[hamishmack]

Summary

Three small changes needed to embed jsaddle in native front ends (a
GTK4/WebKitGTK 6.0 app on Linux and a WebView2 app on Windows). No behaviour
changes on existing platforms.

jsaddle-terminal: build the library on Windows (pure modules only)

The whole package was buildable: False on Windows because the tunnel runner
(Language.Javascript.JSaddle.Terminal) needs raw-mode stdin/termios, which is
POSIX-only. But the framing (.Terminal.Protocol) and the iframe bootstrap JS
(.Terminal.Bootstrap) are pure and build everywhere.

IDE-side consumers only import those two modules, so the library now exposes
them unconditionally and gates just the runner module — plus its deps — behind
if !os(windows). This lets an embedder link jsaddle-terminal on Windows.

The runner's deps (aeson, jsaddle-warp, stm, text, unix, warp,
websockets) move under the same guard. This also drops jsaddle-warp from
the Windows build, which matters because jsaddle-warp caps aeson < 2.3 and
would otherwise constrain the whole plan.

jsaddle-webview2: expose the host window's HWND

Adds wv2GetHwnd (C) / webView2Hwnd :: WebView2 -> IO (Ptr ()) (Haskell) so
the embedding application can reach the Win32 HWND of the window hosting the
WebView2 and do native window integration — install a menu bar, run file
dialogs, etc. Only meaningful once the run' callback has been entered (the
HWND exists by then).

Testing

• jsaddle-terminal library builds on the Windows cross (ucrt64) and unchanged
  on POSIX.
• jsaddle-webview2 builds; webView2Hwnd returns the shim's HWND at runtime.
• Both are consumed by leksah's new leksah-webkitgtk and leksah-webview2
  front ends (Linux native + Windows cross), which build via haskell.nix.

[Copilot]

Pull request overview

This PR adds small integration-oriented features to support embedding jsaddle in native front ends: it makes jsaddle-terminal’s pure library modules build on Windows, and exposes the host window HWND from jsaddle-webview2 for Win32-native integration.

Changes:

• jsaddle-terminal: expose only Terminal.Protocol + Terminal.Bootstrap on Windows while gating the POSIX-only runner module (and its deps) behind if !os(windows).
• jsaddle-webview2: add a new webView2Hwnd Haskell API backed by a C shim function wv2GetHwnd returning the host window handle.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
jsaddle-webview2/src/Language/Javascript/JSaddle/WebView2.hs	Exports webView2Hwnd :: WebView2 -> IO (Ptr ()) via FFI to surface the hosting window’s HWND.
jsaddle-webview2/cbits/WebView2Shim.c	Implements wv2GetHwnd returning app->hwnd for the Haskell binding.
jsaddle-terminal/jsaddle-terminal.cabal	Makes the library buildable on Windows by exposing only pure modules and conditionally including the POSIX runner + deps on non-Windows.

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