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openspec/archive/2026-04-24-enterprise-events-otel/proposal.md

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+# OpenSpec Change: enterprise-events-otel
+
+- **Change ID**: enterprise-events-otel
+- **Package**: `@suaveplan/events-otel`
+- **Category**: universal
+- **Target path**: `universal/events/events-otel`
+- **Status**: PROPOSED
+- **Date**: 2026-04-24
+- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/events-otel.md`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/events-otel` on the genesis branch from scratch at enterprise quality. The package is an opt-in OpenTelemetry tracing companion for `@suaveplan/events`: it wraps each dispatch in a span, propagates W3C Trace Context across synchronous and async subscriber invocations, records event-level attributes on each span, and correctly marks listener exceptions as span errors. Attaches via the public `@suaveplan/events` interceptor API. Sampling-aware: honours the parent sampling decision and supports rule-based head sampling.
+
+---
+
+## Current-state audit (genesis)
+
+The package does not exist on genesis yet — fresh build. No prior source, no test results, no coverage data.
+
+---
+
+## Available workspace deps on genesis
+
+| Package | Role |
+|---|---|
+| `@suaveplan/events` (`workspace:^`) | Event bus and interceptor API |
+| `@suaveplan/error` (`workspace:^`) | Base class for `EventsOtelError`; `defineCodes` for `EVENTS_OTEL.*` codes |
+| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` injection interfaces |
+| `zod` (`catalog:forms`) | Zod schemas for all public option types |
+| `@opentelemetry/api` (`catalog:observability`) | `Tracer`, `Span`, `SpanStatusCode`, W3C context propagation |
+| `tslib` (`catalog:build`) | Runtime helpers |
+
+Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check` (all `catalog:testing`).
+
+---
+
+## Public API surface
+
+### Setup
+
+```ts
+// Attaches OTel tracing companion to an existing EventBus
+function attachEventTracing(bus: EventBusLike, options?: EventTracingOptions): EventTracingHandle
+
+interface EventTracingOptions {
+  tracer?: Tracer                    // default: global tracer from @opentelemetry/api
+  propagator?: TextMapPropagator    // default: W3CTraceContextPropagator
+  eventFilter?: (name: string) => boolean
+  samplingRule?: SamplingRule
+  clock?: Clock
+  logger?: LoggerLike
+}
+
+interface EventTracingHandle {
+  detach(): void
+}
+```
+
+### Span attribute convention
+
+```ts
+// All span attribute keys as stable constants
+const SPAN_ATTRIBUTES = {
+  EVENT_NAME:     "suaveplan.event.name",
+  EVENT_ID:       "suaveplan.event.id",
+  EVENT_CATEGORY: "suaveplan.event.category",
+  LISTENER_ID:    "suaveplan.listener.id",
+  BUS_ID:         "suaveplan.bus.id",
+} as const
+
+// Span names
+const SPAN_NAMES = {
+  DISPATCH: "events.dispatch",
+  LISTENER: "events.listener",
+} as const
+```
+
+### Sampling rule
+
+```ts
+type SamplingRule =
+  | { type: "always" }
+  | { type: "never" }
+  | { type: "rate"; rate: number }               // 0.0–1.0
+  | { type: "event-name"; names: string[] }      // sample only named events
+```
+
+### Trace context envelope (for transport interop)
+
+```ts
+// Serialize current trace context into a plain object for transport
+function serializeTraceContext(): Record<string, string>
+
+// Restore trace context from a serialized envelope
+function deserializeTraceContext(headers: Record<string, string>): Con```text
+
+### Error handling
+
+```ts
+class EventsOtelError extends SuaveplanError<EventsOtelErrorCode>
+
+type EventsOtelErrorCode =
+  | "EVENTS_OTEL_ATTACH_FAILED"
+  | "EVENTS_OTEL_ALREADY_ATTACHED"
+  | "EVENTS_OTEL_PROPAGATION_FAILED"
+
+function registerEventsOtelErrorCodes(): void
+```
+
+### Zod schemas
+
+```ts
+const EventTracingOptionsSchema: ZodSchema
+const SamplingRuleSchema: ZodSchema
+```
+
+---
+
+## New additions for genesis
+
+### 1. W3C Trace Context propagation across async subscribers
+
+The interceptor captures the active `Context` at dispatch time. Each listener invocation runs with that context restored as the active context, so any nested OTel operations inside listeners are correctly parented to the dispatch span.
+
+### 2. Listener exception → span error
+
+If a listener throws, the dispatch span's status is set to `SpanStatusCode.ERROR` with the exception recorded via `span.recordException(err)`. The error is re-thrown after recording.
+
+### 3. Sampling-aware dispatch
+
+When `samplingRule` is `"rate"` or `"event-name"`, spans are only created for the matching subset. The companion checks the parent sampling decision first; if the parent is sampled, the rule is bypassed to maintain trace completeness.
+
+### 4. `serializeTraceContext` / `deserializeTraceContext`
+
+These helpers allow `@suaveplan/events-transport` to inject and extract trace context from transport envelopes, enabling cross-context trace propagation without a direct package dependency on OTel internals.
+
+### 5. Property-based tests (fast-check)
+
+- Parent-child relationship: every listener span is a child of its dispatch span
+- Context propagation under reentrancy: nested dispatches inside listeners produce correct span trees
+- Sampling rate accuracy: at sampling rate 0.5, sampled span count is within 5% of 50% over 10k dispatches
+
+---
+
+## File layout
+
+```text
+universal/events/events-otel/
+  package.json
+  tsconfig.json
+  vitest.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/
+      index.ts
+    core/
+      attach-event-tracing/
+        attach-event-tracing.ts
+        attach-event-tracing.md
+        attach-event-tracing.types.ts
+        attach-event-tracing.test.ts
+        index.ts
+    propagation/
+      trace-context/
+        trace-context.ts
+        trace-context.md
+        trace-context.test.ts
+        index.ts
+    sampling/
+      sampling-rule/
+        sampling-rule.ts
+        sampling-rule.md
+        sampling-rule.types.ts
+        sampling-rule.test.ts
+        index.ts
+  tests/
+    integration.test.ts
+    property.test.ts
+```
+
+---
+
+## Impact
+
+**Downstream packages**: `@suaveplan/events-transport` uses `serializeTraceContext`/`deserializeTraceContext` for cross-context propagation. Any application using `@suaveplan/events` with production tracing can add this companion without code changes to publishers or subscribers.
+
+**Workspace dep prerequisites**: `@suaveplan/events`, `@suaveplan/error`, `@suaveplan/types` must be published to Verdaccio.
+
+**Breaking changes**: none (new package).