broker: make Postgres pool size configurable, bump default 5 → 8

Under concurrent door executions the broker was queueing on its 5-connection
pool, adding latency to tool calls that fanned out from the same run. Bump
the default to 8 (one connection per concurrent door before queueing) and
expose CLAWMATES_BROKER_POOL_SIZE so the fleet can tune it up as the load
grows without a rebuild.

crates/bins/clawmates-broker/src/main.rs

@@ -6,6 +6,7 @@
 //! - `CLAWMATES_DATABASE__URL`     Postgres connection string (required)
 //! - `CLAWMATES_BROKER_SOCKET`     unix socket path (default /tmp/clawmates-broker.sock)
 //! - `CLAWMATES_BROKER_KEY_FILE`   master key file; generated on first boot
+//! - `CLAWMATES_BROKER_POOL_SIZE`  max Postgres connections (default 8)
 
 use std::path::PathBuf;
 use std::process::ExitCode;
@@ -45,7 +46,13 @@ async fn run() -> Result<(), String> {
     }
     let key = FileKey::load(&key_path).map_err(|e| format!("key load failed: {e}"))?;
 
-    let pool = cm_db::connect(&database_url, 5)
+    // Pool size defaults to 8: one broker connection per concurrent door
+    // execution before we start queueing. Tune via env when the fleet grows.
+    let pool_size: u32 = std::env::var("CLAWMATES_BROKER_POOL_SIZE")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(8);
+    let pool = cm_db::connect(&database_url, pool_size)
         .await
         .map_err(|e| format!("database connection failed: {e}"))?;