fix: gate scheduler task concurrency

internal/taskscheduler/gate_test.go

@@ -0,0 +1,29 @@
+package taskscheduler
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestSingleFlightGateBlocksUntilTerminalRelease(t *testing.T) {
+	gate := NewSingleFlightGate()
+	if err := gate.Acquire(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	blocked, cancel := context.WithTimeout(context.Background(), 20*time.Millisecond)
+	defer cancel()
+	if err := gate.Acquire(blocked); err == nil {
+		t.Fatal("second task acquired capacity before release")
+	}
+	gate.Release()
+	gate.Release()
+	if err := gate.Acquire(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	blockedAgain, cancelAgain := context.WithTimeout(context.Background(), 20*time.Millisecond)
+	defer cancelAgain()
+	if err := gate.Acquire(blockedAgain); err == nil {
+		t.Fatal("duplicate terminal release increased capacity")
+	}
+}