diff --git a/api/src/controllers/internal/Execution.ts b/api/src/controllers/internal/Execution.ts
index c1ff197..d256275 100644
--- a/api/src/controllers/internal/Execution.ts
+++ b/api/src/controllers/internal/Execution.ts
@@ -120,7 +120,16 @@ export class ExecutionController {
       : ''
 
     // it should be deleted by scheduleSessionDestroy
-    session.state = SessionState.completed
+    //
+    // Guarded: for JS/PY/R, processProgram sets state to `failed` itself
+    // (without throwing) when the interpreter process exits non-zero - if
+    // we unconditionally set `completed` here we'd silently overwrite that,
+    // and anything downstream inspecting session.state (e.g.
+    // scheduleSessionDestroy's expiresAfterMins branch in Session.ts) would
+    // see a crashed session mis-reported as successful.
+    if ((session.state as SessionState) !== SessionState.failed) {
+      session.state = SessionState.completed
+    }
 
     const resultParts = []
 
diff --git a/api/src/controllers/internal/spec/Execution.spec.ts b/api/src/controllers/internal/spec/Execution.spec.ts
new file mode 100644
index 0000000..ec91cfe
--- /dev/null
+++ b/api/src/controllers/internal/spec/Execution.spec.ts
@@ -0,0 +1,84 @@
+import path from 'path'
+import os from 'os'
+import { deleteFolder, generateTimestamp } from '@sasjs/utils'
+import * as ProcessProgramModule from '../processProgram'
+import { ExecutionController } from '../Execution'
+import { Session, SessionState, PreProgramVars } from '../../../types'
+import { RunTimeType } from '../../../utils'
+
+// Regression coverage: for JS/PY/R, processProgram sets session.state to
+// `failed` itself (without throwing) on a non-zero interpreter exit.
+// ExecutionController.executeProgram used to unconditionally overwrite
+// that back to `completed` right after processProgram returned, silently
+// losing the failure for anything downstream that inspects session.state.
+
+const preProgramVariables: PreProgramVars = {
+  username: 'testUser',
+  userId: 1,
+  displayName: 'Test User',
+  serverUrl: 'http://localhost:5000',
+  httpHeaders: []
+}
+
+describe('ExecutionController.executeProgram (JS/PY/R failure path)', () => {
+  let session: Session
+
+  beforeEach(() => {
+    const sessionId = `test-session-${generateTimestamp()}`
+    session = {
+      id: sessionId,
+      state: SessionState.pending,
+      creationTimeStamp: '0',
+      deathTimeStamp: '0',
+      path: path.join(os.tmpdir(), sessionId)
+    }
+  })
+
+  afterEach(async () => {
+    jest.restoreAllMocks()
+    await deleteFolder(session.path)
+  })
+
+  it('does not overwrite a failed session state back to completed', async () => {
+    // mirrors processProgram's real JS/PY/R branch on a non-zero exit:
+    // it sets state/failureReason itself and resolves - it does not throw
+    jest
+      .spyOn(ProcessProgramModule, 'processProgram')
+      .mockImplementation(async () => {
+        session.state = SessionState.failed
+        session.failureReason = 'Error: process exited with code 1'
+      })
+
+    const controller = new ExecutionController()
+
+    await controller.executeProgram({
+      program: 'throw new Error("boom")',
+      preProgramVariables,
+      vars: {},
+      session,
+      runTime: RunTimeType.JS
+    })
+
+    expect(session.state).toBe(SessionState.failed)
+  })
+
+  it('still marks a genuinely successful session as completed', async () => {
+    jest
+      .spyOn(ProcessProgramModule, 'processProgram')
+      .mockImplementation(async () => {
+        session.state = SessionState.completed
+      })
+
+    const controller = new ExecutionController()
+
+    await controller.executeProgram({
+      program: 'console.log("hello")',
+      preProgramVariables,
+      vars: {},
+      session,
+      runTime: RunTimeType.JS
+    })
+
+    expect(session.state).toBe(SessionState.completed)
+  })
+})