From a98fee4abd8240cf9132f5309379da1db987699d Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Thu, 29 Oct 2026 06:52:35 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20Optimize=20chat=20signature?=
 =?UTF-8?q?s=20by=20replacing=20array=20joins=20with=20string=20concatenat?=
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Replaces `Array.prototype.join()` with direct string concatenation in chat signature generation loops (`messagesSignature` and `useStickToBottom`). This avoids unnecessary intermediate array allocations, reducing memory overhead and garbage collection pauses on hot paths during frequent polling.

Co-authored-by: bobdivx <6737167+bobdivx@users.noreply.github.com>
---
 .jules/bolt.md                              |  4 ++++
 apps/web/src/components/chat/ChatThread.tsx | 26 +++++++++++++--------
 apps/web/src/lib/chat-messages.ts           | 18 ++++++++------
 3 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index edb6874221..c50cfae982 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -5,3 +5,7 @@
 ## 2026-10-15 - [Performance] Prevent unnecessary UI array recalculations
 **Learning:** In the chat component (`useThreadList`), derived state that requires filtering and sorting large arrays (like generating nested agent lists) was running synchronously on every render. Given that chat polling triggers frequent re-renders, this caused unnecessary CPU strain on lists that only rarely change.
 **Action:** Use `useMemo` for derived states like `rows` and `current` in custom hooks when they involve `.filter()`, `.map()`, or `.sort()` and depend on data that updates less frequently than the component renders.
+
+## 2026-10-29 - [Performance] Optimize Chat Signature Generation Hot Paths
+**Learning:** In chat signature generation functions (like `messagesSignature` and `useStickToBottom`), array instantiation combined with `.join('|')` causes unnecessary memory allocation overhead during frequent polling or render cycles.
+**Action:** Replace `Array.prototype.join()` with direct string concatenation on hot paths where signatures are generated frequently.
diff --git a/apps/web/src/components/chat/ChatThread.tsx b/apps/web/src/components/chat/ChatThread.tsx
index 50a0209c1b..067fd672b2 100644
--- a/apps/web/src/components/chat/ChatThread.tsx
+++ b/apps/web/src/components/chat/ChatThread.tsx
@@ -18,16 +18,22 @@ export function useStickToBottom(messages: ChatMessage[], resetKey: unknown) {
     if (!box) return;
     // On ne défile que si le contenu a réellement changé.
     const last = messages[messages.length - 1];
-    const sig = [
-      messages.length,
-      last?.content.length ?? 0,
-      last?.toolCalls?.length ?? 0,
-      last?.actions?.length ?? 0,
-      last?.reflections?.length ?? 0,
-      last?.milestones?.length ?? 0,
-      last?.liveLabel ?? '',
-      last?.streaming ? 1 : 0,
-    ].join('|');
+    const sig =
+      messages.length +
+      '|' +
+      (last?.content.length ?? 0) +
+      '|' +
+      (last?.toolCalls?.length ?? 0) +
+      '|' +
+      (last?.actions?.length ?? 0) +
+      '|' +
+      (last?.reflections?.length ?? 0) +
+      '|' +
+      (last?.milestones?.length ?? 0) +
+      '|' +
+      (last?.liveLabel ?? '') +
+      '|' +
+      (last?.streaming ? 1 : 0);
     if (sig === lastSig.current) return;
     const first = lastSig.current === '';
     lastSig.current = sig;
diff --git a/apps/web/src/lib/chat-messages.ts b/apps/web/src/lib/chat-messages.ts
index 4b5db18523..18fe58b0fb 100644
--- a/apps/web/src/lib/chat-messages.ts
+++ b/apps/web/src/lib/chat-messages.ts
@@ -50,13 +50,17 @@ export function messagesSignature(messages: IdentifiedMessage[]): string {
     }
   }
 
-  return [
-    messages.length,
-    last?.id ?? '',
-    last?.content.length ?? 0,
-    last?.toolCalls?.length ?? 0,
-    reactionsSig,
-  ].join('|');
+  return (
+    messages.length +
+    '|' +
+    (last?.id ?? '') +
+    '|' +
+    (last?.content.length ?? 0) +
+    '|' +
+    (last?.toolCalls?.length ?? 0) +
+    '|' +
+    reactionsSig
+  );
 }
 
 /**