diff --git a/app/vitest.config.tools.mjs b/app/vitest.config.tools.mjs
new file mode 100644
index 00000000..796ba059
--- /dev/null
+++ b/app/vitest.config.tools.mjs
@@ -0,0 +1,12 @@
+import { defineConfig } from 'vitest/config';
+
+// Minimal Vitest config for tools/*.test.mjs (Node environment, no Vue/DOM).
+// Separate from vitest.config.ts which targets tests/Frontend/**/*.ts.
+// Run from repo root: node app/node_modules/vitest/vitest.mjs --config app/vitest.config.tools.mjs run
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: 'node',
+    include: ['../tools/observer-pii-filter.test.mjs'],
+  },
+});
diff --git a/tools/observer-pii-filter.mjs b/tools/observer-pii-filter.mjs
new file mode 100644
index 00000000..9205287e
--- /dev/null
+++ b/tools/observer-pii-filter.mjs
@@ -0,0 +1,41 @@
+/**
+ * PII filter for brain governance observer (B2).
+ * Used by Stop-hook before JSONL write — per Pravila §16.2 + ADR-011 + spec §5.4.
+ *
+ * Patterns covered:
+ *   RU_PHONE      — +7XXXXXXXXXX (10 digits after +7)
+ *   EMAIL         — any user@domain.tld
+ *   SENTRY_TOKEN  — sntrys?_<12+ alphanum>
+ *   OPENAI_TOKEN  — sk-<20+ alphanum>
+ *   GENERIC_BEARER — Bearer <20+ token chars>
+ *
+ * Security Guidance #40: pure regex — no exec/execSync.
+ */
+
+const RU_PHONE = /\+7\d{10}/g;
+const EMAIL = /[\w.+-]+@[\w-]+\.[\w.-]+/g;
+const SENTRY_TOKEN = /sntrys?_[A-Za-z0-9]{12,}/g;
+const OPENAI_TOKEN = /sk-[A-Za-z0-9]{20,}/g;
+const GENERIC_BEARER = /Bearer\s+[A-Za-z0-9._-]{20,}/g;
+
+function sanitizeString(s) {
+  if (typeof s !== 'string') return s;
+  return s
+    .replace(RU_PHONE, '+7XXXXXXXXXX')
+    .replace(EMAIL, '***@***')
+    .replace(SENTRY_TOKEN, '[REDACTED:sentry]')
+    .replace(OPENAI_TOKEN, '[REDACTED:openai]')
+    .replace(GENERIC_BEARER, '[REDACTED:bearer]');
+}
+
+export function sanitize(input) {
+  if (typeof input === 'string') return sanitizeString(input);
+  if (input === null || input === undefined) return input;
+  if (Array.isArray(input)) return input.map(sanitize);
+  if (typeof input === 'object') {
+    const out = {};
+    for (const [k, v] of Object.entries(input)) out[k] = sanitize(v);
+    return out;
+  }
+  return input;
+}
diff --git a/tools/observer-pii-filter.test.mjs b/tools/observer-pii-filter.test.mjs
new file mode 100644
index 00000000..edb00c9b
--- /dev/null
+++ b/tools/observer-pii-filter.test.mjs
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+import { describe, it, expect } from 'vitest';
+import { sanitize } from './observer-pii-filter.mjs';
+
+describe('observer-pii-filter sanitize', () => {
+  it('masks Russian phone numbers', () => {
+    const input = 'Контакт: +79991234567 — позвонить';
+    expect(sanitize(input)).toBe('Контакт: +7XXXXXXXXXX — позвонить');
+  });
+
+  it('masks email addresses', () => {
+    const input = 'Mail: kpd9363@gmail.com';
+    expect(sanitize(input)).toBe('Mail: ***@***');
+  });
+
+  it('masks Sentry-style tokens', () => {
+    const input = 'token sntrys_abc123def456ghi789';
+    expect(sanitize(input)).toContain('[REDACTED');
+    expect(sanitize(input)).not.toContain('sntrys_abc123def456ghi789');
+  });
+
+  it('is idempotent on already-sanitized strings', () => {
+    const sanitized = 'Контакт: +7XXXXXXXXXX, ***@***';
+    expect(sanitize(sanitized)).toBe(sanitized);
+  });
+
+  it('handles empty string', () => {
+    expect(sanitize('')).toBe('');
+  });
+
+  it('handles object input by sanitizing string fields recursively', () => {
+    const input = { task_id: 'x', note: 'call +79991234567' };
+    const out = sanitize(input);
+    expect(out.note).toBe('call +7XXXXXXXXXX');
+    expect(out.task_id).toBe('x');
+  });
+});