diff --git a/apps/sim/app/api/workflows/[id]/execute/route.ts b/apps/sim/app/api/workflows/[id]/execute/route.ts
index 217d26f9b..856a1a3c9 100644
--- a/apps/sim/app/api/workflows/[id]/execute/route.ts
+++ b/apps/sim/app/api/workflows/[id]/execute/route.ts
@@ -30,6 +30,7 @@ import { normalizeName } from '@/executor/constants'
 import { ExecutionSnapshot } from '@/executor/execution/snapshot'
 import type { ExecutionMetadata, IterationContext } from '@/executor/execution/types'
 import type { NormalizedBlockOutput, StreamingExecution } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { Serializer } from '@/serializer'
 import { CORE_TRIGGER_TYPES, type CoreTriggerType } from '@/stores/logs/filters/types'
 
@@ -467,17 +468,17 @@ export async function POST(req: NextRequest, { params }: { params: Promise<{ id:
         }
 
         return NextResponse.json(filteredResult)
-      } catch (error: any) {
-        const errorMessage = error.message || 'Unknown error'
+      } catch (error: unknown) {
+        const errorMessage = error instanceof Error ? error.message : 'Unknown error'
         logger.error(`[${requestId}] Non-SSE execution failed: ${errorMessage}`)
 
-        const executionResult = error.executionResult
+        const executionResult = hasExecutionResult(error) ? error.executionResult : undefined
 
         return NextResponse.json(
           {
             success: false,
             output: executionResult?.output,
-            error: executionResult?.error || error.message || 'Execution failed',
+            error: executionResult?.error || errorMessage || 'Execution failed',
             metadata: executionResult?.metadata
               ? {
                   duration: executionResult.metadata.duration,
@@ -788,11 +789,11 @@ export async function POST(req: NextRequest, { params }: { params: Promise<{ id:
 
           // Cleanup base64 cache for this execution
           await cleanupExecutionBase64Cache(executionId)
-        } catch (error: any) {
-          const errorMessage = error.message || 'Unknown error'
+        } catch (error: unknown) {
+          const errorMessage = error instanceof Error ? error.message : 'Unknown error'
           logger.error(`[${requestId}] SSE execution failed: ${errorMessage}`)
 
-          const executionResult = error.executionResult
+          const executionResult = hasExecutionResult(error) ? error.executionResult : undefined
 
           sendEvent({
             type: 'execution:error',
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-workflow-execution.ts b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-workflow-execution.ts
index fbd432c12..1c0cbcc7a 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-workflow-execution.ts
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-workflow-execution.ts
@@ -16,6 +16,7 @@ import {
 } from '@/lib/workflows/triggers/triggers'
 import { useCurrentWorkflow } from '@/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-current-workflow'
 import type { BlockLog, ExecutionResult, StreamingExecution } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { coerceValue } from '@/executor/utils/start-block'
 import { subscriptionKeys } from '@/hooks/queries/subscription'
 import { useExecutionStream } from '@/hooks/use-execution-stream'
@@ -76,17 +77,6 @@ function normalizeErrorMessage(error: unknown): string {
   return WORKFLOW_EXECUTION_FAILURE_MESSAGE
 }
 
-function isExecutionResult(value: unknown): value is ExecutionResult {
-  if (!isRecord(value)) return false
-  return typeof value.success === 'boolean' && isRecord(value.output)
-}
-
-function extractExecutionResult(error: unknown): ExecutionResult | null {
-  if (!isRecord(error)) return null
-  const candidate = error.executionResult
-  return isExecutionResult(candidate) ? candidate : null
-}
-
 export function useWorkflowExecution() {
   const queryClient = useQueryClient()
   const currentWorkflow = useCurrentWorkflow()
@@ -1138,11 +1128,11 @@ export function useWorkflowExecution() {
 
   const handleExecutionError = (error: unknown, options?: { executionId?: string }) => {
     const normalizedMessage = normalizeErrorMessage(error)
-    const executionResultFromError = extractExecutionResult(error)
 
     let errorResult: ExecutionResult
 
-    if (executionResultFromError) {
+    if (hasExecutionResult(error)) {
+      const executionResultFromError = error.executionResult
       const logs = Array.isArray(executionResultFromError.logs) ? executionResultFromError.logs : []
 
       errorResult = {
diff --git a/apps/sim/executor/execution/engine.ts b/apps/sim/executor/execution/engine.ts
index 58792ef2b..05e7e0484 100644
--- a/apps/sim/executor/execution/engine.ts
+++ b/apps/sim/executor/execution/engine.ts
@@ -13,7 +13,7 @@ import type {
   PausePoint,
   ResumeStatus,
 } from '@/executor/types'
-import { normalizeError } from '@/executor/utils/errors'
+import { attachExecutionResult, normalizeError } from '@/executor/utils/errors'
 
 const logger = createLogger('ExecutionEngine')
 
