[Feature]: Support an install directory outside %LOCALAPPDATA% on Windows

[alex-glez-felix]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

Build, CI, or release tooling

Problem or use case

Managed corporate Windows machines commonly exclude a dedicated volume from real-time scanning so dev tooling is usable, and scan the system volume aggressively. Given the file count in #5876 — 14,687 files written at install, each a separate open/stat/scan on a cold start — the install location matters for startup cost on these machines.

T3 Code cannot target that volume. createBuildConfig in scripts/build-desktop-artifact.ts sets no nsis block, so electron-builder applies oneClick: true and allowToChangeInstallationDirectory: false, fixing the install to %LOCALAPPDATA%\Programs\....

Proposed solution

apps/desktop/resources/installer.nsh — auto-detected via getResource(this.options.include, "installer.nsh") in NsisTarget.ts, so no change to build-desktop-artifact.ts and no new config key:

!macro preInit
  ReadEnvStr $0 "T3CODE_INSTALL_DIR"
  ${if} $0 != ""
    SetRegView 64
    WriteRegExpandStr HKCU "${INSTALL_REGISTRY_KEY}" InstallLocation "$0"
    SetRegView 32
    WriteRegExpandStr HKCU "${INSTALL_REGISTRY_KEY}" InstallLocation "$0"
  ${endif}
!macroend

preInit runs at the top of .onInit, before multiUser.nsh reads InstallLocation to pick $INSTDIR. Unset variable means today's behavior, unchanged.

Why this matters

Unblocks installs on machines where the system volume is scanned and a dev volume is not.

Smallest useful scope

The macro above, HKCU only. No installer UI, no nsis config block.

Alternatives considered

• Pre-seeding InstallLocation manually. Works per electron-builder's docs, but requires computing UUIDv5(appId, 50e065bc-3134-11e6-9bab-38c9862bdaf3) and a manual registry edit — not something to ask of users on a managed machine.
• oneClick: false + allowToChangeInstallationDirectory: true. Adds installer pages for every user.
• A junction from %LOCALAPPDATA%. Exclusions match the accessed path, so the I/O is still scanned.

Risks or tradeoffs

Takes effect on install only, not on an existing one. Per-user path only; an elevated per-machine installer would not inherit the user environment. Needs a line in the Windows install docs to be discoverable.

Examples or references

• electron-builder NSIS docs, "How do I change the default installation directory?" — https://www.electron.build/docs/nsis/
• templates/nsis/multiUser.nsh — reads InstallLocation, falls back to $LocalAppData\Programs
• templates/nsis/include/installer.nsh — rewrites it each install, so the override persists across updates
• Related: [Bug]: Windows installer writes 14,687 files to ship 20 native binaries, costing install time and ~6s of cold start #5876, perf(windows): reduce first-start editor discovery time #6124

Contribution

• I would be open to helping implement this.