Document world time persistence

AGRARIAN_DEVELOPMENT_ROADMAP.md

@@ -755,7 +755,9 @@ Target deliverable: A small group can join a server, spawn into one biome, gathe
   persist stable `ResourceNodeId`, remaining harvest count, and MVP respawn
   flag through `FAgrarianSavedResourceNode`, then restore depletion to matching
   map-authored nodes on load.
-- [ ] Save world time.
+- [x] Save world time. World saves persist `UAgrarianSaveGame::WorldHours`
+  from `AAgrarianGameState::WorldHours` and restore it on server authority
+  during world load.
 - [ ] Save weather seed/state.
 - [ ] Save containers.
 - [ ] Add server-side save interval.

Docs/PersistenceDesignDocument.md

@@ -429,6 +429,10 @@ from `UAgrarianInventoryComponent::Items`, and restored through
 values and broadcasts inventory changes so HUD/debug listeners see loaded item
 state.
 
+World time is stored in `UAgrarianSaveGame::WorldHours`. The persistence
+subsystem captures it from `AAgrarianGameState::WorldHours` during world save
+and restores it only on authority during world load.
+
 ## Testing Gates
 
 Minimum persistence smoke test:

Scripts/verify_world_time_persistence.py

@@ -0,0 +1,43 @@
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+
+EXPECTED = {
+    ROOT / "Source" / "AgrarianGame" / "AgrarianSaveGame.h": [
+        "float WorldHours = 8.0f;",
+    ],
+    ROOT / "Source" / "AgrarianGame" / "AgrarianPersistenceSubsystem.cpp": [
+        "SaveGame->WorldHours = GameState->WorldHours;",
+        "GameState->WorldHours = SaveGame->WorldHours;",
+        "!GameState->HasAuthority()",
+    ],
+    ROOT / "Docs" / "PersistenceDesignDocument.md": [
+        "`UAgrarianSaveGame::WorldHours`",
+        "`AAgrarianGameState::WorldHours`",
+        "restores it only on authority",
+    ],
+    ROOT / "AGRARIAN_DEVELOPMENT_ROADMAP.md": [
+        "[x] Save world time.",
+        "`UAgrarianSaveGame::WorldHours`",
+        "restore it on server authority",
+    ],
+}
+
+
+def main() -> None:
+    missing = []
+    for path, snippets in EXPECTED.items():
+        text = path.read_text(encoding="utf-8")
+        for snippet in snippets:
+            if snippet not in text:
+                missing.append(f"{path.relative_to(ROOT)}: {snippet}")
+
+    if missing:
+        raise RuntimeError("World time persistence verification failed: " + "; ".join(missing))
+
+    print("PASS: world time persists through the authoritative world save state.")
+
+
+if __name__ == "__main__":
+    main()