hive-matrix-mcp: demote matrix-sdk-crypto's benign backup-key WARN by default

hive-matrix-mcp/src/main.rs

@@ -85,8 +85,14 @@ const ACCOUNTS_CHANGED_EXIT: u8 = 75;
 async fn main() -> Result<ExitCode> {
     tracing_subscriber::fmt()
         .with_env_filter(
-            tracing_subscriber::EnvFilter::try_from_default_env()
-                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
+            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| {
+                // matrix-sdk-crypto's own WARN fires every sync tick on any
+                // account with no key-backup set up (the common case here) —
+                // ~1/2s/host swarm-wide, the single largest log message by
+                // count. Demoted only in the no-RUST_LOG default, so an
+                // operator's explicit override still sees it if they ask.
+                tracing_subscriber::EnvFilter::new("info,matrix_sdk_crypto::backups=error")
+            }),
         )
         .with_writer(std::io::stderr)
         // This is a systemd-managed daemon — stderr always goes to journald,