fix(workflow): prevent canvas slowdown cascades (#6881)

* fix(workflow): prevent canvas slowdown cascades

* fix(workflow): make connection picker scrolling seamless

* fix(workflow): correct two regressions in the canvas perf pass

Gating `toolBlocks` on the picker's open state also emptied it for the
always-visible selected-tool chips, which silently fell through to their
`getBlock` fallback — the branch documented as the exception for types
hidden from the picker. Only `toolGroups`, where the expensive group build
lives, is gated now.

Re-invoking the find shortcut while the panel was already open stopped
re-selecting the query: `open()` is a no-op when the panel is mounted, so
the mount-time focus effect never re-ran. The panel publishes its focus
callback so the shortcut can drive it either way.

A saturated `slice` also allocated a fresh array once the limit covered a
whole group, re-rendering the memoized "All blocks" group on every tools
page-in — the frame cost the change set out to remove.

Alongside those: fold the two reconcilers into one generic and decide reuse
by identity rather than a three-write `changed` flag; record why the node
comparison is deliberately asymmetric (React Flow augments node objects in
place, so a symmetric `isEqual` would never reuse anything); give the
browse pagination its own constant instead of borrowing the search-result
cap; drop a redundant clamp and the deps it needed; inline the
single-consumer `sliceGroupsToLimit`; and split the bundled ref so the
hottest component stops allocating an object per render.

---------

Co-authored-by: Waleed Latif <walif6@gmail.com>

Author: j15z

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/connection-block-selector/connection-block-selector.tsx

@@ -1,6 +1,14 @@
 'use client'
 
-import { useCallback, useDeferredValue, useEffect, useMemo, useRef, useState } from 'react'
+import {
+  startTransition,
+  useCallback,
+  useDeferredValue,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+} from 'react'
 import { Button, cn } from '@sim/emcn'
 import { X } from '@sim/emcn/icons'
 import { WorkflowBlockBorder, type WorkflowBorderPort } from '@sim/workflow-renderer'
@@ -45,6 +53,8 @@ const SELECTOR_ACTION_MENU_RIGHT_INSET = 24
 const SELECTOR_ACTION_MENU_AMPLITUDE = 7
 const RECENT_SELECTION_LIMIT = 3
 const RECENT_SELECTION_STORAGE_PREFIX = 'sim:connection-block-selector:recent'
+const BROWSE_PREFETCH_MARGIN_PX = 640
+const BROWSE_PAGE_SIZE = 50
 const POPULAR_BLOCK_TYPES = [
   'agent',
   'function',
@@ -54,6 +64,11 @@ const POPULAR_BLOCK_TYPES = [
   'memory',
 ] as const
 
+/** Ordered prefix that reuses the source array once `count` covers all of it. */
+function takePrefix<T>(items: T[], count: number): T[] {
+  return count >= items.length ? items : items.slice(0, Math.max(0, count))
+}
+
 const SELECTOR_PORTS: WorkflowBorderPort[] = [
   {
     id: 'target',
@@ -136,9 +151,11 @@ export function ConnectionBlockSelector({ id, data }: NodeProps<ConnectionBlockS
   const posthog = usePostHog()
   const inputRef = useRef<HTMLInputElement>(null)
   const listRef = useRef<HTMLDivElement>(null)
+  const browseSentinelRef = useRef<HTMLDivElement>(null)
   const [search, setSearch] = useState('')
   const [selectedValue, setSelectedValue] = useState('')
   const [recentSelections, setRecentSelections] = useState<RecentSelection[]>([])
+  const [browseLimit, setBrowseLimit] = useState(BROWSE_PAGE_SIZE)
   const deferredSearch = useDeferredValue(search)
   const isSearching = deferredSearch.trim().length > 0
   const recentStorageKey = `${RECENT_SELECTION_STORAGE_PREFIX}:${workspaceId}`
@@ -260,6 +277,42 @@ export function ConnectionBlockSelector({ id, data }: NodeProps<ConnectionBlockS
     () => availableTools.filter((tool) => !recentSelectionKeys.has(`tool:${tool.id}`)),
     [availableTools, recentSelectionKeys]
   )
+  const visibleBrowseBlocks = useMemo(
+    () => takePrefix(browseBlocks, browseLimit),
+    [browseBlocks, browseLimit]
+  )
+  const visibleBrowseTools = useMemo(
+    () => takePrefix(browseTools, browseLimit - browseBlocks.length),
+    [browseBlocks.length, browseLimit, browseTools]
+  )
+  const hasMoreBrowseResults = browseLimit < browseBlocks.length + browseTools.length
+
+  /**
+   * Mounting every cmdk item up front caused the frame spike; a manual "show
+   * more" control would leak that constraint into the UI. Prefetching near the
+   * viewport keeps scrolling continuous and cmdk's keyboard navigation intact.
+   */
+  useEffect(() => {
+    const list = listRef.current
+    const sentinel = browseSentinelRef.current
+    if (isSearching || !hasMoreBrowseResults || !list || !sentinel) return
+
+    const observer = new IntersectionObserver(
+      ([entry]) => {
+        if (!entry.isIntersecting) return
+        startTransition(() => {
+          setBrowseLimit((current) => current + BROWSE_PAGE_SIZE)
+        })
+      },
+      {
+        root: list,
+        rootMargin: `0px 0px ${BROWSE_PREFETCH_MARGIN_PX}px 0px`,
+      }
+    )
+
+    observer.observe(sentinel)
+    return () => observer.disconnect()
+  }, [hasMoreBrowseResults, isSearching])
 
