@earendil-works/pi-telemetry

Vendor-neutral telemetry contracts and typed schema utilities for pi packages.

This package provides:

• an explicit, callback-based TelemetryContext / TelemetrySpan contract;
• a shared NOOP_TELEMETRY_CONTEXT;
• a reference InMemoryTelemetryContext implementation;
• serializable schema definitions with inferred TypeScript types;
• no exporter, global current-span state, or dependency on a telemetry backend.

Applications can use the in-memory reference or provide an adapter for OpenTelemetry, Sentry, logs, or another backend. Pi packages pass telemetry contexts explicitly and define their domain schemas separately.

Table of Contents

• Installation
• Telemetry Concepts
• Core Context API
• Adapter Contract
• No-op Context
• In-Memory Reference Adapter
• Adapter Conformance
• Typed Schemas
  • Start and Completion Attributes
• Schema Metadata
• Pi Package Integration
• Security and Portability
• API Reference
• Development
• License

Installation

npm install @earendil-works/pi-telemetry

Telemetry Concepts

Telemetry describes what a program did while it was running. This package models that work using spans, attributes, events, statuses, and explicit context:

For example, loading an account could produce this telemetry:

example.account.load                         span
├─ attributes: account.id=123, found=true   facts about the span
├─ event: example.cache.lookup              occurrence during the span
│  └─ attribute: cache.hit=false            fact about the event
└─ status: ok                               final outcome

A span is diagnostic data, not business state. Recording it must not change whether the account load runs, succeeds, fails, or is persisted. An adapter translates these generic concepts into the corresponding concepts used by OpenTelemetry, Sentry, logs, or another backend.

Core Context API

A TelemetryContext starts a span around a callback. The callback receives a TelemetrySpan, which is also the explicit parent context for child spans.

import {
  NOOP_TELEMETRY_CONTEXT,
  type TelemetryContext,
} from '@earendil-works/pi-telemetry';

async function loadAccount(
  accountId: string,
  telemetryContext: TelemetryContext = NOOP_TELEMETRY_CONTEXT,
) {
  return telemetryContext.startSpan(
    {
      name: 'example.account.load',
      attributes: { 'example.account.id': accountId },
    },
    async (span) => {
      const account = await readAccount(accountId);
      span.setAttributes({ 'example.account.found': account !== undefined });
      return account;
    },
  );
}

Pass the callback span to lower-level work to create explicit nesting:

return telemetryContext.startSpan({ name: 'example.parent' }, async (parentSpan) => {
  return parentSpan.startSpan({ name: 'example.child' }, async (childSpan) => {
    childSpan.addEvent('example.cache.lookup', { 'example.cache.hit': true });
    return performWork();
  });
});

There is no public end() method. startSpan() owns settlement and keeps the span open until the callback's value or promise settles. For an expected failure represented by a normal return value, set the status explicitly:

return telemetryContext.startSpan({ name: 'example.save' }, async (span) => {
  const result = await save();
  if (!result.ok) {
    span.setStatus({
      status: 'error',
      error: { name: 'SaveError', message: result.reason },
    });
  }
  return result;
});

Adapter Contract

An adapter implements TelemetryContext and bridges the generic API to its backend. It must:

• create a child span and invoke the callback synchronously, exactly once;
• preserve the callback's returned value and rejection value, returning a promise rejected with the same value after a synchronous throw;
• keep the native span open until a returned promise settles;
• treat normal completion as ok and throws/rejections as errors unless an explicit status was set;
• make repeated setStatus() calls last-write-wins;
• merge setAttributes() calls, with later defined values replacing earlier values and undefined ignored;
• make recording methods synchronous, passive, and non-throwing;
• ignore calls made after settlement;
• ignore a failed recording call atomically, suppress backend failures, and still execute the business callback exactly once.

Adapters may activate backend-native ambient context internally for automatic instrumentation, but pi code always propagates the parent through TelemetryContext arguments. Exporter buffering, flushing, sampling, backend IDs, and backend-specific context objects belong to the adapter. Use the adapter conformance suite to check these observable semantics.

No-op Context

Use NOOP_TELEMETRY_CONTEXT when telemetry is optional:

import { NOOP_TELEMETRY_CONTEXT } from '@earendil-works/pi-telemetry';

const result = await NOOP_TELEMETRY_CONTEXT.startSpan(
  { name: 'example.operation' },
  () => runOperation(),
);

The no-op context:

• invokes callbacks synchronously;
• preserves returned values and asynchronous rejections, and converts a synchronous throw to a promise rejected with the same value;
• uses one shared frozen inert span, including for nested spans;
• does not inspect or retain names, attributes, events, or statuses.

