diff --git a/e2e/playwright/sketch-tests.spec.ts b/e2e/playwright/sketch-tests.spec.ts
index 980f357c5..e96ad60a5 100644
--- a/e2e/playwright/sketch-tests.spec.ts
+++ b/e2e/playwright/sketch-tests.spec.ts
@@ -943,6 +943,110 @@ sketch002 = startSketchOn(extrude001, 'END')
 `.replace(/\s/g, '')
     )
   })
+
+  /* TODO: once we fix bug turn on.
+   test('empty-scene default-planes act as expected when spaces in file', async ({
+    page,
+    browserName,
+  }) => {
+
+    const u = await getUtils(page)
+    await page.setViewportSize({ width: 1200, height: 500 })
+
+    await u.waitForAuthSkipAppStart()
+
+    await u.openDebugPanel()
+    await u.expectCmdLog('[data-message-type="execution-done"]')
+    await u.closeDebugPanel()
+
+    const XYPlanePoint = { x: 774, y: 116 } as const
+    const unHoveredColor: [number, number, number] = [47, 47, 93]
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await page.mouse.move(XYPlanePoint.x, XYPlanePoint.y)
+    await page.waitForTimeout(200)
+
+    // color should not change for having been hovered
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await u.openAndClearDebugPanel()
+
+    // Fill with spaces
+    await u.codeLocator.fill(`               
+`)
+
+    await u.openDebugPanel()
+    await u.expectCmdLog('[data-message-type="execution-done"]')
+    await u.closeDebugPanel()
+
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await page.mouse.move(XYPlanePoint.x, XYPlanePoint.y)
+    await page.waitForTimeout(200)
+
+    // color should not change for having been hovered
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+  })
+
+  test('empty-scene default-planes act as expected when only code comments in file', async ({
+    page,
+    browserName,
+  }) => {
+
+    const u = await getUtils(page)
+    await page.setViewportSize({ width: 1200, height: 500 })
+
+    await u.waitForAuthSkipAppStart()
+
+    await u.openDebugPanel()
+    await u.expectCmdLog('[data-message-type="execution-done"]')
+    await u.closeDebugPanel()
+
+    const XYPlanePoint = { x: 774, y: 116 } as const
+    const unHoveredColor: [number, number, number] = [47, 47, 93]
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await page.mouse.move(XYPlanePoint.x, XYPlanePoint.y)
+    await page.waitForTimeout(200)
+
+    // color should not change for having been hovered
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await u.openAndClearDebugPanel()
+
+    // Fill with spaces
+    await u.codeLocator.fill(`// this is a code comments ya nerds
+`)
+
+    await u.openDebugPanel()
+    await u.expectCmdLog('[data-message-type="execution-done"]')
+    await u.closeDebugPanel()
+
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+
+    await page.mouse.move(XYPlanePoint.x, XYPlanePoint.y)
+    await page.waitForTimeout(200)
+
+    // color should not change for having been hovered
+    expect(
+      await u.getGreatestPixDiff(XYPlanePoint, unHoveredColor)
+    ).toBeLessThan(8)
+  })*/
+
   test('empty-scene default-planes act as expected', async ({
     page,
     browserName,
diff --git a/src/clientSideScene/CameraControls.ts b/src/clientSideScene/CameraControls.ts
index a0d9553d2..a11b3690f 100644
--- a/src/clientSideScene/CameraControls.ts
+++ b/src/clientSideScene/CameraControls.ts
@@ -155,7 +155,6 @@ export class CameraControls {
       this.camera.zoom = camProps.zoom || 1
     }
     this.camera.updateProjectionMatrix()
-    console.log('doing this thing', camProps)
     this.update(true)
   }
 
diff --git a/src/clientSideScene/ClientSideSceneComp.tsx b/src/clientSideScene/ClientSideSceneComp.tsx
index 9f7dba921..f83be4740 100644
--- a/src/clientSideScene/ClientSideSceneComp.tsx
+++ b/src/clientSideScene/ClientSideSceneComp.tsx
@@ -31,6 +31,7 @@ import {
   recast,
   defaultSourceRange,
   resultIsOk,
+  ProgramMemory,
 } from 'lang/wasm'
 import { CustomIcon, CustomIconName } from 'components/CustomIcon'
 import { ConstrainInfo } from 'lang/std/stdTypes'
@@ -420,9 +421,9 @@ export async function deleteSegment({
 
   const testExecute = await executeAst({
     ast: modifiedAst,
-    idGenerator: kclManager.execState.idGenerator,
-    useFakeExecutor: true,
     engineCommandManager: engineCommandManager,
+    // We make sure to send an empty program memory to denote we mean mock mode.
+    programMemoryOverride: ProgramMemory.empty(),
   })
   if (testExecute.errors.length) {
     toast.error('Segment tag used outside of current Sketch. Could not delete.')
diff --git a/src/clientSideScene/sceneEntities.ts b/src/clientSideScene/sceneEntities.ts
index 75dc75864..8fc5e2d8e 100644
--- a/src/clientSideScene/sceneEntities.ts
+++ b/src/clientSideScene/sceneEntities.ts
@@ -498,10 +498,9 @@ export class SceneEntities {
 
     const { execState } = await executeAst({
       ast: truncatedAst,
-      useFakeExecutor: true,
       engineCommandManager: this.engineCommandManager,
+      // We make sure to send an empty program memory to denote we mean mock mode.
       programMemoryOverride,
-      idGenerator: kclManager.execState.idGenerator,
     })
     const programMemory = execState.memory
     const sketch = sketchFromPathToNode({
@@ -955,10 +954,9 @@ export class SceneEntities {
 
         const { execState } = await executeAst({
           ast: truncatedAst,
-          useFakeExecutor: true,
           engineCommandManager: this.engineCommandManager,
+          // We make sure to send an empty program memory to denote we mean mock mode.
           programMemoryOverride,
-          idGenerator: kclManager.execState.idGenerator,
         })
         const programMemory = execState.memory
         this.sceneProgramMemory = programMemory
@@ -1019,10 +1017,9 @@ export class SceneEntities {
 
         const { execState } = await executeAst({
           ast: _ast,
-          useFakeExecutor: true,
           engineCommandManager: this.engineCommandManager,
+          // We make sure to send an empty program memory to denote we mean mock mode.
           programMemoryOverride,
-          idGenerator: kclManager.execState.idGenerator,
         })
         const programMemory = execState.memory
 
@@ -1120,10 +1117,9 @@ export class SceneEntities {
 
         const { execState } = await executeAst({
           ast: truncatedAst,
-          useFakeExecutor: true,
           engineCommandManager: this.engineCommandManager,
+          // We make sure to send an empty program memory to denote we mean mock mode.
           programMemoryOverride,
-          idGenerator: kclManager.execState.idGenerator,
         })
         const programMemory = execState.memory
         this.sceneProgramMemory = programMemory
@@ -1187,10 +1183,9 @@ export class SceneEntities {
 
           const { execState } = await executeAst({
             ast: _ast,
-            useFakeExecutor: true,
             engineCommandManager: this.engineCommandManager,
+            // We make sure to send an empty program memory to denote we mean mock mode.
             programMemoryOverride,
-            idGenerator: kclManager.execState.idGenerator,
           })
           const programMemory = execState.memory
 
