From 8a6af7b25d4edc3418ebab0189745f00b1826a41 Mon Sep 17 00:00:00 2001
From: Alex Southwell <4596216+saphid@users.noreply.github.com>
Date: Tue, 3 Nov 2026 07:46:46 +1100
Subject: [PATCH] fix(server): side chat and merge-back context no longer cut
 an emoji in half

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../src/orchestration-v2/ContextHandoffService.test.ts       | 5 +++--
 apps/server/src/orchestration-v2/ContextHandoffService.ts    | 4 +++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/apps/server/src/orchestration-v2/ContextHandoffService.test.ts b/apps/server/src/orchestration-v2/ContextHandoffService.test.ts
index b5109cb99d930..0282819d81b56 100644
--- a/apps/server/src/orchestration-v2/ContextHandoffService.test.ts
+++ b/apps/server/src/orchestration-v2/ContextHandoffService.test.ts
@@ -169,12 +169,12 @@ it.effect("caps the side chat context block without summarizing discarded parent
       ...importedItem({
         role: index % 2 === 0 ? "user" : "assistant",
         id: `parent-${index}`,
-        text: `item-${index} ${"x".repeat(300)}`,
+        text: `item-${index} ${"x".repeat(228)}😀${"x".repeat(70)}`,
         ordinal: index,
       }),
       get text() {
         summarizedItems++;
-        return `item-${index} ${"x".repeat(300)}`;
+        return `item-${index} ${"x".repeat(228)}😀${"x".repeat(70)}`;
       },
     }));
     const service = yield* ContextHandoffService.ContextHandoffServiceV2;
@@ -197,6 +197,7 @@ it.effect("caps the side chat context block without summarizing discarded parent
     assert.notInclude(context, "item-0 ");
     assert.include(context, "- Assistant: item-59 ");
     assert.isAtMost(context.length, 8_000);
+    assert.isTrue(context.isWellFormed());
     assert.isTrue(
       context.endsWith(
         `Use t3_thread_read on thread ${parentThreadId} to see the main thread's live state.`,
diff --git a/apps/server/src/orchestration-v2/ContextHandoffService.ts b/apps/server/src/orchestration-v2/ContextHandoffService.ts
index 7eef0afefbc17..dcfffa018c8c0 100644
--- a/apps/server/src/orchestration-v2/ContextHandoffService.ts
+++ b/apps/server/src/orchestration-v2/ContextHandoffService.ts
@@ -109,7 +109,9 @@ function compactText(text: string, maxLength = 240): string {
   if (compacted.length <= maxLength) {
     return compacted;
   }
-  return `${compacted.slice(0, maxLength - 3)}...`;
+  const end = maxLength - 3;
+  const last = compacted.charCodeAt(end - 1);
+  return `${compacted.slice(0, last >= 0xd800 && last <= 0xdbff ? end - 1 : end)}...`;
 }
 
 export function visibleDeltaRunOrdinals(