M7: WASM plugins (#101)

Sandboxed WebAssembly plugins whose API is the command registry:

- figcraft-plugin (new crate, L2): the figcraft-plugin.json manifest
  (menu commands with parameters, read/write access, command allowlist)
  and the sandbox: wasmi (pure Rust, no JIT, also in the web build) with
  fuel metering, a memory cap, no WASI and seven host functions (call,
  selection, reply_len, reply_read, log, notify, set_output).
- Engine: plugin.list / plugin.import / plugin.remove / plugin.run,
  plugins.runLast (Alt+Cmd+P; Ctrl+Alt+Shift+P on Windows/Linux) and
  plugins.manage. A run is one undo step (Session::grouped, which
  command.batch now uses too) and is rolled back when it fails. Files,
  other documents, the undo history, dialogs and plugins are off limits;
  read-only plugins can't change the document. Installed plugins live in
  the preferences; development plugins re-read their module every run.
- UI: installed plugins in the Plugins menu, a parameters form drawn
  from the manifest, Manage plugins, Plugins > Development > Import
  plugin from manifest.
- plugins/: a no_std Rust SDK and two example plugins (Tidy names,
  Swatch grid), built for wasm32 by `cargo xtask plugins` (part of
  `cargo xtask wasm`).
- Docs: docs/plugins.md (manifest, permissions, limits, ABI, SDK),
  docs/mcp.md, docs/control-protocol.md, README, ROADMAP, parity.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

plugins/examples/swatch-grid/src/lib.rs

@@ -0,0 +1,82 @@
+//! Swatch grid: a grid of colour swatches from a palette (hex colours), centred in the view, each
+//! named after its colour and optionally labelled.
+
+use figcraft_plugin_sdk::{Input, Result, Value, call, entry, json, log, notify};
+
+/// Swatches made in one run, at most.
+const MAX_SWATCHES: usize = 256;
+
+/// `#RGB` or `#RRGGBB` (the `#` optional) as `#RRGGBB`.
+fn hex(s: &str) -> Option<String> {
+    let h = s.trim().trim_start_matches('#');
+    if !h.chars().all(|c| c.is_ascii_hexdigit()) {
+        return None;
+    }
+    match h.len() {
+        3 => Some(h.chars().flat_map(|c| [c, c]).collect::<String>()),
+        6 => Some(h.to_string()),
+        _ => None,
+    }
+    .map(|h| format!("#{}", h.to_uppercase()))
+}
+
+/// The palette's valid colours, logging the rest.
+fn palette(text: &str) -> Vec<String> {
+    text.split([',', ' ', ';', '\n'])
+        .filter(|s| !s.trim().is_empty())
+        .filter_map(|s| {
+            let c = hex(s);
+            if c.is_none() {
+                log(&format!("skipped `{s}`: not a hex colour"));
+            }
+            c
+        })
+        .take(MAX_SWATCHES)
+        .collect()
+}
+
+fn run(input: Input) -> Result<Value> {
+    let colors = palette(input.str("palette").unwrap_or_default());
+    if colors.is_empty() {
+        return Err("The palette has no hex colours (like #FF5A5F, #00A699)".into());
+    }
+    let columns = input.f64("columns").unwrap_or(3.0).clamp(1.0, 24.0) as usize;
+    let size = input.f64("size").unwrap_or(64.0).clamp(8.0, 512.0);
+    let gap = input.f64("gap").unwrap_or(16.0).clamp(0.0, 256.0);
+    let labels = input.bool("labels").unwrap_or(true);
+    let rows = colors.len().div_ceil(columns);
+    let cell_h = if labels { size + 20.0 } else { size };
+    let (w, h) = (columns as f64 * (size + gap) - gap, rows as f64 * (cell_h + gap) - gap);
+    // Centred in the view, on whole pixels.
+    let view = call("view.get", &json!({}))?;
+    let (x0, y0) = ((view["cx"].as_f64().unwrap_or(0.0) - w / 2.0).round(), (view["cy"].as_f64().unwrap_or(0.0) - h / 2.0).round());
+    let mut made = Vec::new();
+    for (i, color) in colors.iter().enumerate() {
+        let (x, y) = (x0 + (i % columns) as f64 * (size + gap), y0 + (i / columns) as f64 * (cell_h + gap));
+        let r = call("shape.rectangle", &json!({"x": x, "y": y, "width": size, "height": size, "props": {"name": color, "fill": color}}))?;
+        made.extend(r["id"].as_u64());
+        if labels {
+            let t = call("text.create", &json!({"text": color, "x": x, "y": y + size + 4.0, "props": {"fontSize": 11}}))?;
+            made.extend(t["id"].as_u64());
+        }
+    }
+    call("select.set", &json!({"ids": made}))?;
+    notify(&format!("Made {} swatches", colors.len()));
+    Ok(json!({"swatches": colors.len(), "ids": made}))
+}
+
+entry!(run);
+
+#[cfg(test)]
+mod tests {
+    use super::{hex, palette};
+
+    #[test]
+    fn palettes_parse() {
+        assert_eq!(hex("#f0a"), Some("#FF00AA".into()));
+        assert_eq!(hex(" 00a699 "), Some("#00A699".into()));
+        assert_eq!(hex("#12345"), None);
+        assert_eq!(hex("red"), None);
+        assert_eq!(palette("#FF5A5F, nope;#0f0\n00A699"), vec!["#FF5A5F", "#00FF00", "#00A699"]);
+    }
+}