feat: polish jump hop themed runtime assets

server-rs/crates/spacetime-client/src/jump_hop.rs

@@ -706,6 +706,14 @@ fn merge_action_into_draft(
     {
         draft.cover_composite = Some(value.to_string());
     }
+    if matches!(
+        scope,
+        JumpHopDraftMergeScope::CompileDraft | JumpHopDraftMergeScope::RegenerateTiles
+    ) {
+        if let Some(asset) = payload.back_button_asset.clone() {
+            draft.back_button_asset = Some(asset);
+        }
+    }
     if draft.work_title.trim().is_empty() {
         return Err(SpacetimeClientError::validation_failed(
             "jump-hop work_title 不能为空",
@@ -763,6 +771,11 @@ fn build_compile_input(
         tile_atlas_asset_json: Some(json_string(&tile_atlas_asset)?),
         tile_assets_json: Some(json_string(&tile_assets)?),
         cover_composite,
+        back_button_asset_json: draft
+            .back_button_asset
+            .as_ref()
+            .map(json_string)
+            .transpose()?,
         generation_status: Some("ready".to_string()),
         compiled_at_micros: now_micros,
     })
@@ -848,6 +861,7 @@ fn default_draft() -> JumpHopDraftResponse {
         tile_assets: Vec::new(),
         path: None,
         cover_composite: None,
+        back_button_asset: None,
         generation_status: JumpHopGenerationStatus::Draft,
     }
 }