Reject unversioned party documents

docs/troubleshooting.md

@@ -76,6 +76,27 @@ Safe fix:
 
 Relevant reference: [Configuration](./config.md).
 
+## Party schema version rejected
+
+Symptom:
+
+- configuration loading reports that `party.schema_version` is required or
+  unsupported.
+
+Likely cause:
+
+- the campaign `party.yml` is an unversioned legacy document, or names a
+  schema other than `narratio.party.v1`.
+
+Safe fix:
+
+- replace the file with one exact, single-document
+  [`narratio.party.v1` party](./integrations/party.md); do not add a version
+  marker to an otherwise incompatible legacy structure. Remove competing
+  player and session-party settings while migrating.
+
+Relevant reference: [Canonical Party Input](./integrations/party.md).
+
 ## Unexpected imported or profile value
 
 Symptom: