diff --git a/tests/test_sec_006.py b/tests/test_sec_006.py
new file mode 100644
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--- /dev/null
+++ b/tests/test_sec_006.py
@@ -0,0 +1,329 @@
+"""
+Tests for BATON-SEC-006: Персистентное хранение rate-limit счётчиков.
+
+Acceptance criteria:
+1. Счётчики сохраняются между пересозданием экземпляра приложения (симуляция рестарта).
+2. TTL-очистка корректно сбрасывает устаревшие записи после истечения окна.
+3. Превышение лимита возвращает HTTP 429.
+4. X-Real-IP и X-Forwarded-For корректно парсятся для подсчёта.
+
+UUID note: All UUIDs below satisfy the v4 pattern validated since BATON-SEC-005.
+"""
+from __future__ import annotations
+
+import os
+
+os.environ.setdefault("BOT_TOKEN", "test-bot-token")
+os.environ.setdefault("CHAT_ID", "-1001234567890")
+os.environ.setdefault("WEBHOOK_SECRET", "test-webhook-secret")
+os.environ.setdefault("WEBHOOK_URL", "https://example.com/api/webhook/telegram")
+os.environ.setdefault("FRONTEND_ORIGIN", "http://localhost:3000")
+os.environ.setdefault("ADMIN_TOKEN", "test-admin-token")
+
+import tempfile
+import unittest.mock as mock
+
+import aiosqlite
+import pytest
+
+from backend import config, db
+from tests.conftest import make_app_client
+
+# ── Valid UUID v4 constants ──────────────────────────────────────────────────
+
+_UUID_XREALIP_A = "c0000001-0000-4000-8000-000000000001"  # X-Real-IP exhaustion
+_UUID_XREALIP_B = "c0000002-0000-4000-8000-000000000002"  # IP-B (independent counter)
+_UUID_XFWD      = "c0000003-0000-4000-8000-000000000003"  # X-Forwarded-For test
+_UUID_REG_RL    = "c0000004-0000-4000-8000-000000000004"  # register 429 test
+
+
+# ── Helpers ──────────────────────────────────────────────────────────────────
+
+
+def _tmpdb() -> str:
+    """Set config.DB_PATH to a fresh temp file and return the path."""
+    path = tempfile.mktemp(suffix=".db")
+    config.DB_PATH = path
+    return path
+
+
+def _cleanup(path: str) -> None:
+    for ext in ("", "-wal", "-shm"):
+        try:
+            os.unlink(path + ext)
+        except FileNotFoundError:
+            pass
+
+
+# ── Criterion 1: Persistence across restart ───────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_rate_limits_table_created_by_init_db():
+    """init_db() creates the rate_limits table in SQLite."""
+    path = _tmpdb()
+    try:
+        await db.init_db()
+        async with aiosqlite.connect(path) as conn:
+            async with conn.execute(
+                "SELECT name FROM sqlite_master WHERE type='table' AND name='rate_limits'"
+            ) as cur:
+                row = await cur.fetchone()
+        assert row is not None, "rate_limits table not found after init_db()"
+    finally:
+        _cleanup(path)
+
+
+@pytest.mark.asyncio
+async def test_rate_limit_counter_persists_after_db_reinit():
+    """Counter survives re-initialization of the DB (simulates app restart).
+
+    Before: in-memory app.state.rate_counters was lost on restart.
+    After: SQLite-backed rate_limits table persists across init_db() calls.
+    """
+    path = _tmpdb()
+    try:
+        await db.init_db()
+
+        c1 = await db.rate_limit_increment("persist:test", 600)
+        c2 = await db.rate_limit_increment("persist:test", 600)
+        c3 = await db.rate_limit_increment("persist:test", 600)
+        assert c3 == 3, f"Expected 3 after 3 increments, got {c3}"
+
+        # Simulate restart: re-initialize DB against the same file
+        await db.init_db()
+
+        # Counter must continue from 3, not reset to 0
+        c4 = await db.rate_limit_increment("persist:test", 600)
+        assert c4 == 4, (
+            f"Expected 4 after reinit + 1 more increment (counter must persist), got {c4}"
+        )
+    finally:
+        _cleanup(path)
+
+
+@pytest.mark.asyncio
+async def test_rate_limit_increment_returns_sequential_counts():
+    """rate_limit_increment returns 1, 2, 3 on successive calls within window."""
+    path = _tmpdb()
+    try:
+        await db.init_db()
+        c1 = await db.rate_limit_increment("seq:test", 600)
+        c2 = await db.rate_limit_increment("seq:test", 600)
+        c3 = await db.rate_limit_increment("seq:test", 600)
+        assert (c1, c2, c3) == (1, 2, 3), f"Expected (1,2,3), got ({c1},{c2},{c3})"
+    finally:
+        _cleanup(path)
+
+
+# ── Criterion 2: TTL cleanup resets stale entries ────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_rate_limit_ttl_resets_counter_after_window_expires():
+    """Counter resets to 1 when the time window has expired (TTL cleanup).
