fix(executor): drop the full JSON clone of execution state at run completion

apps/sim/executor/execution/block-executor.ts

@@ -424,9 +424,8 @@ export class BlockExecutor {
           typeof normalizedOutput._childWorkflowInstanceId === 'string'
             ? normalizedOutput._childWorkflowInstanceId
             : undefined
-        const displayOutput = filterOutputForLog(block.metadata?.id || '', normalizedOutput, {
-          block,
-        })
+        // Shallow top-level copy: streaming later writes token/cost keys onto blockLog.output.
+        const displayOutput = { ...blockLog.output }
         const displayInput = this.projectInputsForDisplay(inputsForLog, block, inputDisplayRegistry)
         blockLog.input = displayInput
         const displayProvenance = settledBlockRegistry?.exportCommittedProvenanceForValue({
@@ -680,7 +679,7 @@ export class BlockExecutor {
 
       if (!isSentinel && blockLog) {
         const displayInput = this.projectInputsForDisplay(input, block, inputDisplayRegistry)
-        const displayOutput = filterOutputForLog(block.metadata?.id || '', softOutput, { block })
+        const displayOutput = { ...blockLog.output }
         const displayProvenance =
           ctx.resolvedSecretTraceRegistry?.exportCommittedProvenanceForValue({
             input: displayInput,
@@ -798,7 +797,7 @@ export class BlockExecutor {
       const childWorkflowInstanceId = ChildWorkflowError.isChildWorkflowError(error)
         ? error.childWorkflowInstanceId
         : undefined
-      const displayOutput = filterOutputForLog(block.metadata?.id || '', errorOutput, { block })
+      const displayOutput = { ...blockLog.output }
       const displayInput = this.projectInputsForDisplay(input, block, inputDisplayRegistry)
       const displayProvenance = errorRegistry?.exportCommittedProvenanceForValue({
         input: displayInput,

apps/sim/executor/execution/engine.ts

@@ -5,7 +5,10 @@ import { subscribeToExecutionCancellation } from '@/lib/execution/cancellation'
 import { BlockType, EDGE } from '@/executor/constants'
 import type { DAG } from '@/executor/dag/builder'
 import type { EdgeManager } from '@/executor/execution/edge-manager'
-import { serializePauseSnapshot } from '@/executor/execution/snapshot-serializer'
+import {
+  buildCompletedExecutionState,
+  serializePauseSnapshot,
+} from '@/executor/execution/snapshot-serializer'
 import type { SerializableExecutionState } from '@/executor/execution/types'
 import type { NodeExecutionOrchestrator } from '@/executor/orchestrators/node'
 import type {
@@ -147,7 +150,7 @@ export class ExecutionEngine {
         success: true,
         output: this.finalOutput,
         logs: this.context.blockLogs,
-        executionState: this.getSerializableExecutionState(),
+        executionState: this.getCompletedExecutionState(),
         metadata: this.context.metadata,
       }
     } catch (error) {
@@ -591,6 +594,22 @@ export class ExecutionEngine {
     }
   }
 
+  /**
+   * State for a run whose blocks have all settled, without the JSON round-trip.
+   * Cancelled and failed runs keep {@link getSerializableExecutionState}: a block
+   * still running there could mutate the logs after the run returns.
+   */
+  private getCompletedExecutionState(): SerializableExecutionState | undefined {
+    try {
+      return buildCompletedExecutionState(this.context, this.dag, this.edgeManager)
+    } catch (error) {
+      this.execLogger.warn('Failed to serialize execution state', {
+        error: toError(error).message,
+      })
+      return undefined
+    }
+  }
+
   private collectPauseResponses(): NormalizedBlockOutput {
     const responses = Array.from(this.pausedBlocks.values()).map((pause) => pause.response)
 

apps/sim/executor/execution/snapshot-serializer.test.ts

@@ -1,7 +1,11 @@
 import { describe, expect, it, vi } from 'vitest'
 import type { DAG, DAGNode } from '@/executor/dag/builder'
 import { EdgeManager } from '@/executor/execution/edge-manager'
-import { serializePauseSnapshot } from '@/executor/execution/snapshot-serializer'
+import {
+  buildCompletedExecutionState,
+  isLiveExecutionState,
+  serializePauseSnapshot,
+} from '@/executor/execution/snapshot-serializer'
 import type { ExecutionContext } from '@/executor/types'
 import { ResolvedSecretTraceRegistry } from '@/executor/utils/resolved-secret-trace-registry'
 
