diff --git a/frontend/src/app/canvas/CanvasPage.tsx b/frontend/src/app/canvas/CanvasPage.tsx
index acb230f..46323a6 100644
--- a/frontend/src/app/canvas/CanvasPage.tsx
+++ b/frontend/src/app/canvas/CanvasPage.tsx
@@ -217,9 +217,12 @@ export function CanvasPage({ projectId: _projectId }: CanvasPageProps) {
   )
 
   const isValidConnection = useCallback(
-    (connection: Connection) => {
-      const sourceNode = nodes.find((n) => n.id === connection.source)
-      const targetNode = nodes.find((n) => n.id === connection.target)
+    (connection: Connection | AppEdge) => {
+      const src = 'source' in connection ? connection.source : undefined
+      const tgt = 'target' in connection ? connection.target : undefined
+      if (typeof src !== 'string' || typeof tgt !== 'string') return false
+      const sourceNode = nodes.find((n) => n.id === src)
+      const targetNode = nodes.find((n) => n.id === tgt)
       const sourceType = sourceNode?.type
       const targetType = targetNode?.type
       if (!sourceType || !targetType) return false
@@ -227,13 +230,16 @@ export function CanvasPage({ projectId: _projectId }: CanvasPageProps) {
         const targetData = targetNode?.data as { configType?: string } | undefined
         if (targetData?.configType !== 'markdown') return false
       }
-      return isConnectionAllowed(sourceType, targetType, connection.source, connection.target)
+      return isConnectionAllowed(sourceType, targetType, src, tgt)
     },
     [nodes]
   )
 
