Changes panel does not update after history rewrites

### Description

The Agents window "Changes" panel anchors to session-start HEAD and doesn't re-anchor after git rebase, git reset, filter-branch, or any other history rewrite on the current branch. For any workflow that involves squashing/rebasing/amending during a review cycle — which is most PR workflows — this makes the Changes view show a phantom diff that no longer matches reality. Please either (a) re-anchor to the current merge-base with the branch's upstream (or a configurable base ref), (b) detect history rewrites and re-anchor automatically, or (c) expose a "reset baseline to current HEAD's upstream" command so users can force a refresh without abandoning conversation context.

### Issue Details

Item|Value
---|---
Issue Category|Bug
Target|Agents Window
VS Code Version|Code 1.128.0 (fc3def6774c76082adf699d366f31a557ce5573f, 2026-07-07T15:14:24-07:00)
OS Version|Windows_NT x64 10.0.26200

System Info

Item|Value
---|---
VS Code Version|Code 1.128.0 (fc3def6774c76082adf699d366f31a557ce5573f, 2026-07-07T15:14:24-07:00)
OS Version|Windows_NT x64 10.0.26200
CPUs|AMD EPYC 7763 64-Core Processor (16 x 2445)
GPU Status|2d_canvas: unavailable_software
GPU0: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VENDOR=Microsoft, DRIVER_VERSION=10.0.26100.8521 *ACTIVE*
GPU1: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8521
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8521
Machine model name:
Machine model version:
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: disabled_software
multiple_raster_threads: enabled_on
opengl: disabled_off
rasterization: disabled_software
raw_draw: disabled_off_ok
skia_graphite: disabled_off
trees_in_viz: disabled_off
video_decode: disabled_software
video_encode: disabled_software
webgl: unavailable_software
webgpu: unavailable_software
webnn: unavailable_software
Load (avg)|
Memory (System)|63.95GB (36.64GB free)
Process Argv|. --crash-reporter-id 10d3483e-764f-48db-aa21-f4bfe1fbfaec
Screen Reader|no
VM|0%
User Agent|Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Code/1.128.0 Chrome/148.0.7778.271 Electron/42.5.0 Safari/537.36
Installation pure|true

Extensions (48)

Name|Identifier|Author|Version
---|---|---|---
CLI Timeline|ayushagg31.cli-timeline|ayushagg31|0.4.0
GitHub Markdown Preview|bierner.github-markdown-preview|bierner|0.4.0
Markdown Checkboxes|bierner.markdown-checkbox|bierner|0.4.0
Markdown Emoji|bierner.markdown-emoji|bierner|0.3.1
Markdown Footnotes|bierner.markdown-footnotes|bierner|0.1.1
Markdown Preview Mermaid Support|bierner.markdown-mermaid|bierner|1.32.1
Markdown Preview Github Styling|bierner.markdown-preview-github-styles|bierner|2.2.0
Markdown yaml Preamble|bierner.markdown-yaml-preamble|bierner|0.1.1
markdownlint|davidanson.vscode-markdownlint|DavidAnson|0.61.2
HTML CSS Support|ecmel.vscode-html-css|ecmel|2.0.14
GitHub Pull Requests|github.vscode-pull-request-github|GitHub|0.156.0
Azure Load Testing|ms-azure-load-testing.microsoft-testing|ms-azure-load-testing|0.2.0
Azure Developer CLI|ms-azuretools.azure-dev|ms-azuretools|0.10.0
GitHub Copilot for Azure|ms-azuretools.vscode-azure-github-copilot|ms-azuretools|1.0.209
Azure MCP Server|ms-azuretools.vscode-azure-mcp-server|ms-azuretools|2.0.45
Azure App Service|ms-azuretools.vscode-azureappservice|ms-azuretools|0.27.0
Azure Container Apps|ms-azuretools.vscode-azurecontainerapps|ms-azuretools|0.11.2
Azure Functions|ms-azuretools.vscode-azurefunctions|ms-azuretools|1.22.0
Azure Resources|ms-azuretools.vscode-azureresourcegroups|ms-azuretools|0.12.7
Azure Static Web Apps|ms-azuretools.vscode-azurestaticwebapps|ms-azuretools|0.13.3
Azure Storage|ms-azuretools.vscode-azurestorage|ms-azuretools|0.17.2
Azure Virtual Machines|ms-azuretools.vscode-azurevirtualmachines|ms-azuretools|0.6.11
Container Tools|ms-azuretools.vscode-containers|ms-azuretools|2.4.5
Azure Cosmos DB|ms-azuretools.vscode-cosmosdb|ms-azuretools|0.34.0
Docker|ms-azuretools.vscode-docker|ms-azuretools|2.0.0
C# Dev Kit|ms-dotnettools.csdevkit|ms-dotnettools|3.10.14
C#|ms-dotnettools.csharp|ms-dotnettools|2.140.9
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0
Python Debugger|ms-python.debugpy|ms-python|2026.6.0
Python|ms-python.python|ms-python|2026.4.0
Pylance|ms-python.vscode-pylance|ms-python|2026.2.1
Python Environments|ms-python.vscode-python-envs|ms-python|1.36.0
Dev Containers|ms-vscode-remote.remote-containers|ms-vscode-remote|0.463.0
CMake Tools|ms-vscode.cmake-tools|ms-vscode|1.23.52
C/C++ DevTools|ms-vscode.cpp-devtools|ms-vscode|0.5.13
C/C++|ms-vscode.cpptools|ms-vscode|1.32.2
C/C++ Extension Pack|ms-vscode.cpptools-extension-pack|ms-vscode|1.5.1
PowerShell|ms-vscode.powershell|ms-vscode|2025.4.0
Remote Explorer|ms-vscode.remote-explorer|ms-vscode|0.5.0
Remote - Tunnels|ms-vscode.remote-server|ms-vscode|1.5.3
Azure Tools|ms-vscode.vscode-node-azure-pack|ms-vscode|1.8.2
Foundry Toolkit for VS Code|ms-windows-ai-studio.windows-ai-studio|ms-windows-ai-studio|1.6.3
YAML|redhat.vscode-yaml|redhat|1.23.0
Code Spell Checker|streetsidesoftware.code-spell-checker|streetsidesoftware|4.5.6
Microsoft Foundry|teamsdevapp.vscode-ai-foundry|TeamsDevApp|1.2.4
CMake|twxs.cmake|twxs|0.0.17
vscode-icons|vscode-icons-team.vscode-icons|vscode-icons-team|12.19.0
Markdown All in One|yzhang.markdown-all-in-one|yzhang|3.6.3

Theme extensions: 10

A/B Experiments

```
vsliv368:30146709
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
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ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
ia-use-proxy-models-svc:31452481
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test_treatment2:31471001
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capi_a_098a3278:31544979
idci7584:31464702
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logging_enabled_new:31498466
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cdk-lw-on:31524445
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prpt_ctrl:31518467
jbcp_cls_pctr_t:31531130
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cp_intellij_t_nes:31533504
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sessions_3:31532893
ihg5j128:31534457
f412h606:31546039
9gg7f176:31542112
nes-nc-lc-2k:31546583
```