improvement(copilot): stop persisting tool-call result outputs in transcripts (#4829)

Opening a Mothership task could take many seconds because a single persisted
assistant message in copilot_messages.content can reach hundreds of MB, almost
entirely inside contentBlocks[].toolCall.result.output (e.g. a get_workflow_logs
or run_workflow result). The DB query is ~2ms; the cost is detoasting that
payload, shipping it to the browser, and parsing it.

These outputs are dead weight on the Sim side: they are never rendered (the
thread shows only tool name/title/status) and never replayed to the model (the
upstream copilot service owns conversation memory). So drop result.output before
it is persisted, keeping result.success/error plus the tool metadata.

- add stripToolResultOutput() in persisted-message.ts
- apply it in messages-store toRow (covers every write path) and in
  loadCopilotChatMessages (existing rows render fast on read)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

apps/sim/lib/copilot/chat/lifecycle.test.ts

@@ -71,6 +71,34 @@ describe('lifecycle copilot chat reads (cutover to copilot_messages)', () => {
     expect(dbChainMockFns.orderBy).toHaveBeenCalledTimes(1)
   })
 
+  it('strips tool-result output on read, keeping success/error', async () => {
+    const toolMsg = {
+      id: 'm-tool',
+      role: 'assistant',
+      content: '',
+      timestamp: '2026-01-01T00:00:02.000Z',
+      contentBlocks: [
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 'tc-1',
+            name: 'get_workflow_logs',
+            state: 'success',
+            result: { success: true, output: { huge: 'x'.repeat(5000) } },
+          },
+        },
+      ],
+    }
+    dbChainMockFns.limit.mockResolvedValueOnce([chatRow])
+    dbChainMockFns.orderBy.mockResolvedValueOnce([{ content: toolMsg }])
+
+    const result = await getAccessibleCopilotChatWithMessages(CHAT_ID, USER_ID)
+
+    expect(result?.messages?.[0].contentBlocks?.[0].toolCall?.result).toEqual({ success: true })
+    expect(JSON.stringify(result?.messages)).not.toContain('huge')
+  })
+
   it('returns an empty transcript for a chat with no messages', async () => {
     dbChainMockFns.limit.mockResolvedValueOnce([chatRow])
     dbChainMockFns.orderBy.mockResolvedValueOnce([])

apps/sim/lib/copilot/chat/lifecycle.ts

@@ -6,7 +6,7 @@ import {
   getActiveWorkflowRecord,
 } from '@sim/workflow-authz'
 import { and, asc, eq, isNull, sql } from 'drizzle-orm'
-import type { PersistedMessage } from '@/lib/copilot/chat/persisted-message'
+import { type PersistedMessage, stripToolResultOutput } from '@/lib/copilot/chat/persisted-message'
 import {
   assertActiveWorkspaceAccess,
   checkWorkspaceAccess,
@@ -84,7 +84,8 @@ export async function loadCopilotChatMessages(chatId: string): Promise<Persisted
       asc(copilotMessages.createdAt),
       asc(copilotMessages.id)
     )
-  return rows.map((row) => row.content as PersistedMessage)
+  // Also strip on read: rows written before the backfill still carry outputs.
+  return rows.map((row) => stripToolResultOutput(row.content as PersistedMessage))
 }
 
 type CopilotChatAuthRow = Pick<

apps/sim/lib/copilot/chat/messages-store.test.ts

@@ -26,6 +26,31 @@ const assistantMsg: PersistedMessage = {
   timestamp: '2026-01-01T00:00:01.000Z',
 }
 