   const onConnectStart = useCallback(
-    (_: React.MouseEvent | React.TouchEvent, params: { nodeId?: string | null; handleId?: string | null; handleType?: string | null }) => {
+    (
+      _: React.MouseEvent<Element> | React.TouchEvent<Element> | MouseEvent | TouchEvent,
+      params: { nodeId?: string | null; handleId?: string | null; handleType?: string | null }
+    ) => {
       if (params.handleType !== 'source' || !params.nodeId) {
         setConnectionFrom(null)
         return
@@ -371,14 +377,14 @@ export function CanvasPage({ projectId: _projectId }: CanvasPageProps) {
   const createNode = useCallback(
     (type: string) => {
       const position = getMenuPosition()
-      if (position == null) return
-      const nodeType = type as Node['type']
-      const newId = getNextNodeId(nodeType, nodesRef.current.map((n) => n.id))
-      const dataMap = getDefaultDataForType(nodeType, newId)
-      const style = getDefaultStyle(nodeType)
+      if (position == null || typeof type !== 'string') return
+      const existingIds = nodesRef.current.map((n) => n.id).filter((id): id is string => id != null)
+      const newId = getNextNodeId(type, existingIds)
+      const dataMap = getDefaultDataForType(type, newId)
+      const style = getDefaultStyle(type)
       const newNode: Node = {
         id: newId,
-        type: nodeType,
+        type: type as Node['type'],
         position: { x: position.x, y: position.y },
         data: dataMap,
         style,
@@ -416,14 +422,16 @@ export function CanvasPage({ projectId: _projectId }: CanvasPageProps) {
       const raw = JSON.parse(text) as { id?: string; type?: string; data?: Record<string, unknown>; position?: { x: number; y: number }; style?: unknown }
       const validIds = getRegisteredNodeTypeIds()
       if (!raw || typeof raw.type !== 'string' || !validIds.includes(raw.type)) return
+      const nodeType = raw.type
       setNodes((nds) => {
-        const newId = getNextNodeId(raw.type as Node['type'], nds.map((n) => n.id))
+        const existingIds = nds.map((n) => n.id).filter((id): id is string => id != null)
+        const newId = getNextNodeId(nodeType, existingIds)
         const data = raw.data != null && typeof raw.data === 'object' ? { ...raw.data } : {}
-        if (raw.type === 'config' && data && 'title' in data) data.title = `config-${newId}`
-        const style = getDefaultStyle(raw.type)
+        if (nodeType === 'config' && data && 'title' in data) data.title = `config-${newId}`
+        const style = getDefaultStyle(nodeType)
         const newNode: Node = {
           id: newId,
-          type: raw.type as Node['type'],
+          type: nodeType as Node['type'],
           position: { x: position.x, y: position.y },
           data,
           style,
@@ -560,7 +568,8 @@ export function CanvasPage({ projectId: _projectId }: CanvasPageProps) {
                       nodesConnectable
                       elementsSelectable
                     >
-                      <Background variant="dots" gap={20} />
+                      {/* BackgroundVariant from @xyflow/system expects enum; 'dots' is valid at runtime */}
+                      <Background variant={'dots' as React.ComponentProps<typeof Background>['variant']} gap={20} />
                       <div role="group" aria-label="Canvas controls: zoom and fit view">
                         <Controls />
                       </div>
diff --git a/frontend/src/components/base/AnimatedEdge.tsx b/frontend/src/components/base/AnimatedEdge.tsx
index 9fa9cee..67b6bbc 100644
--- a/frontend/src/components/base/AnimatedEdge.tsx
+++ b/frontend/src/components/base/AnimatedEdge.tsx
@@ -27,7 +27,7 @@ export function AnimatedEdge({
   const nodes = ctx?.nodes ?? []
   const targetNode = useMemo(() => nodes.find((n: any) => n.id === target), [nodes, target])
   const derivedLabel = useMemo(
-    () => getConnectionLabelForTarget(targetNode?.type),
+    () => (targetNode?.type != null ? getConnectionLabelForTarget(targetNode.type) : undefined),
     [targetNode?.type]
   )
   const label = labelProp ?? derivedLabel
diff --git a/frontend/src/components/base/BaseHandle.tsx b/frontend/src/components/base/BaseHandle.tsx
deleted file mode 100644
index 33ac7c9..0000000
--- a/frontend/src/components/base/BaseHandle.tsx
+++ /dev/null
@@ -1,24 +0,0 @@
-import type { ComponentProps } from "react";
-import { Handle, type HandleProps } from "@xyflow/react";
-
-import { cn } from "@/lib/utils";
-
-export type BaseHandleProps = HandleProps;
-
-export function BaseHandle({
-  className,
-  children,
-  ...props
-}: ComponentProps<typeof Handle>) {
-  return (
-    <Handle
-      {...props}
-      className={cn(
-        "dark:border-secondary dark:bg-secondary h-[11px] w-[11px] rounded-full border border-slate-300 bg-slate-100 transition",
-        className,
-      )}
-    >
-      {children}
-    </Handle>
-  );
-}
diff --git a/frontend/src/components/base/FlowKeyboardShortcuts.tsx b/frontend/src/components/base/FlowKeyboardShortcuts.tsx
index 66e1296..0d078a6 100644
--- a/frontend/src/components/base/FlowKeyboardShortcuts.tsx
+++ b/frontend/src/components/base/FlowKeyboardShortcuts.tsx
@@ -34,6 +34,7 @@ export function FlowKeyboardShortcuts() {
       }
       const validIds = getRegisteredNodeTypeIds()
       if (!raw || typeof raw.type !== 'string' || !validIds.includes(raw.type)) return
+      const nodeType = raw.type
       const pane = document.querySelector('.react-flow__viewport')
       const rect = pane?.getBoundingClientRect()
       const center = rect
@@ -41,13 +42,14 @@ export function FlowKeyboardShortcuts() {
         : { x: window.innerWidth / 2, y: window.innerHeight / 2 }
       const position = screenToFlowPosition(center)
       setNodes((nds: Node[]) => {
-        const newId = getNextNodeId(raw.type, nds.map((n) => n.id))
+        const existingIds = nds.map((n) => n.id).filter((id): id is string => id != null)
+        const newId = getNextNodeId(nodeType, existingIds)
         const data: Record<string, unknown> =
           raw.data != null && typeof raw.data === 'object'
             ? { ...raw.data }
-            : (getDefaultDataForType(raw.type, newId) as Record<string, unknown>)
-        if (raw.type === 'config') data.title = `config-${newId}`
-        const style = getDefaultStyle(raw.type)
+            : (getDefaultDataForType(nodeType, newId) as Record<string, unknown>)
+        if (nodeType === 'config') data.title = `config-${newId}`
+        const style = getDefaultStyle(nodeType)
         const newNode: Node = {
           id: newId,
           type: raw.type as Node['type'],
diff --git a/frontend/src/components/base/NodeHandles.tsx b/frontend/src/components/base/NodeHandles.tsx
index ebf2a60..e493113 100644
--- a/frontend/src/components/base/NodeHandles.tsx
+++ b/frontend/src/components/base/NodeHandles.tsx
@@ -19,7 +19,7 @@ export function InputHandle({ id, nodeId }: NodeHandleProps) {
         isConnecting &&
         isValidConnection?.({
             source: connectionFrom!.nodeId,
-            sourceHandle: connectionFrom!.sourceHandle ?? undefined,
+            sourceHandle: connectionFrom!.sourceHandle ?? null,
             target: nodeId!,
             targetHandle: id,
         })
diff --git a/frontend/src/components/base/NodeHeaderTitle.tsx b/frontend/src/components/base/NodeHeaderTitle.tsx
index 053bc94..5bdf195 100644
--- a/frontend/src/components/base/NodeHeaderTitle.tsx
+++ b/frontend/src/components/base/NodeHeaderTitle.tsx
@@ -1,5 +1,6 @@
 import React, { useCallback, useContext, useEffect, useRef, useState } from 'react'
 import FlowContext from '../../lib/flowContext'
+import type { AppNode } from '../../lib/nodeTypes'
 import { replaceNodeIdInGraph } from '../../lib/flowUtils'
 
