feat(campaign): enforce attachment delivery policies

src/govoplan_campaign/backend/attachments/resolver.py

@@ -390,6 +390,27 @@ def _issue_for_ambiguous(config: AttachmentConfig, behavior: Behavior, match_cou
     )
 
 
+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 _issue_for_missing_attachment_coverage(behavior: Behavior) -> AttachmentIssue:
+    messages = {
+        Behavior.BLOCK: "No attachment file was resolved for this message, and campaign policy blocks sending without attachments.",
+        Behavior.ASK: "No attachment file was resolved for this message. Confirm the message should still be sent.",
+        Behavior.DROP: "No attachment file was resolved for this message. Campaign policy excludes messages without attachments.",
+        Behavior.WARN: "No attachment file was resolved for this message. Campaign policy allows sending with a warning.",
+    }
+    return AttachmentIssue(
+        severity=ResolutionSeverity.ERROR if behavior == Behavior.BLOCK else ResolutionSeverity.WARNING,
+        code="missing_attachment_coverage",
+        message=messages.get(behavior, "No attachment file was resolved for this message."),
+        behavior=behavior,
+    )
+
+
 def _resolve_one_config(
     *,
     campaign_file: str | Path,
@@ -495,6 +516,15 @@ def resolve_entry_attachments(
             )
 
     issues = [issue for item in resolved for issue in item.issues]
+    missing_coverage_behavior = _send_without_attachments_behavior(config)
+    if (
+        entry.active
+        and resolved
+        and missing_coverage_behavior != Behavior.CONTINUE
+        and sum(len(item.matches) for item in resolved) == 0
+        and not any(issue.behavior == Behavior.BLOCK for issue in issues)
+    ):
+        issues.append(_issue_for_missing_attachment_coverage(missing_coverage_behavior))
     return EntryAttachmentResolution(
         entry_index=entry_index,
         entry_id=entry.id,