Refuse the welcome mail on a read-only store before it renders anything

generate_and_send_welcome_mail() arrived with the mail templates, after the
read-only guards were added to the other services, and never got one. On a
read-only store it therefore rendered the mail, could hand it to the mail
server, and only failed when it tried to create the archive directory in the
member file -- surfacing a PermissionError instead of the ReadOnlyStoreError
every other write path reports.

The guard now sits at the top, next to the delivery-mode check, so nothing is
rendered, sent or written. The read-only test covers this path (and the SEPA
batch alongside it) and asserts that nothing at all was left behind: no export
file, no archive directory, no "sent" event.

Its member carries an e-mail address now -- without one the mail services bail
out for that reason, and the write the test exists for is never reached.

Note that the SEPA CSV/XML export keeps writing without a guard on purpose: it
writes to a path the board picks outside the store, which a read-only store has
no say over.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_read_only_store.py

@@ -8,6 +8,8 @@ from ccma.domain.models import ContributionData
 from ccma.services.documents import DocumentService
 from ccma.services.housekeeper import Housekeeper
 from ccma.services.reminder_mail import generate_and_send_reminder_mail
+from ccma.services.sepa_mail import generate_debit_mails
+from ccma.services.welcome_mail import generate_and_send_welcome_mail
 from ccma.storage.repository import MemberRepository, ReadOnlyStoreError
 
 # Root ignores the permission bits this test relies on, so the read-only mount it
@@ -32,6 +34,11 @@ def read_only_store(tmp_path):
     member = repository.create_member(
         first_name="Ada", last_name="Lovelace", birth_date="1990-01-01"
     )
+    # A complete member: without an address the mail services would bail out early
+    # for that reason, and the write they are actually being tested for is never
+    # reached.
+    member.email = "ada@example.org"
+    repository.save_member(member)
     repository.save_contributions(
         member.member_id,
         ContributionData(
@@ -126,6 +133,53 @@ def test_documents_and_mails_refuse_before_touching_the_member_file(read_only_st
             sender_email="verwaltung@example.org",
             signature="Der Vorstand",
         )
+    with pytest.raises(ReadOnlyStoreError, match="schreibgeschützt"):
+        generate_and_send_welcome_mail(
+            repository,
+            member.member_id,
+            delivery_mode="local",
+            output_path=tmp_path / "Willkommen.eml",
+            sender_name="Verwaltung",
+            sender_email="verwaltung@example.org",
+            signature="Der Vorstand",
+        )
+    with pytest.raises(ReadOnlyStoreError, match="schreibgeschützt"):
+        generate_debit_mails(
+            repository,
+            [],
+            collection_date=date(2026, 9, 1),
+            delivery_mode="local",
+            output_directory=tmp_path / "sepa",
+            sender_name="Verwaltung",
+            sender_email="verwaltung@example.org",
+            signature="Der Vorstand",
+        )
+
+
+def test_the_welcome_mail_writes_nothing_at_all_when_refused(read_only_store, tmp_path):
+    """The refusal has to come before rendering, sending and archiving -- not out of
+    the failing write at the end, by which point the mail would already be out."""
+    repository, member = read_only_store
+    export_path = tmp_path / "Willkommen.eml"
+
+    with pytest.raises(ReadOnlyStoreError, match="schreibgeschützt"):
+        generate_and_send_welcome_mail(
+            repository,
+            member.member_id,
+            delivery_mode="local",
+            output_path=export_path,
+            sender_name="Verwaltung",
+            sender_email="verwaltung@example.org",
+            signature="Der Vorstand",
+        )
+
+    assert not export_path.exists()
+    files = repository.members_root / member.member_id / "files"
+    assert not (files / "documents" / "Willkommen").exists()
+    assert all(
+        event.event_type != "welcome_email_sent"
+        for event in repository.get_events(member.member_id)
+    )
 
 
 def test_uninitialized_read_only_store_reports_why_it_cannot_be_opened(tmp_path):