@@ -1306,10 +1301,9 @@ export class SceneEntities {
 
         const { execState } = await executeAst({
           ast: modded,
-          useFakeExecutor: true,
           engineCommandManager: this.engineCommandManager,
+          // We make sure to send an empty program memory to denote we mean mock mode.
           programMemoryOverride,
-          idGenerator: kclManager.execState.idGenerator,
         })
         const programMemory = execState.memory
         this.sceneProgramMemory = programMemory
@@ -1691,10 +1685,9 @@ export class SceneEntities {
         codeManager.updateCodeEditor(code)
       const { execState } = await executeAst({
         ast: truncatedAst,
-        useFakeExecutor: true,
         engineCommandManager: this.engineCommandManager,
+        // We make sure to send an empty program memory to denote we mean mock mode.
         programMemoryOverride,
-        idGenerator: kclManager.execState.idGenerator,
       })
       const programMemory = execState.memory
       this.sceneProgramMemory = programMemory
diff --git a/src/components/AvailableVarsHelpers.tsx b/src/components/AvailableVarsHelpers.tsx
index 7f8956d5e..5c6cc4d0b 100644
--- a/src/components/AvailableVarsHelpers.tsx
+++ b/src/components/AvailableVarsHelpers.tsx
@@ -163,9 +163,8 @@ export function useCalc({
       executeAst({
         ast,
         engineCommandManager,
-        useFakeExecutor: true,
+        // We make sure to send an empty program memory to denote we mean mock mode.
         programMemoryOverride: kclManager.programMemory.clone(),
-        idGenerator: kclManager.execState.idGenerator,
       }).then(({ execState }) => {
         const resultDeclaration = ast.body.find(
           (a) =>
diff --git a/src/components/ModelingSidebar/ModelingPanes/MemoryPane.test.tsx b/src/components/ModelingSidebar/ModelingPanes/MemoryPane.test.tsx
index 8d142ddfe..cbe1d0fbb 100644
--- a/src/components/ModelingSidebar/ModelingPanes/MemoryPane.test.tsx
+++ b/src/components/ModelingSidebar/ModelingPanes/MemoryPane.test.tsx
@@ -34,6 +34,10 @@ describe('processMemory', () => {
     expect(output.myVar).toEqual(5)
     expect(output.otherVar).toEqual(3)
     expect(output).toEqual({
+      HALF_TURN: 180,
+      QUARTER_TURN: 90,
+      THREE_QUARTER_TURN: 270,
+      ZERO: 0,
       myVar: 5,
       myFn: '__function(a)__',
       otherVar: 3,
diff --git a/src/components/ProjectSidebarMenu.tsx b/src/components/ProjectSidebarMenu.tsx
index be58d9918..74218288c 100644
--- a/src/components/ProjectSidebarMenu.tsx
+++ b/src/components/ProjectSidebarMenu.tsx
@@ -68,8 +68,8 @@ function AppLogoLink({
       data-testid="app-logo"
       onClick={() => {
         onProjectClose(file || null, project?.path || null, false)
-        // Clear the scene and end the session.
-        engineCommandManager.endSession()
+        // Clear the scene.
+        engineCommandManager.clearScene()
       }}
       to={PATHS.HOME}
       className={wrapperClassName + ' hover:before:brightness-110'}
@@ -190,8 +190,8 @@ function ProjectMenuPopover({
           className: !isDesktop() ? 'hidden' : '',
           onClick: () => {
             onProjectClose(file || null, project?.path || null, true)
-            // Clear the scene and end the session.
-            engineCommandManager.endSession()
+            // Clear the scene.
+            engineCommandManager.clearScene()
           },
         },
       ].filter(
diff --git a/src/lang/KclSingleton.ts b/src/lang/KclSingleton.ts
index 1426be879..c38940e70 100644
--- a/src/lang/KclSingleton.ts
+++ b/src/lang/KclSingleton.ts
@@ -88,7 +88,7 @@ export class KclManager {
     this._programMemoryCallBack(programMemory)
   }
 
-  set execState(execState) {
+  private set execState(execState) {
     this._execState = execState
     this.programMemory = execState.memory
   }
@@ -227,12 +227,6 @@ export class KclManager {
     this.addDiagnostics(complilationErrorsToDiagnostics(result.warnings))
     if (result.errors.length > 0) {
       this._hasErrors = true
-      // TODO: re-eval if session should end?
-      for (const e of result.errors)
-        if (e.message === 'file is empty') {
-          this.engineCommandManager?.endSession()
-          break
-        }
 
       return null
     }
@@ -276,12 +270,9 @@ export class KclManager {
     this._cancelTokens.set(currentExecutionId, false)
 
     this.isExecuting = true
-    // Make sure we clear before starting again. End session will do this.
-    this.engineCommandManager?.endSession()
     await this.ensureWasmInit()
     const { logs, errors, execState, isInterrupted } = await executeAst({
       ast,
-      idGenerator: this.execState.idGenerator,
       engineCommandManager: this.engineCommandManager,
     })
 
@@ -331,8 +322,6 @@ export class KclManager {
     this.logs = logs
     // Do not add the errors since the program was interrupted and the error is not a real KCL error
     this.addDiagnostics(isInterrupted ? [] : kclErrorsToDiagnostics(errors))
-    // Reset the next ID index so that we reuse the previous IDs next time.
-    execState.idGenerator.nextId = 0
     this.execState = execState
     if (!errors.length) {
       this.lastSuccessfulProgramMemory = execState.memory
@@ -373,9 +362,9 @@ export class KclManager {
 
     const { logs, errors, execState } = await executeAst({
       ast: newAst,
-      idGenerator: this.execState.idGenerator,
       engineCommandManager: this.engineCommandManager,
-      useFakeExecutor: true,
+      // We make sure to send an empty program memory to denote we mean mock mode.
+      programMemoryOverride: ProgramMemory.empty(),
     })
 
     this._logs = logs
diff --git a/src/lang/langHelpers.ts b/src/lang/langHelpers.ts
index 9a07aae98..3e604705d 100644
--- a/src/lang/langHelpers.ts
+++ b/src/lang/langHelpers.ts
@@ -2,7 +2,6 @@ import {
   Program,
   _executor,
   ProgramMemory,
-  programMemoryInit,
   kclLint,
   emptyExecState,
   ExecState,
@@ -11,7 +10,6 @@ import { enginelessExecutor } from 'lib/testHelpers'
 import { EngineCommandManager } from 'lang/std/engineConnection'
 import { KCLError } from 'lang/errors'
 import { Diagnostic } from '@codemirror/lint'
-import { IdGenerator } from 'wasm-lib/kcl/bindings/IdGenerator'
 import { Node } from 'wasm-lib/kcl/bindings/Node'
 
 export type ToolTip =
@@ -49,15 +47,13 @@ export const toolTips: Array<ToolTip> = [
 export async function executeAst({
   ast,
   engineCommandManager,
-  useFakeExecutor = false,
+  // If you set programMemoryOverride we assume you mean mock mode. Since that
+  // is the only way to go about it.
   programMemoryOverride,
-  idGenerator,
 }: {
   ast: Node<Program>
   engineCommandManager: EngineCommandManager
-  useFakeExecutor?: boolean
   programMemoryOverride?: ProgramMemory
-  idGenerator?: IdGenerator
   isInterrupted?: boolean
 }): Promise<{
   logs: string[]
@@ -66,22 +62,14 @@ export async function executeAst({
   isInterrupted: boolean
 }> {
   try {
-    if (!useFakeExecutor) {
-      engineCommandManager.endSession()
-      // eslint-disable-next-line @typescript-eslint/no-floating-promises
-      engineCommandManager.startNewSession()
-    }
-    const execState = await (useFakeExecutor
-      ? enginelessExecutor(ast, programMemoryOverride || programMemoryInit())
-      : _executor(
-          ast,
-          programMemoryInit(),
-          idGenerator,
-          engineCommandManager,
-          false
-        ))
+    const execState = await (programMemoryOverride
+      ? enginelessExecutor(ast, programMemoryOverride)
+      : _executor(ast, engineCommandManager))
+
+    await engineCommandManager.waitForAllCommands(
+      programMemoryOverride !== undefined
+    )
 
