add help docs and ?

frontend/src/CustomNode.jsx

@@ -1,7 +1,12 @@
 import React, { useContext, useRef, useCallback, useState, useEffect, memo, lazy, Suspense } from 'react';
+import ReactDOM from 'react-dom';
 import { Handle, NodeResizeControl, Position, useStore } from '@xyflow/react';
+import { marked } from 'marked';
+import { getNodeDoc } from './api';
 import LinePlotOverlay from './LinePlotOverlay';
 
+marked.use({ breaks: true, gfm: true });
+
 const SurfaceView = lazy(() => import('./SurfaceView'));
 const CrossSectionOverlay = lazy(() => import('./CrossSectionOverlay'));
 const CropBoxOverlay = lazy(() => import('./CropBoxOverlay'));
@@ -973,10 +978,48 @@ function NodeTable({ rows }) {
   );
 }
 
+// ── Node help panel (portal) ──────────────────────────────────────────
+
+function NodeHelpPanel({ title, content, onClose }) {
+  useEffect(() => {
+    const handler = (e) => { if (e.key === 'Escape') onClose(); };
+    document.addEventListener('keydown', handler);
+    return () => document.removeEventListener('keydown', handler);
+  }, [onClose]);
+
+  return ReactDOM.createPortal(
+    <div className="node-help-panel">
+      <div className="node-help-panel-header">
+        <span className="node-help-panel-title">{title}</span>
+        <button className="node-help-panel-close" onClick={onClose} title="Close">×</button>
+      </div>
+      <div
+        className="node-help-panel-body nowheel"
+        // eslint-disable-next-line react/no-danger
+        dangerouslySetInnerHTML={{ __html: marked.parse(content || '') }}
+      />
+    </div>,
+    document.body,
+  );
+}
+
 // ── CustomNode component ──────────────────────────────────────────────
 
 function CustomNode({ id, data }) {
   const ctx = useContext(NodeContext);
+  const [helpOpen, setHelpOpen] = useState(false);
+  const [helpContent, setHelpContent] = useState(null);
+
+  const onHelpClick = useCallback(async (e) => {
+    e.stopPropagation();
+    if (helpOpen) { setHelpOpen(false); return; }
+    setHelpOpen(true);
+    if (helpContent === null) {
+      const text = await getNodeDoc(data.label);
+      setHelpContent(text || '*No documentation available for this node.*');
+    }
+  }, [helpOpen, helpContent, data.label]);
+
   if (data.className === 'Group') {
     return <GroupNode id={id} data={data} />;
   }
@@ -1181,7 +1224,10 @@ function CustomNode({ id, data }) {
       {/* Title */}
       <div className="node-title drag-handle" style={{ background: catColor }}>
         <span className="node-title-main">{data.label}</span>
-        {headerMeta && <span className="node-title-meta" title={headerMeta}>{headerMeta}</span>}
+        <div className="node-title-right">
+          {headerMeta && <span className="node-title-meta" title={headerMeta}>{headerMeta}</span>}
+          <button className="node-help-btn nodrag nopan" title="Documentation" onClick={onHelpClick}>?</button>
+        </div>
       </div>
 
       <div className="node-body">
@@ -1528,6 +1574,13 @@ function CustomNode({ id, data }) {
         )}
       </div>
     </div>
+    {helpOpen && (
+      <NodeHelpPanel
+        title={data.label}
+        content={helpContent ?? '*Loading…*'}
+        onClose={() => setHelpOpen(false)}
+      />
+    )}
     </>
   );
 }

frontend/src/api.js

@@ -62,6 +62,12 @@ export async function getNodes() {
   return r.json();
 }
 
+export async function getNodeDoc(displayName) {
+  const r = await sessionFetch(`/docs?name=${encodeURIComponent(displayName)}`);
+  if (!r.ok) return null;
+  return r.text();
+}
+
 export async function getFiles() {
   const r = await sessionFetch('/files');
   if (!r.ok) return [];

