Copilot agent switches to Plan mode and can't switch back

Type: Bug

Switching to the Plan agent is one-way in the chat session. The agent selected Plan while handling an implementation request, then could not switch back to an implementation-capable agent after the user explicitly approved implementation.

Expected: Plan should not be selected for an explicit implementation request, or the user/agent should be able to switch back to an implementation agent without starting a new chat.

Actual: The available switch action supports only switching into Plan. The Plan agent reports it cannot perform edits or implementation, so the active task becomes blocked.

VS Code version: Code 1.129.1 (8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8, 2026-07-17T15:35:09Z)
OS version: Windows_NT x64 10.0.26200
Modes:
Remote OS version: Linux x64 6.8.0-1052-azure

System Info

|Item|Value|
|---|---|
|CPUs|Intel(R) Core(TM) Ultra 9 185H (22 x 3072)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x8086, DEVICE=0x7d55 [Intel(R) Arc(TM) Graphics], DRIVER_VENDOR=Intel, DRIVER_VERSION=32.0.101.8801 *ACTIVE*
GPU1: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875
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)|31.53GB (15.85GB free)|
|Process Argv|--crash-reporter-id 9ebea1eb-8a42-42a4-99de-c1c1e4971529|
|Screen Reader|no|
|VM|0%|

|Item|Value|
|---|---|
|Remote|Codespaces: humble guacamole|
|OS|Linux x64 6.8.0-1052-azure|
|CPUs|AMD EPYC 9V74 80-Core Processor (2 x 0)|
|Memory (System)|7.76GB (3.43GB free)|
|VM|0%|
Extensions (10)

Name|Identifier|Author|Version
---|---|---|---
GitHub Codespaces|github.codespaces|GitHub|1.18.15
Dev Containers|ms-vscode-remote.remote-containers|ms-vscode-remote|0.466.0
Icons – Maintained|yusifaliyevpro.vscicons|yusifaliyevpro|1.2.2
Markdown Preview Mermaid Support|bierner.markdown-mermaid|bierner|1.32.1
markdownlint|davidanson.vscode-markdownlint|DavidAnson|0.61.2
ESLint|dbaeumer.vscode-eslint|dbaeumer|3.0.34
GitHub Codespaces|github.codespaces|GitHub|1.18.15
GitHub Pull Requests|github.vscode-pull-request-github|GitHub|0.158.0
Code Spell Checker|streetsidesoftware.code-spell-checker|streetsidesoftware|4.5.6
Markdown All in One|yzhang.markdown-all-in-one|yzhang|3.6.3

A/B Experiments

```
vsliv368:30146709
pythonvspyt551cf:31249601
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
63221493:31336333
envsactivate1:31551504
478i5457:31544283
cloudbuttont:31379625
3efgi100_wstrepl:31403338
55ia6109:31457054
ec5jj548:31422691
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
test_treatment2:31471001
46204921:31447328
capico_a_098a3278:31551523
idci7584:31464702
e3e4d672:31494082
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
7e187181:31503455
i2gc6536:31499202
52612955:31516516
ghj88844:31499326
h08i8180:31475369
ddid_t:31478206
hmra_i5g22:31518061
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
j0d79568:31499440
jb_cp_cls_t_632:31543129
56dj4588:31512888
32d76977:31512328
ha629193:31508444
cdk-lw-on:31524445
f9bf7985:31543584
a1ije391_t:31540920
g4a0e106:31529594
8hfba999:31537718
jbcp_cls_pctr_t:31531130
61138546:31518536
cp_intellij_t_nes:31548657
jf4hg949:31526829
nes-curr-leftover-1500:31538366
h561g132:31533256
sessions_3:31532893
chatquotatrajectorynudge-enabled:31548767
ihg5j128:31534457
f412h606:31551416
9gg7f176:31542112
allow-none:31553854
fd5dc207:31551400

```