@@ -307,3 +311,82 @@ describe('serializePauseSnapshot', () => {
     expect(serialized.metadata.capabilityGovernedUserId).toBe('requesting-member')
   })
 })
+
+describe('buildCompletedExecutionState', () => {
+  /** The state a completed run used to carry: the pause snapshot's state, JSON round-tripped. */
+  function jsonClonedState(context: ExecutionContext): unknown {
+    return JSON.parse(serializePauseSnapshot(context, []).snapshot).state
+  }
+
+  function contextWithOutput(output: unknown): ExecutionContext {
+    return createContext({
+      blockStates: new Map([['block-1', { output, executed: true, executionTime: 5 }]]),
+      executedBlocks: new Set(['block-1']),
+      blockLogs: [
+        {
+          blockId: 'block-1',
+          blockName: 'Block',
+          blockType: 'function',
+          startedAt: '2026-01-01T00:00:00.000Z',
+          endedAt: '2026-01-01T00:00:01.000Z',
+          durationMs: 1000,
+          success: true,
+          executionOrder: 1,
+          output,
+          input: { note: undefined, list: [undefined, 1] },
+        },
+      ] as ExecutionContext['blockLogs'],
+    })
+  }
+
+  const shared = { rows: [{ id: 1, at: new Date(0) }] }
+  const cyclic: Record<string, unknown> = { a: 1 }
+  cyclic.self = cyclic
+  const cycleBehindToJSON: Record<string, unknown> = { toJSON: () => ({ safe: true }) }
+  cycleBehindToJSON.self = cycleBehindToJSON
+
+  it.each([
+    ['a subtree shared twice', { first: shared, second: shared }],
+    ['a cycle hidden behind toJSON', { value: cycleBehindToJSON }],
+    [
+      'a boxed number carrying a BigInt property',
+      { value: Object.assign(Object(1), { big: BigInt(1) }) },
+    ],
+  ])('serializes like the JSON-cloned pause state for %s', (_name, output) => {
+    const context = contextWithOutput(output)
+    expect(JSON.stringify(buildCompletedExecutionState(context))).toBe(
+      JSON.stringify(jsonClonedState(context))
+    )
+  })
+
+  it.each([
+    ['a cycle', cyclic],
+    ['a BigInt', { big: BigInt(1) }],
+  ])('throws like the pause snapshot for %s', (_name, output) => {
+    const context = contextWithOutput(output)
+    expect(() => jsonClonedState(context)).toThrow(TypeError)
+    expect(() => buildCompletedExecutionState(context)).toThrow(TypeError)
+  })
+
+  it('shares block outputs with the run instead of cloning them', () => {
+    const output = { rows: [{ id: 1 }] }
+    const context = contextWithOutput(output)
+    const state = buildCompletedExecutionState(context)
+
+    expect(state.blockLogs[0].output).toBe(output)
+    expect(state.blockStates['block-1'].output).toBe(output)
+
+    context.blockLogs[0].endedAt = 'later'
+    expect(state.blockLogs[0].endedAt).toBe('2026-01-01T00:00:01.000Z')
+  })
+
+  it('marks completed state as live through spreads but not through JSON', () => {
+    const context = contextWithOutput({ rows: [{ id: 1 }] })
+    const state = buildCompletedExecutionState(context)
+
+    expect(isLiveExecutionState(state)).toBe(true)
+    expect(isLiveExecutionState({ ...state, sourceExecutionId: 'other' })).toBe(true)
+    expect(isLiveExecutionState(jsonClonedState(context))).toBe(false)
+    expect(JSON.stringify(state)).toBe(JSON.stringify(jsonClonedState(context)))
+  })
+})

apps/sim/executor/execution/snapshot-serializer.ts

@@ -183,12 +183,12 @@ function serializeParallelExecutions(
   return result
 }
 
-export function serializePauseSnapshot(
+function buildExecutionSnapshot(
   context: ExecutionContext,
   triggerBlockIds: string[],
   dag?: DAG,
   edgeManager?: EdgeManager
-): SerializedSnapshot {
+): { snapshot: ExecutionSnapshot; state: SerializableExecutionState } {
   const metadataFromContext = context.metadata as ExecutionMetadata | undefined
   let useDraftState: boolean
   if (metadataFromContext?.useDraftState !== undefined) {
@@ -316,9 +316,113 @@ export function serializePauseSnapshot(
     context.selectedOutputs,
     state
   )
+  return { snapshot, state }
+}
 
