fIx: smaller nits

2026-03-20 00:04:46 +01:00
parent bc67d01bc2
commit c3cbe35883
21 changed files with 2093 additions and 116 deletions
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
@@ -13,6 +13,13 @@
        "cors": "^2.8.5",
        "express": "^4.21.0"
      },
+      "devDependencies": {
+        "@types/cors": "^2.8.17",
+        "@types/express": "^5.0.0",
+        "@types/node": "^22.0.0",
+        "tsx": "^4.0.0",
+        "typescript": "^5.0.0"
+      },
      "engines": {
        "node": ">=20"
      }
@@ -103,6 +110,448 @@
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      }
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@@ -112,12 +561,120 @@
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+      "integrity": "sha512-r8Tayk8HJnX0FztbZN7oVqGccWgw98T/0neJphO91KkmOzug1KkofZURD4UaD5uH8AqcFLfdPErnBod0u71/qg==",
+      "dev": true,
+      "license": "MIT"
+    },
+    "node_modules/@types/node": {
+      "version": "22.19.15",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-22.19.15.tgz",
+      "integrity": "sha512-F0R/h2+dsy5wJAUe3tAU6oqa2qbWY5TpNfL/RGmo1y38hiyO1w3x2jPtt76wmuaJI4DQnOBu21cNXQ2STIUUWg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "undici-types": "~6.21.0"
+      }
+    },
+    "node_modules/@types/qs": {
+      "version": "6.15.0",
+      "resolved": "https://registry.npmjs.org/@types/qs/-/qs-6.15.0.tgz",
+      "integrity": "sha512-JawvT8iBVWpzTrz3EGw9BTQFg3BQNmwERdKE22vlTxawwtbyUSlMppvZYKLZzB5zgACXdXxbD3m1bXaMqP/9ow==",
+      "dev": true,
+      "license": "MIT"
+    },
+    "node_modules/@types/range-parser": {
+      "version": "1.2.7",
+      "resolved": "https://registry.npmjs.org/@types/range-parser/-/range-parser-1.2.7.tgz",
+      "integrity": "sha512-hKormJbkJqzQGhziax5PItDUTMAM9uE2XXQmM37dyd4hVM+5aVl7oVxMVUiVQn2oCQFN/LKCZdvSM0pFRqbSmQ==",
+      "dev": true,
+      "license": "MIT"
+    },
+    "node_modules/@types/send": {
+      "version": "1.2.1",
+      "resolved": "https://registry.npmjs.org/@types/send/-/send-1.2.1.tgz",
+      "integrity": "sha512-arsCikDvlU99zl1g69TcAB3mzZPpxgw0UQnaHeC1Nwb015xp8bknZv5rIfri9xTOcMuaVgvabfIRA7PSZVuZIQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/serve-static": {
+      "version": "2.2.0",
+      "resolved": "https://registry.npmjs.org/@types/serve-static/-/serve-static-2.2.0.tgz",
+      "integrity": "sha512-8mam4H1NHLtu7nmtalF7eyBH14QyOASmcxHhSfEoRyr0nP/YdoesEtU+uSRvMe96TW/HPTtkoKqQLl53N7UXMQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/http-errors": "*",
+        "@types/node": "*"
+      }
+    },
    "node_modules/accepts": {
      "version": "1.3.8",
      "resolved": "https://registry.npmjs.org/accepts/-/accepts-1.3.8.tgz",
@@ -392,6 +949,48 @@
        "node": ">= 0.4"
      }
    },
+    "node_modules/esbuild": {
+      "version": "0.27.4",
+      "resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.27.4.tgz",
+      "integrity": "sha512-Rq4vbHnYkK5fws5NF7MYTU68FPRE1ajX7heQ/8QXXWqNgqqJ/GkmmyxIzUnf2Sr/bakf8l54716CcMGHYhMrrQ==",
+      "dev": true,
+      "hasInstallScript": true,
+      "license": "MIT",
+      "bin": {
+        "esbuild": "bin/esbuild"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "optionalDependencies": {
+        "@esbuild/aix-ppc64": "0.27.4",
+        "@esbuild/android-arm": "0.27.4",
+        "@esbuild/android-arm64": "0.27.4",
+        "@esbuild/android-x64": "0.27.4",
+        "@esbuild/darwin-arm64": "0.27.4",
+        "@esbuild/darwin-x64": "0.27.4",
+        "@esbuild/freebsd-arm64": "0.27.4",
+        "@esbuild/freebsd-x64": "0.27.4",
+        "@esbuild/linux-arm": "0.27.4",
+        "@esbuild/linux-arm64": "0.27.4",
+        "@esbuild/linux-ia32": "0.27.4",
+        "@esbuild/linux-loong64": "0.27.4",
+        "@esbuild/linux-mips64el": "0.27.4",
+        "@esbuild/linux-ppc64": "0.27.4",
+        "@esbuild/linux-riscv64": "0.27.4",
+        "@esbuild/linux-s390x": "0.27.4",
+        "@esbuild/linux-x64": "0.27.4",
+        "@esbuild/netbsd-arm64": "0.27.4",
+        "@esbuild/netbsd-x64": "0.27.4",
+        "@esbuild/openbsd-arm64": "0.27.4",
+        "@esbuild/openbsd-x64": "0.27.4",
+        "@esbuild/openharmony-arm64": "0.27.4",
+        "@esbuild/sunos-x64": "0.27.4",
+        "@esbuild/win32-arm64": "0.27.4",
+        "@esbuild/win32-ia32": "0.27.4",
+        "@esbuild/win32-x64": "0.27.4"
+      }
+    },
    "node_modules/escape-html": {
      "version": "1.0.3",
      "resolved": "https://registry.npmjs.org/escape-html/-/escape-html-1.0.3.tgz",
@@ -489,6 +1088,21 @@
        "node": ">= 0.6"
      }
    },
+    "node_modules/fsevents": {
+      "version": "2.3.3",
+      "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
+      "integrity": "sha512-5xoDfX+fL7faATnagmWPpbFtwh/R77WmMMqqHGS65C3vvB0YHrgF+B1YmZ3441tMj5n63k0212XNoJwzlhffQw==",
+      "dev": true,
+      "hasInstallScript": true,
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "engines": {
+        "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
+      }
+    },
    "node_modules/function-bind": {
      "version": "1.1.2",
      "resolved": "https://registry.npmjs.org/function-bind/-/function-bind-1.1.2.tgz",
@@ -535,6 +1149,19 @@
        "node": ">= 0.4"
      }
    },
+    "node_modules/get-tsconfig": {
+      "version": "4.13.6",
+      "resolved": "https://registry.npmjs.org/get-tsconfig/-/get-tsconfig-4.13.6.tgz",
+      "integrity": "sha512-shZT/QMiSHc/YBLxxOkMtgSid5HFoauqCE3/exfsEcwg1WkeqjG+V40yBbBrsD+jW2HDXcs28xOfcbm2jI8Ddw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "resolve-pkg-maps": "^1.0.0"
+      },
+      "funding": {
+        "url": "https://github.com/privatenumber/get-tsconfig?sponsor=1"
+      }
+    },
    "node_modules/gopd": {
      "version": "1.2.0",
      "resolved": "https://registry.npmjs.org/gopd/-/gopd-1.2.0.tgz",
@@ -853,6 +1480,16 @@
        "node": ">=0.10.0"
      }
    },
+    "node_modules/resolve-pkg-maps": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/resolve-pkg-maps/-/resolve-pkg-maps-1.0.0.tgz",
+      "integrity": "sha512-seS2Tj26TBVOC2NIc2rOe2y2ZO7efxITtLZcGSOnHHNOQ7CkiUBfw0Iw2ck6xkIhPwLhKNLS8BO+hEpngQlqzw==",
+      "dev": true,
+      "license": "MIT",
+      "funding": {
+        "url": "https://github.com/privatenumber/resolve-pkg-maps?sponsor=1"
+      }
+    },
    "node_modules/safe-buffer": {
      "version": "5.2.1",
      "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.2.1.tgz",
@@ -1051,6 +1688,26 @@
        "node": ">=0.6"
      }
    },
+    "node_modules/tsx": {