   const dispatchSelection = useCallback(
     (type: string, resultType: 'block' | 'tool' | 'tool_operation', presetOperation?: string) => {
@@ -480,11 +533,14 @@ export function ConnectionBlockSelector({ id, data }: NodeProps<ConnectionBlockS
                 )}
                 <BlocksGroup items={popularBlocks} onSelect={handleBlockSelect} heading='Popular' />
                 <BlocksGroup
-                  items={browseBlocks}
+                  items={visibleBrowseBlocks}
                   onSelect={handleBlockSelect}
                   heading='All blocks'
                 />
-                <ToolsGroup items={browseTools} onSelect={handleToolSelect} />
+                <ToolsGroup items={visibleBrowseTools} onSelect={handleToolSelect} />
+                {hasMoreBrowseResults && (
+                  <div ref={browseSentinelRef} aria-hidden='true' className='h-px' />
+                )}
               </>
             )}
           </CommandFadedList>

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/tool-input/tool-input.tsx

@@ -464,6 +464,9 @@ function UnsupportedToolBadge({ message }: { message: string }) {
   )
 }
 
+const EMPTY_COMBOBOX_GROUPS: ComboboxOptionGroup[] = []
+const EMPTY_COMBOBOX_OPTIONS: ComboboxOption[] = []
+
 export const ToolInput = memo(function ToolInput({
   blockId,
   subBlockId,
@@ -1403,6 +1406,7 @@ export const ToolInput = memo(function ToolInput({
    * @returns Array of option groups for the combobox component
    */
   const toolGroups = useMemo((): ComboboxOptionGroup[] => {
+    if (!open) return EMPTY_COMBOBOX_GROUPS
     const groups: ComboboxOptionGroup[] = []
 
     // MCP Server drill-down: when navigated into a server, show only its tools
@@ -1681,6 +1685,7 @@ export const ToolInput = memo(function ToolInput({
 
     return groups
   }, [
+    open,
     mcpServerDrilldown,
     customTools,
     availableMcpTools,
@@ -1705,7 +1710,7 @@ export const ToolInput = memo(function ToolInput({
   return (
     <div className='w-full space-y-2'>
       <Combobox
-        options={[]}
+        options={EMPTY_COMBOBOX_OPTIONS}
         groups={toolGroups}
         placeholder='Add tool...'
         /* Every list this picker offers — blocks, operations, MCP and custom

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/search-replace/workflow-search-replace.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { type RefObject, useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Button, cn, Input, toast } from '@sim/emcn'
 import { ChevronDown, ChevronRight, ChevronUp, X } from '@sim/emcn/icons'
 import { useParams } from 'next/navigation'
@@ -110,6 +110,30 @@ function createActiveSearchTarget(
 }
 
 export function WorkflowSearchReplace() {
+  const { isOpen, open } = useWorkflowSearchReplaceStore(
+    useShallow((state) => ({ isOpen: state.isOpen, open: state.open }))
+  )
+  const focusSearchInputRef = useRef<(() => void) | null>(null)
+
+  useRegisterGlobalCommands([
+    createCommand({
+      id: 'open-workflow-search-replace',
+      handler: () => {
+        open()
+        focusSearchInputRef.current?.()
+      },
+    }),
+  ])
+
+  return isOpen ? <WorkflowSearchReplacePanel focusRef={focusSearchInputRef} /> : null
+}
+
+interface WorkflowSearchReplacePanelProps {
+  /** Lets the shortcut re-select the query while the panel is already open. */
+  focusRef: RefObject<(() => void) | null>
+}
+
+function WorkflowSearchReplacePanel({ focusRef }: WorkflowSearchReplacePanelProps) {
   const params = useParams()
   const workspaceId = params.workspaceId as string | undefined
   const routeWorkflowId = params.workflowId as string | undefined
@@ -143,38 +167,33 @@ export function WorkflowSearchReplace() {
   >({})
 
