@@ -463,6 +463,83 @@ describe('applyWorkflowOperations', () => {
     expect(mockNotify).not.toHaveBeenCalled()
   })
 
+  describe('a concurrent edit between the base read and the write', () => {
+    /** Runs the write's reader the way the row-locked transaction does. */
+    beforeEach(() => {
+      mocks.replace.mockImplementation(
+        async ({ state }: { state: unknown | ((tx: unknown) => Promise<unknown>) }) => ({
+          warnings: [],
+          state: typeof state === 'function' ? await state({}) : state,
+        })
+      )
+    })
+
+    it('refuses the write instead of overwriting the newer stored graph', async () => {
+      mocks.normalizeState
+        .mockReturnValueOnce({ state: graph(), warnings: [] })
+        .mockReturnValueOnce({
+          state: graph({ 'block-1': BLOCK, 'block-3': { ...BLOCK, id: 'block-3', name: 'Other' } }),
+          warnings: [],
+        })
+
+      const failure = await applyWorkflowOperations
+        .execute({ principal: sessionPrincipal, input: { workflowId: 'workflow-1', operations } })
+        .catch((error: unknown) => error)
+
+      expect(failure).toBeInstanceOf(OrchestrationError)
+      expect((failure as OrchestrationError).code).toBe('conflict')
+      expect(mockRecordAudit).not.toHaveBeenCalled()
+      expect(mockNotify).not.toHaveBeenCalled()
+    })
+
+    /** The loader orders neither rows nor record keys, so a re-read of the same rows must still match. */
+    it('commits when the re-read differs only in row order', async () => {
+      const EDGE_A = { id: 'edge-a', source: 'block-1', target: 'block-2' }
+      const EDGE_B = { id: 'edge-b', source: 'block-2', target: 'block-1' }
+      const block2 = { ...BLOCK, id: 'block-2', name: 'Second' }
+      mocks.normalizeState
+        .mockReturnValueOnce({
+          state: { ...graph({ 'block-1': BLOCK, 'block-2': block2 }), edges: [EDGE_A, EDGE_B] },
+          warnings: [],
+        })
+        .mockReturnValueOnce({
+          state: { ...graph({ 'block-2': block2, 'block-1': BLOCK }), edges: [EDGE_B, EDGE_A] },
+          warnings: [],
+        })
+
+      const result = await applyWorkflowOperations.execute({
+        principal: sessionPrincipal,
+        input: { workflowId: 'workflow-1', operations },
+      })
+
+      expect(result.dryRun).toBe(false)
+    })
+
+    /** Container `nodes` are rebuilt from the block rows, so they inherit the read's row order. */
+    it('commits when only container child order differs on the re-read', async () => {
+      const containers = (nodes: string[]) => ({
+        loops: { 'loop-1': { id: 'loop-1', nodes, iterations: 1, loopType: 'for' } },
+        parallels: { 'parallel-1': { id: 'parallel-1', nodes, count: 2, parallelType: 'count' } },
+      })
+      mocks.normalizeState
+        .mockReturnValueOnce({
+          state: { ...graph(), ...containers(['block-1', 'block-2']) },
+          warnings: [],
+        })
+        .mockReturnValueOnce({
+          state: { ...graph(), ...containers(['block-2', 'block-1']) },
+          warnings: [],
+        })
+
+      const result = await applyWorkflowOperations.execute({
+        principal: sessionPrincipal,
+        input: { workflowId: 'workflow-1', operations },
+      })
+
+      expect(result.dryRun).toBe(false)
+    })
+  })
+
   /**
    * The legacy tool threw a bare `Error(MAX_PLAN_REQUIRED)`, which on a public
    * surface is an unclassified 500.
@@ -529,7 +606,7 @@ describe('applyWorkflowOperations', () => {
       principal: sessionPrincipal,
       input: { workflowId: 'workflow-1', operations, baseGraph },
     })
-    expect(mockLoadNormalized).toHaveBeenCalledWith('workflow-1')
+    expect(mockLoadNormalized).toHaveBeenCalledWith('workflow-1', undefined)
     expect(mocks.applyOperations).not.toHaveBeenCalledWith(baseGraph, operations, null, true)
   })
 