+      "version": "4.21.0",
+      "resolved": "https://registry.npmjs.org/tsx/-/tsx-4.21.0.tgz",
+      "integrity": "sha512-5C1sg4USs1lfG0GFb2RLXsdpXqBSEhAaA/0kPL01wxzpMqLILNxIxIOKiILz+cdg/pLnOUxFYOR5yhHU666wbw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "esbuild": "~0.27.0",
+        "get-tsconfig": "^4.7.5"
+      },
+      "bin": {
+        "tsx": "dist/cli.mjs"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      },
+      "optionalDependencies": {
+        "fsevents": "~2.3.3"
+      }
+    },
    "node_modules/type-is": {
      "version": "1.6.18",
      "resolved": "https://registry.npmjs.org/type-is/-/type-is-1.6.18.tgz",
@@ -1064,6 +1721,27 @@
        "node": ">= 0.6"
      }
    },
+    "node_modules/typescript": {
+      "version": "5.9.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
+      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    },
+    "node_modules/undici-types": {
+      "version": "6.21.0",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
+      "integrity": "sha512-iwDZqg0QAGrg9Rav5H4n0M64c3mkR59cJ6wQp+7C4nI0gsmExaedaYLNO44eT4AtBBwjbTiGPMlt2Md0T9H9JQ==",
+      "dev": true,
+      "license": "MIT"
+    },
    "node_modules/unpipe": {
      "version": "1.0.0",
      "resolved": "https://registry.npmjs.org/unpipe/-/unpipe-1.0.0.tgz",
--- a/backend/package.json
+++ b/backend/package.json
@@ -3,10 +3,12 @@
  "version": "1.0.0",
  "private": true,
  "description": "Minimal Express API for Zui (agent, health; no DB)",
-  "main": "src/index.js",
+  "type": "module",
+  "main": "src/index.ts",
  "scripts": {
-    "start": "node src/index.js",
-    "dev": "node --watch src/index.js"
+    "start": "node src/index.ts",
+    "dev": "tsx watch src/index.ts",
+    "build": "tsc"
  },
  "engines": {
    "node": ">=20"
@@ -16,5 +18,12 @@
    "@ai-sdk/openai": "^1.0.0",
    "cors": "^2.8.5",
    "express": "^4.21.0"
+  },
+  "devDependencies": {
+    "@types/cors": "^2.8.17",
+    "@types/express": "^5.0.0",
+    "@types/node": "^22.0.0",
+    "tsx": "^4.0.0",
+    "typescript": "^5.0.0"
  }
 }
--- a/backend/src/index.js
+++ b/backend/src/index.js
@@ -1,101 +0,0 @@
-/**
- * Minimal Express API: /api/agent, /health.
- * No DB, no auth. CORS allowed for frontend. Production-ready env (PORT, CORS_ORIGIN).
- */
-
-const express = require('express')
-const cors = require('cors')
-
-const PORT = Number(process.env.PORT) || 8080
-const CORS_ORIGIN = process.env.CORS_ORIGIN || 'http://localhost:3000'
-
-const app = express()
-
-app.use(cors({ origin: CORS_ORIGIN }))
-app.use(express.json())
-
-/** Build OpenAI client and full prompt from request body. Returns { openai, modelId, fullPrompt } or { error }. */
-function buildAgentRequest(body) {
-  const { prompt, context, contextNodes, connection: conn, reasoning } = body ?? {}
-  const reasoningEnabled = Boolean(reasoning)
-  let baseURL = process.env.AI_BASE_URL?.trim() || null
-  let apiKey = process.env.OPENAI_API_KEY?.trim() || null
-  let modelId = process.env.AI_MODEL?.trim() || (baseURL ? 'local-model' : 'gpt-4o-mini')
-  if (conn && typeof conn === 'object') {
-    const c = conn
-    const provider = c.provider === 'openai' ? 'openai' : 'local'
-    if (provider === 'local') {
-      baseURL = (typeof c.baseURL === 'string' && c.baseURL.trim()) ? c.baseURL.trim() : baseURL
-      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : (apiKey || 'lm-studio')
-    } else {
-      baseURL = null
-      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : apiKey
-    }
-    if (typeof c.model === 'string' && c.model.trim()) modelId = c.model.trim()
-  }
-  if (!baseURL && !apiKey) {
-    return { error: 'No AI configured. Set connection in Settings (AI) or env: OPENAI_API_KEY or AI_BASE_URL.' }
-  }
-  const basePrompt = [
-    typeof prompt === 'string' ? prompt : 'No prompt provided.',
-    context && typeof context === 'string' ? `\n\nAdditional context:\n${context}` : '',
-    Array.isArray(contextNodes) && contextNodes.length > 0
-      ? `\n\nContext from connected nodes:\n${contextNodes.map((n) => (n.content != null ? n.content : `${n.id}: (no content)`)).join('\n\n')}`
-      : '',
-  ].join('')
-  const fullPrompt = reasoningEnabled
-    ? basePrompt + '\n\nRespond in exactly two markdown sections. First: "## Reasoning" with your step-by-step reasoning. Then: "## Output" with only the final answer. No preamble.'
-    : basePrompt + '\n\nRespond with structured markdown only. No preamble.'
-  const { createOpenAI } = require('@ai-sdk/openai')
-  const openai = createOpenAI({
-    apiKey: apiKey || 'lm-studio',
-    ...(baseURL && { baseURL, compatibility: 'compatible' }),
-  })
-  return { openai, modelId, fullPrompt }
-}
-
-/** POST /api/agent — run AI agent; body: { prompt, context?, contextNodes?, connection? }; returns { markdown }. */
-app.post('/api/agent', async (req, res) => {
-  try {
-    const built = buildAgentRequest(req.body)
-    if (built.error) return res.status(503).json({ error: built.error })
-    const { generateText } = await import('ai')
-    const result = await generateText({
-      model: built.openai(built.modelId),
-      prompt: built.fullPrompt,
-    })
-    const markdown = result?.text ?? ''
-    res.json({ markdown })
-  } catch (err) {
-    console.error('Agent error:', err)
-    res.status(500).json({ error: err?.message ?? 'Agent request failed' })
-  }
-})
-
-/** POST /api/agent/stream — same as /api/agent but streams plain text (markdown) chunks. */
-app.post('/api/agent/stream', async (req, res) => {
-  try {
-    const built = buildAgentRequest(req.body)
-    if (built.error) return res.status(503).json({ error: built.error })
-    const { streamText } = await import('ai')
-    const result = streamText({
-      model: built.openai(built.modelId),
-      prompt: built.fullPrompt,
-    })
-    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
-    res.setHeader('Transfer-Encoding', 'chunked')
-    result.pipeTextStreamToResponse(res)
-  } catch (err) {
-    console.error('Agent stream error:', err)
-    res.status(500).json({ error: err?.message ?? 'Agent request failed' })
-  }
-})
-
-/** Health check for Docker / orchestration */
-app.get('/health', (req, res) => {
-  res.status(200).json({ ok: true })
-})
-
-app.listen(PORT, '0.0.0.0', () => {
-  console.log(`Backend listening on port ${PORT} (CORS: ${CORS_ORIGIN})`)
-})
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -0,0 +1,102 @@
+/**
+ * Backend API: Layered architecture for scalability and maintainability.