-    await engineCommandManager.waitForAllCommands(useFakeExecutor)
     return {
       logs: [],
       errors: [],
diff --git a/src/lang/std/engineConnection.ts b/src/lang/std/engineConnection.ts
index 6aca2062b..6070cca09 100644
--- a/src/lang/std/engineConnection.ts
+++ b/src/lang/std/engineConnection.ts
@@ -1879,7 +1879,7 @@ export class EngineCommandManager extends EventTarget {
     }
     return JSON.stringify(this.defaultPlanes)
   }
-  endSession() {
+  clearScene(): void {
     const deleteCmd: EngineCommand = {
       type: 'modeling_cmd_req',
       cmd_id: uuidv4(),
diff --git a/src/lang/wasm.ts b/src/lang/wasm.ts
index cfa32c43d..62bae87e5 100644
--- a/src/lang/wasm.ts
+++ b/src/lang/wasm.ts
@@ -35,7 +35,6 @@ import { Configuration } from 'wasm-lib/kcl/bindings/Configuration'
 import { DeepPartial } from 'lib/types'
 import { ProjectConfiguration } from 'wasm-lib/kcl/bindings/ProjectConfiguration'
 import { Sketch } from '../wasm-lib/kcl/bindings/Sketch'
-import { IdGenerator } from 'wasm-lib/kcl/bindings/IdGenerator'
 import { ExecState as RawExecState } from '../wasm-lib/kcl/bindings/ExecState'
 import { ProgramMemory as RawProgramMemory } from '../wasm-lib/kcl/bindings/ProgramMemory'
 import { EnvironmentRef } from '../wasm-lib/kcl/bindings/EnvironmentRef'
@@ -216,7 +215,6 @@ export const isPathToNodeNumber = (
 
 export interface ExecState {
   memory: ProgramMemory
-  idGenerator: IdGenerator
 }
 
 /**
@@ -226,21 +224,12 @@ export interface ExecState {
 export function emptyExecState(): ExecState {
   return {
     memory: ProgramMemory.empty(),
-    idGenerator: defaultIdGenerator(),
   }
 }
 
 function execStateFromRaw(raw: RawExecState): ExecState {
   return {
     memory: ProgramMemory.fromRaw(raw.memory),
-    idGenerator: raw.idGenerator,
-  }
-}
-
-export function defaultIdGenerator(): IdGenerator {
-  return {
-    nextId: 0,
-    ids: [],
   }
 }
 
@@ -254,6 +243,19 @@ function emptyEnvironment(): Environment {
   return { bindings: {}, parent: null }
 }
 
+function emptyRootEnvironment(): Environment {
+  return {
+    // This is dumb this is copied from rust.
+    bindings: {
+      ZERO: { type: 'Number', value: 0.0, __meta: [] },
+      QUARTER_TURN: { type: 'Number', value: 90.0, __meta: [] },
+      HALF_TURN: { type: 'Number', value: 180.0, __meta: [] },
+      THREE_QUARTER_TURN: { type: 'Number', value: 270.0, __meta: [] },
+    },
+    parent: null,
+  }
+}
+
 /**
  * This duplicates logic in Rust.  The hope is to keep ProgramMemory internals
  * isolated from the rest of the TypeScript code so that we can move it to Rust
@@ -276,7 +278,7 @@ export class ProgramMemory {
   }
 
   constructor(
-    environments: Environment[] = [emptyEnvironment()],
+    environments: Environment[] = [emptyRootEnvironment()],
     currentEnv: EnvironmentRef = ROOT_ENVIRONMENT_REF,
     returnVal: KclValue | null = null
   ) {
@@ -463,36 +465,31 @@ export function sketchFromKclValue(
 
 export const executor = async (
   node: Node<Program>,
-  programMemory: ProgramMemory | Error = ProgramMemory.empty(),
-  idGenerator: IdGenerator = defaultIdGenerator(),
   engineCommandManager: EngineCommandManager,
-  isMock: boolean = false
+  programMemoryOverride: ProgramMemory | Error | null = null
 ): Promise<ExecState> => {
-  if (err(programMemory)) return Promise.reject(programMemory)
+  if (programMemoryOverride !== null && err(programMemoryOverride))
+    return Promise.reject(programMemoryOverride)
 
   // eslint-disable-next-line @typescript-eslint/no-floating-promises
   engineCommandManager.startNewSession()
   const _programMemory = await _executor(
     node,
-    programMemory,
-    idGenerator,
     engineCommandManager,
-    isMock
+    programMemoryOverride
   )
   await engineCommandManager.waitForAllCommands()
 
-  engineCommandManager.endSession()
   return _programMemory
 }
 
 export const _executor = async (
   node: Node<Program>,
-  programMemory: ProgramMemory | Error = ProgramMemory.empty(),
-  idGenerator: IdGenerator = defaultIdGenerator(),
   engineCommandManager: EngineCommandManager,
-  isMock: boolean
+  programMemoryOverride: ProgramMemory | Error | null = null
 ): Promise<ExecState> => {
-  if (err(programMemory)) return Promise.reject(programMemory)
+  if (programMemoryOverride !== null && err(programMemoryOverride))
+    return Promise.reject(programMemoryOverride)
 
   try {
     let baseUnit = 'mm'
@@ -505,13 +502,10 @@ export const _executor = async (
     }
     const execState: RawExecState = await execute_wasm(
       JSON.stringify(node),
-      JSON.stringify(programMemory.toRaw()),
-      JSON.stringify(idGenerator),
+      JSON.stringify(programMemoryOverride?.toRaw() || null),
       baseUnit,
       engineCommandManager,
-      fileSystemManager,
-      undefined,
-      isMock
+      fileSystemManager
     )
     return execStateFromRaw(execState)
   } catch (e: any) {
diff --git a/src/lib/desktopFS.ts b/src/lib/desktopFS.ts
index 6cde7f726..efa611c5f 100644
--- a/src/lib/desktopFS.ts
+++ b/src/lib/desktopFS.ts
@@ -116,8 +116,8 @@ export async function createAndOpenNewTutorialProject({
   ) => void
   navigate: (path: string) => void
 }) {
-  // Clear the scene and end the session.
-  engineCommandManager.endSession()
+  // Clear the scene.
+  engineCommandManager.clearScene()
 
   // Create a new project with the onboarding project name
   const configuration = await readAppSettingsFile()
diff --git a/src/lib/testHelpers.ts b/src/lib/testHelpers.ts
index 2454e1b0a..4f545ad11 100644
--- a/src/lib/testHelpers.ts
+++ b/src/lib/testHelpers.ts
@@ -4,7 +4,6 @@ import {
   _executor,
   SourceRange,
   ExecState,
-  defaultIdGenerator,
 } from '../lang/wasm'
 import {
   EngineCommandManager,
@@ -16,7 +15,6 @@ import { v4 as uuidv4 } from 'uuid'
 import { DefaultPlanes } from 'wasm-lib/kcl/bindings/DefaultPlanes'
 import { err, reportRejection } from 'lib/trap'
 import { toSync } from './utils'
-import { IdGenerator } from 'wasm-lib/kcl/bindings/IdGenerator'
 import { Node } from 'wasm-lib/kcl/bindings/Node'
 
 type WebSocketResponse = Models['WebSocketResponse_type']
@@ -86,10 +84,9 @@ class MockEngineCommandManager {
 
 export async function enginelessExecutor(
   ast: Node<Program>,
-  pm: ProgramMemory | Error = ProgramMemory.empty(),
-  idGenerator: IdGenerator = defaultIdGenerator()
+  pmo: ProgramMemory | Error = ProgramMemory.empty()
 ): Promise<ExecState> {
-  if (err(pm)) return Promise.reject(pm)
+  if (pmo !== null && err(pmo)) return Promise.reject(pmo)
 
   const mockEngineCommandManager = new MockEngineCommandManager({
     setIsStreamReady: () => {},
@@ -97,21 +94,14 @@ export async function enginelessExecutor(
   }) as any as EngineCommandManager
   // eslint-disable-next-line @typescript-eslint/no-floating-promises
   mockEngineCommandManager.startNewSession()
-  const execState = await _executor(
-    ast,
-    pm,
-    idGenerator,
-    mockEngineCommandManager,
-    true
-  )
+  const execState = await _executor(ast, mockEngineCommandManager, pmo)
   await mockEngineCommandManager.waitForAllCommands()
   return execState
 }
 
