Topics facets empty due to Skipped status

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Summary

Issue: Topics facets appear empty and traces show a Skipped status instead of generating summaries. Cause: Skipped means the default Thread preprocessor found no usable conversation text — this happens when traces do not store conversation content on LLM-type spans, which is what the default preprocessor reads. Resolution: Create a custom preprocessor that extracts conversation from your actual trace shape, set it as the project default, and then re-generate topics.

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Resolution steps

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Step 1: Confirm the cause

Open a trace in Logs and select the Thread tab in the Trace Viewer. If the Thread view is empty, the preprocessor is not finding conversation content.

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Step 2: Create a custom preprocessor

1. In Logs, open any trace.
2. Select the Thread tab.
3. Click the config button.
4. In the Preprocessor dropdown, select + Custom preprocessor.
5. Enter your preprocessor code. See the Enable Topics - Write a custom preprocessor docs for examples.
6. Enter a name, click Test to verify output, then click Save.

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Step 3: Set the preprocessor as the project default

1. Navigate to Settings → Project.
2. Under Default preprocessor, select the preprocessor you just created. The selection saves automatically.

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Step 4: Verify and re-generate topics

1. Open a trace, go to the Thread tab, and confirm the conversation now appears.
2. In the trace’s Evaluators tab, test the facet on the trace to confirm facet output. See the Custom facets - Create a facet docs.
3. In Topics, click Automation and select your automation to open its status sheet.
4. At the bottom of the sheet, click Process existing traces, select a Time range, and click Process traces.