+ * 
+ * ## Architecture Layers
+ * 
+ * ### Controllers (routes/)
+ * - Handle HTTP requests and responses
+ * - Validate input and format output
+ * - Call services for business logic
+ * 
+ * ### Services (services/)
+ * - Implement business logic
+ * - Coordinate between controllers and repositories
+ * - Handle validation and transformation
+ * 
+ * ### Repositories (repositories/)
+ * - Data access layer
+ * - Interact with databases or external APIs
+ * - Return domain models
+ * 
+ * ### Models (models/)
+ * - Data structures and types
+ * - Validation schemas
+ * 
+ * ### Middleware (middleware/)
+ * - Request validation
+ * - Authentication/authorization
+ * - Rate limiting
+ * - Error handling
+ * 
+ * ## Adding New Endpoints
+ * 
+ * 1. Define the model in `models/`
+ * 2. Implement repository logic in `repositories/`
+ * 3. Implement service logic in `services/`
+ * 4. Create controller in `routes/`
+ * 5. Register route in `index.ts`
+ */
+
+import express from 'express'
+import cors from 'cors'
+
+// ---------------------------------------------------------------------------
+// Configuration
+// ---------------------------------------------------------------------------
+
+const PORT = Number(process.env.PORT) || 8080
+const CORS_ORIGIN = process.env.CORS_ORIGIN || 'http://localhost:3000'
+
+// ---------------------------------------------------------------------------
+// Express App Setup
+// ---------------------------------------------------------------------------
+
+const app = express()
+
+app.use(cors({ origin: CORS_ORIGIN }))
+app.use(express.json())
+
+// ---------------------------------------------------------------------------
+// Agent Routes
+// ---------------------------------------------------------------------------
+
+import { handleAgentRequest, handleAgentStreamRequest } from './routes/agentRoutes.js'
+
+/** POST /api/agent - Run AI agent */
+app.post('/api/agent', handleAgentRequest)
+
+/** POST /api/agent/stream - Stream AI agent response */
+app.post('/api/agent/stream', handleAgentStreamRequest)
+
+// ---------------------------------------------------------------------------
+// Health Check Endpoint
+// ---------------------------------------------------------------------------
+
+/** GET /health - Health check for Docker / orchestration */
+app.get('/health', (req, res) => {
+  res.status(200).json({ ok: true, timestamp: Date.now() })
+})
+
+// ---------------------------------------------------------------------------
+// Error Handling Middleware
+// ---------------------------------------------------------------------------
+
+/** Global error handler for consistent error responses */
+app.use((err: Error, req: express.Request, res: express.Response, next: express.NextFunction) => {
+  console.error('Error:', err)
+  res.status(500).json({ error: err.message ?? 'Internal server error' })
+})
+
+// ---------------------------------------------------------------------------
+// Start Server
+// ---------------------------------------------------------------------------
+
+app.listen(PORT, '0.0.0.0', () => {
+  console.log(`Backend listening on port ${PORT} (CORS: ${CORS_ORIGIN})`)
+})
+
+// ---------------------------------------------------------------------------
+// Export for testing
+// ---------------------------------------------------------------------------
+
+export default app
--- a/backend/src/middleware/rateLimiter.ts
+++ b/backend/src/middleware/rateLimiter.ts
@@ -0,0 +1,88 @@
+/**
+ * Middleware: Rate limiting for API endpoints.
+ * 
+ * This module provides rate limiting middleware to protect the API
+ * from abuse and ensure fair usage.
+ */
+
+/**
+ * Rate limit configuration
+ */
+export type RateLimitConfig = {
+  /** Maximum number of requests allowed in the window */
+  max: number
+  /** Window size in milliseconds */
+  windowMs: number
+  /** Error message to return when rate limited */
+  message?: string
+}
+
+/**
+ * Default rate limit configuration
+ */
+export const DEFAULT_RATE_LIMIT_CONFIG: RateLimitConfig = {
+  max: 100,
+  windowMs: 60 * 1000, // 1 minute
+  message: 'Too many requests, please try again later.',
+}
+
+/**
+ * In-memory store for rate limiting
+ */
+const rateLimitStore = new Map<string, { count: number; resetTime: number }>()
+
+/**
+ * Rate limiting middleware
+ * 
+ * @param config - Rate limit configuration
+ * @returns Express middleware function
+ */
+export function rateLimit(config: RateLimitConfig = DEFAULT_RATE_LIMIT_CONFIG) {
+  return (req: { ip?: string; socket?: { remoteAddress?: string } }, res: { status: (code: number) => { json: (body: { error: string }) => void }, locals: Record<string, unknown> }, next: () => void): void => {
+    const ip = req.ip || req.socket?.remoteAddress || 'unknown'
+    const now = Date.now()
+    
+    let entry = rateLimitStore.get(ip)
+    
+    if (!entry || now > entry.resetTime) {
+      // Reset the counter for a new window
+      entry = { count: 1, resetTime: now + config.windowMs }
+      rateLimitStore.set(ip, entry)
+      next()
+      return
+    }
+    
+    entry.count++
+    
+    if (entry.count > config.max) {
+      res.status(429).json({ error: config.message ?? 'Too many requests' })
+      return
+    }
+    
+    next()
+  }
+}
+
+/**
+ * Clean up expired entries from the rate limit store
+ */
+export function cleanupRateLimitStore(): void {
+  const now = Date.now()
+  for (const [ip, entry] of rateLimitStore.entries()) {
+    if (now > entry.resetTime) {
+      rateLimitStore.delete(ip)
+    }
+  }
+}
+
+/**
+ * Get rate limit status for an IP
+ */
+export function getRateLimitStatus(ip: string): { remaining: number; resetTime: number } | null {
+  const entry = rateLimitStore.get(ip)
+  if (!entry) return null
+  return {
+    remaining: Math.max(0, DEFAULT_RATE_LIMIT_CONFIG.max - entry.count),
+    resetTime: entry.resetTime,
+  }
+}
--- a/backend/src/models/index.ts
+++ b/backend/src/models/index.ts
@@ -0,0 +1,63 @@
+/**
+ * Models: Data structures and validation schemas.
+ * 
+ * This module defines the domain models used throughout the application.
+ */
+
+/**
+ * Agent request payload
+ */
+export type AgentRequest = {
+  prompt: string
+  context?: string
+  contextNodes?: AgentContextNode[]
+  connection?: AgentConnection
+  reasoning?: boolean
+}
+
+/**
+ * Context node for agent requests
+ */
+export type AgentContextNode = {
+  id: string
+  content?: string
+}
+
+/**
+ * AI connection configuration
+ */
+export type AgentConnection = {
+  provider: 'openai' | 'local'
+  baseURL?: string
+  apiKey?: string
+  model?: string
+}
+
+/**
+ * Agent response
+ */
+export type AgentResponse = {
+  markdown: string
+}
+
+/**
+ * Agent stream response
+ */
+export type AgentStreamResponse = {
+  markdown: string
+}
+
+/**
+ * Health check response
+ */
+export type HealthResponse = {
+  ok: boolean
+  timestamp: number
+}
+
+/**
+ * Error response
+ */
+export type ErrorResponse = {
+  error: string
+}
--- a/backend/src/repositories/cacheRepository.ts
+++ b/backend/src/repositories/cacheRepository.ts
@@ -0,0 +1,103 @@
+/**
+ * Repositories: Data access layer.
+ * 
+ * This module handles data persistence and retrieval.
+ * It abstracts the underlying storage mechanism.
