Github Copilot chat session not displaying final response

Type: Bug

For the past few Insider builds, when running either in Plan or Agent mode (Local harness; not agent host or CLI/SDK), the last response that the model sends is generated but not displayed - if I go back to the session list and then back to the chat in question it's displayed so nothing is lost, but it's a very suboptimal user experience.

VS Code version: Code - Insiders 1.129.0-insider (323fd70ed6ce56e05ecaee1b0480850abcb1abfc, 2026-07-13T04:23:53Z)
OS version: Windows_NT x64 10.0.19045
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz (8 x 3408)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x8086, DEVICE=0x1912 [Intel(R) HD Graphics 530], DRIVER_VENDOR=Intel, DRIVER_VERSION=30.0.101.1339 *ACTIVE*
GPU1: VENDOR= 0x8086, DEVICE=0x1912 [Intel(R) HD Graphics 530], DRIVER_VERSION=30.0.101.1339
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.19041.7181
Machine model name:
Machine model version:
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: enabled
multiple_raster_threads: enabled_on
opengl: enabled_on
rasterization: enabled
raw_draw: disabled_off_ok
skia_graphite: disabled_off
trees_in_viz: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgpu: enabled
webnn: disabled_off|
|Load (avg)|undefined|
|Memory (System)|31.88GB (7.14GB free)|
|Process Argv|--crash-reporter-id 58a304ea-fc3e-4cda-bd6d-91d16fd366cd|
|Screen Reader|no|
|VM|0%|
Extensions (10)

Name|Identifier|Author|Version
---|---|---|---
Container Tools|ms-azuretools.vscode-containers|ms-azuretools|2.4.5
C# Dev Kit|ms-dotnettools.csdevkit|ms-dotnettools|3.20.199
C#|ms-dotnettools.csharp|ms-dotnettools|2.140.9
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0
Dev Containers|ms-vscode-remote.remote-containers|ms-vscode-remote|0.465.0
PowerShell|ms-vscode.powershell|ms-vscode|2025.4.0
Chat Customizations Evaluations|ms-vscode.vscode-chat-customizations-evaluations|ms-vscode|1.0.8
AI Engineering Fluency|robbos.ai-engineering-fluency|RobBos|0.13.0
vscode-pdf|tomoki1207.pdf|tomoki1207|1.2.2
Mermaid Preview|vstirbu.vscode-mermaid-preview|vstirbu|2.1.2

A/B Experiments

```
vsliv368:30146709
pythonvspyt551cf:31249598
nativeloc1:31118317
dwcopilot:31158714
dwoutputs:31242946
copilot_t_ci:31333650
g012b348:31231168
pythonrdcb7:31268811
pythonpcpt1cf:31399617
6518g693:31302842
b6b4d950:31327385
6abeh943:31336334
envsactivate1:31349248
editstats-enabled:31346256
cloudbuttont:31366566
3efgi100_wstrepl:31403338
55ia6109:31457054
cp_cls_t_966_ss:31526232
4je02754:31455664
8hhj4413:31478653
ge8j1254_inline_auto_hint_haiku:31490507
38bie571_auto:31478677
cp_cls_c_1081:31454833
conptydll_true:31485575
ia-use-proxy-models-svc:31446143
e9c30283:31453065
test_control1:31471004
c9b86496:31447327
idci7584:31454084
e3e4d672:31454087
ei9d7968:31462942
nes-extended-on:31455475
89g7j272:31506658
7e884298:31462391
7e187181:31482583
i2gc6536:31472020
52612955:31508042
h08i8180_copy:31475366
23c7c724:31520045
ddid_c:31478205
hmra_i5g22:31518061
bjc72774_agent_sandbox:31538428
7df3h592:31491241
cp_cls_t_1082:31535311
logging_enabled_new:31490725
jb_cp_cls_t_632:31543129
b1g4i769:31503653
ha629193:31508444
cdk-lw-on:31524445
f9bf7985:31541111
a1ije391_t:31533808
api_cot_off:31509852
g4a0e106:31510899
41836166:31537719
prpt_lrg:31513637
jbcp_cls_pctr_t:31531130
cp_intellij_t_nes:31548657
gf14b233:31526830
hide-eh-duplicates:31543293
h561g132:31534507
replace-eh-with-ah:31545853
ihg5j128:31534457
f412h606:31543414
max-result-20:31547202
rl_cf215966:31548114
52258b4d:31547953
fbihi617_lg_t:31548132

```