+const toolMsg: PersistedMessage = {
+  id: 'msg-tool-1',
+  role: 'assistant',
+  content: '',
+  timestamp: '2026-01-01T00:00:02.000Z',
+  contentBlocks: [
+    {
+      type: 'tool',
+      phase: 'call',
+      toolCall: {
+        id: 'tc-1',
+        name: 'get_workflow_logs',
+        state: 'error',
+        params: { workflowId: 'wf-1' },
+        result: { success: false, output: { huge: 'x'.repeat(5000) }, error: 'too big' },
+      },
+    },
+  ],
+}
+
+/** The persisted `content` of the most recently inserted row at `index`. */
+function lastRowContent(index: number): PersistedMessage {
+  return lastValuesRows()[index].content as PersistedMessage
+}
+
 /** The first arg passed to the most recent `.values(...)` call. */
 function lastValuesRows() {
   const calls = dbChainMockFns.values.mock.calls
@@ -131,6 +156,14 @@ describe('messages-store', () => {
         'connection lost'
       )
     })
+
+    it('strips tool-result output before persisting, keeping success/error', async () => {
+      await appendCopilotChatMessages('chat-1', [toolMsg])
+
+      const toolCall = lastRowContent(0).contentBlocks?.[0].toolCall
+      expect(toolCall?.result).toEqual({ success: false, error: 'too big' })
+      expect(JSON.stringify(lastValuesRows())).not.toContain('huge')
+    })
   })
 
   describe('replaceCopilotChatMessages', () => {
@@ -192,5 +225,13 @@ describe('messages-store', () => {
 
       await expect(replaceCopilotChatMessages('chat-1', [userMsg])).rejects.toThrow('tx aborted')
     })
+
+    it('strips tool-result output before persisting, keeping success/error', async () => {
+      await replaceCopilotChatMessages('chat-1', [toolMsg])
+
+      const toolCall = lastRowContent(0).contentBlocks?.[0].toolCall
+      expect(toolCall?.result).toEqual({ success: false, error: 'too big' })
+      expect(JSON.stringify(lastValuesRows())).not.toContain('huge')
+    })
   })
 })

apps/sim/lib/copilot/chat/messages-store.ts

@@ -1,7 +1,7 @@
 import { db } from '@sim/db'
 import { copilotMessages } from '@sim/db/schema'
 import { and, eq, notInArray, sql } from 'drizzle-orm'
-import type { PersistedMessage } from '@/lib/copilot/chat/persisted-message'
+import { type PersistedMessage, stripToolResultOutput } from '@/lib/copilot/chat/persisted-message'
 import type { DbOrTx } from '@/lib/db/types'
 
 /**
@@ -31,7 +31,7 @@ function toRow(
     chatId,
     messageId: message.id,
     role: message.role,
-    content: message,
+    content: stripToolResultOutput(message),
     seq,
     model: options?.chatModel ?? null,
     streamId: options?.streamId ?? null,

apps/sim/lib/copilot/chat/persisted-message.test.ts

@@ -8,6 +8,8 @@ import {
   buildPersistedAssistantMessage,
   buildPersistedUserMessage,
   normalizeMessage,
+  type PersistedMessage,
+  stripToolResultOutput,
 } from './persisted-message'
 
