net/outbound_session: refactor slot selection algo

Previously, we used slot index to determine which peer color to fetch.
The issue is if slots were dynamically added or removed the ordering
would change.

Now, all slots build the same ordered vector (by color tier) and
check_addrs coordinates which slot gets which address via try_register. We
use fetch_random_with_schemes for address randomization within color tiers.

src/net/session/outbound_session.rs

@@ -259,11 +259,11 @@ impl Slot {
         self.process.stop().await;
     }
 
-    /// Address selection algorithm that works as follows: up to
-    /// gold_count, select from the goldlist. Up to white_count,
-    /// select from the whitelist. For all other slots, select from
-    /// the greylist. If none of these preferences are satisfied, do
-    /// peer discovery.
+    /// Address selection algorithm that builds an ordered vector of addresses:
+    /// gold peers first (up to known_peer_percent), then white peers (filling
+    /// remaining known slots), then grey peers (filling remaining slots).
+    /// All slots use this same ordered vector, and check_addrs coordinates
+    /// which slot gets which address via try_register.
     ///
     /// Selecting from the greylist for some % of the slots is necessary
     /// and healthy since we require the network retains some unreliable
@@ -271,7 +271,6 @@ impl Slot {
     /// connections may be vulnerable to sybil by attackers with good uptime.
     async fn fetch_addrs(&self) -> Option<(Url, u64)> {
         let hosts = self.p2p().hosts();
-        let slot = self.slot as usize;
         let container = &self.p2p().hosts().container;
 
         // Acquire Settings read lock
@@ -285,25 +284,42 @@ impl Slot {
         // Drop Settings read lock
         drop(settings);
 
-        // Calculate the number of slots for known peers (gold or white)
+        let mut addrs = Vec::with_capacity(outbound_connections);
+
+        // Known peers (gold + white) up to known_peer_percent.
+        // NOTE: if we don't have enough gold or white peers, we select from the greylist.
+        // This prioritizes max slot utilization over strictly respecting user preference.
+        // However disable_greys cancels this out.
         let max_known_percent = if disable_greys { 100 } else { 80 };
         let bounded_percent = known_peer_percent.min(max_known_percent);
         let known_count = (bounded_percent * outbound_connections) / 100;
 
-        // For known peer slots, prefer gold then white. Otherwise use grey.
-        let addrs = if slot < known_count {
-            // Try gold first, then white for known peers.
-            // NOTE: We might want to force white connections, otherwise we may
-            // end up connecting to gold hosts only.
-            let gold = container.fetch_with_schemes(HostColor::Gold, &transports, None);
-            if gold.is_empty() {
-                container.fetch_with_schemes(HostColor::White, &transports, None)
-            } else {
-                gold
+        // Add gold up to known_count
+        while let Some(addr) = container.fetch_random_with_schemes(HostColor::Gold, &transports) {
+            if addrs.len() >= known_count {
+                break;
+            }
+            addrs.push(addr);
+        }
+
+        // Add white to fill remaining known slots
+        while let Some(addr) = container.fetch_random_with_schemes(HostColor::White, &transports) {
+            if addrs.len() >= known_count {
+                break;
             }
-        } else {
-            container.fetch_with_schemes(HostColor::Grey, &transports, None)
-        };
+            addrs.push(addr);
+        }
+
+        // Add grey to fill remaining slots
+        if !disable_greys {
+            while let Some(addr) = container.fetch_random_with_schemes(HostColor::Grey, &transports)
+            {
+                if addrs.len() >= outbound_connections {
+                    break;
+                }
+                addrs.push(addr);
+            }
+        }
 
         hosts.check_addrs(addrs).await
     }