+export function serializePauseSnapshot(
+  context: ExecutionContext,
+  triggerBlockIds: string[],
+  dag?: DAG,
+  edgeManager?: EdgeManager
+): SerializedSnapshot {
   return {
-    snapshot: snapshot.toJSON(),
+    snapshot: buildExecutionSnapshot(context, triggerBlockIds, dag, edgeManager).snapshot.toJSON(),
     triggerIds: triggerBlockIds,
   }
 }
+
+const LIVE_EXECUTION_STATE = Symbol('liveExecutionState')
+
+/**
+ * Throws exactly where `JSON.stringify(value)` would — a cycle or a BigInt,
+ * after applying `toJSON` — without building the string. Iterative, so nesting
+ * that native serialization handles cannot overflow the JS stack here.
+ */
+function assertJsonSerializable(value: unknown): void {
+  type Frame = { node: object; keys: string[] | undefined; length: number; index: number }
+  const ancestors = new Set<object>()
+  const stack: Frame[] = []
+
+  const enter = (raw: unknown, key: string): void => {
+    let current = raw
+    if (
+      (typeof current === 'object' && current !== null) ||
+      typeof current === 'function' ||
+      typeof current === 'bigint'
+    ) {
+      const toJSON = (current as { toJSON?: unknown }).toJSON
+      if (typeof toJSON === 'function') current = toJSON.call(current, key)
+    }
+    if (typeof current === 'bigint' || current instanceof BigInt) {
+      throw new TypeError('Do not know how to serialize a BigInt')
+    }
+    if (typeof current !== 'object' || current === null) return
+    // Serialized as their primitive value; their own properties are never read.
+    if (current instanceof Number || current instanceof String || current instanceof Boolean) {
+      return
+    }
+    if (ancestors.has(current)) {
+      throw new TypeError('Converting circular structure to JSON')
+    }
+    ancestors.add(current)
+    const keys = Array.isArray(current) ? undefined : Object.keys(current)
+    stack.push({
+      node: current,
+      keys,
+      length: keys ? keys.length : (current as unknown[]).length,
+      index: 0,
+    })
+  }
+
+  enter(value, '')
+  while (stack.length > 0) {
+    const frame = stack[stack.length - 1]
+    if (frame.index >= frame.length) {
+      ancestors.delete(frame.node)
+      stack.pop()
+      continue
+    }
+    const index = frame.index++
+    const key = frame.keys ? frame.keys[index] : String(index)
+    enter((frame.node as Record<string, unknown>)[key], key)
+  }
+}
+
+/**
+ * Execution state for a run whose blocks have all settled. Validates and fails
+ * exactly like `JSON.parse(serializePauseSnapshot(...).snapshot).state`, but
+ * skips that full JSON clone: block logs and block states are shallow copies
+ * sharing their inputs and outputs with the run, and JSON normalization is left
+ * to whoever serializes the state.
+ */
+export function buildCompletedExecutionState(
+  context: ExecutionContext,
+  dag?: DAG,
+  edgeManager?: EdgeManager
+): SerializableExecutionState {
+  const { snapshot, state } = buildExecutionSnapshot(context, [], dag, edgeManager)
+  assertJsonSerializable(snapshot.toSerializable())
+  const completed: SerializableExecutionState = {
+    ...state,
+    blockLogs: state.blockLogs.map((log) => ({ ...log })),
+    blockStates: Object.fromEntries(
+      Object.entries(state.blockStates).map(([blockId, blockState]) => [blockId, { ...blockState }])
+    ),
+  }
+  // Enumerable so object spreads carry it; JSON serialization ignores symbol keys.
+  Object.defineProperty(completed, LIVE_EXECUTION_STATE, { value: true, enumerable: true })
+  return completed
+}
+
+/**
+ * Whether execution state came from {@link buildCompletedExecutionState} (or a
+ * spread of it) and so still holds live, not-yet-JSON-normalized values.
+ * Other states came out of a JSON round-trip already.
+ */
+export function isLiveExecutionState(state: unknown): boolean {
+  return (
+    typeof state === 'object' &&
+    state !== null &&
+    (state as Record<symbol, unknown>)[LIVE_EXECUTION_STATE] === true
+  )
+}

