perf(desktop): stop tool rows re-rendering on session/cwd change + memo leaves

Two tool-render wins during streaming / on session switch:

1. Every ToolEntry did useStore($activeSessionId)+useStore($currentCwd), so any
   session or cwd change re-rendered *every* mounted tool row — but they're only
   read inside the preview-artifact effect. Read .get() at fire time instead
   (the effect only runs when a previewable target appears); no subscription.

2. memo() AnsiText + CompactMarkdown. Their text props are string values
   (value-equal across renders), so memo skips the re-render — and the per-tick
   ANSI parse / Streamdown re-run — when a parent ToolEntry re-renders on an
   unrelated stream delta.

No behavior change. typecheck + eslint clean; tool fallback tests green (30).

apps/desktop/src/components/assistant-ui/ansi-text.tsx

@@ -1,5 +1,4 @@
-import type { FC } from 'react'
-import { useMemo } from 'react'
+import { memo, useMemo } from 'react'
 
 import { ansiColorClass, hasAnsiCodes, parseAnsi } from '@/lib/ansi'
 import { cn } from '@/lib/utils'
@@ -12,7 +11,7 @@ interface AnsiTextProps {
 /** Renders text with embedded ANSI SGR codes as colored / bold spans. Falls
  *  back to a plain string node when no codes are present so the parser cost
  *  is paid only when there's something to colorize. */
-export const AnsiText: FC<AnsiTextProps> = ({ className, text }) => {
+export const AnsiText = memo(({ className, text }: AnsiTextProps) => {
   const segments = useMemo(() => (hasAnsiCodes(text) ? parseAnsi(text) : null), [text])
 
   if (!segments) {
@@ -31,4 +30,4 @@ export const AnsiText: FC<AnsiTextProps> = ({ className, text }) => {
       ))}
     </span>
   )
-}
+})

apps/desktop/src/components/assistant-ui/tool/fallback.tsx

@@ -311,17 +311,22 @@ function ToolEntry({ part }: ToolEntryProps) {
   // in the composer status stack rather than a bulky inline card. Uses the same
   // detected target the old inline card did, keyed to the active session the
   // stack reads from. Idempotent + dedup'd, so re-renders don't churn.
-  const activeSessionId = useStore($activeSessionId)
-  const currentCwd = useStore($currentCwd)
   const previewTarget = view.previewTarget
 
   useEffect(() => {
-    if (isPending || !activeSessionId || !previewTarget || !isPreviewableTarget(previewTarget)) {
+    if (isPending || !previewTarget || !isPreviewableTarget(previewTarget)) {
       return
     }
 
-    recordPreviewArtifact(activeSessionId, previewTarget, currentCwd || '')
-  }, [activeSessionId, currentCwd, isPending, previewTarget])
+    // Read (don't subscribe) session/cwd: this only fires when a previewable
+    // target appears, and subscribing re-rendered every tool row on any session
+    // or cwd change.
+    const activeSessionId = $activeSessionId.get()
+
+    if (activeSessionId) {
+      recordPreviewArtifact(activeSessionId, previewTarget, $currentCwd.get() || '')
+    }
+  }, [isPending, previewTarget])
 
   const detailSections = useMemo(() => {
     if (!view.detail) {

apps/desktop/src/components/chat/compact-markdown.tsx

@@ -1,4 +1,5 @@
 import type { ComponentProps, ElementType, FC } from 'react'
+import { memo } from 'react'
 import { Streamdown } from 'streamdown'
 
 import { ExternalLink, ExternalLinkIcon } from '@/lib/external-link'
@@ -102,7 +103,13 @@ const COMPONENTS = {
   ul: tagged('ul')
 }
 
-export function CompactMarkdown({ className, text }: { className?: string; text: string }) {
+export const CompactMarkdown = memo(function CompactMarkdown({
+  className,
+  text
+}: {
+  className?: string
+  text: string
+}) {
   return (
     <div className={cn('max-w-full text-xs leading-relaxed text-muted-foreground/90 wrap-anywhere', className)}>
       <Streamdown components={COMPONENTS} controls={false} mode="static" parseIncompleteMarkdown={false}>
@@ -110,4 +117,4 @@ export function CompactMarkdown({ className, text }: { className?: string; text:
       </Streamdown>
     </div>
   )
-}
+})