Add option to display error tracebacks inline and in modal

[wlach]

📝 Summary

Closes #7984

🔍 Description of Changes

Add an optional mode (disabled by default) to display error tracebacks both inline and in a modal when in run (app) mode. This makes it easier for users to report errors in internal environments.

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• Tests have been added for the changes made.
• Documentation has been updated where applicable, including docstrings for API changes.
• Pull request title is a good summary of the changes - it will be used in the release notes.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Feb 19, 2026 7:16pm

[wlach]

@akshayka @manzt per discussion, would love some feedback. Currently lacking docs, happy to try my hand at adding some.

[akshayka]

A couple comments on the API

[akshayka]

Suggested change

	"--show-error-tracebacks/--no-show-error-tracebacks",
	"--show-tracebacks/--no-show-tracebacks",

[akshayka]

Does this need to be in config? This isn't really a runtime configuration in my mind. The console redirection is also not in config

[manzt]

Thanks for pushing this forward.

I'm convinced separating console redirection from tracebacks is the right call. They serve different purposes (as you mentioned), so keeping them independent makes sense.

+1 to removing from config. redirect_console_to_browser is CLI/ASGI-only and this should follow the same pattern. Keeping it out of config also gives us room to easily evolve the API later (if ever):

--show-tracebacks          # bare flag, sensible default
--show-tracebacks=toast
--show-tracebacks=inline

Not needed in this PR, just flagging that staying out of config preserves that optionality.

[manzt]

I believe we can remove the explicit any with type narrowing:

Suggested change

	const exceptionErrors = cell.output.data.filter(
	(error: any) => error.type === "exception" || error.type === "internal",
	);
	const exceptionErrors = cell.output.data.filter(
	(error) =>
	"type" in error &&
	(error.type === "exception" || error.type === "internal"),
	);

[manzt]

I think with changes above this can be removed (type is inferred).

[manzt]

I think with changes above this can be removed (type is inferred).

Suggested change

	const errorWithTraceback = exceptionErrors.find(
	(error: any) => error.traceback,
	);
	const errorWithTraceback = exceptionErrors.find(
	(error) => error.traceback,
	);

[wlach]

Thanks all! Very reasonable requests for changes, I'll try to find some time to polish this up next week.