Frequently claims it's in Plan mode when it's actually in Agents mode

### Description

Often (especially with GPT models) it will tell me that it's a plan agent and read-only, btu when the agent is *actually* set to Agent mode. Toggling between modes doesn't fix it; I have to launch new sessons.

Example from just after the screenshot:

"You’re right: the VS Code UI is in Agent mode. The internal conversation role got stuck in the Plan sub-agent after I invoked it, so my repeated instruction was wrong and unhelpful. I’m persisting the approved plan into repository memory now so a fresh Agent session can pick it up without losing any of the investigation.

You’re right. The UI is in Agent mode; this conversation’s backend got stuck in the Plan sub-agent after my internal switch. That mismatch is on me.

I preserved the approved implementation handoff in repository memory at /memories/repo/anvil-active-implementation.md. Start a fresh Agent chat with:

Implement /memories/repo/anvil-active-implementation.md. Begin with the emergency history repair, then #217/#219. Continue through PR, merge, deploy, and verification.

The new Agent session will retain the root causes, architecture decisions, delivery order, and guardrails without repeating this investigation."

### Issue Details

Item|Value
---|---
Issue Category|Bug
Target|Agents Window
VS Code Version|Code 1.129.1 (8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8, 2026-07-17T15:35:09Z)
OS Version|Windows_NT arm64 10.0.26220

System Info

Item|Value
---|---
VS Code Version|Code 1.129.1 (8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8, 2026-07-17T15:35:09Z)
OS Version|Windows_NT arm64 10.0.26220
CPUs|Snapdragon(R) X 12-core X1E80100 @ 3.40 GHz (12 x 2976)
GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x4d4f4351, DEVICE=0x36334330 [Qualcomm(R) Adreno(TM) X1-85 GPU], DRIVER_VENDOR=Qualcomm, DRIVER_VERSION=31.0.133.1 *ACTIVE*
GPU1: VENDOR= 0x4d4f4351, DEVICE=0x36334330 [Qualcomm(R) Adreno(TM) X1-85 GPU], DRIVER_VERSION=31.0.133.1
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8925
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)|
Memory (System)|63.49GB (28.09GB free)
Process Argv|--crash-reporter-id 9d70e1f1-573d-4da5-8ef2-c7e764e83ab3
Screen Reader|no
VM|0%
User Agent|Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Code/1.129.1 Chrome/148.0.7778.280 Electron/42.6.0 Safari/537.36
Installation pure|true

Extensions (7)

Name|Identifier|Author|Version
---|---|---|---
GitCredScan LM Proxy|dolpheuslabs.gitcredscan-lm-proxy|dolpheuslabs|0.1.0
Agency|microsoft.agency|Microsoft|1.0.260515001
Container Tools|ms-azuretools.vscode-containers|ms-azuretools|2.4.5
Kubernetes|ms-kubernetes-tools.vscode-kubernetes-tools|ms-kubernetes-tools|1.4.0
Dev Containers|ms-vscode-remote.remote-containers|ms-vscode-remote|0.466.0
Akusto Explorer|ms-vscode.kusto-client|ms-vscode|0.5.2026061601
YAML|redhat.vscode-yaml|redhat|1.24.0

Theme extensions: 9

A/B Experiments

```
vsliv368cf:30146710
pythonvspyt551cf:31249601
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
6abeh943:31336334
envsactivate1:31551504
editstats-enabled:31346257
478i5457:31544283
cloudbuttont:31379625
3efgi100_wstrepl:31403338
ec5jj548:31422691
gpt-5-copilot-3x-baseline:31552123
metis_rerank_treatment1:31422731
cp_cls_t_966_ss:31526232
4je02754:31466945
8hhj4413:31478653
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
core-renderer-profiling-on:31440367
e9c30283:31461165
test_treatment2:31471001
c9b86496:31447327
control_6dc23131:31551522
idci7584:31464702
e3e4d672:31494082
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
7e187181:31503455
i2gc6536:31499202
52612955:31516516
ghj88844:31499326
ddid_t:31478206
hmra_i5g22:-9
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
j0d79568:31499440
jb_cp_cls_t_632:31543129
852d2892:31506239
56dj4588:31512888
32d76977:31512328
ha629193:31508444
cdk-lw-on:31524445
f9bf7985:31543584
jh5f2457_c:31540921
g4a0e106:31529594
8hfba999:31537718
jbcp_cls_pctr_t:31531130
61138546:31518536
3f904173:31522231
cp_intellij_t_nes:31548657
jf4hg949:31526829
nes-curr-leftover-1500:31538366
8hjh2968:31552050
h561g132:31533256
session_8:31532895
ihg5j128:31534457
f412h606:31551416
7g2b5551:31542111
max-result-200:31551155
allow-none:31553854
6i51c363:31551401
```

### Attachments