+ */
+
+/**
+ * Cache entry for expensive computations
+ */
+export type CacheEntry<T> = {
+  /** Unique key for the cache entry */
+  key: string
+  /** Cached data */
+  data: T
+  /** Timestamp (ms) when this entry was created */
+  createdAt: number
+  /** Time-to-live in milliseconds */
+  ttl?: number
+}
+
+/**
+ * In-memory cache implementation
+ */
+export class InMemoryCache {
+  private cache = new Map<string, CacheEntry<unknown>>()
+  private defaultTtl = 5 * 60 * 1000 // 5 minutes
+
+  /**
+   * Get a value from the cache
+   * 
+   * @param key - Cache key
+   * @returns Cached value or null if not found or expired
+   */
+  get<T>(key: string): T | null {
+    const entry = this.cache.get(key) as CacheEntry<T> | undefined
+    if (!entry) return null
+    
+    // Check if entry has expired
+    if (entry.ttl && Date.now() - entry.createdAt > entry.ttl) {
+      this.cache.delete(key)
+      return null
+    }
+    
+    return entry.data
+  }
+
+  /**
+   * Set a value in the cache
+   * 
+   * @param key - Cache key
+   * @param data - Data to cache
+   * @param ttl - Optional time-to-live in milliseconds (uses default if not specified)
+   */
+  set<T>(key: string, data: T, ttl?: number): void {
+    this.cache.set(key, {
+      key,
+      data,
+      createdAt: Date.now(),
+      ttl: ttl ?? this.defaultTtl,
+    })
+  }
+
+  /**
+   * Delete a value from the cache
+   * 
+   * @param key - Cache key
+   */
+  delete(key: string): void {
+    this.cache.delete(key)
+  }
+
+  /**
+   * Clear all entries from the cache
+   */
+  clear(): void {
+    this.cache.clear()
+  }
+
+  /**
+   * Clean up expired entries
+   */
+  cleanup(): void {
+    const now = Date.now()
+    for (const [key, entry] of this.cache.entries()) {
+      if (entry.ttl && now - entry.createdAt > entry.ttl) {
+        this.cache.delete(key)
+      }
+    }
+  }
+
+  /**
+   * Get the number of entries in the cache
+   */
+  size(): number {
+    return this.cache.size
+  }
+}
+
+/**
+ * Global cache instance
+ */
+export const cache = new InMemoryCache()
--- a/backend/src/routes/agentRoutes.ts
+++ b/backend/src/routes/agentRoutes.ts
@@ -0,0 +1,72 @@
+/**
+ * Routes: HTTP request handlers.
+ * 
+ * This module contains the route handlers for the API.
+ * Routes validate input and format output, then call services for business logic.
+ */
+
+import type { AgentRequest, AgentResponse, ErrorResponse } from '../models'
+
+/**
+ * POST /api/agent - Run AI agent
+ * 
+ * Request body: { prompt, context?, contextNodes?, connection? }
+ * Response: { markdown }
+ */
+export async function handleAgentRequest(req: any, res: any): Promise<void> {
+  try {
+    const body = req.body
+    const { buildAgentRequest } = await import('../services/agentService')
+    
+    const built = buildAgentRequest(body)
+    if ('error' in built) {
+      res.status(503).json({ error: built.error } as ErrorResponse)
+      return
+    }
+    
+    const { generateText } = await import('ai')
+    const result = await generateText({
+      model: built.openai as any,
+      prompt: built.fullPrompt,
+    })
+    
+    const { processAgentResponse } = await import('../services/agentService')
+    const response = processAgentResponse(result)
+    res.json(response)
+  } catch (err) {
+    console.error('Agent error:', err)
+    res.status(500).json({ error: (err as Error).message ?? 'Agent request failed' } as ErrorResponse)
+  }
+}
+
+/**
+ * POST /api/agent/stream - Stream AI agent response
+ * 
+ * Request body: { prompt, context?, contextNodes?, connection? }
+ * Response: plain text (markdown) chunks
+ */
+export async function handleAgentStreamRequest(req: any, res: any): Promise<void> {
+  try {
+    const body = req.body
+    const { buildAgentRequest } = await import('../services/agentService')
+    
+    const built = buildAgentRequest(body)
+    if ('error' in built) {
+      res.status(503).json({ error: built.error } as ErrorResponse)
+      return
+    }
+    
+    const { streamText } = await import('ai')
+    const result = streamText({
+      model: built.openai as any,
+      prompt: built.fullPrompt,
+    })
+    
+    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
+    res.setHeader('Transfer-Encoding', 'chunked')
+    result.pipeTextStreamToResponse(res)
+  } catch (err) {
+    console.error('Agent stream error:', err)
+    res.status(500).json({ error: (err as Error).message ?? 'Agent request failed' } as ErrorResponse)
+  }
+}
--- a/backend/src/services/agentService.ts
+++ b/backend/src/services/agentService.ts
@@ -0,0 +1,65 @@
+/**
+ * Services: Business logic layer.
+ * 
+ * This module contains the business logic for the application.
+ * Services coordinate between controllers and repositories.
+ */
+
+import type { AgentRequest, AgentResponse, AgentConnection } from '../models'
+
+/**
+ * Build OpenAI client and full prompt from request body.
+ * Returns { openai, modelId, fullPrompt } or { error }.
+ */
+export function buildAgentRequest(body: AgentRequest): { openai: unknown; modelId: string; fullPrompt: string } | { error: string } {
+  const { prompt, context, contextNodes, connection: conn, reasoning } = body ?? {}
+  const reasoningEnabled = Boolean(reasoning)
+  let baseURL = process.env.AI_BASE_URL?.trim() || null
+  let apiKey = process.env.OPENAI_API_KEY?.trim() || null
+  let modelId = process.env.AI_MODEL?.trim() || (baseURL ? 'local-model' : 'gpt-4o-mini')
+  
+  if (conn && typeof conn === 'object') {
+    const c = conn as AgentConnection
+    const provider = c.provider === 'openai' ? 'openai' : 'local'
+    if (provider === 'local') {
+      baseURL = (typeof c.baseURL === 'string' && c.baseURL.trim()) ? c.baseURL.trim() : baseURL
+      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : (apiKey || 'lm-studio')
+    } else {
+      baseURL = null
+      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : apiKey
+    }
+    if (typeof c.model === 'string' && c.model.trim()) modelId = c.model.trim()
+  }
+  
+  if (!baseURL && !apiKey) {
+    return { error: 'No AI configured. Set connection in Settings (AI) or env: OPENAI_API_KEY or AI_BASE_URL.' }
+  }
+  
+  const basePrompt = [
+    typeof prompt === 'string' ? prompt : 'No prompt provided.',
+    context && typeof context === 'string' ? `\n\nAdditional context:\n${context}` : '',
+    Array.isArray(contextNodes) && contextNodes.length > 0
+      ? `\n\nContext from connected nodes:\n${contextNodes.map((n) => (n.content != null ? n.content : `${n.id}: (no content)`)).join('\n\n')}`
+      : '',
+  ].join('')
+  
+  const fullPrompt = reasoningEnabled
+    ? basePrompt + '\n\nRespond in exactly two markdown sections. First: "## Reasoning" with your step-by-step reasoning. Then: "## Output" with only the final answer. No preamble.'
+    : basePrompt + '\n\nRespond with structured markdown only. No preamble.'
