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Migration: C# (.NET 10 / WPF) → Rust (GPUI)

Date: 2026-05-14 Status: historical note — written at the start of the C# build retirement. Related: ADR-0022, spec at docs/superpowers/specs/2026-05-14-csharp-build-retirement-design.md.

Why this happened

CodeScope shipped as a .NET 10 / WPF app from v0.1.0 (2026-03) through v0.2.6 (2026-05-08). The Rust port (codescope-rs/) started in session 30 as a learning exercise / cross-platform experiment, was promoted to a 1:1 functional parity port by session 33, and reached daily-driver quality at 0.3.0-rc.5 (session 41).

Three forces pushed the cutover:

  1. Single-developer signal. Recent work was already Rust-only — roughly the last twenty merged PRs (#194 onward) are (rs)-tagged, and the C# tree had not been touched in weeks.
  2. Cross-platform. Velopack feeds now publish for Windows, macOS (arm64 + x64), and Linux x64 from one Rust pipeline. WPF is Windows-only by construction.
  3. Maintenance tax. Two parallel release pipelines (release.yml + rs--release.yml), two build-property layers (Directory.Build.{props,targets} + Cargo workspace), and a parity audit doc (docs/PARITY-AUDIT.md) that needed manual upkeep on every feature touch.

What was kept

  • %APPDATA%\CodeScope\projects.json — same JSON shape, same path. The Rust port reads and writes the C# schema unchanged. Existing session catalogs roll forward across the install switch with no migration step.
  • %LOCALAPPDATA%\CodeScope\layout.json — same shape with one forward-compatible addition: session_placements replaces the legacy open_tabs array (one-shot migration on first load, see ADR-0021).
  • All user-visible flows — sidebar tree, tab strip, split groups, command palette, overview grid, new-worktree dialog, new-project / clone dialog, context menus, idle toasts. Layouts and labels match the C# build line for line.
  • Velopack auto-update infrastructure — same release-feed concept, different channels (win / osx-arm64 / osx-x64 / linux-x64).
  • Keyboard shortcuts — every mapping from the WPF KeyBindings block carried over identically.

What was dropped

  • EasyWindowsTerminalControl (WPF ConPTY host) — replaced by codescope-terminal, a GPUI-native ConPTY/PTY view that shares ANSI parsing with the rest of GPUI's terminal stack.
  • Wpf.Ui theme system + XAML resource dictionaries — replaced by a small Rust theme module (codescope-rs/src/theme.rs) that mirrors the same token names.
  • CommunityToolkit.Mvvm relay-command plumbing — GPUI uses direct view methods + cx.notify(); no MVVM indirection.
  • Directory.Build.{props,targets}, CodeScope.sln, all .csproj — replaced by the Cargo workspace at codescope-rs/Cargo.toml.
  • C# release.yml workflow — replaced by rs--release.yml, later renamed back to release.yml in cutover-3.

Install hand-off

The Rust build ships as codescope-rs-win-Setup.exe (Velopack pack id codescope-rs) through cutover-2. In cutover-3 the pack id is renamed to codescope, which strands the auto-update lineage exactly once: users on the old codescope-rs install need to uninstall and reinstall from the first post-rename release. The %APPDATA%\CodeScope\ data directory is unchanged across that switch.

Where the old code lives

The last commit with the C# source tree intact is tagged legacy/v0.2.6-final on the cutover-1 merge commit. Historical v0.2.X GitHub releases remain published as archive entries; the update_check floor filter keeps them out of the live update path.

Reference timeline

Phase Tag / PR Notes
C# canonical v0.1.0 … v0.2.6 WPF build, single-platform
Rust port begins session 30 learning exercise
Rust port = parity goal session 33 "C# wins on conflict" rule
Rust port = daily driver rs-v0.3.0-rc.5 session 41
Cutover-1 (this PR) legacy/v0.2.6-final tag docs declare Rust canonical
Cutover-2 TBD C# source removed
Cutover-3 TBD tree flattened, pack id renamed