 export async function executor(
   ast: Node<Program>,
-  pm: ProgramMemory = ProgramMemory.empty(),
-  idGenerator: IdGenerator = defaultIdGenerator()
+  pmo: ProgramMemory = ProgramMemory.empty()
 ): Promise<ExecState> {
   const engineCommandManager = new EngineCommandManager()
   engineCommandManager.start({
@@ -133,13 +123,7 @@ export async function executor(
       toSync(async () => {
         // eslint-disable-next-line @typescript-eslint/no-floating-promises
         engineCommandManager.startNewSession()
-        const execState = await _executor(
-          ast,
-          pm,
-          idGenerator,
-          engineCommandManager,
-          false
-        )
+        const execState = await _executor(ast, engineCommandManager, pmo)
         await engineCommandManager.waitForAllCommands()
         resolve(execState)
       }, reportRejection)
diff --git a/src/lib/useCalculateKclExpression.ts b/src/lib/useCalculateKclExpression.ts
index 51f133564..284137828 100644
--- a/src/lib/useCalculateKclExpression.ts
+++ b/src/lib/useCalculateKclExpression.ts
@@ -103,9 +103,8 @@ export function useCalculateKclExpression({
       const { execState } = await executeAst({
         ast,
         engineCommandManager,
-        useFakeExecutor: true,
+        // We make sure to send an empty program memory to denote we mean mock mode.
         programMemoryOverride: kclManager.programMemory.clone(),
-        idGenerator: kclManager.execState.idGenerator,
       })
       const resultDeclaration = ast.body.find(
         (a) =>
diff --git a/src/machines/modelingMachine.ts b/src/machines/modelingMachine.ts
index 17c4d618a..6930547ed 100644
--- a/src/machines/modelingMachine.ts
+++ b/src/machines/modelingMachine.ts
@@ -1,5 +1,6 @@
 import {
   PathToNode,
+  ProgramMemory,
   VariableDeclaration,
   VariableDeclarator,
   parse,
@@ -730,9 +731,9 @@ export const modelingMachine = setup({
 
         const testExecute = await executeAst({
           ast: modifiedAst,
-          idGenerator: kclManager.execState.idGenerator,
-          useFakeExecutor: true,
           engineCommandManager,
+          // We make sure to send an empty program memory to denote we mean mock mode.
+          programMemoryOverride: ProgramMemory.empty(),
         })
         if (testExecute.errors.length) {
           toast.error('Unable to delete part')
diff --git a/src/wasm-lib/Cargo.lock b/src/wasm-lib/Cargo.lock
index 9c8edca31..8006e4f68 100644
--- a/src/wasm-lib/Cargo.lock
+++ b/src/wasm-lib/Cargo.lock
@@ -4308,6 +4308,7 @@ dependencies = [
  "kcl-lib",
  "kittycad",
  "kittycad-modeling-cmds",
+ "lazy_static",
  "pretty_assertions",
  "reqwest",
  "serde_json",
diff --git a/src/wasm-lib/Cargo.toml b/src/wasm-lib/Cargo.toml
index f537690fc..5a5359edf 100644
--- a/src/wasm-lib/Cargo.toml
+++ b/src/wasm-lib/Cargo.toml
@@ -15,6 +15,7 @@ data-encoding = "2.6.0"
 gloo-utils = "0.2.0"
 kcl-lib = { path = "kcl" }
 kittycad.workspace = true
+lazy_static = "1.5.0"
 serde_json = "1.0.128"
 tokio = { version = "1.41.1", features = ["sync"] }
 toml = "0.8.19"
diff --git a/src/wasm-lib/derive-docs/src/lib.rs b/src/wasm-lib/derive-docs/src/lib.rs
index 3669ba105..1a7dc5c82 100644
--- a/src/wasm-lib/derive-docs/src/lib.rs
+++ b/src/wasm-lib/derive-docs/src/lib.rs
@@ -778,7 +778,7 @@ fn generate_code_block_test(fn_name: &str, code_block: &str, index: usize) -> pr
                 context_type: crate::executor::ContextType::Mock,
             };
 
-            ctx.run(&program, &mut crate::ExecState::default()).await.unwrap();
+            ctx.run(program.into(), &mut crate::ExecState::default()).await.unwrap();
         }
 
         #[tokio::test(flavor = "multi_thread", worker_threads = 5)]
diff --git a/src/wasm-lib/derive-docs/tests/args_with_lifetime.gen b/src/wasm-lib/derive-docs/tests/args_with_lifetime.gen
index 32e218be8..e5157f3c5 100644
--- a/src/wasm-lib/derive-docs/tests/args_with_lifetime.gen
+++ b/src/wasm-lib/derive-docs/tests/args_with_lifetime.gen
@@ -14,7 +14,7 @@ mod test_examples_someFn {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/args_with_refs.gen b/src/wasm-lib/derive-docs/tests/args_with_refs.gen
index 731e208c8..ab2a3786d 100644
--- a/src/wasm-lib/derive-docs/tests/args_with_refs.gen
+++ b/src/wasm-lib/derive-docs/tests/args_with_refs.gen
@@ -14,7 +14,7 @@ mod test_examples_someFn {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/array.gen b/src/wasm-lib/derive-docs/tests/array.gen
index 6e52a2e70..891a5f2c2 100644
--- a/src/wasm-lib/derive-docs/tests/array.gen
+++ b/src/wasm-lib/derive-docs/tests/array.gen
@@ -15,7 +15,7 @@ mod test_examples_show {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
@@ -49,7 +49,7 @@ mod test_examples_show {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/box.gen b/src/wasm-lib/derive-docs/tests/box.gen
index 79c578d90..648514848 100644
--- a/src/wasm-lib/derive-docs/tests/box.gen
+++ b/src/wasm-lib/derive-docs/tests/box.gen
@@ -15,7 +15,7 @@ mod test_examples_show {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/doc_comment_with_code.gen b/src/wasm-lib/derive-docs/tests/doc_comment_with_code.gen
index de85bbe1b..038771738 100644
--- a/src/wasm-lib/derive-docs/tests/doc_comment_with_code.gen
+++ b/src/wasm-lib/derive-docs/tests/doc_comment_with_code.gen
@@ -16,7 +16,7 @@ mod test_examples_my_func {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
@@ -50,7 +50,7 @@ mod test_examples_my_func {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/lineTo.gen b/src/wasm-lib/derive-docs/tests/lineTo.gen
index 27f1f7c8c..725806bdc 100644
--- a/src/wasm-lib/derive-docs/tests/lineTo.gen
+++ b/src/wasm-lib/derive-docs/tests/lineTo.gen
@@ -16,7 +16,7 @@ mod test_examples_line_to {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
@@ -50,7 +50,7 @@ mod test_examples_line_to {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/min.gen b/src/wasm-lib/derive-docs/tests/min.gen
index 96c7040da..bd02474ce 100644
--- a/src/wasm-lib/derive-docs/tests/min.gen
+++ b/src/wasm-lib/derive-docs/tests/min.gen
@@ -15,7 +15,7 @@ mod test_examples_min {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
@@ -49,7 +49,7 @@ mod test_examples_min {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/option.gen b/src/wasm-lib/derive-docs/tests/option.gen
index 21e80e32d..b6ad9ef25 100644
--- a/src/wasm-lib/derive-docs/tests/option.gen
+++ b/src/wasm-lib/derive-docs/tests/option.gen
@@ -15,7 +15,7 @@ mod test_examples_show {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/option_input_format.gen b/src/wasm-lib/derive-docs/tests/option_input_format.gen
index fe40eb931..e2918a608 100644
--- a/src/wasm-lib/derive-docs/tests/option_input_format.gen
+++ b/src/wasm-lib/derive-docs/tests/option_input_format.gen
@@ -15,7 +15,7 @@ mod test_examples_import {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/return_vec_box_sketch.gen b/src/wasm-lib/derive-docs/tests/return_vec_box_sketch.gen
index 72292beeb..c9fa22f4e 100644
--- a/src/wasm-lib/derive-docs/tests/return_vec_box_sketch.gen
+++ b/src/wasm-lib/derive-docs/tests/return_vec_box_sketch.gen
@@ -15,7 +15,7 @@ mod test_examples_import {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/return_vec_sketch.gen b/src/wasm-lib/derive-docs/tests/return_vec_sketch.gen
index c0c97a13b..e00391e37 100644
--- a/src/wasm-lib/derive-docs/tests/return_vec_sketch.gen
+++ b/src/wasm-lib/derive-docs/tests/return_vec_sketch.gen
@@ -15,7 +15,7 @@ mod test_examples_import {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/show.gen b/src/wasm-lib/derive-docs/tests/show.gen
index cfd2bc35f..f0b74f8f4 100644
--- a/src/wasm-lib/derive-docs/tests/show.gen
+++ b/src/wasm-lib/derive-docs/tests/show.gen
@@ -15,7 +15,7 @@ mod test_examples_show {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/derive-docs/tests/test_args_with_exec_state.gen b/src/wasm-lib/derive-docs/tests/test_args_with_exec_state.gen
index d5735273f..d41823404 100644
--- a/src/wasm-lib/derive-docs/tests/test_args_with_exec_state.gen
+++ b/src/wasm-lib/derive-docs/tests/test_args_with_exec_state.gen
@@ -14,7 +14,7 @@ mod test_examples_some_function {
             settings: Default::default(),
             context_type: crate::executor::ContextType::Mock,
         };
-        ctx.run(&program, &mut crate::ExecState::default())
+        ctx.run(program.into(), &mut crate::ExecState::default())
             .await
             .unwrap();
     }
diff --git a/src/wasm-lib/kcl-to-core/src/conn_mock_core.rs b/src/wasm-lib/kcl-to-core/src/conn_mock_core.rs
index c3dea7144..7780381b0 100644
--- a/src/wasm-lib/kcl-to-core/src/conn_mock_core.rs
+++ b/src/wasm-lib/kcl-to-core/src/conn_mock_core.rs
@@ -1,3 +1,8 @@
+use std::{
+    collections::HashMap,
+    sync::{Arc, Mutex},
+};
+
 use anyhow::Result;
 use indexmap::IndexMap;
 use kcl_lib::{
@@ -11,10 +16,6 @@ use kittycad_modeling_cmds::{
     shared::PathSegment::{self, *},
     websocket::{ModelingBatch, ModelingCmdReq, OkWebSocketResponseData, WebSocketRequest, WebSocketResponse},
 };
-use std::{
-    collections::HashMap,
-    sync::{Arc, Mutex},
-};
 use tokio::sync::RwLock;
 
