fix: prevent false "data source not set" error on markdown dashboard tiles

[vinzee]

Problem

Markdown tiles created via the external API or MCP always show the following error:

The data source for this tile is not set. Edit the tile to select a data source.

...even though markdown tiles do not require a data source. Tiles created through the UI do not exhibit this problem.

Root Cause

convertToInternalTileConfig stores source: '' on the internal config for markdown tiles to satisfy the BuilderSavedChartConfig TypeScript type, which requires a source field:

case 'markdown':
  internalConfig = {
    displayType: DisplayType.Markdown,
    markdown: externalConfig.markdown,
    source: '',   // <-- required by type, but semantically empty
    ...
  } satisfies BuilderSavedChartConfig;

The frontend's isSourceUnset check in DBDashboardPage used
!chart.config.source, which evaluates to true for an empty string,
incorrectly triggering the error banner for every API-created markdown tile:

const isSourceUnset =
  !!chart.config &&
  isBuilderSavedChartConfig(chart.config) &&
  !chart.config.source;  // true for '', fires on all markdown tiles

Solution

Add a displayType !== DisplayType.Markdown guard to isSourceUnset so
markdown tiles are never considered to have an unset source:

const isSourceUnset =
  !!chart.config &&
  isBuilderSavedChartConfig(chart.config) &&
  chart.config.displayType !== DisplayType.Markdown &&
  !chart.config.source;

Tests

• packages/common-utils: unit tests for isBuilderSavedChartConfig and
  the isSourceUnset pattern, verifying that markdown tiles evaluate to
  false (no error shown) even when source is ''
• packages/api: unit tests for convertToInternalTileConfig covering
  the markdown tile conversion path and tile layout field preservation

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[changeset-bot]

🦋 Changeset detected

Latest commit: bcfb9b4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@hyperdx/app	Patch
@hyperdx/common-utils	Patch
@hyperdx/api	Patch
@hyperdx/otel-collector	Patch

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[github-actions]

PR Review

✅ The fix is correct and well-targeted. displayTypeRequiresSource cleanly centralizes the exclusion logic.

• ⚠️ Multi-line comment block in guards.ts violates project style (AGENTS.md: "Never write multi-paragraph docstrings or multi-line comment blocks — one short line max") → Collapse the 4-line JSDoc to a single // line
• ⚠️ Multi-line comment blocks in test files (guards.test.ts lines 67–71, 113–116; dashboards.test.ts lines 57–61) → Same rule applies; remove or collapse to one line each
• ℹ️ Number display type is not covered by displayTypeRequiresSource tests — if Number tiles ever omit a source (similar to Markdown), this would re-emerge. Not a blocker since Number currently always needs a source, but worth noting for future additions to the enum.