   const {
-    isOpen,
     query,
     replacement: textReplacement,
     activeMatchId,
     position,
     close,
-    open,
     setPosition,
     setQuery,
     setReplacement,
     setActiveMatchId,
   } = useWorkflowSearchReplaceStore(
     useShallow((state) => ({
-      isOpen: state.isOpen,
       query: state.query,
       replacement: state.replacement,
       activeMatchId: state.activeMatchId,
       position: state.position,
       close: state.close,
-      open: state.open,
       setPosition: state.setPosition,
       setQuery: state.setQuery,
       setReplacement: state.setReplacement,
       setActiveMatchId: state.setActiveMatchId,
     }))
   )
-  const prevQueryRef = useRef(query)
-  const prevIsOpenRef = useRef(false)
+  const prevQueryRef = useRef<string | null>(null)
   const afterReplaceIndexRef = useRef<number | null>(null)
-  const { data: workspaceCredentials } = useWorkspaceCredentials({ workspaceId, enabled: isOpen })
-  const { data: customTools = [] } = useCustomTools(isOpen && workspaceId ? workspaceId : '')
-  const { mcpTools } = useMcpTools(isOpen && workspaceId ? workspaceId : '')
+  const { data: workspaceCredentials } = useWorkspaceCredentials({ workspaceId })
+  const { data: customTools = [] } = useCustomTools(workspaceId ?? '')
+  const { mcpTools } = useMcpTools(workspaceId ?? '')
   const mcpToolNamesById = useMemo(() => {
     const names = new Map<string, string>()
     for (const t of mcpTools) {
@@ -183,19 +202,6 @@ export function WorkflowSearchReplace() {
     return names
   }, [mcpTools])
 
-  useRegisterGlobalCommands([
-    createCommand({
-      id: 'open-workflow-search-replace',
-      handler: () => {
-        open()
-        requestAnimationFrame(() => {
-          searchInputRef.current?.focus()
-          searchInputRef.current?.select()
-        })
-      },
-    }),
-  ])
-
   const searchBlocks = useMemo(
     () =>
       getWorkflowSearchBlocks({
@@ -267,10 +273,17 @@ export function WorkflowSearchReplace() {
   )
 
   useEffect(() => {
-    if (!isOpen) return
-    searchInputRef.current?.focus()
-    searchInputRef.current?.select()
-  }, [isOpen])
+    const focusSearchInput = () => {
+      searchInputRef.current?.focus()
+      searchInputRef.current?.select()
+    }
+    focusSearchInput()
+    focusRef.current = focusSearchInput
+    return () => {
+      focusRef.current = null
+      usePanelEditorSearchStore.getState().setActiveSearchTarget(null)
+    }
+  }, [focusRef])
 
   const panelHeight = isReplaceExpanded
     ? SEARCH_PANEL_EXPANDED_HEIGHT
@@ -288,7 +301,7 @@ export function WorkflowSearchReplace() {
   })
 
   useFloatBoundarySync({
-    isOpen,
+    isOpen: true,
     position: actualPosition,
     width: SEARCH_PANEL_WIDTH,
     height: panelHeight,
@@ -384,14 +397,6 @@ export function WorkflowSearchReplace() {
   }
 
   useEffect(() => {
-    if (!isOpen) {
-      prevIsOpenRef.current = false
-      usePanelEditorSearchStore.getState().setActiveSearchTarget(null)
-      return
-    }
-
-    const justOpened = !prevIsOpenRef.current
-    prevIsOpenRef.current = true
     const queryChanged = prevQueryRef.current !== query
     prevQueryRef.current = query
 
@@ -406,7 +411,7 @@ export function WorkflowSearchReplace() {
       const replaceIndex = afterReplaceIndexRef.current
       afterReplaceIndexRef.current = null
 
-      if (queryChanged || justOpened) {
+      if (queryChanged) {
         handleSelectMatch(hydratedMatches[0].id)
       } else if (replaceIndex !== null) {
         handleSelectMatch(hydratedMatches[Math.min(replaceIndex, hydratedMatches.length - 1)].id)
@@ -422,9 +427,7 @@ export function WorkflowSearchReplace() {
     usePanelEditorSearchStore
       .getState()
       .setActiveSearchTarget(createActiveSearchTarget(activeHydratedMatch, query))
-  }, [activeMatchId, handleSelectMatch, hydratedMatches, isOpen, query, setActiveMatchId])
-
-  if (!isOpen) return null
+  }, [activeMatchId, handleSelectMatch, hydratedMatches, query, setActiveMatchId])
 
   const handleMoveActiveMatch = (delta: number) => {
     if (hydratedMatches.length === 0) return