 const CPP_PREFIX: &str = "const double scaleFactor = 100;\n";
diff --git a/src/wasm-lib/kcl-to-core/src/lib.rs b/src/wasm-lib/kcl-to-core/src/lib.rs
index 8c00f341e..ae8187d7d 100644
--- a/src/wasm-lib/kcl-to-core/src/lib.rs
+++ b/src/wasm-lib/kcl-to-core/src/lib.rs
@@ -1,6 +1,7 @@
+use std::sync::{Arc, Mutex};
+
 use anyhow::Result;
 use kcl_lib::{ExecState, ExecutorContext};
-use std::sync::{Arc, Mutex};
 
 #[cfg(not(target_arch = "wasm32"))]
 mod conn_mock_core;
@@ -15,7 +16,7 @@ pub async fn kcl_to_engine_core(code: &str) -> Result<String> {
     let ctx = ExecutorContext::new_forwarded_mock(Arc::new(Box::new(
         crate::conn_mock_core::EngineConnection::new(ref_result).await?,
     )));
-    ctx.run(&program, &mut ExecState::default()).await?;
+    ctx.run(program.into(), &mut ExecState::default()).await?;
 
     let result = result.lock().expect("mutex lock").clone();
     Ok(result)
diff --git a/src/wasm-lib/kcl-to-core/src/tool.rs b/src/wasm-lib/kcl-to-core/src/tool.rs
index 626b0b880..6706c7cb1 100644
--- a/src/wasm-lib/kcl-to-core/src/tool.rs
+++ b/src/wasm-lib/kcl-to-core/src/tool.rs
@@ -1,6 +1,7 @@
-use kcl_to_core::*;
 use std::{env, fs};
 
+use kcl_to_core::*;
+
 #[tokio::main]
 async fn main() {
     let args: Vec<String> = env::args().collect();
diff --git a/src/wasm-lib/kcl/src/ast/mod.rs b/src/wasm-lib/kcl/src/ast/mod.rs
new file mode 100644
index 000000000..feef6f7cc
--- /dev/null
+++ b/src/wasm-lib/kcl/src/ast/mod.rs
@@ -0,0 +1,3 @@
+pub mod cache;
+pub mod modify;
+pub mod types;
diff --git a/src/wasm-lib/kcl/src/executor.rs b/src/wasm-lib/kcl/src/executor.rs
index 755b1fffb..6ca4952c2 100644
--- a/src/wasm-lib/kcl/src/executor.rs
+++ b/src/wasm-lib/kcl/src/executor.rs
@@ -25,7 +25,10 @@ use crate::{
     engine::{EngineManager, ExecutionKind},
     errors::{KclError, KclErrorDetails},
     fs::{FileManager, FileSystem},
-    parsing::ast::types::{BodyItem, Expr, FunctionExpression, ItemVisibility, Node, NodeRef, TagDeclarator, TagNode},
+    parsing::ast::{
+        cache::{get_changed_program, CacheInformation},
+        types::{BodyItem, Expr, FunctionExpression, ItemVisibility, Node, NodeRef, TagDeclarator, TagNode},
+    },
     settings::types::UnitLength,
     source_range::{ModuleId, SourceRange},
     std::{args::Arg, StdLib},
@@ -55,9 +58,6 @@ pub struct ExecState {
     pub path_to_source_id: IndexMap<std::path::PathBuf, ModuleId>,
     /// Map from module ID to module info.
     pub module_infos: IndexMap<ModuleId, ModuleInfo>,
-    /// The directory of the current project.  This is used for resolving import
-    /// paths.  If None is given, the current working directory is used.
-    pub project_directory: Option<String>,
 }
 
 impl ExecState {
@@ -1484,7 +1484,8 @@ pub struct ExecutorContext {
 }
 
 /// The executor settings.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, ts_rs::TS, JsonSchema)]
+#[ts(export)]
 pub struct ExecutorSettings {
     /// The unit to use in modeling dimensions.
     pub units: UnitLength,
@@ -1785,18 +1786,21 @@ impl ExecutorContext {
         &self,
         exec_state: &mut ExecState,
         source_range: crate::executor::SourceRange,
-    ) -> Result<()> {
+    ) -> Result<(), KclError> {
         self.engine
             .clear_scene(&mut exec_state.id_generator, source_range)
             .await?;
+
+        // We do not create the planes here as the post hook in wasm will do that
+        // AND if we aren't in wasm it doesn't really matter.
         Ok(())
     }
 
     /// Perform the execution of a program.
     /// You can optionally pass in some initialization memory.
     /// Kurt uses this for partial execution.
-    pub async fn run(&self, program: &Program, exec_state: &mut ExecState) -> Result<(), KclError> {
-        self.run_with_session_data(program, exec_state).await?;
+    pub async fn run(&self, cache_info: CacheInformation, exec_state: &mut ExecState) -> Result<(), KclError> {
+        self.run_with_session_data(cache_info, exec_state).await?;
         Ok(())
     }
 
@@ -1805,10 +1809,27 @@ impl ExecutorContext {
     /// Kurt uses this for partial execution.
     pub async fn run_with_session_data(
         &self,
-        program: &Program,
+        cache_info: CacheInformation,
         exec_state: &mut ExecState,
     ) -> Result<Option<ModelingSessionData>, KclError> {
         let _stats = crate::log::LogPerfStats::new("Interpretation");
+
+        // Get the program that actually changed from the old and new information.
+        let cache_result = get_changed_program(cache_info.clone(), &self.settings);
+
+        // Check if we don't need to re-execute.
+        let Some(cache_result) = cache_result else {
+            return Ok(None);
+        };
+
+        if cache_result.clear_scene && !self.is_mock() {
+            // We don't do this in mock mode since there is no engine connection
+            // anyways and from the TS side we override memory and don't want to clear it.
+            self.reset_scene(exec_state, Default::default()).await?;
+            // Pop the execution state, since we are starting fresh.
+            *exec_state = Default::default();
+        }
+
         // TODO: Use the top-level file's path.
         exec_state.add_module(std::path::PathBuf::from(""));
         // Before we even start executing the program, set the units.
@@ -1829,7 +1850,7 @@ impl ExecutorContext {
             )
             .await?;
 
