fix: allow booking the free part of a partly booked day

src/Form/BookingRequest.php

@@ -37,20 +37,30 @@ final class BookingRequest
     {
         $this->date = $date;
 
-        if (null !== $time && !$time->isAllDay()) {
-            $this->allDay = false;
-            $this->startTime = self::timeOf($time->startMinute);
-            $this->endTime = self::timeOf($time->endMinute);
+        if (null === $time || $time->isAllDay()) {
+            return;
         }
+
+        $this->allDay = false;
+        // An edge that is open to the edge of the day is left blank rather than filled in:
+        // 24:00 has no representation in <input type="time"> at all, and a blank already means
+        // "to the end of the day" here, exactly as it does on the board's span picker.
+        $this->startTime = TimeRange::DAY_START === $time->startMinute ? null : self::timeOf($time->startMinute);
+        $this->endTime = TimeRange::DAY_END === $time->endMinute ? null : self::timeOf($time->endMinute);
     }
 
     public function timeRange(): TimeRange
     {
-        if ($this->allDay || null === $this->startTime || null === $this->endTime) {
+        if ($this->allDay || (null === $this->startTime && null === $this->endTime)) {
             return TimeRange::wholeDay();
         }
 
-        return TimeRange::fromTimes($this->startTime, $this->endTime);
+        // One-sided input is open to that edge of the day -- the same rule TimeRange::parse()
+        // applies to the board's ?from=&to= pair, so the two never disagree.
+        return TimeRange::fromMinutes(
+            null === $this->startTime ? TimeRange::DAY_START : self::minutesOf($this->startTime),
+            null === $this->endTime ? TimeRange::DAY_END : self::minutesOf($this->endTime),
+        );
     }
 
     public function repeats(): bool
@@ -66,10 +76,10 @@ final class BookingRequest
     public function validate(ExecutionContextInterface $context): void
     {
         if (!$this->allDay) {
-            foreach (['startTime' => $this->startTime, 'endTime' => $this->endTime] as $field => $value) {
-                if (null === $value) {
-                    $context->buildViolation('Bitte eine Uhrzeit angeben.')->atPath($field)->addViolation();
-                }
+            if (null === $this->startTime && null === $this->endTime) {
+                $context->buildViolation('Bitte eine Uhrzeit angeben oder „Ganzer Tag" wählen.')
+                    ->atPath('startTime')
+                    ->addViolation();
             }
 
             if (null !== $this->startTime && null !== $this->endTime