feat: port el-ui vessels — rename crates→vessels, add El source + manifests

ui/vessels/el-graph/src/canvas.el

@@ -0,0 +1,46 @@
+// canvas.el — Full server-side pipeline: layout -> render -> SVG string.
+//
+// This is the primary integration point for callers that want a static SVG
+// without managing the layout and render steps separately.
+//
+// Public API:
+//   graph_svg_endpoint(nodes_json, edges_json, width, height) -> String
+//     Full pipeline: Coulomb/spring layout (150 iterations) -> SVG string.
+//     Returns a complete <svg>...</svg> string.
+//
+// Client-side interaction (drag, zoom, pan) is deferred until el-ui-compiler
+// gains a JavaScript backend. For now, all rendering is server-side.
+// Clients refresh the SVG on demand (e.g., polling GET /api/graph/svg).
+//
+// Zoom/pan note: SVG viewBox is fixed to [0,0,width,height]. When the JS
+// backend lands, el-ui-compiler will produce an overlay with pointer-event
+// handlers that transform a <g> wrapper inside this SVG. The server-side path
+// stays as a fallback for non-browser consumers (CLI, PDF export, testing).
+
+fn layout_default_iterations() -> Int { 150 }
+
+// ── graph_svg_endpoint ────────────────────────────────────────────────────────
+
+fn graph_svg_endpoint(nodes_json: String, edges_json: String, width: Int, height: Int) -> String {
+    let w_f: Float = int_to_float(width)
+    let h_f: Float = int_to_float(height)
+
+    // Step 1: compute layout
+    let positions_json: String = layout_run(nodes_json, edges_json, w_f, h_f, layout_default_iterations())
+
+    // Step 2: render to SVG
+    let svg: String = graph_render_svg(nodes_json, edges_json, positions_json, width, height)
+    svg
+}
+
+// ── graph_svg_endpoint_custom ─────────────────────────────────────────────────
+//
+// Same as above but with configurable iteration count.
+// Use when you need faster layout (low iters) or higher quality (high iters).
+
+fn graph_svg_endpoint_custom(nodes_json: String, edges_json: String, width: Int, height: Int, iterations: Int) -> String {
+    let w_f: Float = int_to_float(width)
+    let h_f: Float = int_to_float(height)
+    let positions_json: String = layout_run(nodes_json, edges_json, w_f, h_f, iterations)
+    graph_render_svg(nodes_json, edges_json, positions_json, width, height)
+}