web: FieldCraft in the browser (apps/fieldcraft-web)

The desktop's ModelApp in a web page through eframe's web runner
(WebGPU, WebGL2 fallback, `?webgl` to force it), built with Trunk.
The browser services sit behind the UI's host-service seams: File >
Open uses the browser's file picker, dropped files are read
asynchronously, and both go into the page's files; Save, Save As and
Write Deck hand the written file out as a download. Autosaves go to the
recovery folder as on the desktop and are mirrored to local storage, so
File > Recover offers what a closed or crashed page left. `?sample=NAME`
opens a sample. A loading screen with the app icon, and a message
instead of the app when neither WebGPU nor WebGL2 is available.

`cargo xtask wasm` (and so `cargo xtask ci`) now checks fieldcraft-web
for wasm32 with the library crates. docs/web.md: running it locally,
what works in the browser and what does not.

Part of #119

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

apps/fieldcraft-web/src/main.rs

@@ -0,0 +1,76 @@
+//! FieldCraft in the browser.
+//!
+//! Runs the same [`fieldcraft_ui_egui::ModelApp`] as the desktop app through eframe's web runner
+//! (wgpu: WebGPU where available, WebGL2 otherwise). Build with `trunk build --release` from this
+//! directory (output in `dist/web`); docs/web.md says what works in the browser.
+//!
+//! Differences from the desktop app, all behind the UI's host services:
+//! - files live in the page ([`fieldcraft_io::fs`] keeps them in memory): File › Open and drops
+//!   read the computer's files into it; Save, Save As and Write Deck hand the written file out as
+//!   a download;
+//! - autosaves for recovery are kept in the browser's local storage ([`storage`]);
+//! - no control channel (a page can't listen on a socket);
+//! - background jobs (meshing, solving) run on the page's one thread once the window has shown
+//!   that they run.
+//!
+//! Address flags: `?sample` or `?sample=cantilever` opens a sample, `?webgl` forces WebGL2.
+#![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
+#![forbid(unsafe_code)]
+
+#[cfg(target_arch = "wasm32")]
+mod storage;
+#[cfg(target_arch = "wasm32")]
+mod web;
+
+#[cfg(target_arch = "wasm32")]
+fn main() {
+    web::start();
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn main() {
+    eprintln!("fieldcraft-web only runs in the browser: build it with `trunk build --release` in apps/fieldcraft-web (docs/web.md)");
+}
+
+/// The sample an address asks for (`?sample` opens the first sample, `?sample=NAME` that one).
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+fn sample_in_query(query: &str) -> Option<String> {
+    let first = fieldcraft_engine::sample::SAMPLES.first().map_or("", |s| s.name);
+    query.trim_start_matches('?').split('&').find_map(|kv| {
+        let (key, value) = kv.split_once('=').unwrap_or((kv, ""));
+        (key == "sample").then(|| if value.is_empty() { first } else { value }.to_string())
+    })
+}
+
+/// The name a file from the computer is kept under in the page: its last path part, without
+/// characters a path would read as folders.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+fn safe_name(name: &str) -> String {
+    let last = name.rsplit(['/', '\\']).next().unwrap_or_default();
+    let clean: String = last.chars().filter(|c| !c.is_control()).take(200).collect();
+    if clean.is_empty() || clean == "." || clean == ".." { "file".to_string() } else { clean }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn samples_from_the_address() {
+        assert_eq!(sample_in_query(""), None);
+        assert_eq!(sample_in_query("?sample").as_deref(), Some("parts"));
+        assert_eq!(sample_in_query("?webgl&sample=cantilever").as_deref(), Some("cantilever"));
+        assert_eq!(sample_in_query("?sample=").as_deref(), Some("parts"));
+        assert_eq!(sample_in_query("?samples=x"), None);
+    }
+
+    #[test]
+    fn file_names_stay_in_their_folder() {
+        assert_eq!(safe_name("beam.fieldcraft"), "beam.fieldcraft");
+        assert_eq!(safe_name("../../etc/passwd"), "passwd");
+        assert_eq!(safe_name("C:\\work\\plate.solidcraft"), "plate.solidcraft");
+        assert_eq!(safe_name(".."), "file");
+        assert_eq!(safe_name(""), "file");
+        assert_eq!(safe_name("a\u{0}b.3mf"), "ab.3mf");
+    }
+}