# Dependency Flow

```
                    +-------------+   +-----------------+   +-----------+
                    | apps/web-   |   | apps/web-       |   | apps/cms  |
                    | next        |   | tanstack        |   |           |
                    +------+------+   +--------+--------+   +-----+-----+
                           |                   |                  |
        +------------------+--------------+    |                  |
        |                  |              |    |                  |
   +----v-----+      +-----v------+ +-----v----v---+      +-------v------+
   | core-api |      | core-trpc  | | feature      |      | core-cms     |
   |          |      |            | | packages     |      |              |
   +-----+----+      +-----+------+ +------+-------+      +-------+------+
         |                 |               |                      |
         |                 |               |                      |
         +--+-------+------+---------------+----+   +-------------+
            |       |                           |   |
       +----v---+ +-v---------+         +-------v---v---+
       | core-  | | core-ui   |         | core-shared    |
       | shared | |           |         |                |
       +--------+ +-----------+         +----------------+

  Boundary rules (enforced by ESLint + Turborepo boundaries):
    app             → app, core, core-composition, feature, tooling
    feature         → core, tooling
    core            → core, core-composition, tooling
    core-composition → core, core-composition, feature, tooling
    tooling         → tooling
    
    Composition exceptions:
      core-api  → @repo/<feature>/api (subpath only)
      core-cms  → @repo/<feature>/cms (subpath only)

  App-side feature subpaths (Plan 9):
    @repo/<feature>     — contracts (types, errors, schemas, IUseCase aliases, router type, constants)
    @repo/<feature>/ui  — UI artifacts (query builders, components)
```

## Concrete examples

Allowed:
```ts
// in apps/web-next
import { appRouter } from "@repo/core-api";
import { NextTrpcProvider } from "@repo/core-trpc/next";
import { bindProductionBlog } from "@repo/blog/di/bind-production";
import { signInInputSchema, type SignInInput } from "@repo/auth";   // contracts (Plan 9)
import { articleBySlugQuery } from "@repo/blog/ui";                  // queries (Plan 9)

// in packages/blog
import { slugifyIfMissing } from "@repo/core-shared/payload";

// in packages/core-api
import { blogRouter } from "@repo/blog/api";          // composition exception
import { router } from "@repo/core-shared/trpc/init"; // core → core fine

// in packages/core-cms
import { articles } from "@repo/blog/cms";             // composition exception
```

Disallowed:
```ts
// in packages/blog (cross-feature)
import { Article } from "@repo/marketing-pages";     // ❌ feature → feature

// in packages/blog (deep import past public exports)
import { articles } from "@repo/blog/src/integrations/cms/collections/articles"; // ❌ no-private

// in packages/core-shared
import { blogRouter } from "@repo/blog/api";         // ❌ core → feature
import { ArticleNotFoundError } from "@repo/blog";   // ❌ core → feature
                                                     // (defineErrorMiddleware takes Error
                                                     // constructors as args from features —
                                                     // core-shared never imports them)

// in packages/core-shared (or any non-composition core package)
import { someBlogThing } from "@repo/blog";          // ❌ core → feature (only core-api/core-cms have exception)

// in apps (using the wrong subpath)
import { articleBySlugQuery } from "@repo/blog";     // ❌ queries live on ./ui
import { Article } from "@repo/blog/ui";             // ❌ types live on the root subpath
```

## Enforcement strategy

Three layers work in tandem:

1. **`package.json` dependencies** — if you didn't declare it, you can't import it
2. **`exports` map** — blocks deep imports; only public subpaths are accessible
3. **Two parallel automated checks** (both enforcing the same five-tag model):
   - **ESLint `eslint-plugin-boundaries`** runs at lint time, catching direct-import violations
   - **Turborepo `boundaries`** runs at build time, validating the entire workspace graph including transitive dependencies

The two enforcement layers are independent but complementary. ESLint is stricter on per-import context (e.g., file-specific exemptions via `// @boundaries-ignore`), while Turborepo catches transitive issues that lint-time checking misses. Run `pnpm lint` and `pnpm turbo boundaries` in CI to catch all violations.

## TRACER / LOGGER / METRICS / AUDIT (ADR-014, ADR-017, ADR-018)

The instrumentation layer is **per-feature container** but **app-wide instance**: each feature container binds `INSTRUMENTATION_SYMBOLS.ITracer`, `INSTRUMENTATION_SYMBOLS.ILogger`, and `INSTRUMENTATION_SYMBOLS.IMetrics` to the SAME instances, constructed once by the app's `bindAll()` dispatcher (Rule 0).

**Substrate:** OpenTelemetry SDK. Sentry is the exporter via `@sentry/opentelemetry`. PII scrubbing runs at the OTel processor layer (`PiiScrubSpanProcessor` + `PiiScrubLogRecordProcessor`) before the Sentry exporter sees the data. Feature code is never coupled to the OTel SDK or Sentry SDK directly (ADR-017).

