Inspect an AI Agent Run Without Paying for Logs You'll Never Read — Telemetry Shouldn't Be Your Second Biggest Bill

Last time we put hard budgets on cost and guaranteed cleanup. This time we make sure you can inspect an agent run without making telemetry volume the default cost center.

Take a real number. An agent does 200 tool calls per run. Each tool emits 5 events. That's 1,000 events per run. 100K runs/day = 100 million events/day.

At CloudWatch Logs ingestion ($0.50/GB) with 500-byte structured JSON, that is roughly $9,125/year of telemetry that may not be needed on successful runs. Datadog APM, Application Insights, and Honeycomb have different pricing models, but the engineering issue is the same: unbounded event volume turns observability into a cost surface.

WorkIt's core has zero networking imports.

$ grep -E "node:http|node:https|fetch" dist/index.js

That's not a feature claim. That's a gate.

Bench 15-core-zero-network.mjs. Walks the published dist/ tree (excluding the explicit observability, otel, and worker subpaths), greps every .js/.cjs/.mjs for node:http, node:https, raw http/https imports, and fetch(...).

Metric	Result
Files scanned	14
Forbidden imports found	0
Excluded subpaths	observability, otel, worker
assert.equal(hits.length, 0)	passed

If a PR adds a networking import to core, the production gate npm run check:no-network fails. The bench above verifies the same property in the artifact a consumer installs from npm.

Layer 1: Local-first by default (cost: $0)

import { run, renderTree } from "@workit/core";

const result = await run.scope(async (scope) => {
  // your agent code
  console.log(renderTree(scope.status()));
  return await doWork(scope);
});

Zero network calls. Zero log lines. Zero telemetry export cost. scope.status() returns a snapshot. renderTree(...) prints an ASCII tree. That is the built-in observability surface; exporters are opt-in.

When you do want telemetry, you opt in:

import { attachTelemetryExporter } from "@workit/core/observability";

const attachment = attachTelemetryExporter(scope, async (event) => {
  await otlp.write(event);
}, {
  sampling:       { mode: "errors_and_slow", slowThresholdMs: 2_000 },
  circuitBreaker: { failureThreshold: 3, openForMs: 60_000 },
  sanitize:       (event) => stripPII(event),
});

Four words: sampled, aggregated, budgeted, circuit-broken.

Layer 2 — Sampling: errors_and_slow is the production default

Same workload, same agent. With errors_and_slow (slow threshold 2 seconds) and 95% of runs completing fast and successful:

The intended debugging signal is preserved for slow and failing runs. A passing run rarely needs full trace inspection -- you need it when something breaks or hangs, which is exactly what this policy keeps.

Bench 16-sampling-and-aggregation.mjs. 100 root scopes x 5 child tasks each. 5% slow, 2% errored. Both modes attach attachTelemetryExporter to the same workload.

sampling.mode	Exported events	Reduction factor
"all"	1,300	baseline
"errors_and_slow" (slowThresholdMs: 55)	36	~36x

The bench asserts >= 5x to stay tolerant of jitter. The measured ratio came out higher than the article's nominal 20x because the synthetic workload concentrates slow/errored scopes; the savings table above uses the conservative ratio.

Sampling modes — how to choose:

A child scope cannot upgrade itself to "kept" if its root was sampled out. This is the rule that keeps traces causally intact.

Layer 3 — Aggregation, not enumeration

By default, an aggregated exporter receives one summary record per scope, not per task:

interface ScopeSummary {
  scopeId: string;
  parentId: string | null;
  durationMs: number;
  outcome: "completed" | "errored" | "cancelled";
  taskCounts: {
    started: number; succeeded: number; failed: number;
    cancelled: number; retried: number; cleanupFailed: number;
  };
  droppedTelemetryEvents: number;
}

200 tasks succeed -> 1 summary record exported. Not 200. Not 1,000.

import { attachScopeSummaryExporter } from "@workit/core/observability";

attachScopeSummaryExporter(scope, async (summary) => {
  await otlp.writeAggregate(summary);
}, { /* same circuit breaker / queue / sampling options */ });

The summary aggregator is exercised end-to-end by npm run check:exporter-stress -- 100,000 events with bounded queue and drop-front under back-pressure. The bench in this folder skips the summary path on purpose: attachScopeSummaryExporter needs the scope:opened event, which fires before user code can attach inside run.scope. Companion packages wire it earlier; the production gate covers it.

Layer 4 — Telemetry budget (the safety net)

import { TelemetryBudget, run } from "@workit/core";

await run.context.with(
  TelemetryBudget,
  { spent: 0, limit: 100_000, unit: "events" },
  () => agentRun(),
);

The exporter checks the budget before emitting each event. When a scope's event count would exceed the limit, the event is dropped silently. The first overrun emits one warning. Subsequent overruns are counted into the next scope summary's droppedTelemetryEvents field. Tasks continue executing normally.

Telemetry overrun must never affect application behaviour. The companion withOTel wrap sets a default budget at the wrap-call boundary, so the floor is opt-out, not opt-in.