 type Props = {
@@ -41,7 +42,7 @@ export function NodeHeaderTitle({ nodeId, displayTitle }: Props) {
             return
         }
         const { nodes: nextNodes, edges: nextEdges } = replaceNodeIdInGraph(nodes, edges, nodeId, newId)
-        setNodes(nextNodes)
+        setNodes(nextNodes as AppNode[])
         setEdges(nextEdges)
         setRenamingNodeId(null)
     }, [nodeId, inputValue, nodes, edges, setNodes, setEdges, setRenamingNodeId])
diff --git a/frontend/src/components/base/NodeMenubar.tsx b/frontend/src/components/base/NodeMenubar.tsx
index d6b4743..ab91205 100644
--- a/frontend/src/components/base/NodeMenubar.tsx
+++ b/frontend/src/components/base/NodeMenubar.tsx
@@ -60,7 +60,9 @@ export function NodeMenubar({ nodeId, nodeType, editInputsContent, inputsMenuCon
                 data: typeof node.data === 'object' && node.data !== null ? { ...node.data } : node.data,
                 style: getDefaultStyle(nodeType),
             }
-            if (newNode.data?.title && nodeType === 'config') newNode.data.title = `${newId}`
+            if (nodeType === 'config' && newNode.data && typeof newNode.data === 'object' && 'title' in newNode.data) {
+                (newNode.data as { title: string }).title = `${newId}`
+            }
             return nds.concat(newNode)
         })
     }, [node, nodeType, setNodes])
diff --git a/frontend/src/components/nodes/ConfigNode.tsx b/frontend/src/components/nodes/ConfigNode.tsx
index 4adc924..275571c 100644
--- a/frontend/src/components/nodes/ConfigNode.tsx
+++ b/frontend/src/components/nodes/ConfigNode.tsx
@@ -43,7 +43,7 @@ import { NodeFooterEdgeIndicators } from '../base/NodeFooterEdgeIndicators'
 import { NodeHeaderTitle } from '../base/NodeHeaderTitle'
 import { NodeMenubar } from '../base/NodeMenubar'
 
-export type ConfigNodeData = { configType?: ConfigTypeId; content?: string; title?: string }
+export type ConfigNodeData = { configType?: ConfigTypeId; content?: string; title?: string; /** @deprecated use content */ plantuml?: string }
 
 type Props = AbstractNodeProps<ConfigNodeData>
 
@@ -324,7 +324,7 @@ function ConfigNodeComponent({ id, data, width, height, selected }: Props) {
                     />
                 </div>
 