 
@@ -3,6 +3,8 @@ import { type Principal, resolvePrincipalAttribution } from '@sim/auth/principal
 import { db } from '@sim/db'
 import { createLogger } from '@sim/logger'
 import { toError } from '@sim/utils/errors'
+import { sortObjectKeysDeep } from '@sim/utils/object'
+import { compareStrings } from '@sim/utils/string'
 import {
   generateLoopBlocks,
   generateParallelBlocks,
@@ -12,6 +14,7 @@ import { hasWorkspaceSandboxAccess } from '@/lib/billing/core/subscription'
 import { ForbiddenOperationError, principalAuditSource } from '@/lib/core/application'
 import { getBlockVisibility } from '@/lib/core/config/block-visibility'
 import { OrchestrationError } from '@/lib/core/orchestration/types'
+import type { DbOrTx } from '@/lib/db/types'
 import { MAX_PLAN_REQUIRED } from '@/lib/execution/remote-sandbox/entitlement'
 import { resolvePermissionGroupConfig } from '@/lib/permission-groups/config-scope.server'
 import { notifyWorkflowUpdated } from '@/lib/realtime/notify'
@@ -147,8 +150,11 @@ function asGraph(value: Record<string, unknown>): Pick<WorkflowState, 'blocks' |
  * graph. A null result therefore remains a hard failure rather than becoming a
  * fallback graph that a write could persist after a failed read.
  */
-async function loadStoredGraph(workflowId: string): Promise<Record<string, unknown>> {
-  const normalized = await loadWorkflowFromNormalizedTables(workflowId)
+async function loadStoredGraph(
+  workflowId: string,
+  executor?: DbOrTx
+): Promise<Record<string, unknown>> {
+  const normalized = await loadWorkflowFromNormalizedTables(workflowId, executor)
   if (!normalized) {
     throw new OrchestrationError('validation', `Workflow ${workflowId} has no normalized state`)
   }
@@ -216,13 +222,54 @@ function applyBlockEnabledChanges(
   return { blocks: current, applied }
 }
 
+/**
+ * An order-insensitive identity for a stored graph, so two reads of the same
+ * rows compare equal even though the loader neither orders its rows nor fixes
+ * the key order of the records it builds.
+ *
+ * Only blocks and edges are compared: loops and parallels are rebuilt from the
+ * blocks on every load, with child `nodes` in row order.
+ */
+function storedGraphFingerprint(graph: Record<string, unknown>): string {
+  const { blocks, edges } = asGraph(graph)
+  const sortedEdges = [...(edges ?? [])].sort((a, b) => compareStrings(a.id, b.id))
+  return JSON.stringify(sortObjectKeysDeep({ blocks, edges: sortedEdges }))
+}
+
+interface BaseGraph {
+  graph: Record<string, unknown>
+  /** Set when the base was read from storage, so the write can prove it is still current. */
+  storedFingerprint?: string
+}
+
 async function resolveBaseGraph(
   principal: Principal,
   input: ApplyWorkflowOperationsInput,
   context: ActiveWorkflowApplicationContext
-): Promise<Record<string, unknown>> {
-  if (input.baseGraph && principal.kind === 'delegated') return input.baseGraph
-  return loadStoredGraph(context.workflowId)
+): Promise<BaseGraph> {
+  if (input.baseGraph && principal.kind === 'delegated') return { graph: input.baseGraph }
+  const graph = await loadStoredGraph(context.workflowId)
+  return { graph, storedFingerprint: storedGraphFingerprint(graph) }
+}
+
+/**
+ * Refuses the write when the stored graph is no longer the one the batch was
+ * applied to. Runs under the workflow row lock, so a concurrent edit that
+ * committed after the base read surfaces as a conflict instead of being
+ * silently overwritten by a graph that never saw it.
+ */
+async function assertStoredGraphUnchanged(
+  workflowId: string,
+  storedFingerprint: string,
+  tx: DbOrTx
+): Promise<void> {
+  const current = await loadStoredGraph(workflowId, tx)
+  if (storedGraphFingerprint(current) !== storedFingerprint) {
+    throw new OrchestrationError(
+      'conflict',
+      'The workflow changed while these operations were being applied. Re-read it and retry.'
+    )
+  }
 }
 
 /**
@@ -233,6 +280,8 @@ async function resolveBaseGraph(
  * skipped items, and exactly one write of the fully-resolved graph happens at the
  * end, through the shared persistence primitive. A caller that needs all-or-nothing
  * sets `atomic`, which decides between the in-memory apply and that single write.
+ * When the batch was applied to the stored graph, that write is refused as a
+ * `conflict` if another edit committed in between, rather than overwriting it.
  *
  * Copilot's `edit_workflow` tool and `POST /api/v2/workflows/{workflowId}/operations` are
  * both adapters over this; the tool is the only caller allowed to supply
@@ -261,7 +310,11 @@ export const applyWorkflowOperations = defineAuthorizedWorkflowUseCase({
       const subjectUserId = attribution.attributedUserId
 
       input.checkAborted?.()
-      const baseGraph = await resolveBaseGraph(principal, input, context)
+      const { graph: baseGraph, storedFingerprint } = await resolveBaseGraph(
+        principal,
+        input,
+        context
+      )
 
       const [permissionConfig, blockVisibility] = await Promise.all([
         resolvePermissionGroupConfig(
@@ -432,6 +485,7 @@ export const applyWorkflowOperations = defineAuthorizedWorkflowUseCase({
         }
       }
 