Cardinality Discipline And Cost Control

Every exported field is classified bounded or unbounded. Unbounded fields are never emitted as metric labels.

Wrap your metric exporter with createCardinalitySafeMetricExporter and pass an allowedLabels allow-list -- anything outside is rejected at runtime.

Bench 17-cardinality-safe-metrics.mjs. Five candidate metric points, allow-list ["task.kind", "outcome", "scope.name"].

Point	Labels	Outcome
1	{ "task.kind": "io", "outcome": "succeeded" }	yes emitted
2	{ "task.kind": "llm", "outcome": "failed" }	yes emitted
3	{ "task.kind": "tool", "task.id": "uuid-abc" }	no rejected -- Metric label "task.id" is not in the allowed label set
4	{ "task.kind": "io", "error.message": "EHOSTUNREACH at 10.0.0.42 retrying" }	no rejected -- Metric label "error.message" is not in the allowed label set
5	{ "task.kind": "evil" }	yes emitted (label-key check only -- out-of-enum value validation is the OTel-adapter's job)

The wrapper rejects unbounded label keys at runtime. Out-of-enum value rejection (taskKind: "evil" failing in OTel) is enforced by the adapter contract, while the wrapper keeps cardinality control at the label-key boundary.

Correct usage:

task(() => fetch(url),       { kind: "io" });     // yes
task(() => llm.call(prompt), { kind: "llm" });    // yes
task(() => runTool(input),   { kind: "tool" });   // yes
task(() => heavyCalc(),      { kind: "cpu" });    // yes
task(() => custom(),         { kind: "custom" }); // yes

Exporter circuit breaker -- the OOM defence

{
  circuitBreaker: { failureThreshold: 10, openForMs: 5 * 60_000 },
  queue:          { maxItems: 10_000, maxBytes: 10 * 1024 * 1024 },
}

OTLP backend goes down. The exporter sees N consecutive failures -> opens for openForMs -> events drop (counted, not queued). The bounded queue uses drop-front when full, so you keep the most recent context. After openForMs elapses -> half-open -> trial export -> close on success.

Result: process memory growth bounded under 50 MB through 1,000 scopes against a backend that returns 503 for every request. Tracked under tests/perf/exporter-failure.test.ts. This is the feature that prevents the most embarrassing observability incident -- the telemetry agent eating all process memory because the backend is unreachable. Datadog had this. New Relic had this. We design it out.

scope.tree() — the print statement for agents

agent-run
|- ok planLLM (243ms)
|- retry fetchTool (attempt 2/3)
|  `- [running] retry-delay (120ms)
|- [running] summarize (running, 45% -- "embedding chunks")
`- failed auditLog (TimeoutError)

5 tasks * 1 ok * 1 failed * 2 running * 1 retrying * deadline in 12s

Print this when something breaks. Print this in your test runner. Print this from a SIGUSR1 dump.

import { renderTree } from "@workit/core";
console.log(renderTree(scope.status()));

Progress is a typed event, not a log line

Inside any task body, ctx.report({ pct, message, data }) emits a typed task:progress event tagged with the task's stable id and name. Your exporter, your dashboard, your test assertion all pivot on the same shape. No console.log. No string parsing. No grep.

// samples/progress-parallel.sample.js
const TARGET = "embed.batch.7";

await run.scope(async (scope) => {
  scope.onEvent((event) => {
    if (event.type === "task:progress" && taskNames.get(event.taskId) === TARGET) {
      targetProgress.push({ pct: event.pct, message: event.message });
    }
  });

  const handles = Array.from({ length: 16 }, (_, i) => scope.spawn(async (ctx) => {
    if (i === 7) {
      for (const step of [1, 2, 3, 4]) {
        ctx.report({ pct: step / 4, message: `chunk-${step}` });
        await sleep(1, ctx.signal);
      }
    } else { await sleep(8, ctx.signal); }
  }, { name: `embed.batch.${i}`, kind: "llm" }));

  return await Promise.all(handles);
});

// Asserted by the sample:
//   targetProgress.map(e => e.pct) === [0.25, 0.5, 0.75, 1]
//   maxActive === 16

16 parallel embeddings. One of them is embed.batch.7. We filter the event stream to that task's id and watch the progress sequence land -- [0.25, 0.5, 0.75, 1], with the messages chunk-1..chunk-4 attached. The other 15 siblings run concurrently and don't interleave their reports into our channel because every event carries the typed taskId.

npm run sample:progress

That's the difference between "tail the log file and hope" and "subscribe to a typed event stream and pivot on the shape that the type system already validated."

