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pettinarip merged 2 commits into from
Apr 30, 2026
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docs(data-layer): add fetcher isolation rule #18066

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docs(data-layer): add fetcher isolation rule
pettinarip Apr 29, 2026
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Update .claude/skills/data-layer/SKILL.md
pettinarip Apr 30, 2026
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8 changes: 8 additions & 0 deletions .claude/skills/data-layer/SKILL.md
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Expand Up @@ -160,6 +160,14 @@ return { ...event, logoImage: logoUrl ?? "" }

Always handle `null` returns (upload failures) with fallback/empty string.

### 5. Keep fetchers isolated from the app

Fetchers run on Trigger.dev — a separate runtime, deployment, and bundle from the Next.js app. They cannot assume the app's filesystem, environment, or modules are available.

Any import or runtime dependency reaching outside `src/data-layer/` is a warning sign. Allowed: types (`@/lib/types`, `@/lib/interfaces`), pure constants (`@/lib/constants`), and pure utility functions with no app-runtime dependencies. Not allowed: anything that reads `process.cwd()`, anything from `app/` or `public/`, anything from `src/components/`, or `src/lib/data/` (which wraps the data layer and would create a cycle).

If a fetcher needs data that lives in the app — content files, frontmatter, etc. — fetch it over the network via the GitHub API and treat the repo as an external system. See `fetchGitHubContributors.ts` for the pattern. Don't work around this with `additionalFiles` in `trigger.config.ts`; bundling app files into the data-layer deployment re-creates the coupling.

## Adding a New Data Source

1. **Create fetcher** in `src/data-layer/fetchers/fetchNewData.ts`:
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4 changes: 4 additions & 0 deletions src/data-layer/docs.md
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Expand Up @@ -51,6 +51,10 @@ export const getEventsData = createCachedGetter(

Direct `@/data-layer` imports work but have no caching.

### 4. Keep fetchers isolated from the app

Fetchers run on Trigger.dev — a separate runtime from the Next.js app — and cannot assume the app's filesystem or modules are available. Any import or runtime dependency reaching outside `src/data-layer/` is a warning sign; if a fetcher needs app data, fetch it via the GitHub API and treat the repo as an external system. See `fetchGitHubContributors.ts` for the pattern, and the data-layer skill (Rule 5) for the full allow/deny list.

## Adding a New Data Source

1. **Create fetcher** in `src/data-layer/fetchers/fetchNewData.ts`
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