[refactor] Move thumbnail functionality to renderer/core domain (#5586)

Move thumbnail functionality from src/renderer/thumbnail/ to src/renderer/core/thumbnail/
to align with domain-driven design architecture. Thumbnail generation is core rendering
infrastructure and belongs alongside other core renderer utilities.

Changes:
- Move useWorkflowThumbnail.ts and graphThumbnailRenderer.ts to renderer/core/thumbnail/
- Update all import paths in consuming files
- Fix relative imports within moved files

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

src/renderer/core/thumbnail/graphThumbnailRenderer.ts

@@ -0,0 +1,64 @@
+import type { LGraph } from '@/lib/litegraph/src/litegraph'
+import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
+import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
+import {
+  calculateMinimapScale,
+  calculateNodeBounds
+} from '@/renderer/core/spatial/boundsCalculator'
+
+import { renderMinimapToCanvas } from '../../extensions/minimap/minimapCanvasRenderer'
+
+/**
+ * Create a thumbnail of the current canvas's active graph.
+ * Used by workflow thumbnail generation.
+ */
+export function createGraphThumbnail(): string | null {
+  const canvasStore = useCanvasStore()
+  const workflowStore = useWorkflowStore()
+
+  const graph = workflowStore.activeSubgraph || canvasStore.canvas?.graph
+  if (!graph || !graph._nodes || graph._nodes.length === 0) {
+    return null
+  }
+
+  const width = 250
+  const height = 200
+
+  // Calculate bounds using spatial calculator
+  const bounds = calculateNodeBounds(graph._nodes)
+  if (!bounds) {
+    return null
+  }
+
+  const scale = calculateMinimapScale(bounds, width, height)
+
+  // Create detached canvas
+  const canvas = document.createElement('canvas')
+  canvas.width = width
+  canvas.height = height
+
+  // Render the minimap
+  renderMinimapToCanvas(canvas, graph as LGraph, {
+    bounds,
+    scale,
+    settings: {
+      nodeColors: true,
+      showLinks: false,
+      showGroups: true,
+      renderBypass: false,
+      renderError: false
+    },
+    width,
+    height
+  })
+
+  const dataUrl = canvas.toDataURL()
+
+  // Explicit cleanup (optional but good practice)
+  const ctx = canvas.getContext('2d')
+  if (ctx) {
+    ctx.clearRect(0, 0, width, height)
+  }
+
+  return dataUrl
+}

src/renderer/core/thumbnail/useWorkflowThumbnail.ts

@@ -0,0 +1,90 @@
+import { ref } from 'vue'
+
+import { ComfyWorkflow } from '@/platform/workflow/management/stores/workflowStore'
+
+import { createGraphThumbnail } from './graphThumbnailRenderer'
+
+// Store thumbnails for each workflow
+const workflowThumbnails = ref<Map<string, string>>(new Map())
+
+export const useWorkflowThumbnail = () => {
+  /**
+   * Capture a thumbnail of the canvas
+   */
+  const createMinimapPreview = (): Promise<string | null> => {
+    try {
+      const thumbnailDataUrl = createGraphThumbnail()
+      return Promise.resolve(thumbnailDataUrl)
+    } catch (error) {
+      console.error('Failed to capture canvas thumbnail:', error)
+      return Promise.resolve(null)
+    }
+  }
+
+  /**
+   * Store a thumbnail for a workflow
+   */
+  const storeThumbnail = async (workflow: ComfyWorkflow) => {
+    const thumbnail = await createMinimapPreview()
+    if (thumbnail) {
+      // Clean up existing thumbnail if it exists
+      const existingThumbnail = workflowThumbnails.value.get(workflow.key)
+      if (existingThumbnail) {
+        URL.revokeObjectURL(existingThumbnail)
+      }
+      workflowThumbnails.value.set(workflow.key, thumbnail)
+    }
+  }
+
+  /**
+   * Get a thumbnail for a workflow
+   */
+  const getThumbnail = (workflowKey: string): string | undefined => {
+    return workflowThumbnails.value.get(workflowKey)
+  }
+
+  /**
+   * Clear a thumbnail for a workflow
+   */
+  const clearThumbnail = (workflowKey: string) => {
+    const thumbnail = workflowThumbnails.value.get(workflowKey)
+    if (thumbnail) {
+      URL.revokeObjectURL(thumbnail)
+    }
+    workflowThumbnails.value.delete(workflowKey)
+  }
+
+  /**
+   * Clear all thumbnails
+   */
+  const clearAllThumbnails = () => {
+    for (const thumbnail of workflowThumbnails.value.values()) {
+      URL.revokeObjectURL(thumbnail)
+    }
+    workflowThumbnails.value.clear()
+  }
+
+  /**
+   * Move a thumbnail from one workflow key to another (useful for workflow renaming)
+   */
+  const moveWorkflowThumbnail = (oldKey: string, newKey: string) => {
+    // Don't do anything if moving to the same key
+    if (oldKey === newKey) return
+
+    const thumbnail = workflowThumbnails.value.get(oldKey)
+    if (thumbnail) {
+      workflowThumbnails.value.set(newKey, thumbnail)
+      workflowThumbnails.value.delete(oldKey)
+    }
+  }
+
+  return {
+    createMinimapPreview,
+    storeThumbnail,
+    getThumbnail,
+    clearThumbnail,
+    clearAllThumbnails,
+    moveWorkflowThumbnail,
+    workflowThumbnails
+  }
+}