feat: shared C4 layout engine for the canvas + sequence lifeline context

crates/pseudoscript-emit/src/lib.rs

@@ -40,6 +40,7 @@ mod project;
 mod render;
 mod scene;
 
+pub use c4_render::{BoundaryFrame, C4Layout, LaidOutEdge, LaidOutNode, PointI, layout_c4_scene};
 pub use project::{EmitError, View, project, project_symbol};
 pub use render::{Theme, layout_sequence_scene, render_svg, render_svg_themed};
 pub use scene::{

crates/pseudoscript-emit/src/scene.rs

@@ -49,7 +49,10 @@ impl C4View {
 /// A laid-out C4 view: an ordered set of placed nodes and routed edges.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct C4Scene {
-    /// Which C4 view this is.
+    /// Which C4 view this is. Serialised as `c4view`, not `view`: the [`Scene`]
+    /// enum is internally tagged on `view` (`c4`/`sequence`), so the inner field
+    /// must not reuse that key or a round-trip hits a duplicate-`view` error.
+    #[serde(rename = "c4view")]
     pub view: C4View,
     /// The view's boundary node FQN (`of`): the system for a container view, the
     /// container for a component view. `None` for context.

crates/pseudoscript-wasm/src/lib.rs

@@ -40,7 +40,8 @@ use pseudoscript_doc::{
     try_render_site_with,
 };
 use pseudoscript_emit::{
-    Scene, View, graph_of_source, layout_sequence_scene, project, project_symbol, render_svg,
+    Scene, View, graph_of_source, layout_c4_scene, layout_sequence_scene, project, project_symbol,
+    render_svg,
 };
 use pseudoscript_format::format as format_source;
 use pseudoscript_model::{
@@ -329,14 +330,16 @@ pub fn symbol_svg(modules_json: &str, fqn: &str) -> Result<String, JsError> {
     symbol_svg_impl(modules_json, fqn).map_err(|e| JsError::new(&e))
 }
 
-/// Positions a sequence [`Scene`] (as JSON) into absolute coordinates, returning
-/// the layout as JSON. The host collapses the scene to a chosen depth first,
-/// then hands it here; the layout engine owns all geometry. A non-sequence scene
-/// is an error.
+/// Positions a [`Scene`] (as JSON) into absolute coordinates, returning the
+/// layout as JSON. The layout engine owns all geometry: a sequence scene yields
+/// a positioned sequence layout (the host collapses it to a chosen depth first);
+/// a C4 scene yields a [`pseudoscript_emit::C4Layout`] (placed cards + routed
+/// edges + boundary frame), the same geometry the SVG draws. The two layout
+/// shapes are distinguishable by their fields (`participants` vs `nodes`).
 ///
 /// # Errors
 ///
-/// Returns an error for invalid JSON or a non-sequence scene.
+/// Returns an error for invalid JSON.
 #[wasm_bindgen]
 pub fn layout_scene(scene_json: &str) -> Result<String, JsError> {
     layout_scene_impl(scene_json).map_err(|e| JsError::new(&e))
@@ -752,7 +755,7 @@ fn layout_scene_impl(scene_json: &str) -> Result<String, String> {
     let scene: Scene = serde_json::from_str(scene_json).map_err(|e| e.to_string())?;
     match scene {
         Scene::Sequence(seq) => Ok(to_json(&layout_sequence_scene(&seq))),
-        Scene::C4(_) => Err("layout_scene expects a sequence scene".to_owned()),
+        Scene::C4(c4) => Ok(to_json(&layout_c4_scene(&c4))),
     }
 }
 
@@ -1283,6 +1286,18 @@ mod tests {
         assert!(out.contains("m::F"), "{out}");
     }
 
+    #[test]
+    fn layout_scene_lays_out_a_c4_scene() {
+        // The exact IDE path: a projected C4 scene serialised to JSON
+        // (`emit_scene_modules`) and handed back to `layout_scene`. It must
+        // positionally lay out (placed cards), not error as it once did.
+        let scene = project_view("//! m\npublic person P;\npublic system S;", "context", "")
+            .expect("context view projects");
+        let out = layout_scene_impl(&to_json(&scene)).expect("c4 scene lays out");
+        assert!(out.contains(r#""nodes""#), "C4 layout carries nodes: {out}");
+        assert!(out.contains("m::P") && out.contains("m::S"), "{out}");
+    }
+
     #[test]
     fn layout_scene_rejects_a_scene_missing_the_view_tag() {
         // A scene object without the `view` discriminant cannot deserialize into

web-ide/package.json

@@ -53,7 +53,6 @@
     "@codemirror/search": "^6.7.0",
     "@codemirror/state": "^6.6.0",
     "@codemirror/view": "^6.43.0",
-    "@dagrejs/dagre": "3.0.0",
     "@lezer/highlight": "^1.2.3",
     "@lezer/markdown": "^1.6.4",
     "@xyflow/svelte": "1.5.2",

web-ide/src/app.css

@@ -337,9 +337,14 @@ button { font: inherit; cursor: pointer; color: inherit; }
 .svelte-flow__edge-text { fill: var(--ink-soft); font-family: var(--font-mono); font-size: 10px; }
 .svelte-flow__edge-textbg { fill: var(--surface); }
 
-/* kind-coloured card nodes (shared by C4 graph + timeline) */
+/* kind-coloured card nodes (shared by C4 graph + timeline). The C4 graph sizes
+   each card to the layout engine's rect (width/height set on the node), so the
+   box honours those dimensions and clips overflow; the timeline's lifeline head
+   cards (width unset) size to content. */
 .svelte-flow__node.c4-node {
   width: auto;
+  box-sizing: border-box;
+  overflow: hidden;
   padding: 0.55rem 0.9rem;
   font-family: var(--font-mono);
   font-size: 0.8rem;