Prepare canonical party and derived players inputs

docs/integrations/party.md

@@ -47,3 +47,27 @@ must not override their party or players inputs.
 
 Use the canonical document for new campaigns. The configuration rules and
 source-relative path behavior are defined in the [Configuration Reference](../config.md).
+
+## Derived players document
+
+During `prepare`, Narratio copies the canonical party source bytes unchanged
+to `inputs/party.yml` and writes this deterministic players-only projection to
+`inputs/players.yml`:
+
+```yaml
+schema_version: narratio.players.v1
+players:
+    - name: Eric
+      character:
+        id: arannis
+        name: Arannis
+        alias:
+            - Ari
+            - The Grey Owl
+```
+
+There is one entry per character, sorted by stable character ID. Repeated
+player names remain separate entries. The optional `alias` list retains its
+declared order and is omitted when empty. The projection carries no class
+data. Its prepared manifest record is marked `derived_from_party`; it is not a
+separate user-provided `players_file`.