[gh-aw] Protected Files: fix: guard MultiDiffEditorWidget.setViewModel against disposed instantiation service (fixes #324551)

> [!WARNING]
> **Protected Files**
>
> The push to pull request branch was blocked because the patch modifies protected files.
>
> **Target Pull Request:** [#324555](https://github.com/microsoft/vscode/pull/324555)
>
> **Please review the changes carefully** before pushing them to the pull request branch. These files may affect project dependencies, CI/CD pipelines, or agent behaviour.
>
>
> Protected files
>
> - `package-lock.json`
- `package.json`
- `AGENTS.md`
- `README.md`
- [.github/skills/sessions/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/sessions/SKILL.md)
- [.github/instructions/design-tokens.instructions.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/instructions/design-tokens.instructions.md)
- [.github/skills/ux-css-layout/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/ux-css-layout/SKILL.md)
- [.github/skills/ux-theming/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/ux-theming/SKILL.md)
- [.github/instructions/committing.instructions.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/instructions/committing.instructions.md)
- [.vscode/tasks.json](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.vscode/tasks.json)
- [.github/CODENOTIFY](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/CODENOTIFY)
- [.github/skills/agent-host-e2e-tests/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/agent-host-e2e-tests/SKILL.md)
- [.github/skills/symbolicate-crash-dump/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/symbolicate-crash-dump/SKILL.md)
- [.github/skills/agent-host-logs/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/agent-host-logs/SKILL.md)
- [.github/skills/agent-host-logs/scripts/extract.py](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/agent-host-logs/scripts/extract.py)
- [.github/skills/code-oss-logs/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/code-oss-logs/SKILL.md)
- [.github/copilot-instructions.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/copilot-instructions.md)
- [.github/instructions/design-philosophy.instructions.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/instructions/design-philosophy.instructions.md)
- [.github/skills/design-philosophy/SKILL.md](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/skills/design-philosophy/SKILL.md)
- [.github/workflows/pr.yml](https://github.com/microsoft/vscode/blob/fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41/.github/workflows/pr.yml)
>
>

---

Apply the patch after review

The patch is available in the workflow run artifacts:

**Workflow Run:** [View run details and download patch artifact](https://github.com/microsoft/vscode-engineering/actions/runs/29129368279)

```sh
# Download the artifact from the workflow run
gh run download 29129368279 -n agent -D /tmp/agent-29129368279

# Apply the patch to the pull request branch
git fetch origin fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41
git checkout fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41
git am --3way /tmp/agent-29129368279/aw-microsoft-vscode-fix-multidiff-setviewmodel-disposed-324551-5c413627c75acb41.patch
git push origin fix/multidiff-setviewmodel-disposed-324551-5c413627c75acb41
```

To route changes like this to a review issue instead of blocking, configure `protected-files: fallback-to-issue` in your workflow configuration.