perf(desktop): stop eagerly JSON.stringify-ing every tool's args + result

buildToolView ran prettyJson (JSON.stringify + clamp) on part.args AND part.result
for EVERY tool row, on every rebuild:
- rawArgs was dead — assigned + typed, never read anywhere. Removed.
- rawResult is only rendered by the web_search raw-JSON drilldown, yet was
  serialized for read_file/terminal/every tool. Moved to a memoized, web_search-
  only computation in the consumer (fallback.tsx), so a 100KB read_file result
  is no longer stringified just to be discarded.

No behavior change (web_search drilldown identical; clamp still applies via
prettyJson). The oversized-result guard test retargets from view.rawResult to
prettyJson (its real layer now).

typecheck + eslint clean; fallback-model tests green (26).

apps/desktop/src/components/assistant-ui/tool/fallback-model.test.ts

@@ -8,6 +8,7 @@ import {
   countDiffLineStats,
   inlineDiffFromResult,
   MAX_TOOL_RENDER_CHARS,
+  prettyJson,
   type ToolPart
 } from './fallback-model'
 
@@ -342,15 +343,16 @@ describe('clampForDisplay', () => {
 })
 
 // A large tool result (e.g. a 100KB read_file during a `/learn` run) must not
-// be serialized into the rendered rawResult at full size — that JSON.stringify
-// payload is what floods the renderer when many rows stack up.
-describe('buildToolView caps serialized result size', () => {
-  it('clamps rawResult for an oversized result', () => {
+// be serialized at full size — that JSON.stringify payload is what floods the
+// renderer. buildToolView no longer prettyJson's every result eagerly; the
+// web_search drilldown serializes lazily via prettyJson, which clamps.
+describe('prettyJson caps serialized result size', () => {
+  it('clamps an oversized result', () => {
     const huge = 'y'.repeat(MAX_TOOL_RENDER_CHARS * 3)
-    const view = buildToolView(part({ result: { content: huge }, toolName: 'read_file' }), '')
+    const out = prettyJson({ content: huge })
 
-    expect(view.rawResult.length).toBeLessThanOrEqual(MAX_TOOL_RENDER_CHARS + 200)
-    expect(view.rawResult).toContain('truncated')
+    expect(out.length).toBeLessThanOrEqual(MAX_TOOL_RENDER_CHARS + 200)
+    expect(out).toContain('truncated')
   })
 })
 

apps/desktop/src/components/assistant-ui/tool/fallback-model/index.ts

@@ -11,7 +11,6 @@ import {
   isRecord,
   numberValue,
   parseMaybeObject,
-  prettyJson,
   unwrapToolPayload
 } from './format'
 import { findFirstUrl, hostnameOf, looksLikePath, looksLikeUrl } from './targets'
@@ -1409,8 +1408,6 @@ export function buildToolView(part: ToolPart, inlineDiff: string): ToolView {
     imageUrl: toolImageUrl(argsRecord, resultRecord),
     inlineDiff,
     previewTarget: toolPreviewTarget(part.toolName, argsRecord, resultRecord),
-    rawArgs: prettyJson(part.args),
-    rawResult: prettyJson(part.result),
     rendersAnsi: rendersAnsi || undefined,
     searchHits: searchHits?.length ? searchHits : undefined,
     stderr: hasSplitStreams ? stderrRaw || undefined : undefined,

apps/desktop/src/components/assistant-ui/tool/fallback-model/types.ts

@@ -36,8 +36,6 @@ export interface ToolView {
   imageUrl?: string
   inlineDiff: string
   previewTarget?: string
-  rawArgs: string
-  rawResult: string
   /** Set for tools whose output naturally contains ANSI escape codes
    *  (terminal/execute_code) so the renderer knows to run them through
    *  the ANSI parser instead of printing them as literals. */

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

@@ -62,6 +62,7 @@ import {
   type ToolStatus,
   type ToolTitleAction
 } from './fallback-model'
+import { prettyJson } from './fallback-model/format'
 
 // `true` when a ToolEntry is rendered inside an embedding wrapper that owns
 // the per-row chrome (timer / preview). The flat ToolGroupSlot sets this
@@ -367,11 +368,15 @@ function ToolEntry({ part }: ToolEntryProps) {
   const hasSearchHits = Boolean(view.searchHits?.length)
   const searchResultsLabel = part.toolName === 'web_search' ? 'Search results' : view.detailLabel
 
+  // Only web_search renders the raw JSON drilldown, so serialize the result
+  // lazily here instead of prettyJson-ing every tool's result in buildToolView.
+  const rawResult = useMemo(
+    () => (part.toolName === 'web_search' && toolViewMode !== 'technical' ? prettyJson(part.result) : ''),
+    [part.toolName, part.result, toolViewMode]
+  )
+
   const showRawSearchDrilldown =
-    part.toolName === 'web_search' &&
-    part.result !== undefined &&
-    toolViewMode !== 'technical' &&
-    Boolean(view.rawResult.trim())
+    part.toolName === 'web_search' && part.result !== undefined && toolViewMode !== 'technical' && Boolean(rawResult.trim())
 
   const hasExpandableContent = Boolean(
     view.imageUrl || view.inlineDiff || showDetail || hasSearchHits || toolViewMode === 'technical'
@@ -587,7 +592,7 @@ function ToolEntry({ part }: ToolEntryProps) {
             <details className="max-w-full">
               <summary className={cn(TOOL_SECTION_LABEL_CLASS, 'mb-0')}>{copy.rawResponse}</summary>
               <pre className={cn(TOOL_SECTION_PRE_CLASS, 'mt-1 whitespace-pre-wrap wrap-anywhere')}>
-                {view.rawResult}
+                {rawResult}
               </pre>
             </details>
           )}