Resolve Client.Go-002, -003 code-review findings

Client.Go-002: the Events/EventsAfter compatibility path silently dropped
events when the 16-slot results channel filled — it cancelled the stream and
closed the channel with no error delivered. sendEventResult now evicts an
old buffered event and delivers a terminal EventResult carrying the new
exported ErrEventBufferOverflow before close, so the overflow is observable.

Client.Go-003: parseInt32List panicked on a malformed -item-handles token,
crashing the CLI with a stack trace. It now returns an error that
runUnsubscribeBulk propagates, exiting 2 with a clean message.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/go/cmd/mxgw-go/main_test.go

@@ -56,3 +56,32 @@ func TestParseValueBuildsTypedValue(t *testing.T) {
 		t.Fatalf("int32 value = %d, want 123", got)
 	}
 }
+
+func TestParseInt32ListParsesValidTokens(t *testing.T) {
+	items, err := parseInt32List("1, 2 ,3")
+	if err != nil {
+		t.Fatalf("parseInt32List() error = %v", err)
+	}
+	want := []int32{1, 2, 3}
+	if len(items) != len(want) {
+		t.Fatalf("parseInt32List() = %v, want %v", items, want)
+	}
+	for i := range want {
+		if items[i] != want[i] {
+			t.Fatalf("parseInt32List()[%d] = %d, want %d", i, items[i], want[i])
+		}
+	}
+}
+
+func TestParseInt32ListReturnsErrorOnMalformedToken(t *testing.T) {
+	items, err := parseInt32List("1,foo")
+	if err == nil {
+		t.Fatalf("parseInt32List() error = nil, want a parse error; items = %v", items)
+	}
+	if items != nil {
+		t.Fatalf("parseInt32List() items = %v, want nil on error", items)
+	}
+	if !strings.Contains(err.Error(), "foo") {
+		t.Fatalf("parseInt32List() error = %q, want it to name the bad token", err.Error())
+	}
+}