apps/sim/executor/execution/snapshot.ts

@@ -69,8 +69,9 @@ export class ExecutionSnapshot {
     this.state = state
   }
 
-  toJSON(): string {
-    return JSON.stringify({
+  /** The value {@link toJSON} stringifies, built without serializing it. */
+  toSerializable(): Record<string, unknown> {
+    return {
       metadata: {
         ...this.metadata,
         principal: serializePrincipal(this.metadata.principal),
@@ -81,7 +82,11 @@ export class ExecutionSnapshot {
       workflowVariables: this.workflowVariables,
       selectedOutputs: this.selectedOutputs,
       state: this.state,
-    })
+    }
+  }
+
+  toJSON(): string {
+    return JSON.stringify(this.toSerializable())
   }
 
   static fromJSON(json: string): ExecutionSnapshot {

apps/sim/executor/utils/output-filter.test.ts

@@ -33,4 +33,17 @@ describe('output filtering', () => {
     expect(output).not.toHaveProperty('childTraceSpans')
     expect(output.answer).toBe(42)
   })
+
+  it('shares untouched nested output with the block state instead of copying it', () => {
+    const rows = [{ id: 1, data: { name: 'a' } }]
+    const nestedSpans = { childTraceSpans: [{ id: 's1' }], kept: { value: 1 } }
+    const blockOutput = { rows, nested: nestedSpans }
+
+    const output = filterOutputForLog('table', blockOutput as never)
+
+    expect(output.rows).toBe(rows)
+    expect(output.nested).not.toBe(nestedSpans)
+    expect(output.nested).not.toHaveProperty('childTraceSpans')
+    expect((output.nested as typeof nestedSpans).kept).toBe(nestedSpans.kept)
+  })
 })

apps/sim/lib/core/utils/bounded-json.ts

@@ -1,8 +1,11 @@
 const MAX_JSON_NODES = 100_000
 const MAX_JSON_DEPTH = 64
 
-/** Counts JSON escapes without allocating the escaped string. */
-function quotedStringBytes(value: string, remaining: number): number | undefined {
+/**
+ * UTF-8 byte length of `JSON.stringify(value)` for a string, counted without
+ * allocating the escaped copy. Returns `undefined` once it exceeds `remaining`.
+ */
+export function quotedStringBytes(value: string, remaining: number): number | undefined {
   let bytes = 2
   for (let index = 0; index < value.length && bytes <= remaining; index++) {
     const code = value.charCodeAt(index)

apps/sim/lib/execution/payloads/serializer.test.ts

@@ -258,6 +258,22 @@ describe('compactExecutionPayload', () => {
     expect(compacted.every(isLargeArrayManifest)).toBe(true)
   })
 
+  it('reuses already-compacted subflow entries instead of rebuilding them', async () => {
+    const unchanged = { rows: [{ id: 1, data: { name: 'a' } }], meta: { count: 1 } }
+    const file = { id: 'f1', key: 'k1', url: 'u', name: 'a.txt', size: 3, type: 'text/plain' }
+    const withBase64 = { file: { ...file, base64: 'YWJj' }, other: { kept: true } }
+
+    const [reused, stripped] = (await compactSubflowResults([unchanged, withBase64], {})) as [
+      typeof unchanged,
+      typeof withBase64,
+    ]
+
+    expect(reused).toBe(unchanged)
+    expect(stripped).not.toBe(withBase64)
+    expect(stripped.file).toEqual(file)
+    expect(stripped.other).toBe(withBase64.other)
+  })
+
   it('rejects durable compaction when storage context is incomplete', async () => {
     await expect(
       compactExecutionPayload(