diff --git a/docs/RUNTIME_CONFIG_AUDIT.md b/docs/RUNTIME_CONFIG_AUDIT.md
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+# Runtime Configuration Auditing and Drift Detection
+
+This design introduces a system-wide runtime configuration audit layer for Utility Protocol services. The first implementation ships with the meter simulator and defines the rollout pattern for contracts, dashboards, relayers, and operational services.
+
+## Goals
+
+- Capture deterministic runtime configuration snapshots for each service.
+- Hash redacted configuration state so operators can compare services without exposing secrets.
+- Detect path-level drift between an approved baseline and current runtime state.
+- Keep critical-path audits below the 100 ms P99 target by using in-process canonicalization and SHA-256 hashing only.
+- Emit data that can be wired into monitoring, alerting, dashboards, blue-green deploys, and canary analysis.
+
+## Architecture
+
+1. **Baseline creation**: each service creates a redacted snapshot after configuration loading and stores the approved hash with deployment metadata.
+2. **Runtime audit**: services periodically compare their current effective configuration against the baseline.
+3. **Drift report**: reports include the service name, baseline hash, current hash, drift flag, path-level changes, runtime duration, and budget status.
+4. **Monitoring**: drift reports should be exported as metrics and structured logs. Alert on `driftDetected=true` or `withinBudget=false`.
+5. **Deployment safety**: blue-green and canary flows should compare baseline hashes before shifting traffic and fail the rollout if unexpected drift appears.
+
+## Security Model
+
+- Secret-like paths containing `password`, `private`, `secret`, `token`, or `key` are redacted before hashing and reporting.
+- Drift reports expose paths and redacted values, not raw credentials.
+- Baseline updates are treated as privileged operational changes and should go through the same security review as contract configuration changes.
+
+## Runbook
+
+1. Create or refresh the baseline for the target service during deployment.
+2. Verify the baseline hash is recorded in deployment metadata.
+3. Enable periodic audits and export reports to monitoring.
+4. If drift is detected, compare changed paths against the approved change record.
+5. If drift is unapproved, freeze rollout, page the service owner, and restore the approved configuration.
+6. For canaries, block promotion until drift reports remain clean for the canary analysis window.
+
+## Meter Simulator Implementation
+
+The meter simulator exposes `RuntimeConfigAuditor` from `src/runtime-config-auditor.js`. It provides:
+
+- `setBaseline(config)` to create the approved snapshot.
+- `audit(config)` to produce a drift report.
+- Deterministic hashing that is stable across object key ordering.
+- Secret redaction before hashing or reporting.
diff --git a/meter-simulator/src/runtime-config-auditor.js b/meter-simulator/src/runtime-config-auditor.js
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+++ b/meter-simulator/src/runtime-config-auditor.js
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+const crypto = require('crypto');
+
+const DEFAULT_CRITICAL_PATH_BUDGET_MS = 100;
+
+function canonicalize(value) {
+  if (Array.isArray(value)) {
+    return value.map(canonicalize);
+  }
+  if (value && typeof value === 'object') {
+    return Object.keys(value)
+      .sort()
+      .reduce((acc, key) => {
+        acc[key] = canonicalize(value[key]);
+        return acc;
+      }, {});
+  }
+  return value;
+}
+
+function stableStringify(value) {
+  return JSON.stringify(canonicalize(value));
+}
+
+function hashConfig(config) {
+  return crypto.createHash('sha256').update(stableStringify(config)).digest('hex');
+}
+
+function redactValue(key, value) {
+  if (/password|private|secret|token|key/i.test(key)) {
+    return '[REDACTED]';
+  }
+  return value;
+}
+
+function flattenConfig(config, prefix = '') {
+  if (!config || typeof config !== 'object' || Array.isArray(config)) {
+    return { [prefix || 'value']: config };
+  }
+
+  return Object.keys(config).reduce((acc, key) => {
+    const path = prefix ? `${prefix}.${key}` : key;
+    const value = config[key];
+
+    if (value && typeof value === 'object' && !Array.isArray(value)) {
+      Object.assign(acc, flattenConfig(value, path));
+    } else {
+      acc[path] = redactValue(path, value);
+    }
+
+    return acc;
+  }, {});
+}
+
+class RuntimeConfigAuditor {
+  constructor(options = {}) {
+    this.serviceName = options.serviceName || 'unknown-service';
+    this.criticalPathBudgetMs = options.criticalPathBudgetMs || DEFAULT_CRITICAL_PATH_BUDGET_MS;
+    this.baseline = null;
+  }
+
+  createSnapshot(config, observedAt = new Date()) {
+    const started = process.hrtime.bigint();
+    const redacted = flattenConfig(config);
+    const snapshot = {
+      service: this.serviceName,
+      observedAt: observedAt.toISOString(),
+      hash: hashConfig(redacted),
+      values: redacted
+    };
+    const durationMs = Number(process.hrtime.bigint() - started) / 1_000_000;
+
+    return {
+      ...snapshot,
+      durationMs,
+      withinBudget: durationMs < this.criticalPathBudgetMs
+    };
+  }
+
+  setBaseline(config, observedAt = new Date()) {
+    this.baseline = this.createSnapshot(config, observedAt);
+    return this.baseline;
+  }
+
+  audit(config, observedAt = new Date()) {
+    if (!this.baseline) {
+      throw new Error('Runtime configuration baseline has not been set');
+    }
+
+    const current = this.createSnapshot(config, observedAt);
+    const changes = diffValues(this.baseline.values, current.values);
+
+    return {
+      service: this.serviceName,
+      baselineHash: this.baseline.hash,
+      currentHash: current.hash,
+      driftDetected: changes.length > 0,
+      changes,
+      durationMs: current.durationMs,
+      withinBudget: current.withinBudget,
+      observedAt: current.observedAt
+    };
+  }
+}
+
+function diffValues(expected, actual) {
+  const keys = new Set([...Object.keys(expected), ...Object.keys(actual)]);
+  return Array.from(keys)
+    .sort()
+    .filter((key) => expected[key] !== actual[key])
+    .map((key) => ({
+      path: key,
+      expected: expected[key],
+      actual: actual[key]
+    }));
+}
+
+module.exports = {
+  RuntimeConfigAuditor,
+  DEFAULT_CRITICAL_PATH_BUDGET_MS,
+  flattenConfig,
+  hashConfig,
+  stableStringify,
+  diffValues
+};
diff --git a/meter-simulator/tests/runtime-config-auditor.test.js b/meter-simulator/tests/runtime-config-auditor.test.js
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+const {
+  RuntimeConfigAuditor,
+  diffValues,
+  flattenConfig,
+  hashConfig
+} = require('../src/runtime-config-auditor');
+
+const baseConfig = {
+  contract: {
+    network: 'testnet',
+    rpcUrl: 'https://soroban-testnet.stellar.org'
+  },
+  mqtt: {
+    host: 'localhost',
+    password: 'super-secret',
+    qos: 1
+  }
+};
+
+describe('RuntimeConfigAuditor', () => {
+  test('creates deterministic redacted hashes independent of key order', () => {
+    const reordered = {
+      mqtt: { qos: 1, password: 'super-secret', host: 'localhost' },
+      contract: { rpcUrl: 'https://soroban-testnet.stellar.org', network: 'testnet' }
+    };
+
+    expect(hashConfig(flattenConfig(baseConfig))).toBe(hashConfig(flattenConfig(reordered)));
+    expect(flattenConfig(baseConfig)['mqtt.password']).toBe('[REDACTED]');
+  });
+
+  test('detects runtime configuration drift with path-level changes', () => {
+    const auditor = new RuntimeConfigAuditor({ serviceName: 'meter-simulator' });
+    auditor.setBaseline(baseConfig, new Date('2026-07-17T00:00:00.000Z'));
+
+    const report = auditor.audit({
+      ...baseConfig,
+      mqtt: { ...baseConfig.mqtt, qos: 2 }
+    }, new Date('2026-07-17T00:01:00.000Z'));
+
+    expect(report.driftDetected).toBe(true);
+    expect(report.changes).toEqual([
+      { path: 'mqtt.qos', expected: 1, actual: 2 }
+    ]);
+    expect(report.withinBudget).toBe(true);
+  });
+
+  test('reports no drift for unchanged effective configuration', () => {
+    const auditor = new RuntimeConfigAuditor({ serviceName: 'meter-simulator' });
+    auditor.setBaseline(baseConfig);
+
+    const report = auditor.audit({ ...baseConfig });
+
+    expect(report.driftDetected).toBe(false);
+    expect(report.changes).toEqual([]);
+  });
+
+  test('diffValues reports additions and removals', () => {
+    expect(diffValues({ a: 1, b: 2 }, { b: 2, c: 3 })).toEqual([
+      { path: 'a', expected: 1, actual: undefined },
+      { path: 'c', expected: undefined, actual: 3 }
+    ]);
+  });
+});