From 8bf2e69942d4e6cedc1c88464ba5a7813baede5e Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 01:37:17 -0800
Subject: [PATCH 1/6] fix(child-workflow): nested spans handoff

---
 .../executor/errors/child-workflow-error.ts   | 31 ++++++++++++++++
 apps/sim/executor/execution/block-executor.ts | 23 +++++++-----
 .../handlers/workflow/workflow-handler.ts     | 36 +++++++++----------
 3 files changed, 63 insertions(+), 27 deletions(-)
 create mode 100644 apps/sim/executor/errors/child-workflow-error.ts

diff --git a/apps/sim/executor/errors/child-workflow-error.ts b/apps/sim/executor/errors/child-workflow-error.ts
new file mode 100644
index 0000000000..373b42444a
--- /dev/null
+++ b/apps/sim/executor/errors/child-workflow-error.ts
@@ -0,0 +1,31 @@
+import type { TraceSpan } from '@/lib/logs/types'
+import type { ExecutionResult } from '@/executor/types'
+
+interface ChildWorkflowErrorOptions {
+  message: string
+  childWorkflowName: string
+  childTraceSpans?: TraceSpan[]
+  executionResult?: ExecutionResult
+  cause?: Error
+}
+
+/**
+ * Error raised when a child workflow execution fails.
+ */
+export class ChildWorkflowError extends Error {
+  readonly childTraceSpans: TraceSpan[]
+  readonly childWorkflowName: string
+  readonly executionResult?: ExecutionResult
+
+  constructor(options: ChildWorkflowErrorOptions) {
+    super(options.message, { cause: options.cause })
+    this.name = 'ChildWorkflowError'
+    this.childWorkflowName = options.childWorkflowName
+    this.childTraceSpans = options.childTraceSpans ?? []
+    this.executionResult = options.executionResult
+  }
+
+  static isChildWorkflowError(error: unknown): error is ChildWorkflowError {
+    return error instanceof ChildWorkflowError
+  }
+}
diff --git a/apps/sim/executor/execution/block-executor.ts b/apps/sim/executor/execution/block-executor.ts
index 5a271f7f18..59ae418f74 100644
--- a/apps/sim/executor/execution/block-executor.ts
+++ b/apps/sim/executor/execution/block-executor.ts
@@ -13,6 +13,7 @@ import {
   isSentinelBlockType,
 } from '@/executor/constants'
 import type { DAGNode } from '@/executor/dag/builder'
+import { ChildWorkflowError } from '@/executor/errors/child-workflow-error'
 import type { BlockStateWriter, ContextExtensions } from '@/executor/execution/types'
 import {
   generatePauseContextId,
@@ -213,24 +214,28 @@ export class BlockExecutor {
         ? resolvedInputs
         : ((block.config?.params as Record<string, any> | undefined) ?? {})
 
-    if (blockLog) {
-      blockLog.endedAt = new Date().toISOString()
-      blockLog.durationMs = duration
-      blockLog.success = false
-      blockLog.error = errorMessage
-      blockLog.input = input
-    }
-
     const errorOutput: NormalizedBlockOutput = {
       error: errorMessage,
     }
 
-    if (error && typeof error === 'object' && 'childTraceSpans' in error) {
+    if (ChildWorkflowError.isChildWorkflowError(error)) {
+      errorOutput.childTraceSpans = error.childTraceSpans
+      errorOutput.childWorkflowName = error.childWorkflowName
+    } else if (error && typeof error === 'object' && 'childTraceSpans' in error) {
       errorOutput.childTraceSpans = (error as any).childTraceSpans
     }
 
     this.state.setBlockOutput(node.id, errorOutput, duration)
 
+    if (blockLog) {
+      blockLog.endedAt = new Date().toISOString()
+      blockLog.durationMs = duration
+      blockLog.success = false
+      blockLog.error = errorMessage
+      blockLog.input = input
+      blockLog.output = this.filterOutputForLog(block, errorOutput)
+    }
+
     logger.error(
       phase === 'input_resolution' ? 'Failed to resolve block inputs' : 'Block execution failed',
       {
diff --git a/apps/sim/executor/handlers/workflow/workflow-handler.ts b/apps/sim/executor/handlers/workflow/workflow-handler.ts
index d8f7ced358..7ee6dec6ec 100644
--- a/apps/sim/executor/handlers/workflow/workflow-handler.ts
+++ b/apps/sim/executor/handlers/workflow/workflow-handler.ts
@@ -4,6 +4,7 @@ import type { TraceSpan } from '@/lib/logs/types'
 import type { BlockOutput } from '@/blocks/types'
 import { Executor } from '@/executor'
 import { BlockType, DEFAULTS, HTTP } from '@/executor/constants'
+import { ChildWorkflowError } from '@/executor/errors/child-workflow-error'
 import type {
   BlockHandler,
   ExecutionContext,
@@ -145,31 +146,30 @@ export class WorkflowBlockHandler implements BlockHandler {
       const childWorkflowName = workflowMetadata?.name || workflowId
 
       const originalError = error.message || 'Unknown error'
-      const wrappedError = new Error(
-        `Error in child workflow "${childWorkflowName}": ${originalError}`
-      )
-
+      let childTraceSpans: WorkflowTraceSpan[] = []
+      let executionResult: ExecutionResult | undefined
       if (error.executionResult?.logs) {
-        const executionResult = error.executionResult as ExecutionResult
+        executionResult = error.executionResult as ExecutionResult
 
         logger.info(`Extracting child trace spans from error.executionResult`, {
           hasLogs: (executionResult.logs?.length ?? 0) > 0,
           logCount: executionResult.logs?.length ?? 0,
         })
 
-        const childTraceSpans = this.captureChildWorkflowLogs(
-          executionResult,
-          childWorkflowName,
-          ctx
-        )
+        childTraceSpans = this.captureChildWorkflowLogs(executionResult, childWorkflowName, ctx)
 
         logger.info(`Captured ${childTraceSpans.length} child trace spans from failed execution`)
-        ;(wrappedError as any).childTraceSpans = childTraceSpans
       } else if (error.childTraceSpans && Array.isArray(error.childTraceSpans)) {
-        ;(wrappedError as any).childTraceSpans = error.childTraceSpans
+        childTraceSpans = error.childTraceSpans
       }
 
-      throw wrappedError
+      throw new ChildWorkflowError({
+        message: `Error in child workflow "${childWorkflowName}": ${originalError}`,
+        childWorkflowName,
+        childTraceSpans,
+        executionResult,
+        cause: error,
+      })
     }
   }
 
@@ -441,11 +441,11 @@ export class WorkflowBlockHandler implements BlockHandler {
 
     if (!success) {
       logger.warn(`Child workflow ${childWorkflowName} failed`)
-      const error = new Error(
-        `Error in child workflow "${childWorkflowName}": ${childResult.error || 'Child workflow execution failed'}`
-      )
-      ;(error as any).childTraceSpans = childTraceSpans || []
-      throw error
+      throw new ChildWorkflowError({
+        message: `Error in child workflow "${childWorkflowName}": ${childResult.error || 'Child workflow execution failed'}`,
+        childWorkflowName,
+        childTraceSpans: childTraceSpans || [],
+      })
     }
 
     return {

From 587d44ad6f8898817031e4d19df683ea210ee765 Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 01:44:53 -0800
Subject: [PATCH 2/6] remove overly defensive programming

---
 apps/sim/executor/execution/block-executor.ts | 2 --
 1 file changed, 2 deletions(-)

diff --git a/apps/sim/executor/execution/block-executor.ts b/apps/sim/executor/execution/block-executor.ts
index 59ae418f74..5e2ec09cc5 100644
--- a/apps/sim/executor/execution/block-executor.ts
+++ b/apps/sim/executor/execution/block-executor.ts
@@ -221,8 +221,6 @@ export class BlockExecutor {
     if (ChildWorkflowError.isChildWorkflowError(error)) {
       errorOutput.childTraceSpans = error.childTraceSpans
       errorOutput.childWorkflowName = error.childWorkflowName
-    } else if (error && typeof error === 'object' && 'childTraceSpans' in error) {
-      errorOutput.childTraceSpans = (error as any).childTraceSpans
     }
 
     this.state.setBlockOutput(node.id, errorOutput, duration)

From d3f20311d047c0cc42332cb695cdfa653570a616 Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 01:45:03 -0800
Subject: [PATCH 3/6] update type check

---
 apps/sim/executor/handlers/workflow/workflow-handler.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/apps/sim/executor/handlers/workflow/workflow-handler.ts b/apps/sim/executor/handlers/workflow/workflow-handler.ts
index 7ee6dec6ec..7bd2955024 100644
--- a/apps/sim/executor/handlers/workflow/workflow-handler.ts
+++ b/apps/sim/executor/handlers/workflow/workflow-handler.ts
@@ -159,7 +159,7 @@ export class WorkflowBlockHandler implements BlockHandler {
         childTraceSpans = this.captureChildWorkflowLogs(executionResult, childWorkflowName, ctx)
 
         logger.info(`Captured ${childTraceSpans.length} child trace spans from failed execution`)
-      } else if (error.childTraceSpans && Array.isArray(error.childTraceSpans)) {
+      } else if (ChildWorkflowError.isChildWorkflowError(error)) {
         childTraceSpans = error.childTraceSpans
       }
 

From 594bcac5f28b920e794a93e8f0e1626975414fa0 Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 01:54:09 -0800
Subject: [PATCH 4/6] type more code

---
 .../app/api/workflows/[id]/execute/route.ts   | 15 +++++-----
 .../hooks/use-workflow-execution.ts           | 16 ++--------
 apps/sim/executor/execution/engine.ts         |  6 ++--
 .../handlers/workflow/workflow-handler.ts     |  6 ++--
 apps/sim/executor/utils/errors.ts             | 29 ++++++++++++++++++-
 apps/sim/hooks/use-execution-stream.ts        |  9 ++++--
 6 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/apps/sim/app/api/workflows/[id]/execute/route.ts b/apps/sim/app/api/workflows/[id]/execute/route.ts
index 217d26f9bc..856a1a3c94 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 fbd432c12e..1c0cbcc7a0 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 58792ef2b8..05e7e04843 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 7bd2955024..6759af5ff5 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 0f078d84e1..3144d9c715 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 3516c93664..b9d1cc6858 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) {

From eb767b5edea67336b003e594c9ee3edc504b595c Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 01:58:02 -0800
Subject: [PATCH 5/6] remove more dead code

---
 apps/sim/background/schedule-execution.ts         |  5 ++---
 apps/sim/background/webhook-execution.ts          | 15 ++++++++-------
 apps/sim/background/workflow-execution.ts         |  5 ++---
 .../handlers/workflow/workflow-handler.ts         |  6 +++---
 apps/sim/lib/workflows/executor/execution-core.ts | 12 ++++--------
 5 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/apps/sim/background/schedule-execution.ts b/apps/sim/background/schedule-execution.ts
index 54ce24e5ea..c52676b8df 100644
--- a/apps/sim/background/schedule-execution.ts
+++ b/apps/sim/background/schedule-execution.ts
@@ -21,7 +21,7 @@ import {
 } from '@/lib/workflows/schedules/utils'
 import { ExecutionSnapshot } from '@/executor/execution/snapshot'
 import type { ExecutionMetadata } from '@/executor/execution/types'
-import type { ExecutionResult } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { MAX_CONSECUTIVE_FAILURES } from '@/triggers/constants'
 
 const logger = createLogger('TriggerScheduleExecution')
@@ -231,8 +231,7 @@ async function runWorkflowExecution({
   } catch (error: unknown) {
     logger.error(`[${requestId}] Early failure in scheduled workflow ${payload.workflowId}`, error)
 
-    const errorWithResult = error as { executionResult?: ExecutionResult }
-    const executionResult = errorWithResult?.executionResult
+    const executionResult = hasExecutionResult(error) ? error.executionResult : undefined
     const { traceSpans } = executionResult ? buildTraceSpans(executionResult) : { traceSpans: [] }
 
     await loggingSession.safeCompleteWithError({
diff --git a/apps/sim/background/webhook-execution.ts b/apps/sim/background/webhook-execution.ts
index a32ce09021..e5e3d3007f 100644
--- a/apps/sim/background/webhook-execution.ts
+++ b/apps/sim/background/webhook-execution.ts
@@ -16,7 +16,7 @@ import { loadDeployedWorkflowState } from '@/lib/workflows/persistence/utils'
 import { getWorkflowById } from '@/lib/workflows/utils'
 import { ExecutionSnapshot } from '@/executor/execution/snapshot'
 import type { ExecutionMetadata } from '@/executor/execution/types'
-import type { ExecutionResult } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { safeAssign } from '@/tools/safe-assign'
 import { getTrigger, isTriggerValid } from '@/triggers'
 
@@ -578,12 +578,13 @@ async function executeWebhookJobInternal(
         deploymentVersionId,
       })
 
-      const errorWithResult = error as { executionResult?: ExecutionResult }
-      const executionResult = errorWithResult?.executionResult || {
-        success: false,
-        output: {},
-        logs: [],
-      }
+      const executionResult = hasExecutionResult(error)
+        ? error.executionResult
+        : {
+            success: false,
+            output: {},
+            logs: [],
+          }
       const { traceSpans } = buildTraceSpans(executionResult)
 
       await loggingSession.safeCompleteWithError({
diff --git a/apps/sim/background/workflow-execution.ts b/apps/sim/background/workflow-execution.ts
index f7e061fbf0..99e83d54cc 100644
--- a/apps/sim/background/workflow-execution.ts
+++ b/apps/sim/background/workflow-execution.ts
@@ -9,7 +9,7 @@ import { PauseResumeManager } from '@/lib/workflows/executor/human-in-the-loop-m
 import { getWorkflowById } from '@/lib/workflows/utils'
 import { ExecutionSnapshot } from '@/executor/execution/snapshot'
 import type { ExecutionMetadata } from '@/executor/execution/types'
-import type { ExecutionResult } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import type { CoreTriggerType } from '@/stores/logs/filters/types'
 
 const logger = createLogger('TriggerWorkflowExecution')
@@ -160,8 +160,7 @@ export async function executeWorkflowJob(payload: WorkflowExecutionPayload) {
       executionId,
     })
 
-    const errorWithResult = error as { executionResult?: ExecutionResult }
-    const executionResult = errorWithResult?.executionResult
+    const executionResult = hasExecutionResult(error) ? error.executionResult : undefined
     const { traceSpans } = executionResult ? buildTraceSpans(executionResult) : { traceSpans: [] }
 
     await loggingSession.safeCompleteWithError({
diff --git a/apps/sim/executor/handlers/workflow/workflow-handler.ts b/apps/sim/executor/handlers/workflow/workflow-handler.ts
index 6759af5ff5..3ec7319ebf 100644
--- a/apps/sim/executor/handlers/workflow/workflow-handler.ts
+++ b/apps/sim/executor/handlers/workflow/workflow-handler.ts
@@ -139,14 +139,14 @@ export class WorkflowBlockHandler implements BlockHandler {
       )
 
       return mappedResult
-    } catch (error: any) {
+    } catch (error: unknown) {
       logger.error(`Error executing child workflow ${workflowId}:`, error)
 
       const { workflows } = useWorkflowRegistry.getState()
       const workflowMetadata = workflows[workflowId]
       const childWorkflowName = workflowMetadata?.name || workflowId
 
-      const originalError = error.message || 'Unknown error'
+      const originalError = error instanceof Error ? error.message : 'Unknown error'
       let childTraceSpans: WorkflowTraceSpan[] = []
       let executionResult: ExecutionResult | undefined
 
@@ -170,7 +170,7 @@ export class WorkflowBlockHandler implements BlockHandler {
         childWorkflowName,
         childTraceSpans,
         executionResult,
-        cause: error,
+        cause: error instanceof Error ? error : undefined,
       })
     }
   }
diff --git a/apps/sim/lib/workflows/executor/execution-core.ts b/apps/sim/lib/workflows/executor/execution-core.ts
index d128d9e208..c2b300f084 100644
--- a/apps/sim/lib/workflows/executor/execution-core.ts
+++ b/apps/sim/lib/workflows/executor/execution-core.ts
@@ -24,6 +24,7 @@ import type {
   IterationContext,
 } from '@/executor/execution/types'
 import type { ExecutionResult, NormalizedBlockOutput } from '@/executor/types'
+import { hasExecutionResult } from '@/executor/utils/errors'
 import { Serializer } from '@/serializer'
 import { mergeSubblockState } from '@/stores/workflows/server-utils'
 
@@ -383,20 +384,15 @@ export async function executeWorkflowCore(
   } catch (error: unknown) {
     logger.error(`[${requestId}] Execution failed:`, error)
 
-    const errorWithResult = error as {
-      executionResult?: ExecutionResult
-      message?: string
-      stack?: string
-    }
-    const executionResult = errorWithResult?.executionResult
+    const executionResult = hasExecutionResult(error) ? error.executionResult : undefined
     const { traceSpans } = executionResult ? buildTraceSpans(executionResult) : { traceSpans: [] }
 
     await loggingSession.safeCompleteWithError({
       endedAt: new Date().toISOString(),
       totalDurationMs: executionResult?.metadata?.duration || 0,
       error: {
-        message: errorWithResult?.message || 'Execution failed',
-        stackTrace: errorWithResult?.stack,
+        message: error instanceof Error ? error.message : 'Execution failed',
+        stackTrace: error instanceof Error ? error.stack : undefined,
       },
       traceSpans,
     })

From bf22dd75ad7a44fb6293a5a214e3d06fd14e57be Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 24 Jan 2026 02:13:06 -0800
Subject: [PATCH 6/6] address bugbot comments

---
 apps/sim/executor/utils/errors.ts | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/apps/sim/executor/utils/errors.ts b/apps/sim/executor/utils/errors.ts
index 3144d9c715..f92c9c1ff4 100644
--- a/apps/sim/executor/utils/errors.ts
+++ b/apps/sim/executor/utils/errors.ts
@@ -11,14 +11,20 @@ export interface ErrorWithExecutionResult extends Error {
 
 /**
  * Type guard to check if an error carries an ExecutionResult.
+ * Validates that executionResult has required fields (success, output).
  */
 export function hasExecutionResult(error: unknown): error is ErrorWithExecutionResult {
-  return (
-    error instanceof Error &&
-    'executionResult' in error &&
-    error.executionResult != null &&
-    typeof error.executionResult === 'object'
-  )
+  if (
+    !(error instanceof Error) ||
+    !('executionResult' in error) ||
+    error.executionResult == null ||
+    typeof error.executionResult !== 'object'
+  ) {
+    return false
+  }
+
+  const result = error.executionResult as Record<string, unknown>
+  return typeof result.success === 'boolean' && result.output != null
 }
 
 /**