fix(gun_harness): random tiebreak + drop AntiSurfer + raise MinObsBeforeCompete

- bestGun: replace first-index-wins argmax with random pick among guns
  within TieMargin (2%) of best rate. HeadOn at index 0 was silently
  winning every tie, starving Tsetlin/Linear/etc.
- MinObsBeforeCompete 15 -> 50 (Pattern entered competition on noise)
- add MinHitRateFloor 0.10: if no gun clears it, fall back to HeadOn
  instead of selecting the best of a bad field
- ModularBot: remove AntiSurfer gun (0% virtual hit rate everywhere),
  14 -> 13 guns, renumber ids and selection counters

common_libs/gun_harness/virtual_bullets.nim

@@ -5,6 +5,7 @@
 
 import std/math
 import std/tables
+import std/random
 import gun_interface
 
 const
@@ -12,7 +13,9 @@ const
   WindowSize*   = 100                     ## rolling window ticks for fitness
   MaxBullets*   = 2048                    ## hard cap; ponytail: ring buffer, resize if more guns added
   MinHitRate*          = 0.40   ## 40% threshold for acceptable power selection
-  MinObsBeforeCompete* = 15    ## min observations before a gun×bin enters competition
+  MinObsBeforeCompete* = 50    ## min observations before a gun×bin enters competition
+  TieMargin*           = 0.02  ## guns within this hit-rate margin of best are tied
+  MinHitRateFloor*     = 0.10  ## if best gun < this, fall back to gun 0 (HeadOn)
 
 type
   GunId*   = int  ## index into the guns seq
@@ -168,11 +171,11 @@ proc bestGun*(t: VirtualTracker, targetId: int = -1): GunId =
   ## Guns with fewer than MinObsBeforeCompete observations are skipped
   ## unless every gun is below threshold (then fall back to best of all).
   ## Uses per-enemy fitness when targetId >= 0 and data exists; else aggregate.
+  ## Ties (within TieMargin) are broken randomly to avoid index-0 bias.
   ## ponytail: O(n*bins), fine for small gun counts
   let fit = t.fitnessFor(targetId)
   proc bestAmong(fit: seq[GunFitness], requireMin: bool): GunId =
     var bestRate = -1.0
-    result = 0
     for gunId in 0..<fit.len:
       var maxCount = 0
       for binIdx in 0..<len(PowerBins):
@@ -180,9 +183,22 @@ proc bestGun*(t: VirtualTracker, targetId: int = -1): GunId =
       if requireMin and maxCount < MinObsBeforeCompete: continue
       for binIdx in 0..<len(PowerBins):
         let r = fit[gunId].bins[binIdx].hitRate()
-        if r > bestRate:
-          bestRate = r
-          result = gunId
+        if r > bestRate: bestRate = r
+    # Floor check: if nothing hits well enough, HeadOn is the safe default
+    if bestRate < MinHitRateFloor: return 0
+    var tied: seq[GunId]
+    for gunId in 0..<fit.len:
+      var maxCount = 0
+      for binIdx in 0..<len(PowerBins):
+        maxCount = max(maxCount, fit[gunId].bins[binIdx].count)
+      if requireMin and maxCount < MinObsBeforeCompete: continue
+      for binIdx in 0..<len(PowerBins):
+        let r = fit[gunId].bins[binIdx].hitRate()
+        if r >= bestRate - TieMargin:
+          tied.add(gunId)
+          break
+    if tied.len == 0: return 0
+    return tied[rand(tied.len - 1)]
 
   var anyQualifies = false
   for gunId in 0..<fit.len: