feat: error connections

frontend/src/lib/connectionStatus.ts

@@ -0,0 +1,48 @@
+/**
+ * Connection status: visual state of an edge (color/class).
+ * Priority when multiple apply: error > paused > updating > default.
+ * Nodes report state via FlowContext (e.g. addConnectionPathError); edges derive status here.
+ */
+
+export type ConnectionStatus = 'default' | 'updating' | 'paused' | 'error'
+
+export type ConnectionStatusInputs = {
+  source: string
+  target: string
+  pathNodeIds: Set<string>
+  pausedSegmentNodeIds: Set<string>
+  activeSegmentNodeIds: Set<string>
+  errorTargetNodeIds: Set<string>
+}
+
+/**
+ * Compute the single connection status for an edge (priority: error > paused > updating > default).
+ * Use in edge components; add new statuses by extending the type and adding a branch here.
+ */
+export function getConnectionStatus(inputs: ConnectionStatusInputs): ConnectionStatus {
+  const { target, pathNodeIds, pausedSegmentNodeIds, activeSegmentNodeIds, errorTargetNodeIds, source } = inputs
+  if (errorTargetNodeIds.has(target)) return 'error'
+  if (
+    pathNodeIds.has(source) &&
+    pathNodeIds.has(target) &&
+    pausedSegmentNodeIds.has(source) &&
+    pausedSegmentNodeIds.has(target)
+  )
+    return 'paused'
+  if (
+    pathNodeIds.has(source) &&
+    pathNodeIds.has(target) &&
+    activeSegmentNodeIds.has(source) &&
+    activeSegmentNodeIds.has(target)
+  )
+    return 'updating'
+  return 'default'
+}
+
+/** CSS class suffix for each status (animated-edge-path--{status}). */
+export const CONNECTION_STATUS_CLASS: Record<ConnectionStatus, string> = {
+  default: '',
+  updating: 'animated-edge-path--updating',
+  paused: 'animated-edge-path--paused',
+  error: 'animated-edge-path--error',
+}

frontend/src/lib/flowContext.tsx

@@ -46,6 +46,12 @@ export type FlowContextValue = {
     addConnectionPathPausedNode: (nodeId: string) => void
     /** Remove this node from paused. */
     removeConnectionPathPausedNode: (nodeId: string) => void
+    /** Node ids that have an error (e.g. Render node). Incoming edges show error status (red). */
+    connectionPathErrorNodeIds: string[]
+    /** Call when this node has an error; remove when error is cleared. */
+    addConnectionPathError: (nodeId: string) => void
+    /** Call when this node's error is cleared. */
+    removeConnectionPathError: (nodeId: string) => void
     /** Call when a path update starts for this node. Animation runs at least CONNECTION_PATH_UPDATE_MIN_MS. */
     startConnectionPathUpdate: (nodeId: string) => void
     /** Call when a path update ends for this node. If min duration not reached, animation continues until then. */