Native Windows port: Direct2D/DirectWrite rendering over ConPTY

[ucsandman]

Summary

This PR adds a complete native Windows port of Zentty as a self-contained Rust workspace under rust/ — no Electron, no web views. It brings the core Zentty experience to Windows: worklanes, panes with splits, a sidebar with live agent-status pills, the command palette, global search, and theming.

Nothing outside rust/ is touched except: a "Windows" section in the README, a short "Windows port" note in AGENTS.md, and two .gitignore entries (rust/target/, rust/dist/). The macOS app is unaffected.

Architecture

Four crates, with the platform-agnostic logic kept separate so it stays reusable:

Crate	Role
zentty-core	Worklanes, panes, layout, command palette, themes, task runner, agent-IPC protocol, session restore
zentty-terminal	Screen model, selection, search, clipboard, clean-copy pipeline
zentty-pty	ConPTY pseudo-console sessions, output streaming, shell-exit detection
zentty-win	Win32 shell: DXGI flip-model swapchain + ID2D1DeviceContext rendering, DirectWrite text, all UI chrome

Notable Windows-specific engineering:

• Rendering: flip-model swapchain (plain ID2D1HwndRenderTarget never composites under DWM), grayscale text AA, per-monitor DPI scaling of fonts and chrome, device-loss recovery (D2DERR_RECREATE_TARGET, device-removed, resize failures) with HARDWARE→WARP fallback.
• Terminal: measured DirectWrite cell metrics drive PTY sizing and pixel-accurate selection hit-testing; cursor blinks at the system caret rate (respects reduced-motion); window title follows OSC titles; bell flashes the taskbar.
• Robustness: a pane closes itself when its shell exits (last pane closes the window); PTY spawn failures surface a MessageBox at startup and degrade gracefully in-session; ellipsis trimming on all chrome text; WCAG AA contrast on status pills.
• Packaging: multi-resolution icon embedded via winresource, GUI subsystem with a MessageBox fatal-error fallback, rust/scripts/package-windows.ps1 produces a portable zip with per-user install/uninstall scripts (Start-menu shortcut, no admin); the cargo-wix MSI route is documented in the README.

Testing

From rust/ on Windows (Rust MSVC toolchain + Windows 10/11 SDK):

cargo build --release --workspace
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace

All green at time of submission: 549 tests passing, clippy clean with -D warnings. The suite covers the logic crates plus the Win32 shell (input encoding, layout/metrics, agent-IPC named-pipe transport, ConPTY exit detection, desktop session behavior).

Run it: .\target\release\zentty-win-desktop.exe — Ctrl+Shift+P opens the palette, Ctrl+D splits. Full keyboard map is in the README's Windows section.

Known limitations

• ConPTY repaints the viewport differentially and never feeds scrollback, so the scrollback model is implemented and tested but stays empty in live sessions (documented in code).
• The zip package is unsigned; MSI/signing steps are documented but require the WiX toolset and a certificate.

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