@@ -170,8 +170,8 @@ export class ExecutionEngine {
         metadata: this.context.metadata,
       }
 
-      if (error && typeof error === 'object') {
-        ;(error as any).executionResult = executionResult
+      if (error instanceof Error) {
+        attachExecutionResult(error, executionResult)
       }
       throw error
     }
diff --git a/apps/sim/executor/handlers/workflow/workflow-handler.ts b/apps/sim/executor/handlers/workflow/workflow-handler.ts
index 7bd295502..6759af5ff 100644
--- a/apps/sim/executor/handlers/workflow/workflow-handler.ts
+++ b/apps/sim/executor/handlers/workflow/workflow-handler.ts
@@ -11,6 +11,7 @@ import type {
   ExecutionResult,
   StreamingExecution,
 } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { buildAPIUrl, buildAuthHeaders } from '@/executor/utils/http'
 import { parseJSON } from '@/executor/utils/json'
 import { lazyCleanupInputMapping } from '@/executor/utils/lazy-cleanup'
@@ -148,8 +149,9 @@ export class WorkflowBlockHandler implements BlockHandler {
       const originalError = error.message || 'Unknown error'
       let childTraceSpans: WorkflowTraceSpan[] = []
       let executionResult: ExecutionResult | undefined
-      if (error.executionResult?.logs) {
-        executionResult = error.executionResult as ExecutionResult
+
+      if (hasExecutionResult(error) && error.executionResult.logs) {
+        executionResult = error.executionResult
 
         logger.info(`Extracting child trace spans from error.executionResult`, {
           hasLogs: (executionResult.logs?.length ?? 0) > 0,
diff --git a/apps/sim/executor/utils/errors.ts b/apps/sim/executor/utils/errors.ts
index 0f078d84e..3144d9c71 100644
--- a/apps/sim/executor/utils/errors.ts
+++ b/apps/sim/executor/utils/errors.ts
@@ -1,6 +1,33 @@
-import type { ExecutionContext } from '@/executor/types'
+import type { ExecutionContext, ExecutionResult } from '@/executor/types'
 import type { SerializedBlock } from '@/serializer/types'
 
+/**
+ * Interface for errors that carry an ExecutionResult.
+ * Used when workflow execution fails and we want to preserve partial results.
+ */
+export interface ErrorWithExecutionResult extends Error {
+  executionResult: ExecutionResult
+}
+
+/**
+ * Type guard to check if an error carries an ExecutionResult.
+ */
+export function hasExecutionResult(error: unknown): error is ErrorWithExecutionResult {
+  return (
+    error instanceof Error &&
+    'executionResult' in error &&
+    error.executionResult != null &&
+    typeof error.executionResult === 'object'
+  )
+}
+
+/**
+ * Attaches an ExecutionResult to an error for propagation to parent workflows.
+ */
+export function attachExecutionResult(error: Error, executionResult: ExecutionResult): void {
+  Object.assign(error, { executionResult })
+}
+
 export interface BlockExecutionErrorDetails {
   block: SerializedBlock
   error: Error | string
diff --git a/apps/sim/hooks/use-execution-stream.ts b/apps/sim/hooks/use-execution-stream.ts
index 3516c9366..b9d1cc685 100644
--- a/apps/sim/hooks/use-execution-stream.ts
+++ b/apps/sim/hooks/use-execution-stream.ts
@@ -100,8 +100,13 @@ export function useExecutionStream() {
       })
 
       if (!response.ok) {
-        const error = await response.json()
-        throw new Error(error.error || 'Failed to start execution')
+        const errorResponse = await response.json()
+        const error = new Error(errorResponse.error || 'Failed to start execution')
+        // Attach the execution result from server response for error handling
+        if (errorResponse && typeof errorResponse === 'object') {
+          Object.assign(error, { executionResult: errorResponse })
+        }
+        throw error
       }
 
       if (!response.body) {