[BUG] edit_notebook_file tool silent failure on .ipynb files

Type: Bug

The edit_notebook_file deferred tool is non-functional. It accepts edits, claims success, but silently discards all changes without writing to the .ipynb file. Meanwhile, identical operations on .py files work perfectly with replace_string_in_file, proving the file system and permissions are fine. This is a critical tool defect.

VS Code version: Code 1.136.1 (a44adf7f53e00964ab890f9f8758a334f1fc15bc, 2026-09-03T05:06:41Z)
OS version: Windows_NT x64 10.0.26200
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|12th Gen Intel(R) Core(TM) i7-12700H (20 x 2688)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x8086, DEVICE=0x46a6 [Intel(R) Iris(R) Xe Graphics], DRIVER_VENDOR=Intel, DRIVER_VERSION=31.0.101.3358 *ACTIVE*
GPU1: VENDOR= 0x10de, DEVICE=0x2420 [NVIDIA GeForce RTX 3080 Ti Laptop GPU], DRIVER_VERSION=31.0.15.2756
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8972
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)|63.71GB (45.88GB free)|
|Process Argv|--crash-reporter-id 968a9306-905b-4d25-b0e2-e1f9de5ed6d0|
|Screen Reader|no|
|VM|0%|
Extensions (45)

Name|Identifier|Author|Version
---|---|---|---
Path Intellisense|christian-kohler.path-intellisense|christian-kohler|2.10.0
Office Viewer|cweijan.vscode-office|cweijan|4.2.0
Git History|donjayamanne.githistory|donjayamanne|0.6.20
Python Environment Manager (deprecated)|donjayamanne.python-environment-manager|donjayamanne|1.2.7
Python Extension Pack|donjayamanne.python-extension-pack|donjayamanne|1.7.0
GitLens — Git supercharged|eamodio.gitlens|eamodio|16.0.4
EditorConfig for VS Code|editorconfig.editorconfig|EditorConfig|0.16.4
Prettier - Code formatter|esbenp.prettier-vscode|esbenp|11.0.0
Debugger for Firefox|firefox-devtools.vscode-firefox-debug|firefox-devtools|2.9.11
GitHub Codespaces|github.codespaces|GitHub|1.17.3
GitHub Repositories|github.remotehub|GitHub|0.64.0
Draw.io Integration|hediet.vscode-drawio|hediet|1.6.6
Output Colorizer|ibm.output-colorizer|IBM|0.1.2
LaTeX Workshop|james-yu.latex-workshop|James-Yu|10.6.1
Python Indent|kevinrose.vsc-python-indent|KevinRose|1.21.0
MATLAB|mathworks.language-matlab|MathWorks|1.3.8
Rainbow CSV|mechatroner.rainbow-csv|mechatroner|3.13.0
Git Graph|mhutchie.git-graph|mhutchie|1.30.0
Microsoft Edge Tools for VS Code|ms-edgedevtools.vscode-edge-devtools|ms-edgedevtools|2.1.6
Python Debugger|ms-python.debugpy|ms-python|2025.4.1
Python|ms-python.python|ms-python|2025.16.0
Pylance|ms-python.vscode-pylance|ms-python|2025.3.2
Python Environments|ms-python.vscode-python-envs|ms-python|1.36.0
Jupyter|ms-toolsai.jupyter|ms-toolsai|2025.9.1
Jupyter Keymap|ms-toolsai.jupyter-keymap|ms-toolsai|1.1.2
Jupyter Notebook Renderers|ms-toolsai.jupyter-renderers|ms-toolsai|1.3.0
Jupyter Cell Tags|ms-toolsai.vscode-jupyter-cell-tags|ms-toolsai|0.1.9
Jupyter Slide Show|ms-toolsai.vscode-jupyter-slideshow|ms-toolsai|0.1.6
Remote - SSH|ms-vscode-remote.remote-ssh|ms-vscode-remote|0.119.0
Remote - SSH: Editing Configuration Files|ms-vscode-remote.remote-ssh-edit|ms-vscode-remote|0.87.0
WSL|ms-vscode-remote.remote-wsl|ms-vscode-remote|0.88.0
C/C++|ms-vscode.cpptools|ms-vscode|1.22.11
Hex Editor|ms-vscode.hexeditor|ms-vscode|1.11.1
PowerShell|ms-vscode.powershell|ms-vscode|2024.4.0
Remote Explorer|ms-vscode.remote-explorer|ms-vscode|0.4.3
Remote Repositories|ms-vscode.remote-repositories|ms-vscode|0.42.0
VS Code Speech|ms-vscode.vscode-speech|ms-vscode|0.12.1
Live Share|ms-vsliveshare.vsliveshare|ms-vsliveshare|1.0.5941
autoDocstring - Python Docstring Generator|njpwerner.autodocstring|njpwerner|0.6.1
Codex – OpenAI’s coding agent|openai.chatgpt|openai|26.901.22334
Optuna Dashboard|optuna.optuna-dashboard|Optuna|0.3.0
Live Server|ritwickdey.liveserver|ritwickdey|5.7.9
Code Spell Checker|streetsidesoftware.code-spell-checker|streetsidesoftware|4.0.45
vscode-pdf|tomoki1207.pdf|tomoki1207|1.2.2
Markdown All in One|yzhang.markdown-all-in-one|yzhang|3.6.2

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
envsactivate1:31551504
cloudbuttont:31379625
3efgi100_wstrepl:31403338
839jf696:31457053
ec5jj548:31422691
diffpatch-lysithea-24-production:31578711
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
46204921:31447328
ei9d7968:31496641
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
ddid_t:31478206
hmra_i5g22:31518061
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
db5d2638:31499441
jb_cp_cls_t_632:31543129
748c7209:31512887
32d76977:31512328
ha629193:31508444
a1ije391_t:31540920
jbcp_cls_pctr_t:31531130
cp_intellij_t_nes:31548657
jf4hg949:31526829
ahp-both-windows:31556933
ihg5j128:31534457
9gg7f176:31542112
enable_editor_pane_layout:31569726
allow-none:31555437
36h42362:31564511
c7c27ce7:31554789
1h923230:31564177
1532g621_copy:31554320
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0d8dfbc3:31570291
switchtoauto:31559321
maidictation:31565333
0c1h4866:31566224
vrbsty_fls:31561059
session-mark-done:31558131
5b8j3302:31564601
mangle-name-control:31572633
39a5d156:31574986
2bfb8b39:31576696
permission_prompt_control:1332567
ccr_pr_nudge_adoption:1319471
vsc_wsm_t:1340632
eh853263:1370294
auto_mode_treatment:1367907

```