+      const nextState = { blocks: graph.blocks, edges: graph.edges }
       const persisted = await replaceWorkflowNormalizedState({
         workflowId: context.workflowId,
         workspaceId: context.workspaceId,
@@ -442,7 +496,18 @@ export const applyWorkflowOperations = defineAuthorizedWorkflowUseCase({
          * governed subject are the same human and cannot diverge here.
          */
         subjectUserId,
-        state: { blocks: graph.blocks, edges: graph.edges },
+        /**
+         * Applying the batch reaches credential lookups, MCP server discovery,
+         * and lint queries, so it ran outside the lock; only the staleness check
+         * runs under it.
+         */
+        state:
+          storedFingerprint === undefined
+            ? nextState
+            : async (tx) => {
+                await assertStoredGraphUnchanged(context.workflowId, storedFingerprint, tx)
+                return nextState
+              },
       })
 
       logger.info('Applied workflow operations', {
 
@@ -154,6 +154,11 @@ function graph(includeCustom = false) {
   }
 }
 
+/** Resolves the graph the write is given, running its reader the way the row-locked transaction does. */
+async function resolveWrittenState(state: unknown) {
+  return typeof state === 'function' ? state({}) : state
+}
+
 const add: EditWorkflowOperation = {
   operation_type: 'add',
   block_id: 'new-worker',
@@ -171,7 +176,9 @@ describe('custom blocks in authorized workflow authoring', () => {
       workflowRecord: context.workflow,
       normalizedData: graph(true),
     }))
-    mocks.replace.mockImplementation(async ({ state }) => prepareWorkflowStateForPersistence(state))
+    mocks.replace.mockImplementation(async ({ state }) =>
+      prepareWorkflowStateForPersistence(await resolveWrittenState(state))
+    )
   })
 
   it.each([session, copilot])(
@@ -218,7 +225,7 @@ describe('custom blocks in authorized workflow authoring', () => {
       expect(result.lint.fieldIssues).toEqual([])
       expect(mocks.replace).toHaveBeenCalledTimes(dryRun ? 0 : 1)
       if (!dryRun) {
-        const persisted = mocks.replace.mock.calls[0][0].state
+        const { state: persisted } = await mocks.replace.mock.results[0].value
         expect(persisted.blocks.worker.subBlocks['input-text']).toMatchObject({
           value: 'updated',
           type: 'short-input',
@@ -265,7 +272,7 @@ describe('custom blocks in authorized workflow authoring', () => {
     mocks.replace.mockImplementation(async ({ state, workspaceId }) => {
       const foreignType = workspaceId === 'one' ? other.type : customBlock.type
       expect(getBlock(foreignType)).toBeUndefined()
-      return prepareWorkflowStateForPersistence(state)
+      return prepareWorkflowStateForPersistence(await resolveWrittenState(state))
     })
     const results = await Promise.all(
       [customBlock, other].map((row, index) =>
@@ -298,7 +305,7 @@ describe('custom blocks in authorized workflow authoring', () => {
       expect(result.lint.fieldIssues).toEqual([])
       expect(mocks.replace).toHaveBeenCalledTimes(dryRun ? 0 : 1)
       if (!dryRun) {
-        const persisted = mocks.replace.mock.calls[0][0].state
+        const { state: persisted } = await mocks.replace.mock.results[0].value
         expect(persisted.blocks.worker.subBlocks['input-text']).toMatchObject({
           value: 'hello',
           type: 'short-input',
 
@@ -209,7 +209,9 @@ export interface ReplaceWorkflowNormalizedStateInput {
    * lock is taken, inside the same transaction, so a concurrent write that
    * commits between a caller's own read and this one cannot be silently
    * overwritten by a stale graph. Passing an already-read value is correct only
-   * when the caller composed it without reading the stored graph.
+   * when the caller composed it without reading the stored graph. A caller that
+   * cannot compose its graph under the lock re-reads the stored graph in the
+   * reader and refuses the write when it changed.
    */
   state: ReplaceWorkflowState | ((tx: DbOrTx) => Promise<ReplaceWorkflowState>)
   requestId?: string