-        self.inner_execute(&program.ast, exec_state, crate::executor::BodyType::Root)
+        self.inner_execute(&cache_result.program, exec_state, crate::executor::BodyType::Root)
             .await?;
         let session_data = self.engine.get_session_data();
         Ok(session_data)
@@ -1857,11 +1878,7 @@ impl ExecutorContext {
                             source_ranges: vec![source_range],
                         }));
                     }
-                    let resolved_path = if let Some(project_dir) = &exec_state.project_directory {
-                        std::path::PathBuf::from(project_dir).join(&path)
-                    } else {
-                        std::path::PathBuf::from(&path)
-                    };
+                    let resolved_path = std::path::PathBuf::from(&path);
                     if exec_state.import_stack.contains(&resolved_path) {
                         return Err(KclError::ImportCycle(KclErrorDetails {
                             message: format!(
@@ -2097,7 +2114,7 @@ impl ExecutorContext {
         program: &Program,
         exec_state: &mut ExecState,
     ) -> std::result::Result<TakeSnapshot, ExecError> {
-        self.run(program, exec_state).await?;
+        self.run(program.clone().into(), exec_state).await?;
 
         // Zoom to fit.
         self.engine
@@ -2243,7 +2260,7 @@ mod tests {
             context_type: ContextType::Mock,
         };
         let mut exec_state = ExecState::default();
-        ctx.run(&program, &mut exec_state).await?;
+        ctx.run(program.into(), &mut exec_state).await?;
 
         Ok(exec_state.memory)
     }
diff --git a/src/wasm-lib/kcl/src/lib.rs b/src/wasm-lib/kcl/src/lib.rs
index 05bf07795..a6bde55cb 100644
--- a/src/wasm-lib/kcl/src/lib.rs
+++ b/src/wasm-lib/kcl/src/lib.rs
@@ -89,7 +89,11 @@ pub use lsp::{
     copilot::Backend as CopilotLspBackend,
     kcl::{Backend as KclLspBackend, Server as KclLspServerSubCommand},
 };
-pub use parsing::ast::{modify::modify_ast_for_sketch, types::FormatOptions};
+pub use parsing::ast::{
+    cache::{CacheInformation, OldAstState},
+    modify::modify_ast_for_sketch,
+    types::FormatOptions,
+};
 pub use settings::types::{project::ProjectConfiguration, Configuration, UnitLength};
 pub use source_range::{ModuleId, SourceRange};
 
@@ -125,7 +129,7 @@ use crate::log::{log, logln};
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub struct Program {
     #[serde(flatten)]
-    ast: parsing::ast::types::Node<parsing::ast::types::Program>,
+    pub ast: parsing::ast::types::Node<parsing::ast::types::Program>,
 }
 
 #[cfg(any(test, feature = "lsp-test-util"))]
diff --git a/src/wasm-lib/kcl/src/lsp/kcl/mod.rs b/src/wasm-lib/kcl/src/lsp/kcl/mod.rs
index 9a023bcfe..b5cb024f8 100644
--- a/src/wasm-lib/kcl/src/lsp/kcl/mod.rs
+++ b/src/wasm-lib/kcl/src/lsp/kcl/mod.rs
@@ -45,11 +45,14 @@ use crate::{
     errors::Suggestion,
     lsp::{backend::Backend as _, util::IntoDiagnostic},
     parsing::{
-        ast::types::{Expr, Node, VariableKind},
+        ast::{
+            cache::{CacheInformation, OldAstState},
+            types::{Expr, Node, VariableKind},
+        },
         token::TokenType,
         PIPE_OPERATOR,
     },
-    ExecState, ModuleId, Program, SourceRange,
+    ModuleId, Program, SourceRange,
 };
 
 lazy_static::lazy_static! {
@@ -105,6 +108,12 @@ pub struct Backend {
     pub token_map: DashMap<String, Vec<crate::parsing::token::Token>>,
     /// AST maps.
     pub ast_map: DashMap<String, Node<crate::parsing::ast::types::Program>>,
+    /// Last successful execution.
+    /// This gets set to None when execution errors, or we want to bust the cache on purpose to
+    /// force a re-execution.
+    /// We do not need to manually bust the cache for changed units, that's handled by the cache
+    /// information.
+    pub last_successful_ast_state: Arc<RwLock<Option<OldAstState>>>,
     /// Memory maps.
     pub memory_map: DashMap<String, crate::executor::ProgramMemory>,
     /// Current code.
@@ -189,6 +198,7 @@ impl Backend {
             diagnostics_map: Default::default(),
             symbols_map: Default::default(),
             semantic_tokens_map: Default::default(),
+            last_successful_ast_state: Default::default(),
             is_initialized: Default::default(),
         })
     }
@@ -262,6 +272,13 @@ impl crate::lsp::backend::Backend for Backend {
     }
 
     async fn inner_on_change(&self, params: TextDocumentItem, force: bool) {
+        if force {
+            // Bust the execution cache.
+            let mut old_ast_state = self.last_successful_ast_state.write().await;
+            *old_ast_state = None;
+            drop(old_ast_state);
+        }
+
         let filename = params.uri.to_string();
         // We already updated the code map in the shared backend.
 
@@ -674,23 +691,43 @@ impl Backend {
             return Ok(());
         }
 
-        let mut exec_state = ExecState::default();
+        let mut last_successful_ast_state = self.last_successful_ast_state.write().await;
 
-        // Clear the scene, before we execute so it's not fugly as shit.
-        executor_ctx
-            .engine
-            .clear_scene(&mut exec_state.id_generator, SourceRange::default())
-            .await?;
+        let mut exec_state = if let Some(last_successful_ast_state) = last_successful_ast_state.clone() {
+            last_successful_ast_state.exec_state
+        } else {
+            Default::default()
+        };
 
-        if let Err(err) = executor_ctx.run(ast, &mut exec_state).await {
+        if let Err(err) = executor_ctx
+            .run(
+                CacheInformation {
+                    old: last_successful_ast_state.clone(),
+                    new_ast: ast.ast.clone(),
+                },
+                &mut exec_state,
+            )
+            .await
+        {
             self.memory_map.remove(params.uri.as_str());
             self.add_to_diagnostics(params, &[err], false).await;
 
+            // Update the last successful ast state to be None.
+            *last_successful_ast_state = None;
+
             // Since we already published the diagnostics we don't really care about the error
             // string.
             return Err(anyhow::anyhow!("failed to execute code"));
         }
 
+        // Update the last successful ast state.
+        *last_successful_ast_state = Some(OldAstState {
+            ast: ast.ast.clone(),
+            exec_state: exec_state.clone(),
+            settings: executor_ctx.settings.clone(),
+        });
+        drop(last_successful_ast_state);
+
         self.memory_map
             .insert(params.uri.to_string(), exec_state.memory.clone());
 
