.
+
+return [
+
+    // Framework's default derives this from APP_NAME via Str::snake(), which does
+    // not strip characters like "." or spaces. PHP mangles dots in incoming
+    // cookie/GET/POST variable names to underscores when parsing a request, so an
+    // APP_NAME such as "example.com" produces a cookie the app can never read back
+    // (it looks for "example.com_session" but PHP only ever hands it
+    // "example_com_session"). That desyncs the session on every request, so the
+    // CSRF token embedded in a page never matches on submit -> 419 on every POST.
+    // Pinning the cookie name keeps it independent of APP_NAME entirely.
+    'cookie' => env('SESSION_COOKIE', 'heimdall_session'),
+
+];