frontend/src/styles.css

@@ -435,6 +435,149 @@ html, body, #root {
   text-overflow: ellipsis;
 }
 
+.node-title-right {
+  display: flex;
+  align-items: center;
+  gap: 5px;
+  flex-shrink: 0;
+}
+
+.node-help-btn {
+  width: 15px;
+  height: 15px;
+  border-radius: 50%;
+  background: rgba(255, 255, 255, 0.12);
+  border: 1px solid rgba(255, 255, 255, 0.25);
+  color: rgba(255, 255, 255, 0.75);
+  font-size: 9px;
+  font-weight: 700;
+  line-height: 1;
+  padding: 0;
+  cursor: pointer;
+  flex-shrink: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  transition: background 0.15s, border-color 0.15s;
+}
+
+.node-help-btn:hover {
+  background: rgba(255, 255, 255, 0.28);
+  border-color: rgba(255, 255, 255, 0.5);
+}
+
+/* ── Node help panel ─────────────────────────────────────── */
+
+.node-help-panel {
+  position: fixed;
+  top: 60px;
+  right: 20px;
+  width: 420px;
+  max-height: calc(100vh - 80px);
+  background: #1e293b;
+  border: 1px solid #334155;
+  border-radius: 8px;
+  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.55);
+  display: flex;
+  flex-direction: column;
+  z-index: 9999;
+  overflow: hidden;
+}
+
+.node-help-panel-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 9px 12px;
+  border-bottom: 1px solid #334155;
+  background: #0f172a;
+  flex-shrink: 0;
+}
+
+.node-help-panel-title {
+  font-weight: 600;
+  font-size: 13px;
+  color: #f1f5f9;
+}
+
+.node-help-panel-close {
+  background: none;
+  border: none;
+  color: #64748b;
+  font-size: 20px;
+  line-height: 1;
+  padding: 0 2px;
+  cursor: pointer;
+  transition: color 0.12s;
+}
+
+.node-help-panel-close:hover {
+  color: #f1f5f9;
+}
+
+.node-help-panel-body {
+  padding: 14px 16px;
+  overflow-y: auto;
+  flex: 1;
+  font-size: 12.5px;
+  color: #cbd5e1;
+  line-height: 1.65;
+}
+
+.node-help-panel-body h1,
+.node-help-panel-body h2,
+.node-help-panel-body h3 {
+  color: #f1f5f9;
+  margin: 14px 0 5px;
+  font-weight: 600;
+}
+
+.node-help-panel-body h1 { font-size: 15px; margin-top: 0; }
+.node-help-panel-body h2 { font-size: 13px; }
+.node-help-panel-body h3 { font-size: 12px; }
+
+.node-help-panel-body p { margin: 4px 0 8px; }
+
+.node-help-panel-body table {
+  border-collapse: collapse;
+  width: 100%;
+  font-size: 11.5px;
+  margin: 8px 0 12px;
+}
+
+.node-help-panel-body th,
+.node-help-panel-body td {
+  border: 1px solid #334155;
+  padding: 4px 8px;
+  text-align: left;
+}
+
+.node-help-panel-body th {
+  background: #0f172a;
+  color: #94a3b8;
+  font-weight: 600;
+}
+
+.node-help-panel-body code {
+  background: #0f172a;
+  padding: 1px 5px;
+  border-radius: 3px;
+  font-size: 11px;
+  color: #7dd3fc;
+}
+
+.node-help-panel-body ul,
+.node-help-panel-body ol {
+  padding-left: 18px;
+  margin: 4px 0 8px;
+}
+
+.node-help-panel-body li { margin: 2px 0; }
+
+.node-help-panel-body em { color: #94a3b8; }
+
+.node-help-panel-body strong { color: #e2e8f0; }
+
 .node-body {
   padding: 4px 0;
   display: flex;