Prune redundant traceback item at start of all traces

[yairchu]

📝 Summary

Fixse #6576

🔍 Description of Changes

When sending tracebacks to the front-end, the backend prunes the first redundant traceback item in marimo's own engine

📋 Checklist

• I have read the contributor guidelines.
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

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Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Sep 29, 2025 3:48pm

[mscolnick]

@yairchu - can you run make py-snapshots

[yairchu]

@yairchu - can you run make py-snapshots

Sure:

(marimo) yairchu@Yair-M4 marimo % make py-snapshots
hatch run +py=3.12 test:test \
        tests/_server/templates/test_templates.py \
        tests/_server/api/endpoints/test_export.py \
        tests/test_api.py
────────────────────────────────────────────────────────────── test.py3.12 ───────────────────────────────────────────────────────────────
========================================================== test session starts ===========================================================
platform darwin -- Python 3.12.9, pytest-8.3.5, pluggy-1.6.0
rootdir: /Users/yairchu/dev/marimo
configfile: pyproject.toml
plugins: inline-snapshot-0.29.1, anyio-4.11.0, rerunfailures-15.1, hypothesis-6.102.6, codecov-0.6.1, asyncio-0.26.0, timeout-2.3.1, cov-7.0.0
asyncio: mode=Mode.AUTO, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
timeout: 30.0s
timeout method: signal
timeout func_only: False
collected 44 items                                                                                                                       

tests/_server/templates/test_templates.py ..........................                                                               [ 59%]
tests/_server/api/endpoints/test_export.py ......X.....ss...                                                                       [ 97%]
tests/test_api.py .                                                                                                                [100%]

================================================================ XPASSES =================================================================
======================================================== short test summary info =========================================================
SKIPPED [1] tests/_server/mocks.py:97: nbformat not installed
SKIPPED [1] tests/_server/mocks.py:97: nbformat not installed or on Windows
XPASS tests/_server/api/endpoints/test_export.py::test_export_markdown - flakey
================================================ 41 passed, 2 skipped, 1 xpassed in 8.60s ================================================

[mscolnick]

@yairchu it looks like there is still an error with:

tests/_cli/test_cli_export.py::TestExportIpynb::test_export_ipynb_with_errors

unsure if it is because of different tracebacks for different python versions

[yairchu]

I'll have a look

[yairchu]

Locally I get same results in main both for hatch run +py=3.12 test:test tests/_cli/test_cli_export.py (for the specific test) and for make py-snapshots

[mscolnick]

can you try: hatch run +py=3.9 test:test tests/_cli/test_cli_export.py

[mscolnick]

if it is just 3.9 causing issues, you can just ignore that version for this test

[mscolnick]

nvm its just flakiness, i will merge this