diff --git a/src/wasm-lib/kcl/src/lsp/test_util.rs b/src/wasm-lib/kcl/src/lsp/test_util.rs
index a97cdce20..3480ce8eb 100644
--- a/src/wasm-lib/kcl/src/lsp/test_util.rs
+++ b/src/wasm-lib/kcl/src/lsp/test_util.rs
@@ -37,6 +37,7 @@ pub async fn kcl_lsp_server(execute: bool) -> Result<crate::lsp::kcl::Backend> {
         can_send_telemetry: true,
         executor_ctx: Arc::new(tokio::sync::RwLock::new(executor_ctx)),
         can_execute: Arc::new(tokio::sync::RwLock::new(can_execute)),
+        last_successful_ast_state: Default::default(),
         is_initialized: Default::default(),
     })
     .custom_method("kcl/updateUnits", crate::lsp::kcl::Backend::update_units)
diff --git a/src/wasm-lib/kcl/src/parsing/ast/cache.rs b/src/wasm-lib/kcl/src/parsing/ast/cache.rs
new file mode 100644
index 000000000..628f5b0c4
--- /dev/null
+++ b/src/wasm-lib/kcl/src/parsing/ast/cache.rs
@@ -0,0 +1,373 @@
+//! Functions for helping with caching an ast and finding the parts the changed.
+
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+
+use crate::{
+    executor::ExecState,
+    parsing::ast::types::{Node, Program},
+};
+
+/// Information for the caching an AST and smartly re-executing it if we can.
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, ts_rs::TS, JsonSchema)]
+#[ts(export)]
+pub struct CacheInformation {
+    /// The old information.
+    pub old: Option<OldAstState>,
+    /// The new ast to executed.
+    pub new_ast: Node<Program>,
+}
+
+/// The old ast and program memory.
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, ts_rs::TS, JsonSchema)]
+#[ts(export)]
+pub struct OldAstState {
+    /// The ast.
+    pub ast: Node<Program>,
+    /// The exec state.
+    pub exec_state: ExecState,
+    /// The last settings used for execution.
+    pub settings: crate::executor::ExecutorSettings,
+}
+
+impl From<crate::Program> for CacheInformation {
+    fn from(program: crate::Program) -> Self {
+        CacheInformation {
+            old: None,
+            new_ast: program.ast,
+        }
+    }
+}
+
+/// The result of a cache check.
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, ts_rs::TS, JsonSchema)]
+#[ts(export)]
+pub struct CacheResult {
+    /// Should we clear the scene and start over?
+    pub clear_scene: bool,
+    /// The program that needs to be executed.
+    pub program: Node<Program>,
+}
+
+// Given an old ast, old program memory and new ast, find the parts of the code that need to be
+// re-executed.
+// This function should never error, because in the case of any internal error, we should just pop
+// the cache.
+pub fn get_changed_program(
+    info: CacheInformation,
+    new_settings: &crate::executor::ExecutorSettings,
+) -> Option<CacheResult> {
+    let Some(old) = info.old else {
+        // We have no old info, we need to re-execute the whole thing.
+        return Some(CacheResult {
+            clear_scene: true,
+            program: info.new_ast,
+        });
+    };
+
+    // If the settings are different we need to bust the cache.
+    // We specifically do this before checking if they are the exact same.
+    if old.settings != *new_settings {
+        return Some(CacheResult {
+            clear_scene: true,
+            program: info.new_ast,
+        });
+    }
+
+    // If the ASTs are the EXACT same we return None.
+    // We don't even need to waste time computing the digests.
+    if old.ast == info.new_ast {
+        return None;
+    }
+
+    let mut old_ast = old.ast.inner;
+    old_ast.compute_digest();
+    let mut new_ast = info.new_ast.inner.clone();
+    new_ast.compute_digest();
+
+    // Check if the digest is the same.
+    if old_ast.digest == new_ast.digest {
+        return None;
+    }
+
+    // Check if the changes were only to Non-code areas, like comments or whitespace.
+
+    // For any unhandled cases just re-execute the whole thing.
+    Some(CacheResult {
+        clear_scene: true,
+        program: info.new_ast,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use anyhow::Result;
+    use pretty_assertions::assert_eq;
+
+    use super::*;
+
+    async fn execute(program: &crate::Program) -> Result<ExecState> {
+        let ctx = crate::executor::ExecutorContext {
+            engine: Arc::new(Box::new(crate::engine::conn_mock::EngineConnection::new().await?)),
+            fs: Arc::new(crate::fs::FileManager::new()),
+            stdlib: Arc::new(crate::std::StdLib::new()),
+            settings: Default::default(),
+            context_type: crate::executor::ContextType::Mock,
+        };
+        let mut exec_state = crate::executor::ExecState::default();
+        ctx.run(program.clone().into(), &mut exec_state).await?;
+
+        Ok(exec_state)
+    }
+
+    // Easy case where we have no old ast and memory.
+    // We need to re-execute everything.
+    #[test]
+    fn test_get_changed_program_no_old_information() {
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program = crate::Program::parse_no_errs(new).unwrap().ast;
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: None,
+                new_ast: program.clone(),
+            },
+            &Default::default(),
+        );
+
+        assert!(result.is_some());
+
+        let result = result.unwrap();
+
+        assert_eq!(result.program, program);
+        assert!(result.clear_scene);
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_get_changed_program_same_code() {
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program = crate::Program::parse_no_errs(new).unwrap();
+
+        let executed = execute(&program).await.unwrap();
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: Some(OldAstState {
+                    ast: program.ast.clone(),
+                    exec_state: executed,
+                    settings: Default::default(),
+                }),
+                new_ast: program.ast.clone(),
+            },
+            &Default::default(),
+        );
+
+        assert_eq!(result, None);
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_get_changed_program_same_code_changed_whitespace() {
+        let old = r#" // Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch) "#;
+
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program_old = crate::Program::parse_no_errs(old).unwrap();
+
+        let executed = execute(&program_old).await.unwrap();
+
+        let program_new = crate::Program::parse_no_errs(new).unwrap();
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: Some(OldAstState {
+                    ast: program_old.ast.clone(),
+                    exec_state: executed,
+                    settings: Default::default(),
+                }),
+                new_ast: program_new.ast.clone(),
+            },
+            &Default::default(),
+        );
+
+        assert_eq!(result, None);
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_get_changed_program_same_code_changed_code_comment_start_of_program() {
+        let old = r#" // Removed the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch) "#;
+
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program_old = crate::Program::parse_no_errs(old).unwrap();
+
+        let executed = execute(&program_old).await.unwrap();
+
+        let program_new = crate::Program::parse_no_errs(new).unwrap();
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: Some(OldAstState {
+                    ast: program_old.ast.clone(),
+                    exec_state: executed,
+                    settings: Default::default(),
+                }),
+                new_ast: program_new.ast.clone(),
+            },
+            &Default::default(),
+        );
+
+        assert_eq!(result, None);
+    }
+
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_get_changed_program_same_code_changed_code_comments() {
+        let old = r#" // Removed the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %) // my thing
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch) "#;
+
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program_old = crate::Program::parse_no_errs(old).unwrap();
+
+        let executed = execute(&program_old).await.unwrap();
+
+        let program_new = crate::Program::parse_no_errs(new).unwrap();
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: Some(OldAstState {
+                    ast: program_old.ast.clone(),
+                    exec_state: executed,
+                    settings: Default::default(),
+                }),
+                new_ast: program_new.ast.clone(),
+            },
+            &Default::default(),
+        );
+
+        assert!(result.is_some());
+
+        let result = result.unwrap();
+
+        assert_eq!(result.program, program_new.ast);
+        assert!(result.clear_scene);
+    }
+
+    // Changing the units with the exact same file should bust the cache.
+    #[tokio::test(flavor = "multi_thread")]
+    async fn test_get_changed_program_same_code_but_different_units() {
+        let new = r#"// Remove the end face for the extrusion.
+firstSketch = startSketchOn('XY')
+  |> startProfileAt([-12, 12], %)
+  |> line([24, 0], %)
+  |> line([0, -24], %)
+  |> line([-24, 0], %)
+  |> close(%)
+  |> extrude(6, %)
+
+// Remove the end face for the extrusion.
+shell({ faces = ['end'], thickness = 0.25 }, firstSketch)"#;
+        let program = crate::Program::parse_no_errs(new).unwrap();
+
+        let executed = execute(&program).await.unwrap();
+
+        let result = get_changed_program(
+            CacheInformation {
+                old: Some(OldAstState {
+                    ast: program.ast.clone(),
+                    exec_state: executed,
+                    settings: Default::default(),
+                }),
+                new_ast: program.ast.clone(),
+            },
+            &crate::ExecutorSettings {
+                units: crate::UnitLength::Cm,
+                ..Default::default()
+            },
+        );
+
+        assert!(result.is_some());
+
+        let result = result.unwrap();
+
+        assert_eq!(result.program, program.ast);
+        assert!(result.clear_scene);
+    }
+}
diff --git a/src/wasm-lib/kcl/src/parsing/ast/mod.rs b/src/wasm-lib/kcl/src/parsing/ast/mod.rs
index fa2e039ae..d4fd0bb35 100644
--- a/src/wasm-lib/kcl/src/parsing/ast/mod.rs
+++ b/src/wasm-lib/kcl/src/parsing/ast/mod.rs
@@ -1,3 +1,4 @@
+pub(crate) mod cache;
 pub(crate) mod digest;
 pub(crate) mod execute;
 pub mod modify;
diff --git a/src/wasm-lib/kcl/src/parsing/ast/source_range.rs b/src/wasm-lib/kcl/src/parsing/ast/source_range.rs
index f76976c75..436c5db85 100644
--- a/src/wasm-lib/kcl/src/parsing/ast/source_range.rs
+++ b/src/wasm-lib/kcl/src/parsing/ast/source_range.rs
@@ -1,5 +1,7 @@
-use crate::parsing::ast::types::{BinaryPart, BodyItem, Expr, LiteralIdentifier, MemberObject};
-use crate::source_range::ModuleId;
+use crate::{
+    parsing::ast::types::{BinaryPart, BodyItem, Expr, LiteralIdentifier, MemberObject},
+    source_range::ModuleId,
+};
 
