Add better email verification

apps/submissions/forms.py

@@ -81,6 +81,9 @@ class SubmissionForm(forms.ModelForm):
 
     def __init__(self, *args, user=None, **kwargs):
         super().__init__(*args, **kwargs)
+        # Stash for `clean()` -- the per-email cap needs to know whether the
+        # incoming submission is OAuth (user.email) or guest (guest_email).
+        self.user = user
 
         # Filament dropdown shows only operator-curated, currently-loaded rows.
         self.fields["requested_filament"].queryset = Filament.objects.filter(
@@ -118,6 +121,26 @@ class SubmissionForm(forms.ModelForm):
 
     def clean(self):
         cleaned = super().clean()
+
+        # Per-email cap (plan.md §6). Run this BEFORE the source-type checks
+        # so a user already at quota doesn't get a misleading "pick a source"
+        # error message; the cap is the real reason their submission failed.
+        owner_email = (
+            self.user.email
+            if (self.user and self.user.is_authenticated)
+            else cleaned.get("guest_email")
+        )
+        if owner_email:
+            active = Submission.active_count_for_email(owner_email)
+            cap = Submission.MAX_ACTIVE_SUBMISSIONS_PER_EMAIL
+            if active >= cap:
+                raise forms.ValidationError(
+                    f"You already have {active} active submission(s) -- "
+                    f"that's the per-email cap of {cap}. Wait for some to "
+                    f"finish printing (or be cleaned up after rejection) "
+                    f"before submitting another."
+                )
+
         source_type = cleaned.get("source_type")
         stl_file = cleaned.get("stl_file")
         source_url = cleaned.get("source_url")