 describe('persisted-message', () => {
@@ -234,3 +236,137 @@ describe('persisted-message', () => {
     expect(msg.contexts).toBeUndefined()
   })
 })
+
+describe('stripToolResultOutput', () => {
+  it('drops result.output but keeps success and error', () => {
+    const message: PersistedMessage = {
+      id: 'msg-1',
+      role: 'assistant',
+      content: '',
+      timestamp: '2026-01-01T00:00:00.000Z',
+      contentBlocks: [
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 'tool-1',
+            name: 'get_workflow_logs',
+            state: 'error',
+            params: { workflowId: 'wf-1' },
+            display: { title: 'Reading logs' },
+            result: { success: false, output: { huge: 'x'.repeat(1000) }, error: 'boom' },
+          },
+        },
+      ],
+    }
+
+    const stripped = stripToolResultOutput(message)
+
+    expect(stripped.contentBlocks?.[0].toolCall).toEqual({
+      id: 'tool-1',
+      name: 'get_workflow_logs',
+      state: 'error',
+      params: { workflowId: 'wf-1' },
+      display: { title: 'Reading logs' },
+      result: { success: false, error: 'boom' },
+    })
+    expect(message.contentBlocks?.[0].toolCall?.result).toHaveProperty('output')
+  })
+
+  it('omits error when the original result had none', () => {
+    const message: PersistedMessage = {
+      id: 'msg-1',
+      role: 'assistant',
+      content: '',
+      timestamp: '2026-01-01T00:00:00.000Z',
+      contentBlocks: [
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 't',
+            name: 'read',
+            state: 'success',
+            result: { success: true, output: [1, 2, 3] },
+          },
+        },
+      ],
+    }
+
+    expect(stripToolResultOutput(message).contentBlocks?.[0].toolCall?.result).toEqual({
+      success: true,
+    })
+  })
+
+  it('returns the same reference when there is nothing to strip', () => {
+    const noBlocks: PersistedMessage = {
+      id: 'u',
+      role: 'user',
+      content: 'hi',
+      timestamp: '2026-01-01T00:00:00.000Z',
+    }
+    expect(stripToolResultOutput(noBlocks)).toBe(noBlocks)
+
+    const noOutput: PersistedMessage = {
+      id: 'msg',
+      role: 'assistant',
+      content: 'done',
+      timestamp: '2026-01-01T00:00:00.000Z',
+      contentBlocks: [
+        { type: 'text', channel: 'assistant', content: 'done' },
+        { type: 'tool', phase: 'call', toolCall: { id: 't', name: 'read', state: 'pending' } },
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 't2',
+            name: 'read',
+            state: 'error',
+            result: { success: false, error: 'x' },
+          },
+        },
+      ],
+    }
+    expect(stripToolResultOutput(noOutput)).toBe(noOutput)
+  })
+
+  it('strips every tool block while leaving text/thinking blocks intact', () => {
+    const message: PersistedMessage = {
+      id: 'msg',
+      role: 'assistant',
+      content: '',
+      timestamp: '2026-01-01T00:00:00.000Z',
+      contentBlocks: [
+        { type: 'text', channel: 'thinking', content: 'hmm' },
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 'a',
+            name: 'run_workflow',
+            state: 'success',
+            result: { success: true, output: { big: 1 } },
+          },
+        },
+        { type: 'text', channel: 'assistant', content: 'answer' },
+        {
+          type: 'tool',
+          phase: 'call',
+          toolCall: {
+            id: 'b',
+            name: 'read',
+            state: 'success',
+            result: { success: true, output: 'file contents' },
+          },
+        },
+      ],
+    }
+
+    const blocks = stripToolResultOutput(message).contentBlocks ?? []
+    expect(blocks[0]).toEqual({ type: 'text', channel: 'thinking', content: 'hmm' })
+    expect(blocks[1].toolCall?.result).toEqual({ success: true })
+    expect(blocks[2]).toEqual({ type: 'text', channel: 'assistant', content: 'answer' })
+    expect(blocks[3].toolCall?.result).toEqual({ success: true })
+    expect(JSON.stringify(blocks)).not.toContain('file contents')
+  })
+})

apps/sim/lib/copilot/chat/persisted-message.ts

@@ -79,6 +79,34 @@ export interface PersistedMessage {
   contexts?: PersistedMessageContext[]
 }
 
+/**
+ * Drop the `output` of every persisted tool result, keeping `success` and
+ * `error`. Tool outputs are never rendered (the chat thread shows only the tool
+ * name/title/status) and never replayed to the model (the upstream copilot
+ * service owns conversation memory), so storing them only bloats
+ * `copilot_messages.content` — a single `get_workflow_logs`/`run_workflow`
+ * result can reach hundreds of MB and stall task loads.
+ *
+ * Applied on both the write path (so new rows never store outputs) and the read
+ * path (so already-bloated rows still load fast). Returns the original
+ * reference when there is nothing to strip, preserving memoized identity for
+ * read-side consumers.
+ */
+export function stripToolResultOutput(message: PersistedMessage): PersistedMessage {
+  if (!message.contentBlocks?.length) return message
+  let changed = false
+  const contentBlocks = message.contentBlocks.map((block) => {
+    const toolCall = block.toolCall
+    const result = toolCall?.result
+    if (!toolCall || !result || typeof result !== 'object' || !('output' in result)) return block
+    changed = true
+    const strippedResult: { success: boolean; error?: string } = { success: result.success }
+    if (result.error !== undefined) strippedResult.error = result.error
+    return { ...block, toolCall: { ...toolCall, result: strippedResult } }
+  })
+  return changed ? { ...message, contentBlocks } : message
+}
+
 // ---------------------------------------------------------------------------
 // Write: OrchestratorResult → PersistedMessage
 // ---------------------------------------------------------------------------