-                <div ref={editorContainerRef} className="min-h-0 flex-1 w-full nodrag nopan overflow-hidden border-t border-input">
+                <div ref={editorContainerRef as React.RefObject<HTMLDivElement>} className="min-h-0 flex-1 w-full nodrag nopan overflow-hidden border-t border-input">
                     <CodeMirror
                         // @ts-expect-error ref is { view, state, editor }; package ref type not in our node_modules
                         ref={editorRef}
diff --git a/frontend/src/components/nodes/FunctionNode.tsx b/frontend/src/components/nodes/FunctionNode.tsx
index a53d29b..f972fff 100644
--- a/frontend/src/components/nodes/FunctionNode.tsx
+++ b/frontend/src/components/nodes/FunctionNode.tsx
@@ -131,7 +131,7 @@ function FunctionNodeComponent({ id, data, width, height, selected }: Props) {
                         }
                     />
                 </div>
-                <div ref={editorContainerRef} className="min-h-0 flex-1 w-full nodrag nopan overflow-hidden border-t border-input">
+                <div ref={editorContainerRef as React.RefObject<HTMLDivElement>} className="min-h-0 flex-1 w-full nodrag nopan overflow-hidden border-t border-input">
                     <CodeMirror
                         // @ts-expect-error ref is { view, state, editor }; package ref type not in our node_modules
                         ref={editorRef}
diff --git a/frontend/src/components/nodes/RenderingNode.tsx b/frontend/src/components/nodes/RenderingNode.tsx
index eaeb8e3..b59483a 100644
--- a/frontend/src/components/nodes/RenderingNode.tsx
+++ b/frontend/src/components/nodes/RenderingNode.tsx
@@ -51,8 +51,8 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
     const incomingIds = sourceIds
     const srcId = incomingIds.length > 0 ? incomingIds[0] : null
     const srcNode = nodes.find((n: any) => n.id === srcId)
-    const configTypeId = srcNode?.type === 'config' ? getConfigTypeId(srcNode.data) : 'plantuml'
-    const sourceContent = srcNode?.type === 'config' ? getConfigContent(srcNode.data) : ''
+    const configTypeId = srcNode?.type === 'config' ? getConfigTypeId((srcNode.data ?? undefined) as Record<string, unknown> | undefined) : 'plantuml'
+    const sourceContent = srcNode?.type === 'config' ? getConfigContent((srcNode.data ?? undefined) as Record<string, unknown> | undefined) : ''
     const srcData = srcNode?.data ?? {}
 
     /** Set of node IDs that can affect this render node (configs in the chain + variables/functions feeding them) */
@@ -94,7 +94,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
             if (!node) return
             visited.add(nodeId)
             out.add(nodeId)
-            const content = getConfigContent(node.data)
+            const content = getConfigContent((node.data ?? undefined) as Record<string, unknown> | undefined)
             for (const ref of getTemplateRefs(content)) {
                 const refId = resolveRef(ref)
                 if (refId && nodes.some((n: any) => n.id === refId && n.type === 'config') && isReachable(refId, id))
@@ -223,7 +223,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                         throw new Error(`Referenced config not connected to renderer: ${templateName}`)
                     visited.add(refId)
                     configIdsUsed.add(refId)
-                    const content = getConfigContent(node.data)
+                    const content = getConfigContent((node.data ?? undefined) as Record<string, unknown> | undefined)
                     for (const ref of getTemplateRefs(content)) addConfigAndRefs(ref, visited)
                 }
 
