# AGENTS.md — core-shared

Generic, reusable primitives with **zero business knowledge**. This package is the foundation for all other packages and exports utilities, Payload field/hook definitions, and tRPC initialization.

## Responsibilities

- **Generic primitives** — environment helpers, date utilities, type guards
- **Payload utilities** — field definitions (slug, SEO), blocks (CTA), access controls (is-admin), hooks (slugify, publish timestamp)
- **tRPC platform** — `initTRPC.create()`, shared context factory, procedure builders
- **No business domain knowledge** — no awareness of articles, users, media, or any feature

## Must NOT import

- Any feature package (`@repo/auth`, `@repo/blog`, etc.)
- Any app package
- Framework-specific code (Next.js, TanStack React Query)

## Public exports

From `package.json`:
- `.` — all utilities, Payload exports, tRPC init
- `./payload` — Payload field/hook/block utilities only
- `./trpc/init` — tRPC `initTRPC` instance + builders. **Plan 9:** also exports `t` (the raw `initTRPC.create({...})` instance) so feature packages can build their own procedures via `t.procedure.use(...)`
- `./trpc/context` — tRPC context factory only
- `./trpc/define-error-middleware` — **Plan 9:** factory that builds a tRPC middleware translating domain errors to `TRPCError`. Takes `ReadonlyArray<readonly [ErrorCtor, TRPC_ERROR_CODE_KEY]>` tuples; uses `instanceof` discrimination; preserves the original error as `.cause`. **Owned by features:** each feature passes its own constructors in via `integrations/api/procedures.ts`. core-shared never enumerates feature-specific error classes — this stays boundary-clean

## Test conventions

- Tests colocated: `src/lib/slug-field.ts` → `src/lib/slug-field.test.ts`
- Vitest environment: `node`
- Alias: `@/` resolves to `src/`
- Run: `pnpm test --filter @repo/core-shared`

Covered areas:
- Slug field generation + validation
- Payload hooks (publish-at timestamp, slugify-if-missing)
- Access control helpers

## src/instrumentation/

**Substrate:** OpenTelemetry SDK (ADR-017). Sentry is the exporter via `@sentry/opentelemetry`. Feature packages depend only on the interfaces below — no Sentry or OTel SDK imports.

**Three interfaces:** `ITracer` (`tracer.interface.ts`), `ILogger` (`logger.interface.ts`), `IMetrics` (`metrics.interface.ts`).

**Three implementation pairs:**

- `NoopTracer` / `NoopLogger` / `NoopMetrics` — pass-through. Default everywhere.
- `OtelTracer` / `OtelLogger` / `OtelMetrics` — emit via OTel API (`@opentelemetry/api`, `@opentelemetry/api-logs`). Live in `otel/` subfolder. **The `otel/` subfolder is the only path in `packages/` permitted to import `@opentelemetry/sdk-*` or `@sentry/opentelemetry`** (R52).
- `RecordingTracer` / `RecordingLogger` / `RecordingMetrics` — in `@repo/core-testing/instrumentation`, not here.

**`with-span.ts` + `with-capture.ts`:** two higher-order helpers used at DI binding time to wrap use case + controller factory results. The binders apply them as a sandwich — `withSpan` outermost, `withCapture` between span and factory:

```ts
const wrapped = withSpan(
  tracer,
  { name: "blog.getArticles", op: "use-case" },
  withCapture(
    logger,
    { feature: "blog", layer: "use-case", name: "blog.getArticles" },
    factory(deps),
  ),
);
```

`withSpan` is pure delegation to `tracer.startSpan`. `withCapture` catches thrown errors, calls `logger.captureException(err, { tags })`, marks the `__sentryReported` flag, and re-throws — but bails if the flag is already set so the inner-most layer wins.

**`reported-flag.ts`:** small module exporting `markReported(err)` and `isReported(err)`. Used by `withCapture` and `OtelLogger`. `RecordingLogger` carries an inlined copy (tooling → core import is disallowed by the boundary rule).

**Symbols:** `INSTRUMENTATION_SYMBOLS.ITracer`, `INSTRUMENTATION_SYMBOLS.ILogger`, `INSTRUMENTATION_SYMBOLS.IMetrics` (all `Symbol.for(...)` so cross-realm equality holds).

**`otel/pii-fields.ts`:** vendor-neutral PII substring list (`PII_KEY_SUBSTRINGS`, `PII_QUERY_PARAM_SUBSTRINGS`). Used by `otel/pii-scrub-processor.ts` (server) and imported by `sentry/init-client*.ts` (browser).

**`otel/pii-scrub-processor.ts`:** `PiiScrubSpanProcessor` + `PiiScrubLogRecordProcessor`. Registered FIRST in the OTel processor chain so all downstream exporters (Sentry) see scrubbed data. Replaces Sentry's `beforeSend`/`beforeSendTransaction` hooks on the server side (ADR-017 §7).

**`sentry/init-server.ts` + `sentry/init-client.ts`:** centralized init helpers (Next.js flavor). `init-server.ts` calls `Sentry.init` with `sendDefaultPii: false` (R31) — no `beforeSend` hook (PII scrubbed at OTel layer). `init-client.ts` retains `beforeSend`/`beforeSendTransaction` because browser does not use the OTel pipeline.

**`sentry/init-server-node.ts` + `sentry/init-client-react.ts`:** Vite/non-Next variants used by `apps/web-tanstack`. Same posture as their Next.js counterparts.

**`di/bind-noop-instrumentation.ts` + `bind-otel-instrumentation.ts`:** bind ITracer + ILogger + IMetrics symbols to a Container. Returns the resolved instances so callers can use them without container lookup. `bindSentryInstrumentation` kept as a deprecated alias for one release.

**Subpath exports** (`package.json#exports`):

- `./instrumentation` — barrel (interfaces + Noops + OtelTracer/OtelLogger + withSpan + withCapture + reported-flag + symbols + binders)
- `./instrumentation/otel` — OTel init helper + resource builder barrel
- `./instrumentation/otel/init-server-node` — `initOtelServerNode` (app bootstrap, server-side OTel SDK)
- `./instrumentation/sentry/init-server` — Next.js server Sentry.init helper
- `./instrumentation/sentry/init-client` — Next.js browser Sentry.init helper
- `./instrumentation/sentry/init-server-node` — `@sentry/node` server init (TanStack Start)
- `./instrumentation/sentry/init-client-react` — `@sentry/react` browser init (TanStack Start)

**Boundaries:**

- `core-shared/instrumentation/otel/**` MAY import from `@opentelemetry/sdk-*` and `@sentry/opentelemetry`.
- `core-shared/instrumentation/sentry/**` MAY import from `@sentry/*` (browser init files).
- Everything else in `packages/core-shared/src/` MUST NOT.
- ESLint rules R40 + R52 in `core-eslint/base.js` enforce the broader monorepo boundary.
