Follow-up to #1878 (merged). While building the Windows desktop
installer locally, `pnpm deploy`'s final temp-dir rename hits `EPERM` on
the orca-managed Windows workspace mount and litters deeply-nested
`deploy_tmp_*` dirs that are painful to remove.
This lets local Windows installer builds redirect the staged production
closure to an external, plain-NTFS path via a new
`FUSION_DESKTOP_DEPLOY_DIR` env var. **CI and the default in-tree
`packages/desktop/deploy` path are unchanged** — the override is opt-in.
Verified locally: with
`FUSION_DESKTOP_DEPLOY_DIR=C:\Users\...\fusion-build\deploy`, `pnpm
--filter @fusion/desktop build` stages the full closure externally
without the EPERM race, and `electron-builder --projectDir <that dir>
--win nsis --x64` produces a signed installer.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Desktop deployment staging can now be configured with an environment
variable, making it easier to customize where build files are prepared.
* **Documentation**
* Added notes about updated desktop deployment behavior on Windows,
including common rename and cleanup issues.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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