Stored a bounded per-login overflow backlog and promoted deferred events oldest-first as rolling-window capacity became available. Surfaced the deferred state through the dashboard contract and documented admission behavior.
Fixes#5882
parse_issue_ref now accepts owner/repo#NN or a github issue url (with or without scheme, www., trailing slash, query, fragment). The dashboard trigger, CLI, and replay endpoint pick this up automatically; UI hints updated to match.