Cerfa mécénat rempli envoyé par email à la confirmation du paiement

Quand un paiement « mécénat » est confirmé, l'email de confirmation porte
en pièce jointe le reçu fiscal (cerfa 11580*05) rempli du bénévole, avec
une phrase l'annonçant dans le corps. Généré en tâche de fond : un échec
de génération envoie l'email sans pièce jointe plutôt que rien.

- build_message/send acceptent des pièces jointes
- app/mecenat/receipts.py : passage Volunteer → MecenatReceipt, partagé
  avec l'export coordination
- modèle cerfa remplacé par une version pré-remplie avec l'association
  (organisme bénéficiaire, cases 200/978, signature) ; position de la
  date du versement ajustée

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/tests/test_forms_api.py

@@ -912,6 +912,81 @@ def test_choosing_a_mecenat_option_requires_the_address_step_first(
     assert fiche["mecenat_country"] == "France"
 
 
+def _attachments(message) -> list:
+    return [
+        part
+        for part in message.iter_attachments()
+        if part.get_content_disposition() == "attachment"
+    ]
+
+
+def test_mecenat_payment_emails_the_filled_cerfa(raw_client, client, edition, monkeypatch, outbox):
+    client.put(_form_url(edition, "/fields"), json={"fields": ["WILLING_TO_PAY_FEE", "EMAIL"]})
+    client.patch(
+        _form_url(edition), json={"sumup_merchant_code": _MERCHANT, "sumup_api_key": _API_KEY}
+    )
+    option_id = client.post(
+        _form_url(edition, "/payment-options"),
+        json={"label": "Mécénat", "amount": 50, "requires_mecenat_info": True},
+    ).json()["id"]
+    token = _submit(
+        raw_client, edition,
+        first_name="Alex", last_name="Martin", hcaptcha_token="x",
+        email="alex@example.org",
+        payment_option_id=option_id,
+    ).json()["pending_token"]
+    monkeypatch.setattr(
+        "app.api.forms.create_checkout",
+        lambda **kw: SumUpCheckout(id="co_don", status="PENDING", hosted_checkout_url="https://don"),
+    )
+    raw_client.post(
+        _form_url(edition, f"/public/pending/{token}/mecenat-info"),
+        json={
+            "address": "1 rue du Festival",
+            "city": "Rennes",
+            "postal_code": "35000",
+            "country": "France",
+        },
+    )
+    assert outbox == []  # pas encore payé : ni email ni reçu
+
+    _pay(raw_client, edition, monkeypatch, checkout_id="co_don")
+
+    assert len(outbox) == 1
+    attachments = _attachments(outbox[0])
+    assert len(attachments) == 1
+    assert attachments[0].get_content_type() == "application/pdf"
+    assert attachments[0].get_filename().endswith(".pdf")
+    assert attachments[0].get_content().startswith(b"%PDF")
+    assert "reçu fiscal" in plain_text(outbox[0])
+
+
+def test_classic_payment_email_has_no_cerfa(raw_client, client, edition, monkeypatch, outbox):
+    client.put(_form_url(edition, "/fields"), json={"fields": ["WILLING_TO_PAY_FEE", "EMAIL"]})
+    client.patch(
+        _form_url(edition), json={"sumup_merchant_code": _MERCHANT, "sumup_api_key": _API_KEY}
+    )
+    option_id = client.post(
+        _form_url(edition, "/payment-options"),
+        json={"label": "Cotisation classique", "amount": 12.5},
+    ).json()["id"]
+    monkeypatch.setattr(
+        "app.api.forms.create_checkout",
+        lambda **kw: SumUpCheckout(id="co_1", status="PENDING", hosted_checkout_url="https://x"),
+    )
+    _submit(
+        raw_client, edition,
+        first_name="Alex", last_name="Martin", hcaptcha_token="x",
+        email="alex@example.org",
+        payment_option_id=option_id,
+    )
+    _pay(raw_client, edition, monkeypatch, checkout_id="co_1")
+
+    assert len(outbox) == 1
+    assert _attachments(outbox[0]) == []
+    assert "reçu fiscal" not in plain_text(outbox[0])
+
+
 def test_mecenat_info_requires_every_field(raw_client, client, edition, monkeypatch):
     client.put(_form_url(edition, "/fields"), json={"fields": ["WILLING_TO_PAY_FEE"]})
     client.patch(
@@ -1002,3 +1077,4 @@ def test_pending_status_polling_is_rate_limited_per_token(
     for _ in range(pending_status_limiter.max_attempts):
         pending_status_limiter.hit(token)
     assert raw_client.get(_form_url(edition, f"/public/pending/{token}")).status_code == 429
+