@@ -238,7 +238,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                         if (refId !== srcId && !isReachable(refId, id))
                             throw new Error(`Referenced config not connected to renderer: ${name}`)
                         return {
-                            src: getConfigContent(node.data),
+                            src: getConfigContent((node.data ?? undefined) as Record<string, unknown> | undefined),
                             path: name,
                         }
                     },
@@ -338,7 +338,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                 for (const fid of functionIdsToRegister) {
                     const src = nodes.find((n: any) => n.id === fid)
                     if (!src || src.type !== 'function') continue
-                    const body = src.data?.body ?? 'return args[0];'
+                    const body = (src.data as { body?: string } | undefined)?.body ?? 'return args[0];'
                     const parsed = parseFunctionSignature(body)
                     const connectedVarIds = new Set<string>(functionConnectedVariableIds[fid] ?? [])
                     const connectedFuncIds = functionConnectedFunctionIds[fid] ?? []
@@ -432,7 +432,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                 env.render(srcId!, nunjucksContext, async (nunjucksErr: Error | null, afterNunjucks: string) => {
                     if (cancelled || thisRunId !== runIdRef.current) return
                     if (nunjucksErr) {
-                        setSvgContent(null)
+                        setRenderedContent(null)
                         setError({ kind: 'render', message: `Nunjucks: ${nunjucksErr.message}` })
                         setLoading(false)
                         return
@@ -677,10 +677,10 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                                 </EmptyContent>
                             </Empty>
                         ) : error ? (
-                            srcData?.renderError ? (
-                                srcData.renderError(error)
-                            ) : srcData?.errorHtml ? (
-                                <div className="p-3 text-xs text-red-700 dark:text-red-400" dangerouslySetInnerHTML={{ __html: String(srcData.errorHtml) }} />
+                            (srcData as { renderError?: (err: { kind: string; message: string }) => React.ReactNode; errorHtml?: string })?.renderError ? (
+                                (srcData as { renderError: (err: { kind: string; message: string }) => React.ReactNode }).renderError(error)
+                            ) : (srcData as { errorHtml?: string })?.errorHtml ? (
+                                <div className="p-3 text-xs text-red-700 dark:text-red-400" dangerouslySetInnerHTML={{ __html: String((srcData as { errorHtml: string }).errorHtml) }} />
                             ) : (
                                 <div className="flex flex-col gap-2 p-3">
                                     <p className="text-xs text-red-700 dark:text-red-400">{error.message}</p>
@@ -706,7 +706,7 @@ function RenderingNodeComponent({ id, data, width, height, selected }: Props) {
                                         minScale={0.2}
                                         maxScale={4}
                                         centerOnInit
-                                        onInit={(ref) => ref?.centerView(1, 0, 0)}
+                                        onInit={(ref) => ref?.centerView(1, 200, 'easeOut')}
                                         panning={{ disabled: true }}
                                         wheel={{ disabled: true }}
                                         doubleClick={{ disabled: true }}
diff --git a/frontend/src/lib/abstractNode.ts b/frontend/src/lib/abstractNode.ts
index de49f55..c2a85a2 100644
--- a/frontend/src/lib/abstractNode.ts
+++ b/frontend/src/lib/abstractNode.ts
@@ -13,6 +13,7 @@
 import React, { useCallback, useContext, useMemo } from 'react'
 import FlowContext from './flowContext'
 import { nodePropsAreEqual } from './flowUtils'
+import type { AppNode } from './nodeTypes'
 
 // ---------------------------------------------------------------------------
 // Types
@@ -74,10 +75,10 @@ export function useAbstractNode<TData = Record<string, unknown>>(
   const updateData = useCallback(
     (partial: Partial<TData>) => {
       if (!setNodes) return
-      setNodes((nds: FlowNode[]) =>
+      setNodes((nds: AppNode[]) =>
         nds.map((n) =>
           n.id === id ? { ...n, data: { ...(n.data as object), ...partial } } : n
-        )
+        ) as AppNode[]
       )
     },
     [id, setNodes]
@@ -105,7 +106,7 @@ export function useAbstractNode<TData = Record<string, unknown>>(
     data,
     nodes,
     edges,
-    setNodes: setNodes ?? (() => {}),
+    setNodes: ((setNodes ?? (() => {})) as AbstractNodeContext<TData>['setNodes']),
     setEdges: setEdges ?? (() => {}),
     updateData,
     incomingEdges,
diff --git a/frontend/src/lib/flowUtils.ts b/frontend/src/lib/flowUtils.ts
index 60bc48d..c6a5fb3 100644
--- a/frontend/src/lib/flowUtils.ts
+++ b/frontend/src/lib/flowUtils.ts
@@ -8,7 +8,6 @@ import {
   getIdPrefix,
   getDefaultDataForType as getDefaultDataFromRegistry,
   getResetDataForType as getResetDataFromRegistry,
-  getDefaultStyle,
 } from './nodeRegistry'
 
 export function nodePropsAreEqual<P extends { id?: string; data?: any; width?: number; height?: number; selected?: boolean }>(
@@ -24,14 +23,6 @@ export function nodePropsAreEqual<P extends { id?: string; data?: any; width?: n
   )
 }
 
