Secondary SpiderMonkeyError thrown while deserializing an already-handled Python exception (error cascade / double-fault)

[dan-distributive]

Issue type

Bug

How did you install PythonMonkey?

Installed from pip

OS platform and distribution

macOS Sequoia 15.5 (24F74), M2 chip

Python version (python --version)

3.12.6

PythonMonkey version (pip show pythonmonkey)

1.3.0

Bug Description

I wrote a DCP job that deliberately imports a package that isn't available nor exists, e.g. "nanana", to observe the error message.

When a Python exception originating from a JS/wasm environment (via Pyodide) is surfaced correctly as a structured error object, pythonmonkey subsequently throws a secondary SpiderMonkeyError during deserialization, even though the original error has already been delivered to user code and handled.

This results in a noisy, cascading failure where a handled error still causes an uncatchable exception at the PythonMonkey layer.

Standalone code to reproduce the issue

import dcp
dcp.init()

my_inputs = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

my_args = [25, 11]

def my_function(x, a, b):
    dcp.progress()
    import nanana
    result = x + a + b
    return result

my_job = dcp.compute_for(my_inputs, my_function, my_args)

my_job.computeGroups = [
    {"joinKey": "demo"}
]

# Prompt for join secrets at runtime
from getpass import getpass
for g in my_job.computeGroups:
    if g.get("joinKey") != "public":
        g["joinSecret"] = getpass(f"Enter join secret for compute group '{g['joinKey']}': ")

my_job.on('readystatechange', lambda sta: print(f"State: {sta}"))
my_job.on('accepted',   lambda _: print(f"  Job ID: {my_job.id}\n  Job accepted, awaiting results..."))
import json
my_job.on('noProgress', lambda nop: print(json.dumps(nop, indent=4).replace('\\n', '\n')))
my_job.on('error',      lambda err: print(json.dumps(err, indent=4).replace('\\n', '\n')))


my_job.exec()
results = my_job.wait()

print(results)

Relevant log output or backtrace

{
    "name": "PythonError",
    "message": "Traceback (most recent call last):
  File \"<exec>\", line 105, in slice_handler_deserialization_wrapper
  File \"<string>\", line 3, in my_function
ModuleNotFoundError: No module named 'nanana'
",
    "timestamp": "2026-01-11T13:59:09.149Z",
    "code": "EUNCAUGHT",
    "stack": "PythonError: Traceback (most recent call last):
  File \"<exec>\", line 105, in slice_handler_deserialization_wrapper
  File \"<string>\", line 3, in my_function
ModuleNotFoundError: No module named 'nanana'

    at new_error (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/pyodide-core.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:2:1002009)
    at wasm://wasm/020fb45e:wasm-function[261]:0x10f02c
    at wasm://wasm/020fb45e:wasm-function[262]:0x10f0f4
    at callPyObjectKwargs (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/pyodide-core.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:2:1045919)
    at Module.callPyObject (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/pyodide-core.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:2:1047481)
    at Function.apply (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/pyodide-core.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:2:1063661)
    at Object.apply (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/pyodide-core.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:2:1060100)
    at workFunctionWrapper (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/bravojs-env.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:246:40)
    at async runWorkFunction_inner (https://scheduler.distributed.computer/dcp-client/libexec/sandbox/bravojs-env.js?d91005494a226e4361d9ae1a2f739dc2dc45750a:403:16)",
    "jobName": "Ad-Hoc Job9La7w7",
    "job": "jjK71iUUHCZIyYLa9La7w7",
    "sliceNumber": 7.0
}
[SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n'), SpiderMonkeyError('Error in file , on line 0, column 881757:\nPythonError: Traceback (most recent call last):\n  File "<exec>", line 105, in slice_handler_deserialization_wrapper\n  File "<string>", line 3, in my_function\nModuleNotFoundError: No module named \'nanana\'\n\nStack Trace:\n  unprepare$object@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:881757\n  unprepare@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:880640\n  serialize$$unmarshal@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893473\n  deserialize@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:893840\n  utils$$decodeData@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1506660\n  219/fetchUri$$fetchURI/<@/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/dcp/js/node_modules/dcp-client/dist/dcp-client-bundle.js:1:1505128\n')]

Additional info if applicable

What branch of PythonMonkey were you developing on? (If applicable)

No response