fix(scheduler): make model unload order deterministic (#10185)

server/sched.go

@@ -667,13 +667,19 @@ func (runner *runnerRef) waitForVRAMRecovery() chan any {
 	return finished
 }
 
-type ByDuration []*runnerRef
-
-func (a ByDuration) Len() int      { return len(a) }
-func (a ByDuration) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
-func (a ByDuration) Less(i, j int) bool {
-	// uint64 to turn negative time (never unload) to largest
-	return uint64(a[i].sessionDuration) < uint64(a[j].sessionDuration)
+type ByDurationAndName []*runnerRef
+
+func (a ByDurationAndName) Len() int      { return len(a) }
+func (a ByDurationAndName) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a ByDurationAndName) Less(i, j int) bool {
+	// Primary sort by session duration (uint64 to handle negatives)
+	d1 := uint64(a[i].sessionDuration)
+	d2 := uint64(a[j].sessionDuration)
+	if d1 != d2 {
+		return d1 < d2
+	}
+	// Secondary sort by model path lex order
+	return a[i].modelPath < a[j].modelPath
 }
 
 // TODO - future consideration to pick runners based on size
@@ -775,7 +781,7 @@ func (s *Scheduler) findRunnerToUnload() *runnerRef {
 
 	// In the future we can enhance the algorithm to be smarter about picking the optimal runner to unload
 	// e.g., if we have multiple options, will one make room for the request?
-	sort.Sort(ByDuration(runnerList))
+	sort.Sort(ByDurationAndName(runnerList))
 
 	// First try to find a runner that's already idle
 	for _, runner := range runnerList {