In-Memory Reference Adapter

InMemoryTelemetryContext is the backend-neutral reference implementation. It is useful for tests, local diagnostics, and applications that intentionally want process-local capture without an exporter:

import { InMemoryTelemetryContext } from '@earendil-works/pi-telemetry';

const telemetry = new InMemoryTelemetryContext();

await telemetry.startSpan(
  { name: 'example.operation', attributes: { input: 'demo' } },
  async (span) => {
    span.addEvent('example.started');
    span.setAttributes({ output_count: 3 });
  },
);

console.log(telemetry.getSpans());

getSpans() returns detached snapshots in span-start order. Each RecordedTelemetrySpan contains a deterministic numeric ID, parent ID, merged attributes, ordered events, final status, settlement state, and deterministic end sequence. It records no timestamps.

The adapter is safe to use as an ordinary TelemetryContext, but storage is unbounded and process-local. Create a fresh instance to isolate tests or recording scopes, and do not capture sensitive attributes unless the caller's data policy allows them.

Adapter Conformance

@earendil-works/pi-telemetry/testing exports a runner-independent conformance suite modeled as grouped cases. A fixture supplies a fresh context and converts its backend's finished spans into normalized RecordedTelemetrySpan snapshots:

import {
  createTelemetryAdapterConformance,
  type TelemetryAdapterFixture,
} from '@earendil-works/pi-telemetry/testing';
import { describe, it } from 'vitest';

const conformance = createTelemetryAdapterConformance(async () => {
  const adapter = createMyTelemetryAdapter();
  return {
    context: adapter.context,
    getSpans: async () => adapter.normalizedSpans(),
    async [Symbol.asyncDispose]() {
      await adapter.close();
    },
  } satisfies TelemetryAdapterFixture;
});

for (const group of new Set(conformance.map((testCase) => testCase.group))) {
  describe(group, () => {
    for (const testCase of conformance.filter((candidate) => candidate.group === group)) {
      it(testCase.name, () => testCase.run());
    }
  });
}

The suite checks synchronous single admission, result and rejection identity, automatic and explicit status, attribute merging, event ordering, inert post-settlement calls, nested and concurrent parentage, and suppression of unreadable telemetry payload failures. getSpans() may flush an asynchronous exporter before returning. The testing subpath uses Node's assertion APIs; the root telemetry package remains runtime-neutral.

Typed Schemas

The low-level span API intentionally accepts open names and attribute bags so adapters remain generic. Domain packages can define closed, serializable schemas and infer exact TypeScript types from them.

import {
  createTypedSpanStarter,
  defineTelemetrySchema,
} from '@earendil-works/pi-telemetry';

export const EXAMPLE_TELEMETRY_SCHEMA = defineTelemetrySchema({
  version: 1,
  spans: {
    'example.read': {
      description: 'Read one resource',
      parents: { kind: 'any' },
      startAttributes: {
        'example.resource': {
          type: 'string',
          required: true,
          values: ['account', 'project'],
          description: 'Resource kind',
        },
      },
      endAttributes: {
        'example.item_count': {
          type: 'number',
          description: 'Number of returned items',
        },
      },
      events: {
        'example.cache': {
          description: 'Cache lookup result',
          attributes: {
            'example.cache.hit': {
              type: 'boolean',
              required: true,
              description: 'Whether the cache contained the resource',
            },
          },
        },
      },
      status: {
        default: 'ok',
        errorWhen: 'The read throws or returns an error result',
      },
    },
  },
} as const);

const startSpan = createTypedSpanStarter(
  telemetryContext,
  [EXAMPLE_TELEMETRY_SCHEMA],
);

The starter exposes one overload per span and checks names and attributes at compile time. Union-valued names must be narrowed before a call, preserving the relationship between each runtime name and its attribute schema. Its callback receives a child starter over the same schemas, already bound to the callback span:

await startSpan(
  'example.read',
  { 'example.resource': 'account' },
  async (span, startChildSpan) => {
    span.addEvent('example.cache', { 'example.cache.hit': true });
    const accounts = await readAccounts();
    span.setAttributes({ 'example.item_count': accounts.length });

    await startChildSpan(
      'example.read',
      { 'example.resource': 'project' },
      async (childSpan) => {
        const projects = await readProjects();
        childSpan.setAttributes({ 'example.item_count': projects.length });
      },
    );

    return accounts;
  },
);