Snapshots: the stable view of a live runtime

The hot runtime exposes stable snapshots, not live references. Pull one whenever you need to inspect -- the engine doesn't mutate it, you can hand it to anything (logger, diagnostics, test assertion, JSON wire).

import type { ScopeSnapshot, TaskSnapshot } from "@workit/core";

const snapshot: ScopeSnapshot = scope.status();

interface ScopeSnapshot {
  id: ScopeId;
  name: string;
  status: "running" | "cancelling" | "closed";
  startedAt: number;
  deadlineAt: number;
  pendingCount: number;
  completedCount: number;
  failedCount: number;
  cancelledCount: number;
  tasks:  TaskSnapshot[];     // every task currently owned by this scope
  scopes: ScopeSnapshot[];    // every child scope, recursively
}

interface TaskSnapshot {
  id: TaskId;
  name: string;
  kind: TaskKind;             // "io" | "llm" | "tool" | "cpu" | "custom"
  status: "pending" | "running" | "succeeded" | "failed" | "cancelled";
  attempt: number;
  startedAt: number;
  durationMs: number;
  progress: ProgressReport;
  meta: Record<string, unknown>;
}

Three properties matter:

• Snapshot is immutable -- taking one twice gives you two independent objects. The runtime never mutates one you already hold.
• Snapshot is recursive -- scopes is the same shape as the root, all the way down. Tools that walk it (the diagnoser, the renderer, your test assertions) share one shape.
• Snapshot is the only public surface -- renderTree consumes it, diagnoseSnapshot consumes it, you consume it. The hot runtime owns the live state; rich tooling lives outside core.

That's the architectural boundary that keeps core small. Anything that wants to inspect the runtime asks for a snapshot.

@workit/core/diagnostics -- the stuck-task detector

import { diagnoseSnapshot } from "@workit/core/diagnostics";

const report = diagnoseSnapshot(scope.status(), {
  staleTaskMs: 30_000,
  events:      recentEvents,
});

if (report.findings.length > 0) {
  console.warn("agent stalled:", report.findings);
}

Diagnoses live, on demand, against an existing snapshot. Subpath-only so the root runtime stays small.

Bench 18-diagnostics-finding-codes.mjs. Five hand-crafted snapshots, one per finding code.

Scenario	report.status	Finding codes emitted
Healthy snapshot	ok	(none)
Task running > 30 s	needs_attention	old_pending_task
Scope status cancelling	needs_attention	scope_cancelling
Pending child scope	needs_attention	pending_child_scope + recursive old_pending_task
task:cleanup_timeout event in window	needs_attention	cleanup_timeout

Wire it to a SIGUSR1 handler in production:

process.on("SIGUSR1", () => {
  console.error(renderTree(rootScope.status()));
  console.error(JSON.stringify(diagnoseSnapshot(rootScope.status(), { staleTaskMs: 30_000 }), null, 2));
});

Something hangs at 3 a.m. -> one signal gives you the live tree and a list of suspicious tasks. No APM. No external service. Stderr.

OpenTelemetry -- opt-in, with optional peer

import { attachOpenTelemetry } from "@workit/core/otel";

const detach = attachOpenTelemetry(scope, { tracer, meter });

@opentelemetry/api is an optional peer. The root WorkIt package stays at zero runtime dependencies. Install OTel only when you need it:

npm install @opentelemetry/api

If the peer is missing, attachOpenTelemetry throws a message that names exactly the install command -- no cryptic "cannot resolve module" trace.

Three canonical configurations

// Local development -- default. No setup needed.
await run.scope(async (scope) => { /* ... */ });
// Inspect: console.log(renderTree(scope.status()))

// Production -- sampled, aggregated, budgeted, circuit-broken.
await withOTel(
  {
    exporter:       otlpExporter,
    sampling:       { mode: "errors_and_slow", slowThresholdMs: 2_000 },
    aggregation:    "per_scope",
    eventBudget:    50_000,
    redact:         ["context.user.email"],
    circuitBreaker: { failureThreshold: 10, openForMs: 300_000 },
  },
  () => agentRun(),
);
// Typical bill, 100K runs/day: ~$456/year.

// Full trace debugging: one-off, manual, full event stream.
await withOTel(
  { exporter: otlpExporter, sampling: { mode: "all" }, aggregation: "per_task" },
  () => problemReproduction(),
);

Receipts

node benchmarks/articles/15-core-zero-network.mjs       # 0 hits in 14 dist files
node benchmarks/articles/16-sampling-and-aggregation.mjs # 1,300 -> 36 events
node benchmarks/articles/17-cardinality-safe-metrics.mjs # 2 of 5 unbounded labels rejected
node benchmarks/articles/18-diagnostics-finding-codes.mjs # 4 finding codes proven
node benchmarks/articles/run-all.mjs                    # full article suite

Production-side gates that back the same surface:

What's coming

You now have an agent that holds itself to a budget, releases its connections, and tells you what's happening inside without sending a byte to the cloud unless you ask.

Tomorrow: the final article. Agent scopes and tool lifecycles.

The same ownership tree that cancels streams and bounds observability also
governs agent tool calls, token budgets, progress events, and replayable
execution logs. The point is not a new agent framework; it is one lifecycle
contract for the agent loop and the rest of the application.

Source, Benchmarks, And Evidence

• Source: https://github.com/WorkRuntime/workit
• NPM: https://www.npmjs.com/package/@workit/core
• Article source: https://github.com/WorkRuntime/workit/blob/main/articles/06-observability-without-core-bloat.md
• Reproduce: npm run bench:articles and npm run test:evidence