-/** @deprecated Use getIdPrefix from nodeRegistry for new code. Kept for compatibility. */
-export const PREFIX_BY_TYPE: Record<string, string> = {
-  config: 'cfg_',
-  render: 'rnd_',
-  variable: 'var_',
-  function: 'fn_',
-}
-
 /** Next node id for type: prefix + 3-digit increasing number (001, 002, …). Uses nodeRegistry for prefix when available. */
 export function getNextNodeId(type: string, existingIds: string[]): string {
   const prefix = getIdPrefix(type)
@@ -91,7 +82,3 @@ export function getResetDataForType(type: string, nodeId?: string): any {
   return getResetDataFromRegistry(type, nodeId)
 }
 
-/** Default style for a type. Uses nodeRegistry when type is registered. */
-export function getDefaultStyleForType(type: string): { width: number; height: number } {
-  return getDefaultStyle(type)
-}
diff --git a/frontend/src/lib/plantumlLanguage.ts b/frontend/src/lib/plantumlLanguage.ts
index 7c05cd6..247f911 100644
--- a/frontend/src/lib/plantumlLanguage.ts
+++ b/frontend/src/lib/plantumlLanguage.ts
@@ -1,7 +1,7 @@
 import { StreamLanguage } from '@codemirror/language'
 
 /** Nunjucks block comment {# ... #} */
-function tokenNunjucksComment(stream: { match: (re: RegExp) => string | null; next: () => string; eol: () => boolean }) {
+function tokenNunjucksComment(stream: { match: (re: RegExp) => unknown; next: () => string | void; eol: () => boolean }) {
     if (stream.match(/^\{#/)) {
         while (!stream.eol()) {
             if (stream.match(/#\}/)) return 'comment'
@@ -13,7 +13,7 @@ function tokenNunjucksComment(stream: { match: (re: RegExp) => string | null; ne
 }
 
 /** Nunjucks variable {{ ... }} or tag {% ... %} - tokenize the whole block */
-function tokenNunjucksBlock(stream: { match: (re: RegExp) => string | null; next: () => string; eol: () => boolean }) {
+function tokenNunjucksBlock(stream: { match: (re: RegExp) => unknown; next: () => string | void; eol: () => boolean }) {
     if (stream.match(/^\{\{/)) {
         while (!stream.eol()) {
             if (stream.match(/\}\}/)) return 'variableName.special'
diff --git a/frontend/src/nunjucks.d.ts b/frontend/src/nunjucks.d.ts
new file mode 100644
index 0000000..de84fbb
--- /dev/null
+++ b/frontend/src/nunjucks.d.ts
@@ -0,0 +1,18 @@
+declare module 'nunjucks' {
+  export interface Loader {
+    getSource(name: string): { src: string; path: string } | null
+  }
+  export interface Environment {
+    render(name: string, context: Record<string, unknown>, callback: (err: Error | null, res: string) => void): void
+    addFilter(name: string, fn: (...args: unknown[]) => void, async?: boolean): void
+    getFilter(name: string): (...args: unknown[]) => void
+  }
+  export class Environment {
+    constructor(loaders?: Loader[], opts?: { autoescape?: boolean })
+    render(name: string, context: Record<string, unknown>, callback: (err: Error | null, res: string) => void): void
+    addFilter(name: string, fn: (...args: unknown[]) => void, async?: boolean): void
+    getFilter(name: string): (...args: unknown[]) => void
+  }
+  const nunjucks: { Environment: typeof Environment }
+  export default nunjucks
+}