Since the introduction of the synapse-usage-exporter role (55f869254, #3442), group_vars/matrix_servers was overriding matrix_synapse_report_stats_endpoint with an empty string whenever synapse-usage-exporter was disabled, clobbering the role's matrix.org default.

For deployments that enable matrix_synapse_report_stats, Synapse would then try reporting statistics to an empty URL, failing with:

> synapse.app.homeserver - 210 - WARNING - phone_stats_home-0 - Error reporting stats: Invalid URI b''

The default endpoint URL now lives in a dedicated matrix_synapse_report_stats_endpoint_default variable, which group_vars/matrix_servers falls back to when synapse-usage-exporter is not enabled.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>