build(web): restore the wasm build — gate native-only deps off wasm

The web build had bit-rotted: native-only features added since it last
compiled pulled crates that don't build for wasm32-unknown-unknown.

- printpdf (PDF export / printing) → native-only target; the web build gets
  stub export_pdf / print_wires. It pulls a wasm-incompatible memchr 1.0.2
  via lopdf → nom_locate, and the web has no filesystem.
- getrandom 0.3 (via ahash via acadrust) → enable its wasm_js feature and add
  the matching --cfg getrandom_backend rustflag in .cargo/config.toml.
- ocs_plugin_api "host" feature (out-of-process plugin runtime: interprocess,
  libloading, memmap2, rkyv) → native-only target; the web gets the
  dependency-free manifest/ribbon contract. The host code was already
  wasm-gated; only the Cargo wiring pulled it in unconditionally.

`trunk build --release` succeeds again.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/io/pdf_export.rs

@@ -9,15 +9,43 @@
 // drawing origin at the paper origin.
 
 use crate::io::plot_style::PlotStyleTable;
-use crate::scene::model::hatch_model::{HatchModel, HatchPattern};
+use crate::scene::model::hatch_model::HatchModel;
+#[cfg(not(target_arch = "wasm32"))]
+use crate::scene::model::hatch_model::HatchPattern;
 use crate::scene::WireModel;
+#[cfg(not(target_arch = "wasm32"))]
 use printpdf::{
     Color, Line, LineCapStyle, LineJoinStyle, LinePoint, Mm, Op, PaintMode, PdfDocument, PdfPage,
     PdfSaveOptions, Point, Polygon, PolygonRing, Pt, Rgb, WindingOrder,
 };
+#[cfg(not(target_arch = "wasm32"))]
 use std::io::Write;
 use std::path::Path;
 
+// The web build has no `printpdf` (it pulls a wasm-incompatible `memchr` via
+// lopdf → nom_locate) and no filesystem, so PDF export is native-only; the web
+// build gets these stubs so the call sites still compile.
+#[cfg(target_arch = "wasm32")]
+pub fn export_pdf(
+    _wires: &[WireModel],
+    _hatches: &[HatchModel],
+    _wipeouts: &[HatchModel],
+    _paper_w: f64,
+    _paper_h: f64,
+    _offset_x: f32,
+    _offset_y: f32,
+    _rotation_deg: i32,
+    _path: &Path,
+    _plot_style: Option<&PlotStyleTable>,
+) -> Result<(), String> {
+    Err("PDF export is not available in the web version.".into())
+}
+
+#[cfg(target_arch = "wasm32")]
+pub async fn pick_pdf_path_owned(_stem: String) -> Option<std::path::PathBuf> {
+    None
+}
+
 // ── Public entry point ────────────────────────────────────────────────────
 
 /// Export `wires` to a PDF file.
@@ -26,6 +54,7 @@ use std::path::Path;
 /// - `offset_x` / `offset_y`: added to every wire coordinate so the drawing
 ///   origin maps to the bottom-left corner of the page.
 /// - `rotation_deg`: 0 | 90 | 180 | 270 — rotates the entire drawing on the page.
+#[cfg(not(target_arch = "wasm32"))]
 pub fn export_pdf(
     wires: &[WireModel],
     hatches: &[HatchModel],
@@ -54,6 +83,7 @@ pub fn export_pdf(
 }
 
 /// Show a PDF save-file dialog and return the chosen path (or None if cancelled).
+#[cfg(not(target_arch = "wasm32"))]
 pub async fn pick_pdf_path_owned(stem: String) -> Option<std::path::PathBuf> {
     rfd::AsyncFileDialog::new()
         .set_title("Export as PDF")
@@ -67,6 +97,7 @@ pub async fn pick_pdf_path_owned(stem: String) -> Option<std::path::PathBuf> {
 
 // ── PDF builder ───────────────────────────────────────────────────────────
 
+#[cfg(not(target_arch = "wasm32"))]
 fn build_pdf(
     wires: &[WireModel],
     hatches: &[HatchModel],
@@ -235,6 +266,7 @@ fn build_pdf(
     doc.save(&PdfSaveOptions::default(), &mut warnings)
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn flush_line(ops: &mut Vec<Op>, pts: &[LinePoint]) {
     if pts.len() < 2 {
         return;
@@ -252,6 +284,7 @@ fn flush_line(ops: &mut Vec<Op>, pts: &[LinePoint]) {
 /// rings so islands and holes render correctly under the even-odd rule.
 /// Mirrors `scene::paper_canvas::draw_hatch`: solid → fill, pattern → outline,
 /// gradient → solid fill of the averaged colour.
+#[cfg(not(target_arch = "wasm32"))]
 fn emit_hatch(ops: &mut Vec<Op>, hatch: &HatchModel, ox: f32, oy: f32) {
     if hatch.boundary.is_empty() {
         return;

src/io/print_to_printer.rs

@@ -7,15 +7,34 @@
 //
 // The function is async so the UI remains responsive while the job is queued.
 
+#[cfg(not(target_arch = "wasm32"))]
 use crate::io::pdf_export;
 use crate::io::plot_style::PlotStyleTable;
 use crate::scene::model::hatch_model::HatchModel;
 use crate::scene::WireModel;
 
+// Printing routes through the native PDF pipeline + the OS print command, so it
+// is native-only; the web build gets a stub so the call site still compiles.
+#[cfg(target_arch = "wasm32")]
+pub async fn print_wires(
+    _wires: Vec<WireModel>,
+    _hatches: Vec<HatchModel>,
+    _wipeouts: Vec<HatchModel>,
+    _paper_w: f64,
+    _paper_h: f64,
+    _offset_x: f32,
+    _offset_y: f32,
+    _rotation_deg: i32,
+    _plot_style: Option<PlotStyleTable>,
+) -> Result<String, String> {
+    Err("Printing is not available in the web version.".into())
+}
+
 /// Render `wires` (plus hatch / wipeout fills) to a temp PDF and dispatch it
 /// to the default system printer.
 ///
 /// Returns `Ok(printer_name)` on success or `Err(message)` on failure.
+#[cfg(not(target_arch = "wasm32"))]
 pub async fn print_wires(
     wires: Vec<WireModel>,
     hatches: Vec<HatchModel>,
@@ -47,6 +66,7 @@ pub async fn print_wires(
 }
 
 /// Platform-specific dispatch of a PDF path to the system printer.
+#[cfg(not(target_arch = "wasm32"))]
 fn dispatch_to_printer(path: &std::path::Path) -> Result<String, String> {
     #[cfg(target_os = "windows")]
     {