feat: add deterministic order to mob/player tick processing, document how tick processing works

1 files changed, 17 insertions, 1 deletions

diff --git a/internal/world/mob.go b/internal/world/mob.go
index fa0cdbf..f33b2f9 100644
--- a/internal/world/mob.go
+++ b/internal/world/mob.go
@@ -5,6 +5,7 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"sync"
 
@@ -476,6 +477,7 @@ func (s *MobStore) AllInstances() []*MobInstance {
 	for _, inst := range s.instances {
 		out = append(out, inst)
 	}
+	sort.SliceStable(out, func(i, j int) bool { return out[i].InstanceID < out[j].InstanceID })
 	return out
 }
 
@@ -499,6 +501,20 @@ func (s *MobStore) MobsInRoom(roomID int) []*MobInstance {
 			out = append(out, inst)
 		}
 	}
+	sort.SliceStable(out, func(i, j int) bool { return out[i].InstanceID < out[j].InstanceID })
+	return out
+}
+
+// sortedInstancesLocked returns every mob instance sorted by InstanceID. It
+// must be called with s.mu held; callers iterate the returned slice instead of
+// ranging s.instances directly so per-tick processing order is stable across
+// Go's randomized map iteration.
+func (s *MobStore) sortedInstancesLocked() []*MobInstance {
+	out := make([]*MobInstance, 0, len(s.instances))
+	for _, inst := range s.instances {
+		out = append(out, inst)
+	}
+	sort.SliceStable(out, func(i, j int) bool { return out[i].InstanceID < out[j].InstanceID })
 	return out
 }
 
@@ -506,7 +522,7 @@ func (s *MobStore) Tick() {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	for _, inst := range s.instances {
+	for _, inst := range s.sortedInstancesLocked() {
 		if inst.Shop != nil {
 			s.tickShopLocked(inst)
 		}