diff --git a/apps/desktop/src/components/assistant-ui/tool/fallback-model/index.ts b/apps/desktop/src/components/assistant-ui/tool/fallback-model/index.ts
index f1e2675002363..2a21657f68e63 100644
--- a/apps/desktop/src/components/assistant-ui/tool/fallback-model/index.ts
+++ b/apps/desktop/src/components/assistant-ui/tool/fallback-model/index.ts
@@ -2,6 +2,7 @@ import { type ToolTitleKey, translateNow } from '@/i18n'
 import { normalizeExternalUrl } from '@/lib/external-link'
 import { summarizeShellCommand } from '@/lib/summarize-command'
 import { capitalize, normalize } from '@/lib/text'
+import { isCardTool, isFileEditTool, isSilentTool } from '@/lib/tool-render-class'
 import { extractToolErrorMessage, formatToolResultSummary } from '@/lib/tool-result-summary'
 
 import {
@@ -31,11 +32,10 @@ export * from './format'
 export * from './targets'
 export * from './types'
 
-const FILE_EDIT_TOOL_NAMES = new Set(['edit_file', 'patch', 'write_file'])
-
-export function isFileEditTool(toolName: string): boolean {
-  return FILE_EDIT_TOOL_NAMES.has(toolName)
-}
+// The transcript's render budget prices a turn by the same classification, so
+// it lives in `@/lib/tool-render-class` where both sides can reach it without
+// pulling this module's formatting/i18n weight into the cost path.
+export { isCardTool, isFileEditTool, isSilentTool }
 
 export interface DiffLineStats {
   added: number
diff --git a/apps/desktop/src/components/assistant-ui/tool/fallback.test.ts b/apps/desktop/src/components/assistant-ui/tool/fallback.test.ts
index abe38c26f7dd6..b9847bff08357 100644
--- a/apps/desktop/src/components/assistant-ui/tool/fallback.test.ts
+++ b/apps/desktop/src/components/assistant-ui/tool/fallback.test.ts
@@ -1,6 +1,8 @@
 import { describe, expect, it } from 'vitest'
 
-import { isCardTool, splitRunItems, technicalTrace } from './fallback'
+import { isCardTool, isSilentTool } from '@/lib/tool-render-class'
+
+import { splitRunItems, technicalTrace } from './fallback'
 
 describe('isCardTool', () => {
   it('keeps what the user has to look at out of a summary', () => {
@@ -19,6 +21,16 @@ describe('isCardTool', () => {
   })
 })
 
+describe('isSilentTool', () => {
+  it('names the rows that render nothing in the transcript', () => {
+    // `todo` is hoisted to its own panel; a reaction's UI is the emoji on the
+    // bubble. The render budget must not charge for either.
+    expect(isSilentTool('todo')).toBe(true)
+    expect(isSilentTool('react_to_message')).toBe(true)
+    expect(isSilentTool('terminal')).toBe(false)
+  })
+})
+
 describe('splitRunItems', () => {
   it('collapses a stretch of activity into one run', () => {
     expect(splitRunItems(['read_file', 'search_files', 'terminal'])).toEqual([{ end: 2, kind: 'run', start: 0 }])
diff --git a/apps/desktop/src/components/assistant-ui/tool/fallback.tsx b/apps/desktop/src/components/assistant-ui/tool/fallback.tsx
index 0ea7f4760fd31..6e56d0918c194 100644
--- a/apps/desktop/src/components/assistant-ui/tool/fallback.tsx
+++ b/apps/desktop/src/components/assistant-ui/tool/fallback.tsx
@@ -53,6 +53,7 @@ import {
   cleanVisibleText,
   countDiffLineStats,
   inlineDiffFromResult,
+  isCardTool,
   isFileEditTool,
   isPreviewableTarget,
   looksRedundant,
@@ -738,22 +739,9 @@ function TerminalTranscript({ command, exitCode }: TerminalTranscriptProps) {
 }
 
 // Tools that draw their own surface and must never be folded into a run's
-// summary. Two kinds, for the same reason — the thing on screen IS the point:
-//
-//   - File edits are the deliverable, not scaffolding. The diff is what the
-//     user reviews, so it stays visible at its place in the turn, live and
-//     settled, the way a PR shows its changes.
-//   - `clarify`, `image_generate` and `delegate_task` bypass ToolEntry to
-//     render their own markup: a question the user has to answer, an image
-//     they asked for, the several agents a fan-out is running.
-//
-// Everything else is ephemeral activity — reads, searches, commands — which is
-// what a run summarizes and what the live ticker cycles through.
-const CARD_TOOLS = new Set(['clarify', 'delegate_task', 'image_generate'])
-
-export function isCardTool(toolName: string): boolean {
-  return CARD_TOOLS.has(toolName) || isFileEditTool(toolName)
-}
+// summary live in `fallback-model` (`isCardTool`) — the DOM render budget
+// prices a turn by the same rule, so both sides have to agree on which rows
+// collapse into a summary line and which mount their own markup.
 
 export type RunItem = { end: number; kind: 'run'; start: number } | { index: number; kind: 'card' }
 
diff --git a/apps/desktop/src/lib/tool-render-class.ts b/apps/desktop/src/lib/tool-render-class.ts
new file mode 100644
index 0000000000000..810b35fe57613
--- /dev/null
+++ b/apps/desktop/src/lib/tool-render-class.ts
@@ -0,0 +1,44 @@
+/**
+ * Which surface a tool call renders as.
+ *
+ * Two consumers have to agree on this and they sit on opposite sides of the
+ * app: the transcript decides what to draw, and the DOM render budget decides
+ * how much of the transcript to mount. Pricing a turn correctly means pricing
+ * what the grouping actually renders, so the classification lives on its own
+ * rather than inside either one.
+ */
+
+const FILE_EDIT_TOOL_NAMES = new Set(['edit_file', 'patch', 'write_file'])
+
+/** Renders a diff — the deliverable of the turn, and the one card whose cost scales. */
+export function isFileEditTool(toolName: string): boolean {
+  return FILE_EDIT_TOOL_NAMES.has(toolName)
+}
+
+// Tools that draw their own surface and must never be folded into a run's
+// summary. Two kinds, for the same reason — the thing on screen IS the point:
+//
+//   - File edits are the deliverable, not scaffolding. The diff is what the
+//     user reviews, so it stays visible at its place in the turn, live and
+//     settled, the way a PR shows its changes.
+//   - `clarify`, `image_generate` and `delegate_task` bypass ToolEntry to
+//     render their own markup: a question the user has to answer, an image
+//     they asked for, the several agents a fan-out is running.
+//
+// Everything else is ephemeral activity — reads, searches, commands — which is
+// what a run summarizes and what the live ticker cycles through.
+const CARD_TOOL_NAMES = new Set(['clarify', 'delegate_task', 'image_generate'])
+
+export function isCardTool(toolName: string): boolean {
+  return CARD_TOOL_NAMES.has(toolName) || isFileEditTool(toolName)
+}
+
+// Activity tools that render nothing at all: `todo` parts are hoisted to a
+// dedicated panel above the message content, and a reaction's UI is the emoji
+// landing on the bubble. Both still render when they FAIL, which is a bounded
+// error row either way.
+const SILENT_TOOL_NAMES = new Set(['react_to_message', 'todo'])
+
+export function isSilentTool(toolName: string): boolean {
+  return SILENT_TOOL_NAMES.has(toolName)
+}