feat(campaign): enforce attachment delivery policies

src/govoplan_campaign/backend/messages/builder.py

@@ -245,6 +245,26 @@ def _message_issues_from_attachment_resolution(resolution: EntryAttachmentResolu
     ]
 
 
+def _append_no_attachment_coverage_issue(issues: list[MessageIssue]) -> None:
+    if any(issue.code == "missing_attachment_coverage" for issue in issues):
+        return
+    issues.append(
+        MessageIssue(
+            severity="error",
+            code="missing_attachment_coverage",
+            message="No attachment file was resolved for this message, and sending without attachments is not allowed.",
+            behavior=Behavior.BLOCK.value,
+            source="attachments",
+        )
+    )
+
+
+def _send_without_attachments_behavior(config: CampaignConfig) -> Behavior:
+    return config.attachments.send_without_attachments_behavior or (
+        Behavior.CONTINUE if config.attachments.send_without_attachments else Behavior.BLOCK
+    )
+
+
 def _safe_filename(value: str | None, fallback: str) -> str:
     raw = value or fallback
     safe = re.sub(r"[^A-Za-z0-9_.-]+", "_", raw).strip("._")
@@ -391,6 +411,7 @@ def _attach_files(
     for attachment in resolution.attachments:
         attachment.message_filenames = []
         attachment.zip_entry_names = []
+        attachment.zip_filename = None
 
     for attachment in resolution.attachments:
         if attachment.status != AttachmentMatchStatus.OK or not attachment.matches:
@@ -435,6 +456,7 @@ def _attach_files(
             work_dir / "_zip" / f"entry-{entry_index:04d}" / _safe_filename(archive.id, "archive") / filename,
             members,
             password,
+            archive.method.value,
         )
         data, maintype, subtype = _attachment_bytes(archive_path)
         message.add_attachment(data, maintype=maintype, subtype=subtype, filename=filename)
@@ -740,6 +762,14 @@ def _build_mime_message(
             values=rendered.values,
             work_dir=work_dir,
         )
+        if attachment_count == 0 and context.resolution.attachments and _send_without_attachments_behavior(config) == Behavior.BLOCK:
+            _append_no_attachment_coverage_issue(context.issues)
+            return _MimeBuildResult(
+                message=None,
+                build_status=BuildStatus.BUILD_FAILED,
+                validation_status=MessageValidationStatus.BLOCKED,
+                attachment_count=0,
+            )
         return _MimeBuildResult(
             message=message,
             build_status=BuildStatus.BUILT,