diff --git a/apps/sim/lib/copilot/client-sse/subagent-handlers.ts b/apps/sim/lib/copilot/client-sse/subagent-handlers.ts
index d78360cad..98abb45e4 100644
--- a/apps/sim/lib/copilot/client-sse/subagent-handlers.ts
+++ b/apps/sim/lib/copilot/client-sse/subagent-handlers.ts
@@ -227,7 +227,18 @@ export const subAgentSSEHandlers: Record<string, SSEHandler> = {
 
     const resultData = asRecord(data?.data)
     const toolCallId: string | undefined = data?.toolCallId || (resultData.id as string | undefined)
-    const success: boolean | undefined = data?.success !== false
+    // Determine success: explicit `success` field takes priority; otherwise
+    // infer from presence of result data vs error (same logic as server-side
+    // inferToolSuccess).  The Go backend uses `*bool` with omitempty so
+    // `success` is present when explicitly set, and absent for non-tool events.
+    const hasExplicitSuccess =
+      data?.success !== undefined || resultData.success !== undefined
+    const explicitSuccess = data?.success ?? resultData.success
+    const hasResultData = data?.result !== undefined || resultData.result !== undefined
+    const hasError = !!data?.error || !!resultData.error
+    const success: boolean = hasExplicitSuccess
+      ? !!explicitSuccess
+      : hasResultData && !hasError
     if (!toolCallId) return
 
     if (!context.subAgentToolCalls[parentToolCallId]) return
diff --git a/apps/sim/lib/copilot/orchestrator/sse-handlers/handlers.ts b/apps/sim/lib/copilot/orchestrator/sse-handlers/handlers.ts
index 9a061029e..8b5025897 100644
--- a/apps/sim/lib/copilot/orchestrator/sse-handlers/handlers.ts
+++ b/apps/sim/lib/copilot/orchestrator/sse-handlers/handlers.ts
@@ -7,7 +7,10 @@ import {
   markToolResultSeen,
   wasToolResultSeen,
 } from '@/lib/copilot/orchestrator/sse-utils'
-import { markToolComplete } from '@/lib/copilot/orchestrator/tool-executor'
+import {
+  isToolAvailableOnSimSide,
+  markToolComplete,
+} from '@/lib/copilot/orchestrator/tool-executor'
 import type {
   ContentBlock,
   ExecutionContext,
@@ -360,6 +363,15 @@ export const subAgentHandlers: Record<string, SSEHandler> = {
       return
     }
 
+    // Tools that only exist on the Go backend (e.g. search_patterns,
+    // search_errors, remember_debug) should NOT be re-executed on the Sim side.
+    // The Go backend already executed them and will send its own tool_result
+    // SSE event with the real outcome.  Trying to execute them here would fail
+    // with "Tool not found" and incorrectly mark the tool as failed.
+    if (!isToolAvailableOnSimSide(toolName)) {
+      return
+    }
+
     if (options.autoExecuteTools !== false) {
       await executeToolAndReport(toolCallId, context, execContext, options)
     }
diff --git a/apps/sim/lib/copilot/orchestrator/tool-executor/index.ts b/apps/sim/lib/copilot/orchestrator/tool-executor/index.ts
index 12dbbf598..b56abd436 100644
--- a/apps/sim/lib/copilot/orchestrator/tool-executor/index.ts
+++ b/apps/sim/lib/copilot/orchestrator/tool-executor/index.ts
@@ -136,6 +136,21 @@ const SIM_WORKFLOW_TOOL_HANDLERS: Record<
     executeCreateWorkspaceMcpServer(p as CreateWorkspaceMcpServerParams, c),
 }
 
+/**
+ * Check whether a tool can be executed on the Sim (TypeScript) side.
+ *
+ * Tools that are only available on the Go backend (e.g. search_patterns,
+ * search_errors, remember_debug) will return false.  The subagent tool_call
+ * handler uses this to decide whether to execute a tool locally or let the
+ * Go backend's own tool_result SSE event handle it.
+ */
+export function isToolAvailableOnSimSide(toolName: string): boolean {
+  if (SERVER_TOOLS.has(toolName)) return true
+  if (toolName in SIM_WORKFLOW_TOOL_HANDLERS) return true
+  const resolvedToolName = resolveToolId(toolName)
+  return !!getTool(resolvedToolName)
+}
+
 /**
  * Execute a tool server-side without calling internal routes.
  */