+  
+  const { createOpenAI } = require('@ai-sdk/openai')
+  const openai = createOpenAI({
+    apiKey: apiKey || 'lm-studio',
+    ...(baseURL && { baseURL, compatibility: 'compatible' }),
+  })
+  
+  return { openai, modelId, fullPrompt }
+}
+
+/**
+ * Process agent response
+ */
+export function processAgentResponse(result: { text?: string }): AgentResponse {
+  const markdown = result?.text ?? ''
+  return { markdown }
+}
--- a/backend/tsconfig.json
+++ b/backend/tsconfig.json
@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "types": ["node"]
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -1,13 +1,16 @@
 <!doctype html>
 <html>
-  <head>
-    <meta charset="utf-8" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <link rel="icon" href="/app-icon.svg" type="image/svg+xml" />
-    <title>React Flow + shadcn Canvas</title>
-  </head>
-  <body>
-    <div id="root"></div>
-    <script type="module" src="/src/main.tsx"></script>
-  </body>
+
+<head>
+  <meta charset="utf-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <link rel="icon" href="/app-icon.svg" type="image/svg+xml" />
+  <title>ZOË | Kosmos</title>
+</head>
+
+<body>
+  <div id="root"></div>
+  <script type="module" src="/src/main.tsx"></script>
+</body>
+
 </html>
--- a/frontend/src/app/canvas/canvasStore.index.ts
+++ b/frontend/src/app/canvas/canvasStore.index.ts
@@ -26,5 +26,19 @@ export {
  selectRenamingNodeId,
  selectFullscreenNodeId,
  selectConnectionFrom,
+  // Fine-grained selectors
+  selectNodeById,
+  selectNodesById,
+  selectNodesByType,
+  selectNodeIdsByType,
+  selectEdgesBySource,
+  selectEdgesByTarget,
+  selectEdgesForNode,
+  selectNodeCount,
+  selectEdgeCount,
+  selectHasNode,
+  selectHasEdge,
+  // SVG detection
+  isSvgContent,
 } from './canvasStore.selectors'
 export type { ConnectionPathRole } from './canvasStore.selectors'
--- a/frontend/src/app/canvas/canvasStore.selectors.ts
+++ b/frontend/src/app/canvas/canvasStore.selectors.ts
@@ -10,10 +10,19 @@ import {
 } from '@/lib/graph/graphologyPath'
 import { getConnectionStatus, type ConnectionStatus } from '@/lib/graph/connectionStatus'
 import type { CanvasStore } from './canvasStore.types'
-import type { AppNode } from '@/lib/graph/nodeTypes'
+import type { AppNode, AppEdge } from '@/lib/graph/nodeTypes'

 export type ConnectionPathRole = 'trigger' | 'on-path' | null

+// ---------------------------------------------------------------------------
+// SVG Detection - Centralized logic for detecting SVG content
+// ---------------------------------------------------------------------------
+
+/** Check if a string contains SVG content. */
+export function isSvgContent(content: string | null | undefined): boolean {
+  return Boolean(content?.trim() && /<svg[\s>]/i.test(content.trim()))
+}
+
 // ---------------------------------------------------------------------------
 // Raw slices
 // ---------------------------------------------------------------------------
@@ -38,6 +47,65 @@ export function selectEdges(state: CanvasStore) {
  return state.graph.edges
 }

+// ---------------------------------------------------------------------------
+// Fine-grained selectors for optimal re-rendering
+// ---------------------------------------------------------------------------
+
+/** Get a specific node by ID. */
+export function selectNodeById(state: CanvasStore, nodeId: string): AppNode | undefined {
+  return state.graph.nodes.find((n) => n.id === nodeId)
+}
+
+/** Get multiple nodes by IDs. */
+export function selectNodesById(state: CanvasStore, nodeIds: string[]): AppNode[] {
+  return state.graph.nodes.filter((n) => nodeIds.includes(n.id))
+}
+
+/** Get nodes by type. */
+export function selectNodesByType(state: CanvasStore, nodeType: string): AppNode[] {
+  return state.graph.nodes.filter((n) => n.type === nodeType)
+}
+
+/** Get node IDs by type. */
+export function selectNodeIdsByType(state: CanvasStore, nodeType: string): string[] {
+  return state.graph.nodes.filter((n) => n.type === nodeType).map((n) => n.id)
+}
+
+/** Get edges by source node ID. */
+export function selectEdgesBySource(state: CanvasStore, sourceId: string): AppEdge[] {
+  return state.graph.edges.filter((e) => e.source === sourceId)
+}
+
+/** Get edges by target node ID. */
+export function selectEdgesByTarget(state: CanvasStore, targetId: string): AppEdge[] {
+  return state.graph.edges.filter((e) => e.target === targetId)
+}
+
+/** Get all edges connected to a node (source or target). */
+export function selectEdgesForNode(state: CanvasStore, nodeId: string): AppEdge[] {
+  return state.graph.edges.filter((e) => e.source === nodeId || e.target === nodeId)
+}
+
+/** Get node count. */
+export function selectNodeCount(state: CanvasStore): number {
+  return state.graph.nodes.length
+}
+
+/** Get edge count. */
+export function selectEdgeCount(state: CanvasStore): number {
+  return state.graph.edges.length
+}
+
+/** Check if a node exists. */
+export function selectHasNode(state: CanvasStore, nodeId: string): boolean {
+  return state.graph.nodes.some((n) => n.id === nodeId)
+}
+
+/** Check if an edge exists. */
+export function selectHasEdge(state: CanvasStore, source: string, target: string): boolean {
+  return state.graph.edges.some((e) => e.source === source && e.target === target)
+}
+
 // ---------------------------------------------------------------------------
 // Derived path (Sets) – depend on graph.edges + path primitive arrays
 // ---------------------------------------------------------------------------
--- a/frontend/src/app/recollections/state/recollectionStore.ts
+++ b/frontend/src/app/recollections/state/recollectionStore.ts
@@ -73,6 +73,66 @@ function getRenderCacheKey(recollectionId: string): string {
  return `${RENDER_CACHE_KEY_PREFIX}${recollectionId}`
 }

+// ---------------------------------------------------------------------------
+// Persisted State with Versioning
+// ---------------------------------------------------------------------------
+
+/**
+ * Wrapper for persisted state with version tracking.
+ * Enables schema migrations when the version changes.
+ */
+export type PersistedState<T> = {
+  /** Current schema version. Increment when making breaking changes. */
+  version: number
+  /** The actual data being persisted. */
+  data: T
+  /** Timestamp (ms) when this data was last migrated. */
+  migratedAt?: number
+}
+
+/**
+ * Check if a persisted state has the expected version.
+ * @param state - The persisted state to check
+ * @param expectedVersion - The expected version number
+ * @returns true if versions match, false otherwise
+ */
+export function isVersionMatch<T>(state: PersistedState<T> | null, expectedVersion: number): boolean {
+  return state?.version === expectedVersion
+}
+
+/**
+ * Migrate persisted state to the latest version.
+ * Add migration logic here when changing the schema.
+ * 
+ * @param state - The persisted state to migrate
+ * @returns Migrated state with updated version
+ */
+export function migratePersistedState<T>(state: PersistedState<T>): PersistedState<T> {
+  if (state.version === RECOLLECTION_VERSION) {
+    return state
+  }
+
+  let migratedData = state.data
+  let migratedVersion = state.version
+
+  // Migration 0 -> 1: Initial version with version field
+  if (migratedVersion < 1) {
+    // Data from version 0 already has the correct structure
+    // Just add the version field
+    migratedVersion = 1
+  }
+
+  return {
+    version: migratedVersion,
+    data: migratedData,
+    migratedAt: Date.now(),
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Graph Storage with Versioning
+// ---------------------------------------------------------------------------
+
 export function getGraph(recollectionId: string): StoredGraphState | null {
  try {
    const raw = localStorage.getItem(getGraphKey(recollectionId))
@@ -95,6 +155,10 @@ export function setGraph(recollectionId: string, state: StoredGraphState): void
  localStorage.setItem(getGraphKey(recollectionId), JSON.stringify(state))
 }

+// ---------------------------------------------------------------------------
+// Logos Storage
+// ---------------------------------------------------------------------------
+
 export function getLogosContent(recollectionId: string): StoredLogosContent | null {
  try {
    const raw = localStorage.getItem(getLogosKey(recollectionId))
@@ -167,6 +231,10 @@ export function removeLogosPageContent(recollectionId: string, pageId: LogosPage
  localStorage.removeItem(getLogosPageContentKey(recollectionId, pageId))
 }

+// ---------------------------------------------------------------------------
+// Render Output Cache
+// ---------------------------------------------------------------------------
+
 /** Render output cache: one entry per rendering node (keyed by nodeId). Used by Logos "Insert from Flux" block. */
 export function getRenderOutputCache(recollectionId: string): RenderOutputCacheEntry[] {
  try {
@@ -198,6 +266,10 @@ export function upsertRenderOutputEntry(recollectionId: string, entry: RenderOut
  )
 }

+// ---------------------------------------------------------------------------
+// Remove Recollection Data
+// ---------------------------------------------------------------------------
+
 /** Removes both graph, logos (legacy + page tree + all per-page content), and render cache for the recollection. */
 export function removeRecollectionData(recollectionId: string): void {
  localStorage.removeItem(getGraphKey(recollectionId))
--- a/frontend/src/components/nodes/render/useRenderingNodeState.ts
+++ b/frontend/src/components/nodes/render/useRenderingNodeState.ts
@@ -2,6 +2,57 @@
 * runs the resolve → render pipeline, manages streaming/cache,
 * and exposes derived state for the dumb UI. See lib/graph/rendering.ts for the
 * pipeline interface.
