From d79b4146b242007c7bcb8d9cad2b34e72307b30e Mon Sep 17 00:00:00 2001
From: spoukyii <61633921+spoukyii@users.noreply.github.com>
Date: Tue, 3 Nov 2026 12:41:49 -0800
Subject: [PATCH 1/2] test(client-runtime): expect a subagent preview cut at an
 emoji to keep no half of it

---
 packages/client-runtime/src/state/subagentDisplay.test.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/client-runtime/src/state/subagentDisplay.test.ts b/packages/client-runtime/src/state/subagentDisplay.test.ts
index 5bdd434388ec6..9b1536a7aacb1 100644
--- a/packages/client-runtime/src/state/subagentDisplay.test.ts
+++ b/packages/client-runtime/src/state/subagentDisplay.test.ts
@@ -36,6 +36,6 @@ it("normalizes Unicode whitespace and ignores a large hidden suffix", () => {
     subagentDetailPreview({ status: "running", progress: "\uFEFF\u2029", result: " Done " }),
   ).toBe("Done");
   expect(subagentDetailPreview({ status: "failed", result: "x".repeat(279) + "😀" })).toBe(
-    "x".repeat(279) + "\uD83D…",
+    "x".repeat(279) + "…",
   );
 });

From adf15a992b86fc7d9ecd9c2187305986dae0b9aa Mon Sep 17 00:00:00 2001
From: spoukyii <61633921+spoukyii@users.noreply.github.com>
Date: Tue, 3 Nov 2026 12:42:06 -0800
Subject: [PATCH 2/2] fix(client-runtime): subagent previews no longer end in a
 broken character
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

A subagent's progress or result preview is cut at 280 UTF-16 code units
with "…" added. When an emoji straddled the cut, the preview kept only its
high surrogate and showed a replacement character before the "…". The
web subagent hover cards show the end of that preview.

The cut now steps back one unit when it would land between a high and a
low surrogate, the same check #29158 added to context chip labels and
#29563 added to thread titles. The existing test had pinned the split
half; it now expects the emoji dropped whole.

Bug: a subagent preview ends in a broken character when an emoji sits at the 280-unit cut
---
 packages/client-runtime/src/state/subagentDisplay.ts | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/packages/client-runtime/src/state/subagentDisplay.ts b/packages/client-runtime/src/state/subagentDisplay.ts
index 124c45e264f79..5f1a65fb8a22e 100644
--- a/packages/client-runtime/src/state/subagentDisplay.ts
+++ b/packages/client-runtime/src/state/subagentDisplay.ts
@@ -132,7 +132,15 @@ export function subagentDetailPreview(input: {
       if (compact.length > 0) compact += " ";
     }
     compact += detail[index];
-    if (compact.length > 280) return `${compact.slice(0, 280).trimEnd()}…`;
+    if (compact.length > 280) {
+      let end = 280;
+      const previous = compact.charCodeAt(end - 1);
+      const next = compact.charCodeAt(end);
+      if (previous >= 0xd800 && previous <= 0xdbff && next >= 0xdc00 && next <= 0xdfff) {
+        end -= 1;
+      }
+      return `${compact.slice(0, end).trimEnd()}…`;
+    }
   }
   return compact || null;
 }