 impl BodyItem {
     pub fn module_id(&self) -> ModuleId {
diff --git a/src/wasm-lib/kcl/src/parsing/math.rs b/src/wasm-lib/kcl/src/parsing/math.rs
index 3f4e08be5..9cf718b86 100644
--- a/src/wasm-lib/kcl/src/parsing/math.rs
+++ b/src/wasm-lib/kcl/src/parsing/math.rs
@@ -1,13 +1,12 @@
 // TODO optimise size of CompilationError
 #![allow(clippy::result_large_err)]
 
+use super::CompilationError;
 use crate::{
     parsing::ast::types::{BinaryExpression, BinaryOperator, BinaryPart, Node},
     SourceRange,
 };
 
-use super::CompilationError;
-
 /// Parses a list of tokens (in infix order, i.e. as the user typed them)
 /// into a binary expression tree.
 pub fn parse(infix_tokens: Vec<BinaryExpressionToken>) -> Result<Node<BinaryExpression>, CompilationError> {
@@ -127,8 +126,7 @@ impl From<BinaryOperator> for BinaryExpressionToken {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::parsing::ast::types::Literal;
-    use crate::source_range::ModuleId;
+    use crate::{parsing::ast::types::Literal, source_range::ModuleId};
 
     #[test]
     fn parse_and_evaluate() {
diff --git a/src/wasm-lib/src/wasm.rs b/src/wasm-lib/src/wasm.rs
index 171b12309..3bceb3d83 100644
--- a/src/wasm-lib/src/wasm.rs
+++ b/src/wasm-lib/src/wasm.rs
@@ -4,27 +4,42 @@ use std::{str::FromStr, sync::Arc};
 
 use futures::stream::TryStreamExt;
 use gloo_utils::format::JsValueSerdeExt;
-use kcl_lib::{CoreDump, EngineManager, ExecState, ModuleId, Program};
+use kcl_lib::{CacheInformation, CoreDump, EngineManager, ExecState, ModuleId, OldAstState, Program};
+use tokio::sync::RwLock;
 use tower_lsp::{LspService, Server};
 use wasm_bindgen::prelude::*;
 
+lazy_static::lazy_static! {
+    /// A static mutable lock for updating the last successful execution state for the cache.
+    static ref OLD_AST_MEMORY: Arc<RwLock<Option<OldAstState>>> = Default::default();
+}
+
+// Read the old ast memory from the lock, this should never fail since
+// in failure scenarios we should just bust the cache and send back None as the previous
+// state.
+async fn read_old_ast_memory() -> Option<OldAstState> {
+    let lock = OLD_AST_MEMORY.read().await;
+    lock.clone()
+}
+
 // wasm_bindgen wrapper for execute
 #[wasm_bindgen]
 pub async fn execute_wasm(
     program_str: &str,
-    memory_str: &str,
-    id_generator_str: &str,
+    program_memory_override_str: &str,
     units: &str,
     engine_manager: kcl_lib::wasm_engine::EngineCommandManager,
     fs_manager: kcl_lib::wasm_engine::FileSystemManager,
-    project_directory: Option<String>,
-    is_mock: bool,
 ) -> Result<JsValue, String> {
     console_error_panic_hook::set_once();
 
     let program: Program = serde_json::from_str(program_str).map_err(|e| e.to_string())?;
-    let memory: kcl_lib::exec::ProgramMemory = serde_json::from_str(memory_str).map_err(|e| e.to_string())?;
-    let id_generator: kcl_lib::exec::IdGenerator = serde_json::from_str(id_generator_str).map_err(|e| e.to_string())?;
+    let program_memory_override: Option<kcl_lib::exec::ProgramMemory> =
+        serde_json::from_str(program_memory_override_str).map_err(|e| e.to_string())?;
+
+    // If we have a program memory override, assume we are in mock mode.
+    // You cannot override the memory in non-mock mode.
+    let is_mock = program_memory_override.is_some();
 
     let units = kcl_lib::UnitLength::from_str(units).map_err(|e| e.to_string())?;
     let ctx = if is_mock {
@@ -33,14 +48,55 @@ pub async fn execute_wasm(
         kcl_lib::ExecutorContext::new(engine_manager, fs_manager, units).await?
     };
 
-    let mut exec_state = ExecState {
-        memory,
-        id_generator,
-        project_directory,
-        ..ExecState::default()
-    };
+    let mut exec_state = ExecState { ..ExecState::default() };
 
-    ctx.run(&program, &mut exec_state).await.map_err(String::from)?;
+    let mut old_ast_memory = None;
+
+    // Populate from the old exec state if it exists.
+    if let Some(program_memory_override) = program_memory_override {
+        exec_state.memory = program_memory_override;
+    } else {
+        // If we are in mock mode, we don't want to use any cache.
+        if let Some(old) = read_old_ast_memory().await {
+            exec_state = old.exec_state.clone();
+            old_ast_memory = Some(old);
+        }
+    }
+
+    if let Err(err) = ctx
+        .run(
+            CacheInformation {
+                old: old_ast_memory,
+                new_ast: program.ast.clone(),
+            },
+            &mut exec_state,
+        )
+        .await
+        .map_err(String::from)
+    {
+        if !is_mock {
+            // We don't use the cache in mock mode.
+            let mut current_cache = OLD_AST_MEMORY.write().await;
+            // Set the cache to None.
+            *current_cache = None;
+        }
+
+        // Throw the error.
+        return Err(err);
+    }
+
+    if !is_mock {
+        // We don't use the cache in mock mode.
+        let mut current_cache = OLD_AST_MEMORY.write().await;
+
+        // If we aren't in mock mode, save this as the last successful execution to the cache.
+        *current_cache = Some(OldAstState {
+            ast: program.ast.clone(),
+            exec_state: exec_state.clone(),
+            settings: ctx.settings.clone(),
+        });
+        drop(current_cache);
+    }
 
     // The serde-wasm-bindgen does not work here because of weird HashMap issues so we use the
     // gloo-serialize crate instead.
diff --git a/src/wasm-lib/tests/modify/main.rs b/src/wasm-lib/tests/modify/main.rs
index ea99388f2..677eb895d 100644
--- a/src/wasm-lib/tests/modify/main.rs
+++ b/src/wasm-lib/tests/modify/main.rs
@@ -11,7 +11,7 @@ async fn setup(code: &str, name: &str) -> Result<(ExecutorContext, Program, Modu
     let program = Program::parse_no_errs(code)?;
     let ctx = kcl_lib::ExecutorContext::new_with_default_client(Default::default()).await?;
     let mut exec_state = ExecState::default();
-    ctx.run(&program, &mut exec_state).await?;
+    ctx.run(program.clone().into(), &mut exec_state).await?;
 
     // We need to get the sketch ID.
     // Get the sketch ID from memory.