fix: recover chat state after idle reconnects

Resyncs active sessions after hidden upstream stream reconnects
Recovers orphaned streaming parts with active-session snapshots
Adds coverage for event-stream reconnect behavior

packages/ui/src/sync/sync-context.tsx

@@ -874,15 +874,20 @@ const childStoreHasSessionState = (
     || Object.prototype.hasOwnProperty.call(state.session_status ?? {}, sessionID)
 }
 
-const childStoreHasMessagePartState = (
-  childStores: ChildStoreManager,
-  directory: string,
-  messageID: string,
-): boolean => {
+const childStoreHasMessagePartState = (
+  childStores: ChildStoreManager,
+  directory: string,
+  messageID: string,
+): boolean => {
   const store = childStores.getChild(directory)
   if (!store) return false
-  return Object.prototype.hasOwnProperty.call(store.getState().part, messageID)
-}
+  return Object.prototype.hasOwnProperty.call(store.getState().part, messageID)
+}
+
+const getActiveDirectoryFallback = (childStores: ChildStoreManager): string | null => {
+  if (!_activeDirectory || !_activeSession) return null
+  return childStores.getChild(_activeDirectory) ? _activeDirectory : null
+}
 
 const resolveDirectoryFromRoutingIndex = (
   routingIndex: EventRoutingIndex,
@@ -927,12 +932,21 @@ const resolveDirectoryFromRoutingIndex = (
     }
 
     // Scan child stores for a store that has parts for this message
-    for (const [dir, store] of childStores.children) {
-      if (Object.prototype.hasOwnProperty.call(store.getState().part, messageID)) {
-        return dir
-      }
-    }
-  }
+    for (const [dir, store] of childStores.children) {
+      if (Object.prototype.hasOwnProperty.call(store.getState().part, messageID)) {
+        return dir
+      }
+    }
+
+    // Some reconnect/idle gaps can deliver part events before the matching
+    // message.updated event and without a sessionID. If the user is actively
+    // viewing a session, route the orphaned part event there so the reducer can
+    // trigger HTTP materialization instead of dropping it as a global event.
+    const activeDirectory = getActiveDirectoryFallback(childStores)
+    if (activeDirectory) {
+      return activeDirectory
+    }
+  }
 
   // Single-store fallback: if there's only one directory, use it
   if (
@@ -946,8 +960,25 @@ const resolveDirectoryFromRoutingIndex = (
     }
   }
 
-  return normalizedDirectory
-}
+  return normalizedDirectory
+}
+
+const resolveMaterializationSessionID = (
+  materializationSessionID: string | undefined,
+  messageID: string | undefined,
+  resolvedDirectory: string,
+  routingIndex: EventRoutingIndex,
+): string | undefined => {
+  if (materializationSessionID) return materializationSessionID
+  if (messageID) {
+    const indexedSessionID = routingIndex.messageSessionById.get(messageID)
+    if (indexedSessionID) return indexedSessionID
+  }
+  if (resolvedDirectory && resolvedDirectory === _activeDirectory && _activeSession) {
+    return _activeSession
+  }
+  return undefined
+}
 
 const updateRoutingIndexFromEvent = (
   routingIndex: EventRoutingIndex,
@@ -1559,14 +1590,19 @@ function handleEvent(
 
   }
 
-  // Snapshot materialization is driven by typed reducer outcomes, not by
-  // inferring meaning from a generic false/no-change result.
-  if (materializationResult) {
-    const materializationSessionID = materializationResult.sessionID ?? getSessionIdFromPayload(payload) ?? undefined
-    if (materializationSessionID) {
-      enqueueSessionMaterialization(resolvedDirectory, materializationSessionID, childStores)
-    }
-  }
+  // Snapshot materialization is driven by typed reducer outcomes, not by
+  // inferring meaning from a generic false/no-change result.
+  if (materializationResult) {
+    const materializationSessionID = resolveMaterializationSessionID(
+      materializationResult.sessionID ?? getSessionIdFromPayload(payload) ?? undefined,
+      materializationResult.messageID ?? getMessageIdFromPayload(payload) ?? undefined,
+      resolvedDirectory,
+      routingIndex,
+    )
+    if (materializationSessionID) {
+      enqueueSessionMaterialization(resolvedDirectory, materializationSessionID, childStores)
+    }
+  }
 
   updateRoutingIndexFromEvent(routingIndex, resolvedDirectory, payload)
 }