1 files changed, 18 insertions, 0 deletions
diff --git a/packages/app/src/context/global-sync/event-reducer.ts b/packages/app/src/context/global-sync/event-reducer.ts
index fa1a43d47..66fcac66d 100644
--- a/packages/app/src/context/global-sync/event-reducer.ts
+++ b/packages/app/src/context/global-sync/event-reducer.ts
@@ -231,6 +231,24 @@ export function applyDirectoryEvent(input: {
       }
       break
     }
+    case "message.part.delta": {
+      const props = event.properties as { messageID: string; partID: string; field: string; delta: string }
+      const parts = input.store.part[props.messageID]
+      if (!parts) break
+      const result = Binary.search(parts, props.partID, (p) => p.id)
+      if (!result.found) break
+      input.setStore(
+        "part",
+        props.messageID,
+        produce((draft) => {
+          const part = draft[result.index]
+          const field = props.field as keyof typeof part
+          const existing = part[field] as string | undefined
+          ;(part[field] as string) = (existing ?? "") + props.delta
+        }),
+      )
+      break
+    }
     case "vcs.branch.updated": {
       const props = event.properties as { branch: string }
       if (input.store.vcs?.branch === props.branch) break