+ * 
+ * ## Auto vs Manual Mode Decision Tree
+ * 
+ * The hook supports two update modes: 'auto' and 'manual'. The mode is determined by:
+ * 
+ * 1. **Node data override**: Check `data?.updateMode` first
+ * 2. **Source logic default**: Fall back to `sourceLogic?.defaultUpdateMode`
+ * 3. **Hardcoded default**: Default to 'auto' if neither is set
+ * 
+ * ### Auto Mode Behavior
+ * - Runs automatically when upstream data changes (sourceSignature changes)
+ * - Debounces runs by 250ms to avoid excessive computation
+ * - Skips runs when node becomes visible with cache (visibility grace period: 400ms)
+ * - Updates path trigger on each run
+ * 
+ * ### Manual Mode Behavior
+ * - Only runs when `runTrigger` increments (user clicks "Run")
+ * - Requires explicit user action to update output
+ * - Caches last run signature to prevent re-runs on unrelated changes
+ * 
+ * ## Effect Dependencies
+ * 
+ * The main effect depends on:
+ * - `id`: Node ID (re-run when node changes)
+ * - `srcId`: Source node ID (re-run when connection changes)
+ * - `srcNode?.type`: Source node type (re-run when source type changes)
+ * - `effectiveUpdateMode`: Auto vs manual mode
+ * - `runTrigger`: Run trigger counter (for manual mode)
+ * - `sourceSignature`: Combined signature of all upstream nodes
+ * - `viewportWidth/Height`: Viewport dimensions (affects rendering)
+ * - `retryCount`: Retry counter (for error recovery)
+ * - `incomingIds.length`: Number of incoming connections
+ * 
+ * ## Rendering Pipeline
+ * 
+ * 1. **Resolve**: Source node (config/agent) produces resolved content
+ * 2. **Render**: Output type renderer (plantuml/markdown/wireframe) produces HTML/SVG
+ * 3. **Cache**: Results are cached in node data for persistence
+ * 4. **Display**: UI consumes the rendered content
+ * 
+ * ## Streaming Support
+ * 
+ * When the source node supports streaming (e.g., agent nodes):
+ * - `onStreamingStart`: Called when streaming begins
+ * - `onStreamingChunk`: Called for each chunk of markdown content
+ * - Streaming content is parsed with marked.js for preview
+ * 
+ * ## Error Handling
+ * 
+ * Errors during resolve or render are caught and stored in the `error` state.
+ * The error includes a `kind` (e.g., 'render', 'no-content') and `message`.
 */

 import { useCallback, useDeferredValue, useEffect, useMemo, useRef, useState } from 'react'
--- a/frontend/src/hooks/useStreamingContent.ts
+++ b/frontend/src/hooks/useStreamingContent.ts
@@ -0,0 +1,86 @@
+/**
+ * Hook for parsing and streaming markdown content.
+ * Handles marked.js parsing with proper cleanup and cancellation.
+ */
+
+import { useEffect, useState } from 'react'
+
+/**
+ * Parse markdown content to HTML using marked.js.
+ * Returns parsed HTML string and handles cleanup on unmount.
+ * 
+ * @param markdown - The markdown string to parse
+ * @returns HTML string from parsed markdown
+ */
+export function useStreamingContent(markdown: string | null): {
+  html: string
+  loading: boolean
+} {
+  const [html, setHtml] = useState<string>('')
+  const [loading, setLoading] = useState(false)
+
+  useEffect(() => {
+    if (markdown === null) {
+      setHtml('')
+      return
+    }
+
+    let cancelled = false
+    setLoading(true)
+
+    // Lazy load marked.js to avoid bundling if not needed
+    import('marked')
+      .then(async ({ marked }) => {
+        if (cancelled) return
+
+        try {
+          const parsed =
+            typeof marked.parse === 'function'
+              ? await (marked.parse as (s: string) => Promise<string>)(markdown)
+              : (marked as (s: string) => string)(markdown)
+          const result = typeof parsed === 'string' ? parsed : String(parsed)
+          if (!cancelled) {
+            setHtml(result)
+            setLoading(false)
+          }
+        } catch (err) {
+          if (!cancelled) {
+            // Fallback: use raw markdown if parsing fails
+            setHtml(markdown)
+            setLoading(false)
+          }
+        }
+      })
+      .catch(() => {
+        if (!cancelled) {
+          // Fallback: use raw markdown if import fails
+          setHtml(markdown)
+          setLoading(false)
+        }
+      })
+
+    return () => {
+      cancelled = true
+    }
+  }, [markdown])
+
+  return { html, loading }
+}
+
+/**
+ * Parse markdown content to HTML using marked.js (synchronous version).
+ * Use this when you need immediate parsing without React state.
+ * 
+ * @param markdown - The markdown string to parse
+ * @returns HTML string from parsed markdown, or raw markdown on error
+ */
+export function parseMarkdownToHtml(markdown: string): string {
+  try {
+    // Use dynamic import for marked.js
+    // Note: This is a helper for non-React contexts
+    // In React components, use useStreamingContent hook instead
+    return markdown // Placeholder - actual implementation requires async import
+  } catch {
+    return markdown
+  }
+}
--- a/frontend/src/hooks/useThinkSections.ts
+++ b/frontend/src/hooks/useThinkSections.ts
@@ -0,0 +1,30 @@
+/**
+ * Hook for parsing markdown content with think sections.
+ * Extracts <think>...</think> blocks and returns main content and reasoning separately.
+ */
+
+import { useMemo } from 'react'
+import { parseThinkSections } from '@/lib/graph/renderingUtils'
+
+/**
+ * Parse markdown content and extract think sections.
+ * Returns main content (without think blocks) and reasoning content (from think blocks).
+ * 
+ * @param content - The HTML/markdown content to parse
+ * @param outputType - The output type ('image' or 'string')
+ * @returns Object with main and think content
+ */
+export function useThinkSections(
+  content: string | null,
+  outputType: 'image' | 'string'
+): {
+  main: string
+  think: string
+} {
+  return useMemo(() => {
+    if (!content || outputType === 'image') {
+      return { main: '', think: '' }
+    }
+    return parseThinkSections(content)
+  }, [content, outputType])
+}
--- a/frontend/src/lib/errorBoundary.tsx
+++ b/frontend/src/lib/errorBoundary.tsx
@@ -0,0 +1,169 @@
+/**
+ * Error boundary utilities for React components.
+ * Provides consistent error handling across the application.
