fix: keep marimo running when tracing dependencies are missing

[Light2Dark]

📝 Summary

MARIMO_TRACING=1 currently prevents marimo from starting when OpenTelemetry is unavailable, including inside isolated notebook sandboxes. Tracing is an optional observability feature and must not make the application unavailable.

This change initializes tracing once and selects either the OpenTelemetry backend or no-op tracers. Missing or incomplete OpenTelemetry installations now produce one actionable warning and disable tracing for that process. Editable sandbox installs also retain requested marimo extras instead of silently dropping them.

Seems the only simple way to run with otel is this

uv add --script new_file.py 'marimo[otel]'
MARIMO_TRACING=1 marimo edit --sandbox new_file.py

📋 Pre-Review Checklist

• This change is focused and does not affect the public API.
• Any AI generated code has been reviewed line-by-line by the human PR author, who stands by it.
• This change has no visual behavior that requires media evidence.

✅ Merge Checklist

• I have read the contributor guidelines.
• Documentation has been updated where applicable, including docstrings for API changes.
• Tests have been added for the changes made.

Written by GPT-5 on Codex

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Project	Deployment	Actions	Updated
marimo-docs	Ready	Preview	Sep 8, 2026 5:35am UTC

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[cubic-dev-ai]

All reported issues were addressed across 5 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[Copilot]

🟡 Changes recommended

There is a functional gap where tracing isn’t fully disabled (request-path still attempts OpenTelemetry imports), and the new subprocess test script construction is likely to fail due to indentation.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR makes tracing truly optional: when MARIMO_TRACING=1 but OpenTelemetry isn’t available (common in isolated/sandboxed environments), marimo should still start, emit a single actionable warning, and use no-op tracers for the rest of the process. It also ensures editable sandbox installs preserve requested marimo extras.

Changes:

• Initialize tracing once at import-time and fall back to no-op tracing when OpenTelemetry cannot be imported or initialization fails.
• Preserve additional_features (extras) when marimo is installed editable in sandboxes.
• Add tests and docs to cover “missing OpenTelemetry should not prevent startup” behavior.

File summaries

File	Description
marimo/_tracer.py	Adds one-time tracing initialization with warning + no-op fallback; wires tracers off a global availability flag.
tests/test_tracer.py	Updates tracer tests to reflect one-time initialization; adds subprocess test ensuring import marimo works without OpenTelemetry.
marimo/_cli/sandbox.py	Preserves extras for editable marimo sandbox dependencies (-e /path[extras]).
tests/_cli/test_sandbox.py	Extends sandbox dependency normalization tests for editable installs retaining extras.
development_docs/traces.md	Documents that missing tracing deps disables tracing but keeps marimo running.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 3
• Review effort level: Lite

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