fix(agent): handle partial room timestamps without crashing

docs/api/rest.md

@@ -627,6 +627,25 @@ messages/DOM grow with explicit older loads and live updates. Offscreen web rows
 use CSS `content-visibility: auto`, which skips rendering work while retaining
 chronological DOM, selection, find and accessibility; it is not DOM virtualization.
 
+Every room message, including protected tool rows and `activity.queuedMessages`,
+has a string `id`, `role`, `content`, and ISO-8601 `createdAt`. Privacy filtering
+retains this envelope and tool lifecycle metadata (`kind`, `toolCallId`,
+`toolName`, `entryId`, `status`, and available `startedAt`/`completedAt`). Protected
+tools use their public tool name as `content`; private arguments, previews, and
+errors are withheld. Result-only pages may omit initiation metadata.
+
+Historical entries without a known time use `1970-01-01T00:00:00.000Z` as an
+unknown-time sentinel. For compatibility with older partial responses, clients
+may recover missing/invalid `createdAt` from `metadata.startedAt`, then
+`metadata.completedAt`, or use that sentinel; never substitute the current time.
+Older redacted tool rows containing only `id`, `role`, and `name` can retain their
+identity with a tool-name label until a complete upsert arrives. The web client
+uses the same normalization for REST, WebSocket, and queued activity, retains
+known times across partial upserts, and orders by time, numeric `entryId` (when
+present, before absent), then stable `id`. Unknown times display as “Earlier”
+without a clock time. Invalid identities or non-tool message bodies reject the
+page before advancing its replay cursor; timestamps never replace cursors.
+
 ### `POST /v1/agent/messages`
 
 Body: `{ "content": "Check the oven", "requestId": "client-generated-uuid" }`.