fix(gateway): sanitize bounded SSE refresh + deduplicate constant

- Bounded/cursor SSE refresh path now sanitizes through
  sanitizeChatHistoryMessages before paginating, matching the
  unbounded path and initial history load.
- Export DEFAULT_CHAT_HISTORY_TEXT_MAX_CHARS from chat.ts and
  import in sessions-history-http.ts instead of duplicating.

src/agents/pi-embedded-subscribe.handlers.messages.ts

@@ -289,7 +289,6 @@ export function handleMessageUpdate(
     assistantRecord?.partial && typeof assistantRecord.partial === "object"
       ? (assistantRecord.partial as AssistantMessage)
       : msg;
-  const phaseAwareVisibleText = coerceText(extractAssistantVisibleText(partialAssistant)).trim();
   const deliveryPhase = resolveAssistantMessagePhase(partialAssistant);
   if (deliveryPhase === "commentary") {
     return;

src/gateway/server-methods/chat.ts

@@ -102,7 +102,7 @@ type ChatAbortRequester = {
   isAdmin: boolean;
 };
 
-const DEFAULT_CHAT_HISTORY_TEXT_MAX_CHARS = 12_000;
+export const DEFAULT_CHAT_HISTORY_TEXT_MAX_CHARS = 12_000;
 const CHAT_HISTORY_MAX_SINGLE_MESSAGE_BYTES = 128 * 1024;
 const CHAT_HISTORY_OVERSIZED_PLACEHOLDER = "[chat.history omitted: message too large]";
 let chatHistoryPlaceholderEmitCount = 0;

src/gateway/sessions-history-http.ts

@@ -25,10 +25,10 @@ import {
   resolveGatewaySessionStoreTarget,
   resolveSessionTranscriptCandidates,
 } from "./session-utils.js";
-import { sanitizeChatHistoryMessages } from "./server-methods/chat.js";
+import { DEFAULT_CHAT_HISTORY_TEXT_MAX_CHARS, sanitizeChatHistoryMessages } from "./server-methods/chat.js";
 
 const MAX_SESSION_HISTORY_LIMIT = 1000;
-const DEFAULT_CHAT_HISTORY_TEXT_MAX_CHARS = 12_000;
+
 function resolveSessionHistoryPath(req: IncomingMessage): string | null {
   const url = new URL(req.url ?? "/", `http://${req.headers.host ?? "localhost"}`);
   const match = url.pathname.match(/^\/sessions\/([^/]+)\/history$/);
@@ -295,7 +295,10 @@ export async function handleSessionHistoryHttpRequest(
       }
     }
     sentHistory = paginateSessionMessages(
-      readSessionMessages(entry.sessionId, target.storePath, entry.sessionFile),
+      sanitizeChatHistoryMessages(
+        readSessionMessages(entry.sessionId, target.storePath, entry.sessionFile),
+        effectiveMaxChars,
+      ),
       limit,
       cursor,
     );