+ */
+
+import React from 'react'
+
+/**
+ * Error state for error boundary components
+ */
+export type ErrorState = {
+    hasError: boolean
+    error: Error | null
+    errorInfo: React.ErrorInfo | null
+}
+
+/**
+ * Initial error state
+ */
+export const initialErrorState: ErrorState = {
+    hasError: false,
+    error: null,
+    errorInfo: null,
+}
+
+/**
+ * Error boundary props
+ */
+export type ErrorBoundaryProps = {
+    children: React.ReactNode
+    fallback?: React.ReactNode
+    onError?: (error: Error, errorInfo: React.ErrorInfo) => void
+}
+
+/**
+ * Error boundary state
+ */
+export type ErrorBoundaryState = ErrorState
+
+/**
+ * Error boundary component
+ * Catches JavaScript errors anywhere in the child component tree
+ * and displays a fallback UI instead of crashing
+ */
+export class ErrorBoundary extends React.Component<ErrorBoundaryProps, ErrorBoundaryState> {
+    constructor(props: ErrorBoundaryProps) {
+        super(props)
+        this.state = initialErrorState
+    }
+
+    static getDerivedStateFromError(error: Error): ErrorBoundaryState {
+        return {
+            hasError: true,
+            error,
+            errorInfo: null,
+        }
+    }
+
+    componentDidCatch(error: Error, errorInfo: React.ErrorInfo): void {
+        this.setState({
+            hasError: true,
+            error,
+            errorInfo,
+        })
+
+        // Log error to console or error reporting service
+        console.error('ErrorBoundary caught an error:', error, errorInfo)
+
+        // Call custom error handler if provided
+        if (this.props.onError) {
+            this.props.onError(error, errorInfo)
+        }
+    }
+
+    handleReset = (): void => {
+        this.setState(initialErrorState)
+    }
+
+    render(): React.ReactNode {
+        if (this.state.hasError) {
+            // You can render any custom fallback UI
+            if (this.props.fallback) {
+                return this.props.fallback
+            }
+            return (
+                <div className="error-boundary">
+                    <h1>Something went wrong.</h1>
+                    <details>
+                        <summary>Error Details</summary>
+                        <pre>{this.state.error?.toString()}</pre>
+                        <pre>{this.state.errorInfo?.componentStack}</pre>
+                    </details>
+                    <button onClick={this.handleReset}>Try Again</button>
+                </div>
+            )
+        }
+
+        return this.props.children
+    }
+}
+
+/**
+ * Hook for error handling in functional components
+ */
+export function useErrorHandler<T extends Error = Error>(): {
+    error: T | null
+    setError: (error: T | null) => void
+    hasError: boolean
+    resetError: () => void
+} {
+    const [error, setError] = React.useState<T | null>(null)
+
+    const hasError = error !== null
+    const resetError = React.useCallback(() => setError(null), [])
+
+    return { error, setError, hasError, resetError }
+}
+
+/**
+ * Utility to update error state consistently
+ */
+export function updateErrorState<T extends { error?: unknown }>(
+    state: T,
+    setError: (error: null | { kind: string; message: string }) => void,
+    error: unknown
+): void {
+    setError({
+        kind: 'render',
+        message: (error as { message?: string })?.message ?? 'Render error',
+    })
+}
+
+/**
+ * Utility to clear error state
+ */
+export function clearErrorState<T extends { error?: unknown }>(
+    state: T,
+    setError: (error: null) => void
+): void {
+    setError(null)
+}
+
+/**
+ * Utility to check if an error is recoverable
+ */
+export function isRecoverableError(error: unknown): boolean {
+  if (!(error instanceof Error)) return false
+  // Common recoverable errors
+  const recoverableMessages = [
+    'Network error',
+    'Timeout',
+    'Connection refused',
+    'Rate limit exceeded',
+  ]
+  return recoverableMessages.some((msg) => (error as Error).message.includes(msg))
+}
+
+/**
+ * Utility to format error message for display
+ */
+export function formatErrorMessage(error: unknown): string {
+    if (error instanceof Error) {
+        return error.message
+    }
+    if (typeof error === 'string') {
+        return error
+    }
+    return 'An unknown error occurred'
+}
--- a/frontend/src/lib/errorHandling.ts
+++ b/frontend/src/lib/errorHandling.ts
@@ -0,0 +1,155 @@
+/**
+ * Error handling utilities for consistent error management.
+ * Provides centralized error handling logic across the application.
+ */
+
+/**
+ * Error kind for categorizing errors
+ */
+export type ErrorKind = 
+  | 'render'
+  | 'network'
+  | 'validation'
+  | 'authentication'
+  | 'authorization'
+  | 'notFound'
+  | 'server'
+  | 'unknown'
+
+/**
+ * Error object with kind and message
+ */
+export type AppError = {
+  kind: ErrorKind
+  message: string
+  details?: Record<string, unknown>
+  timestamp: number
+}
+
+/**
+ * Create an error object with consistent structure
+ */
+export function createAppError(
+  kind: ErrorKind,
+  message: string,
+  details?: Record<string, unknown>
+): AppError {
+  return {
+    kind,
+    message,
+    details,
+    timestamp: Date.now(),
+  }
+}
+
+/**
+ * Extract error message from unknown error
+ */
+export function getErrorMessage(error: unknown): string {
+  if (error instanceof Error) {
+    return error.message
+  }
+  if (typeof error === 'string') {
+    return error
+  }
+  if (typeof error === 'object' && error !== null && 'message' in error) {
+    return String(error.message)
+  }
+  return 'An unknown error occurred'
+}
+
+/**
+ * Extract error kind from error
+ */
+export function getErrorKind(error: unknown): ErrorKind {
+  if (error instanceof Error) {
+    const message = error.message.toLowerCase()
+    if (message.includes('network')) return 'network'
+    if (message.includes('validation') || message.includes('invalid')) return 'validation'
+    if (message.includes('auth')) return 'authentication'
+    if (message.includes('forbidden') || message.includes('unauthorized')) return 'authorization'
+    if (message.includes('not found') || message.includes('404')) return 'notFound'
+    if (message.includes('server') || message.includes('500')) return 'server'
+  }
+  return 'unknown'
+}
+
+/**
+ * Format error for display
+ */
+export function formatError(error: AppError | Error | string): string {
+  if (typeof error === 'string') {
+    return error
+  }
+  if (error instanceof Error) {
+    return error.message
+  }
+  return error.message
+}
+
+/**
+ * Check if error is recoverable
+ */
+export function isRecoverableError(error: AppError | Error | string): boolean {
+  if (typeof error === 'string') return false
+  if (error instanceof Error) {
+    const message = error.message.toLowerCase()
+    return ['network', 'timeout', 'connection'].some((term) => message.includes(term))
+  }
+  // error is AppError at this point
+  return ['network', 'server'].includes((error as AppError).kind)
+}
+
+/**
+ * Update error state consistently
+ */
+export function updateErrorState<T extends { error?: unknown }>(
+  state: T,
+  setError: (error: null | { kind: string; message: string }) => void,
+  error: unknown
+): void {
+  setError({
+    kind: 'render',
+    message: getErrorMessage(error),
+  })
+}
+
+/**
+ * Clear error state
+ */
+export function clearErrorState<T extends { error?: unknown }>(
+  state: T,
+  setError: (error: null) => void
+): void {
+  setError(null)
+}
+
+/**
+ * Handle error with consistent logging
+ */
+export function handleError(
+  error: unknown,
+  context?: Record<string, unknown>
+): AppError {
+  const appError = createAppError(
+    getErrorKind(error),
+    getErrorMessage(error),
+    context
+  )
+  
+  console.error('[Error]', appError, context)
+  return appError
+}
+
+/**
+ * Create error handler for async functions
+ */
+export function createErrorHandler<T>(
+  onError?: (error: AppError) => void
+): (error: unknown) => T {
+  return (error: unknown) => {
+    const appError = handleError(error)
+    onError?.(appError)
+    throw error
+  }
+}
--- a/frontend/src/lib/graph/nodeFactory.ts
+++ b/frontend/src/lib/graph/nodeFactory.ts
@@ -0,0 +1,182 @@
+/**
+ * Node factory utilities for creating and managing nodes.
+ * Centralizes node creation logic to reduce duplication.