Start and Completion Attributes

startAttributes and endAttributes describe when an attribute is normally known, not separate runtime storage:

Both sets become ordinary attributes on the same backend span. There is no separate end-attribute payload or end callback. In the preceding example, example.resource is known when example.read starts, while example.item_count is known only after readAccounts() returns:

await startSpan(
  'example.read',
  { 'example.resource': 'account' }, // required start attribute
  async (span) => {
    const accounts = await readAccounts();
    span.setAttributes({
      'example.item_count': accounts.length, // optional completion attribute
    });
    return accounts;
  },
); // resolving the callback settles the span

“End” means completion enrichment: an end attribute may be set at any point while the callback is active, and it may be omitted when unavailable. Calling setAttributes() zero times is valid. This matters for early failures, cancellation, and provider-specific data that may not exist on every path.

Repeated setAttributes() calls merge into the same attribute bag. A later defined value replaces an earlier value for the same key, while undefined is ignored. The schema-scoped method accepts only the current span's declared end attributes.

Attributes do not end the span. Returning, resolving, throwing, or rejecting from the callback controls settlement; startSpan() performs the actual end operation. Adapter calls made after settlement are inert.

A starter can compose multiple independently versioned schemas:

import { AGENT_TELEMETRY_SCHEMAS } from '@earendil-works/pi-agent-core';

const startAgentSpan = createTypedSpanStarter(
  telemetryContext,
  AGENT_TELEMETRY_SCHEMAS,
);

Inline schema arrays retain their tuple types automatically. Separately declared arrays should use as const. Literal duplicate span names across the array are rejected at compile time; schemas are not merged, inspected, or retained at runtime.

Schema-derived types reject missing required attributes, unknown keys, invalid closed-set values, undeclared events, and attributes on empty schemas. End attributes are always optional enrichment; the type system does not require setAttributes() to be called.

defineTelemetrySchema() is a typed identity function. It returns ordinary JSON-serializable data and performs no runtime validation or parent-rule enforcement.

Schema Metadata

Supported attribute types are:

• string, number, and boolean;
• string[], number[], and boolean[].

Attribute definitions support:

• values: a closed set for scalar values;
• elementValues: a closed set for array elements;
• examples: documentation examples;
• sensitive: marks data requiring special handling;
• cardinality: records expected low or high cardinality.

Start and event attributes declare required. End attributes do not; see Start and Completion Attributes.

Parent metadata is descriptive schema data:

• { kind: 'any' }: root or any caller span;
• { kind: 'root_or_external' }: root or a caller-owned span outside the schema;
• { kind: 'spans', spans: [...] }: only the listed schema spans.

Adapters do not need to understand schema objects. Instrumentation helpers and tests use them to keep emitted names and attributes consistent.

Pi Package Integration

Package ownership is intentionally split:

• @earendil-works/pi-telemetry owns the vendor-neutral contract, no-op and in-memory reference contexts, schema utilities, and adapter conformance suite;
• @earendil-works/pi-ai accepts and propagates telemetryContext in provider request options but owns no telemetry schema;
• @earendil-works/pi-agent-core owns and exports the pi AI-request and harness schemas, their combined readonly schema tuple, and typed span helpers.

import {
  AGENT_TELEMETRY_SCHEMAS,
  AI_TELEMETRY_SCHEMA,
  HARNESS_TELEMETRY_SCHEMA,
  startAiSpan,
  startHarnessSpan,
} from '@earendil-works/pi-agent-core';

The pi schemas use pi-owned pi.ai.*, pi.harness.*, and pi.session.* names. Adapters may translate them to backend conventions without changing the emitted pi vocabulary.

Security and Portability

Telemetry is process-local diagnostics, not durable application state. Do not persist a TelemetryContext, TelemetrySpan, or backend-native trace object in records, messages, snapshots, or deferred handles.

Attribute values are intentionally limited to primitive scalars and arrays. Domain instrumentation should avoid prompts, completions, tool arguments or output, file contents, provider payloads, headers, credentials, and free-form error details unless its schema and data policy explicitly allow them.

The package does not use AsyncLocalStorage or another runtime-specific ambient context API. It is suitable for Node.js, Bun, browsers, and workers; backend adapters remain responsible for their own runtime compatibility.

API Reference

Core types and values

Schema definitions and inference

Testing subpath

Development

From this package directory:

npm test
npm run build

Repository-wide type checking, formatting, linting, and smoke checks run with:

npm run check

License

MIT