**Audit is a parallel channel** with different durability and redaction contracts (ADR-018). Whereas OTel is sampled and pruned (best-effort observability), audit is append-only and retained for compliance. `auditLog` is bound by `resolveAudit` and added to `ctx` for feature binders that opt in; the binding is wrapped in `TraceIdEnrichingAuditLog` so every `AuditEntry` auto-correlates with the active OTel span via `correlationId`. See `docs/guides/audit-and-compliance.md` and the visual explainer at `docs/architecture/audit-and-compliance-explainer.html`.

```
apps/web-next/src/server/bind-production.ts (bindAll)
        │
        ├─ Rule 0: WEB_NEXT_SENTRY_DSN set?
        │     yes → bindOtelInstrumentation(sharedContainer, { dsn, app: "web-next" })
        │             → initOtelServerNode(dsn, ...) → OTel SDK + Sentry exporter + PII scrub processors
        │     no  → bindNoopInstrumentation(sharedContainer)
        │     ↓
        │   tracer (OtelTracer) + logger (OtelLogger) + metrics (OtelMetrics) instances
        │     ↓
        ├─ resolveEventsAndJobs* → IEventBus + IJobQueue (ADR-015)
        │     production  → PayloadJobsEventBus + PayloadJobQueue
        │     dev-seed    → InMemoryEventBus  + InMemoryJobQueue
        │     ↓
        ├─ resolveRealtime → IRealtimeBroadcaster + IRealtimeHandlerRegistry (ADR-016)
        │     server.ts   → SocketIORealtimeBroadcaster + RealtimeHandlerRegistry (passed in from server.ts)
        │     page/test   → InMemoryRealtimeBroadcaster + RealtimeHandlerRegistry (defaults)
        │     ↓
        ├─ resolveAudit → IAuditLog (ADR-018)
        │     production  → TraceIdEnrichingAuditLog( MultiSinkAuditLog([StdoutJsonAuditLog, PayloadAuditLog]) )
        │     dev-seed    → TraceIdEnrichingAuditLog( StdoutJsonAuditLog ) — or Noop when core-audit is absent
        │     ↓
        ├─ build ctx: BindProductionContext = { config, tracer, logger, metrics?, bus, queue, realtime, realtimeRegistry, auditLog }
        │     Required: tracer, logger, config (production only)
        │     Optional: metrics, bus, queue, realtime, realtimeRegistry, auditLog (guard with ?. when used)
        │     ↓
        ├─ bindProductionBlog(ctx: BindProductionContext)
        │     │
        │     ├─ blogContainer.bind(TRACER).toConstantValue(tracer)
        │     ├─ blogContainer.bind(LOGGER).toConstantValue(logger)
        │     ├─ ArticlesRepository(config, tracer, logger) → bound to IArticlesRepository
        │     │     (real repo: inline this.tracer.startSpan + this.logger.captureException per method)
        │     ├─ withSpan(tracer, ..., withCapture(logger, ..., useCase(deps))) → UseCase symbol
        │     ├─ withSpan(tracer, ..., withCapture(logger, ..., controller(uc))) → Controller symbol
        │     ├─ // <gen:event-handlers>    bus.subscribe(...) (ADR-015, gen event consume)
        │     ├─ // <gen:jobs>              queue.register(...) in dev-seed; Payload task in prod
        │     └─ // <gen:realtime-handlers> realtimeRegistry.register(...) (ADR-016, gen realtime handler)
        │
        └─ (same for auth, marketing-pages, navigation, media — each receives the same ctx)
```

**`BindContext` shape (from `@repo/core-shared/di`):**

| Field | Type | Required | Notes |
|---|---|---|---|
| `tracer` | `ITracer` | always | Resolved by Rule 0 (OTel+Sentry vs Noop) |
| `logger` | `ILogger` | always | Resolved by Rule 0 |
| `metrics` | `MetricsProtocol?` | optional | Resolved by Rule 0; per-feature adoption is opportunistic |
| `config` | `SanitizedConfig` | production only | Present in `BindProductionContext`, absent in `BindContext` |
| `bus` | `EventBusProtocol?` | optional | `IEventBus` at the aggregator; protocol surface at binders |
| `queue` | `IJobQueue?` | optional | Present when `core-shared/jobs` is wired |
| `realtime` | `RealtimeBroadcasterProtocol?` | optional | `IRealtimeBroadcaster` at the aggregator |
| `realtimeRegistry` | `RealtimeRegistryProtocol?` | optional | `IRealtimeHandlerRegistry` at the aggregator |
| `auditLog` | `AuditLogProtocol?` | optional | `IAuditLog` at the aggregator; pre-wrapped in `TraceIdEnrichingAuditLog` so callers don't supply `correlationId` (ADR-018) |

Feature binders destructure `ctx` and use optional fields with `?.` or cast to the full interface when the feature unconditionally requires them (e.g. `bus as IEventBus` when a use case always needs the event bus).

**Why per-feature containers also get the binding:** lets internal DI-resolved code in a feature pull TRACER/LOGGER without going through the app dispatcher. In practice, only repository classes and feature-internal services would use this — controllers and use cases receive instrumentation via the bind-time wrapper.

**Why the shared container exists at all:** isolates Rule 0 resolution from feature containers. Feature containers don't need to know if Sentry is the exporter or not — they just receive an `ITracer` instance.

**Boundary rule:** feature packages MUST NOT import `@sentry/*` or `@opentelemetry/sdk-*` directly (R40 + R52, ESLint-enforced). The OTel bridge (`otel/sentry-bridge.ts`), browser init files (`sentry/init-client*.ts`), and app-level `instrumentation*.{ts,mjs}` / `next.config.{mjs}` / `vite.config.{ts}` entries are the only allowlisted paths. Likewise, features MUST NOT import `@repo/core-audit` directly — they consume `IAuditLog` via the `AuditLogProtocol` type re-exported from `@repo/core-shared/di/bind-protocols`.