+ */
+
+import type { Node, Edge } from '@xyflow/react'
+import type { AppNode, AppEdge } from '@/lib/graph/nodeTypes'
+import {
+  getDefaultDataForType,
+  getNextNodeId,
+} from '@/lib/graph/flowUtils'
+import { getRegisteredNodeTypeIds, getDefaultStyle } from '@/lib/graph/nodeRegistry'
+
+/**
+ * Create a new node with auto-generated ID and default data.
+ * 
+ * @param type - Node type ID (e.g., 'config', 'render')
+ * @param position - Node position { x, y }
+ * @param data - Optional additional data to merge with defaults
+ * @returns New node with generated ID
+ */
+export function createNode(
+  type: string,
+  position: { x: number; y: number },
+  data?: Record<string, unknown>
+): AppNode {
+  const existingIds = getRegisteredNodeTypeIds()
+  const newId = getNextNodeId(type, existingIds)
+  return {
+    id: newId,
+    type,
+    position,
+    data: { ...getDefaultDataForType(type, newId), ...(data ?? {}) },
+    style: getDefaultStyle(type),
+  }
+}
+
+/**
+ * Create a new node with a specific ID.
+ * Use this when you need to control the node ID (e.g., when duplicating).
+ * 
+ * @param type - Node type ID
+ * @param id - Node ID to use
+ * @param position - Node position { x, y }
+ * @param data - Optional additional data to merge with defaults
+ * @returns New node with specified ID
+ */
+export function createNodeWithId(
+  type: string,
+  id: string,
+  position: { x: number; y: number },
+  data?: Record<string, unknown>
+): AppNode {
+  return {
+    id,
+    type,
+    position,
+    data: { ...getDefaultDataForType(type, id), ...(data ?? {}) },
+    style: getDefaultStyle(type),
+  }
+}
+
+/**
+ * Create a new edge connecting two nodes.
+ * 
+ * @param source - Source node ID
+ * @param target - Target node ID
+ * @param id - Optional edge ID (auto-generated if not provided)
+ * @param data - Optional edge data
+ * @returns New edge
+ */
+export function createEdge(
+  source: string,
+  target: string,
+  id?: string,
+  data?: Record<string, unknown>
+): AppEdge {
+  return {
+    id: id ?? `e-${source}-${target}`,
+    source,
+    target,
+    data: data ?? {},
+  }
+}
+
+/**
+ * Create multiple nodes from a template.
+ * 
+ * @param template - Template node to copy
+ * @param count - Number of nodes to create
+ * @param offset - Position offset between nodes { x, y }
+ * @returns Array of new nodes
+ */
+export function createNodesFromTemplate(
+  template: Partial<AppNode>,
+  count: number,
+  offset: { x: number; y: number }
+): AppNode[] {
+  const nodes: AppNode[] = []
+  for (let i = 0; i < count; i++) {
+    const position = {
+      x: (template.position?.x ?? 0) + i * offset.x,
+      y: (template.position?.y ?? 0) + i * offset.y,
+    }
+    nodes.push({
+      id: template.id ?? getNextNodeId(template.type ?? 'node', nodes.map((n) => n.id)),
+      type: template.type ?? 'node',
+      position,
+      data: { ...template.data },
+      style: template.style ?? getDefaultStyle(template.type ?? 'node'),
+    })
+  }
+  return nodes
+}
+
+/**
+ * Get existing node IDs for a specific type.
+ * 
+ * @param nodes - Array of nodes to search
+ * @param type - Node type to filter by
+ * @returns Array of node IDs for the specified type
+ */
+export function getNodeIdsByType(nodes: AppNode[], type: string): string[] {
+  return nodes.filter((n) => n.type === type).map((n) => n.id)
+}
+
+/**
+ * Get the next available node ID for a type based on existing nodes.
+ * 
+ * @param type - Node type
+ * @param existingNodes - Array of existing nodes
+ * @returns Next available node ID
+ */
+export function getNextNodeIdForType(type: string, existingNodes: AppNode[]): string {
+  const existingIds = existingNodes.map((n) => n.id)
+  return getNextNodeId(type, existingIds)
+}
+
+/**
+ * Duplicate a node with a new ID and offset position.
+ * 
+ * @param node - Node to duplicate
+ * @param offset - Position offset for the duplicate
+ * @returns Duplicated node
+ */
+export function duplicateNode(node: AppNode, offset: { x: number; y: number } = { x: 30, y: 30 }): AppNode {
+  const existingIds = [node.id] // Start with current node ID
+  const newId = getNextNodeId(node.type ?? 'node', existingIds)
+  const pos = node.position ?? { x: 0, y: 0 }
+  return {
+    id: newId,
+    type: node.type ?? 'node',
+    position: { x: pos.x + offset.x, y: pos.y + offset.y },
+    data: typeof node.data === 'object' && node.data !== null ? { ...(node.data as object) } : node.data,
+    style: node.style ?? getDefaultStyle(node.type ?? 'node'),
+  }
+}
+
+/**
+ * Create a connection between two nodes.
+ * 
+ * @param sourceNodeId - Source node ID
+ * @param sourceHandle - Source handle ID (optional)
+ * @param targetNodeId - Target node ID
+ * @param targetHandle - Target handle ID (optional)
+ * @returns Edge object connecting the nodes
+ */
+export function createConnection(
+  sourceNodeId: string,
+  sourceHandle?: string,
+  targetNodeId: string = '',
+  targetHandle?: string
+): Edge {
+  const edge: Edge = {
+    id: `e-${sourceNodeId}-${targetNodeId}`,
+    source: sourceNodeId,
+    target: targetNodeId,
+    sourceHandle,
+    targetHandle,
+  }
+  return edge
+}
--- a/frontend/src/lib/svgUtils.ts
+++ b/frontend/src/lib/svgUtils.ts
@@ -0,0 +1,48 @@
+/**
+ * SVG detection utilities.
+ * Centralized logic for detecting and processing SVG content.
+ */
+
+/** Check if a string contains SVG content. */
+export function isSvgContent(content: string | null | undefined): boolean {
+  return Boolean(content?.trim() && /<svg[\s>]/i.test(content.trim()))
+}
+
+/** Check if a file path or URL points to an SVG file. */
+export function isSvgPath(path: string | null | undefined): boolean {
+  return Boolean(path?.toLowerCase().endsWith('.svg'))
+}
+
+/** Process SVG HTML for viewport display (aspect ratio, fill container). */
+export function processSvgDisplay(html: string): string {
+  let out = html
+  // Change preserveAspectRatio from 'none' to 'xMidYMid meet' for proper scaling
+  out = out.replace(/\bpreserveAspectRatio\s*=\s*["']none["']/gi, 'preserveAspectRatio="xMidYMid meet"')
+  // Set width to 100% to fill container
+  out = out.replace(/\bwidth\s*=\s*["'][^"']*["']/i, 'width="100%"')
+  // Set height to 100% to fill container
+  out = out.replace(/\bheight\s*=\s*["'][^"']*["']/i, 'height="100%"')
+  // Override width/height in style attributes
+  out = out.replace(/\bstyle\s*=\s*["']([^"']*)["']/i, (_, style) => {
+    const overridden = style.replace(/\b(width|height):[^;]+/gi, '$1:100%')
+    return `style="${overridden}"`
+  })
+  return out
+}
+
+/** Extract SVG content from an HTML string. */
+export function extractSvgContent(html: string): string | null {
+  const svgMatch = html.match(/<svg[\s\S]*?<\/svg>/i)
+  return svgMatch ? svgMatch[0] : null
+}
+
+/** Check if content is an SVG data URL. */
+export function isSvgDataUrl(content: string | null | undefined): boolean {
+  return Boolean(content?.trim().startsWith('data:image/svg+xml'))
+}
+
+/** Convert SVG string to data URL. */
+export function svgToDataUrl(svg: string): string {
+  const encoded = btoa(unescape(encodeURIComponent(svg)))
+  return `data:image/svg+xml;base64,${encoded}`
+}