signaltree-guardrails

Using @signaltree/guardrails

Dev-only enhancer — instruments every update() call, tracks hot paths, watches memory growth, runs rule registry against each change. In production builds, package exports swap to a noop via the production export condition — the enhancer call stays in source but costs zero. If bundler doesn't set production condition, guard manually: isDevMode() ? guardrails({...}) : ((t) => t).

Install (dev dependency):

npm install --save-dev @signaltree/guardrails

Peer: @signaltree/core ^9. Don't install @signaltree/shared — private workspace package; npm will fail to resolve it.

Basic — performance budget + console warnings:

import { signalTree } from '@signaltree/core';
import { guardrails } from '@signaltree/guardrails';

interface AppState {
  items: unknown[];
  ui: { search: string };
}

const tree = signalTree<AppState>({ items: [], ui: { search: '' } }).with(
  guardrails({
    mode: 'warn', // 'warn' | 'throw' | 'silent'
    budgets: {
      maxUpdateTime: 16, // ms per update
    },
    hotPaths: { enabled: true, threshold: 10, topN: 5 },
    reporting: { console: true, interval: 5000, maxIssuesPerReport: 20 },
  })
);

Memory-leak detection + intent suppression:

const tree = signalTree(initial).with(
  guardrails({
    memoryLeaks: {
      enabled: true,
      checkInterval: 5000,
      retentionThreshold: 200,
      growthRate: 0.25,
    },
    suppression: {
      autoSuppress: ['hydrate', 'reset', 'bulk', 'migration', 'time-travel', 'serialization'], // values from intent/source that silence budget warnings
      respectMetadata: true,
    },
  })
);

Valid autoSuppress values (union of intent and source channels that suppression respects): 'hydrate', 'reset', 'bulk', 'migration', 'time-travel', 'serialization'. Valid intent values on UpdateMetadata: 'user', 'system', 'hydrate', 'reset', 'bulk', 'migration'. Valid source values on UpdateMetadata: 'user', 'system', 'devtools', 'time-travel', 'serialization'.

Custom rule (rules run per changed leaf; context.path = string[], context.value = new leaf value; test returns true when rule fires):

import { guardrails, rules } from '@signaltree/guardrails';

const tree = signalTree({ ui: { when: '' } }).with(
  guardrails({
    customRules: [
      rules.noDeepNesting(6),
      rules.noSensitiveData(),
      {
        name: 'no-date-strings-in-ui',
        severity: 'warning',
        test: (context) => context.path[0] === 'ui' && typeof context.value === 'string' && /^\d{4}-\d{2}-\d{2}/.test(context.value as string),
        message: (context) => `ui path "${context.path.join('.')}" holds a date string; use Date in state.`,
      },
    ],
  })
);

Built-in rules from rules registry: rules.noDeepNesting(n), rules.noFunctionsInState(), rules.maxPayloadSize(kb), rules.noSensitiveData().

Pre-baked factory trees (@signaltree/guardrails/factories): createFeatureTree, createAngularFeatureTree, createAppShellTree (strict 4ms budget), createPerformanceTree, createTestTree (mode: 'throw'). Accept (signalTree, initial):

import { createAppShellTree } from '@signaltree/guardrails/factories';
const shell = createAppShellTree(signalTree, initial);

Use mode: 'throw' in test harnesses to fail tests on over-budget updates. Use P50/P95/P99 reporting via reporting.customReporter: (report) => fetch('/telemetry', ...).

Gotchas:

• Don't install @signaltree/shared — private package, npm resolution fails.
• maxTreeDepth counts object nesting depth, not path length. A 12-deep branch trips a maxTreeDepth: 10 budget even if rest of tree is flat.
• trackDownstream: true walks consumer computeds — more accurate, noticeably slower. Only enable when chasing re-computation cycles.
• Memory-leak checks use structuredClone when available; falls back to JSON clone (skips non-serializable values).
• Never apply in production without relying on production export condition or isDevMode() guard.