fix(gateway): unify chat display projection

ui/src/ui/app-gateway.ts

@@ -407,10 +407,14 @@ function handleTerminalChatEvent(
   host: GatewayHost,
   payload: ChatEventPayload | undefined,
   state: ReturnType<typeof handleChatEvent>,
+  activeRunIdBeforeEvent: string | null,
 ): boolean {
   if (state !== "final" && state !== "error" && state !== "aborted") {
     return false;
   }
+  if (isEventForDifferentActiveRun(payload, activeRunIdBeforeEvent)) {
+    return false;
+  }
   // Check if tool events were seen before resetting (resetToolStream clears toolStreamOrder).
   const toolHost = host as unknown as Parameters<typeof resetToolStream>[0];
   const hadToolEvents = toolHost.toolStreamOrder.length > 0;
@@ -447,6 +451,13 @@ function handleTerminalChatEvent(
   return false;
 }
 
+function isEventForDifferentActiveRun(
+  payload: ChatEventPayload | undefined,
+  activeRunId: string | null,
+): boolean {
+  return Boolean(activeRunId && payload?.runId && payload.runId !== activeRunId);
+}
+
 function handleChatGatewayEvent(host: GatewayHost, payload: ChatEventPayload | undefined) {
   if (payload?.sessionKey) {
     setLastActiveSessionKey(
@@ -463,8 +474,13 @@ function handleChatGatewayEvent(host: GatewayHost, payload: ChatEventPayload | u
     sideResultHost.chatSideResultTerminalRuns?.delete(payload.runId);
     return;
   }
+  const activeRunIdBeforeEvent = host.chatRunId;
   const state = handleChatEvent(host as unknown as ChatState, payload);
-  const historyReloaded = handleTerminalChatEvent(host, payload, state);
+  const terminalEventIsForDifferentActiveRun = isEventForDifferentActiveRun(
+    payload,
+    activeRunIdBeforeEvent,
+  );
+  const historyReloaded = handleTerminalChatEvent(host, payload, state, activeRunIdBeforeEvent);
   const deferredReloadHost = host as GatewayHostWithDeferredSessionMessageReload;
   const deferredSessionKey = deferredReloadHost.pendingSessionMessageReloadSessionKey?.trim();
   const payloadSessionKey = payload?.sessionKey?.trim();
@@ -479,7 +495,12 @@ function handleChatGatewayEvent(host: GatewayHost, payload: ChatEventPayload | u
   if (deferredSessionKey && payloadSessionKey && deferredSessionKey === payloadSessionKey) {
     deferredReloadHost.pendingSessionMessageReloadSessionKey = null;
   }
-  if (state === "final" && !historyReloaded && shouldReloadHistoryForFinalEvent(payload)) {
+  if (
+    state === "final" &&
+    !historyReloaded &&
+    !terminalEventIsForDifferentActiveRun &&
+    shouldReloadHistoryForFinalEvent(payload)
+  ) {
     void loadChatHistory(host as unknown as ChatState);
     return;
   }

ui/src/ui/app-tool-stream.ts

@@ -501,7 +501,12 @@ export function handleAgentEvent(host: ToolStreamHost, payload?: AgentEventPaylo
   if (!entry) {
     // Commit any in-progress streaming text as a segment so it renders
     // above the tool card instead of below it.
-    if (host.chatStream && host.chatStream.trim().length > 0) {
+    if (
+      host.chatRunId &&
+      payload.runId === host.chatRunId &&
+      host.chatStream &&
+      host.chatStream.trim().length > 0
+    ) {
       host.chatStreamSegments = [...host.chatStreamSegments, { text: host.chatStream, ts: now }];
       host.chatStream = null;
       host.chatStreamStartedAt = null;