added form for DomainApplicationAdmin which limits the list of statuses to those which are available to transition to

src/registrar/admin.py

@@ -1,4 +1,6 @@
 import logging
+from django import forms
+from django_fsm import get_available_FIELD_transitions
 from django.contrib import admin, messages
 from django.contrib.auth.admin import UserAdmin as BaseUserAdmin
 from django.contrib.contenttypes.models import ContentType
@@ -224,6 +226,29 @@ class ContactAdmin(ListHeaderAdmin):
     search_help_text = "Search by firstname, lastname or email."
 
 
+class DomainApplicationAdminForm(forms.ModelForm):
+    """Custom form to limit transitions to available transitions"""
+    class Meta:
+        model = models.DomainApplication
+        fields = '__all__'
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        instance = kwargs.get('instance')
+        if instance and instance.pk:
+            current_state = instance.status
+            transitions = get_available_FIELD_transitions(
+                instance, models.DomainApplication._meta.get_field('status'))
+            # first option in status transitions is current state
+            available_transitions = [(current_state, current_state)]
+
+            for transition in transitions:
+                available_transitions.append((transition.target, transition.target))
+
+            self.fields['status'].widget.choices = available_transitions
+
+
 class DomainApplicationAdmin(ListHeaderAdmin):
 
     """Customize the applications listing view."""
@@ -255,6 +280,7 @@ class DomainApplicationAdmin(ListHeaderAdmin):
     search_help_text = "Search by domain or submitter."
 
     # Detail view
+    form = DomainApplicationAdminForm
     fieldsets = [
         (None, {"fields": ["status", "investigator", "creator"]}),
         (