+
+    time.time() is mocked — no real sleep required.
+    """
+    path = _tmpdb()
+    try:
+        await db.init_db()
+
+        with mock.patch("backend.db.time") as mock_time:
+            mock_time.time.return_value = 1000.0  # window_start = t0
+
+            c1 = await db.rate_limit_increment("ttl:test", 10)
+            c2 = await db.rate_limit_increment("ttl:test", 10)
+            c3 = await db.rate_limit_increment("ttl:test", 10)
+            assert c3 == 3
+
+            # Jump 11 seconds ahead (window = 10s → expired)
+            mock_time.time.return_value = 1011.0
+
+            c4 = await db.rate_limit_increment("ttl:test", 10)
+
+        assert c4 == 1, (
+            f"Expected counter reset to 1 after window expired, got {c4}"
+        )
+    finally:
+        _cleanup(path)
+
+
+@pytest.mark.asyncio
+async def test_rate_limit_ttl_does_not_reset_within_window():
+    """Counter is NOT reset when the window has NOT expired yet."""
+    path = _tmpdb()
+    try:
+        await db.init_db()
+
+        with mock.patch("backend.db.time") as mock_time:
+            mock_time.time.return_value = 1000.0
+
+            await db.rate_limit_increment("ttl:within", 10)
+            await db.rate_limit_increment("ttl:within", 10)
+            c3 = await db.rate_limit_increment("ttl:within", 10)
+            assert c3 == 3
+
+            # Only 5 seconds passed (window = 10s, still active)
+            mock_time.time.return_value = 1005.0
+
+            c4 = await db.rate_limit_increment("ttl:within", 10)
+
+        assert c4 == 4, (
+            f"Expected 4 (counter continues inside window), got {c4}"
+        )
+    finally:
+        _cleanup(path)
+
+
+@pytest.mark.asyncio
+async def test_rate_limit_ttl_boundary_exactly_at_window_end():
+    """Counter resets when elapsed time equals exactly the window duration."""
+    path = _tmpdb()
+    try:
+        await db.init_db()
+
+        with mock.patch("backend.db.time") as mock_time:
+            mock_time.time.return_value = 1000.0
+
+            await db.rate_limit_increment("ttl:boundary", 10)
+            await db.rate_limit_increment("ttl:boundary", 10)
+
+            # Exactly at window boundary (elapsed == window → stale)
+            mock_time.time.return_value = 1010.0
+
+            c = await db.rate_limit_increment("ttl:boundary", 10)
+
+        assert c == 1, (
+            f"Expected reset at exact window boundary (elapsed == window), got {c}"
+        )
+    finally:
+        _cleanup(path)
+
+
+# ── Criterion 3: HTTP 429 when rate limit exceeded ────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_register_returns_429_after_rate_limit_exceeded():
+    """POST /api/register returns 429 on the 6th request from the same IP.
+
+    Register limit = 5 requests per 600s window.
+    """
+    async with make_app_client() as client:
+        ip_hdrs = {"X-Real-IP": "192.0.2.10"}
+        statuses = []
+        for _ in range(6):
+            r = await client.post(
+                "/api/register",
+                json={"uuid": _UUID_REG_RL, "name": "RateLimitTest"},
+                headers=ip_hdrs,
+            )
+            statuses.append(r.status_code)
+
+    assert statuses[-1] == 429, (
+        f"Expected 429 on 6th register request, got statuses: {statuses}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_register_first_5_requests_are_allowed():
+    """First 5 POST /api/register requests from the same IP must all return 200."""
+    async with make_app_client() as client:
+        ip_hdrs = {"X-Real-IP": "192.0.2.11"}
+        statuses = []
+        for _ in range(5):
+            r = await client.post(
+                "/api/register",
+                json={"uuid": _UUID_REG_RL, "name": "RateLimitTest"},
+                headers=ip_hdrs,
+            )
+            statuses.append(r.status_code)
+
+    assert all(s == 200 for s in statuses), (
+        f"Expected all 5 register requests to return 200, got: {statuses}"
+    )
+
+
+# ── Criterion 4: X-Real-IP and X-Forwarded-For for rate counting ──────────────
+
+
+@pytest.mark.asyncio
+async def test_x_real_ip_header_is_used_for_rate_counting():
+    """Rate counter keys are derived from X-Real-IP: two requests sharing
+    the same X-Real-IP share the same counter and collectively hit the 429 limit.
+    """
+    async with make_app_client() as client:
+        await client.post(
+            "/api/register", json={"uuid": _UUID_XREALIP_A, "name": "RealIPUser"}
+        )
+
+        ip_hdrs = {"X-Real-IP": "203.0.113.10"}
+        payload = {"user_id": _UUID_XREALIP_A, "timestamp": 1742478000000}
+
+        statuses = []
+        for _ in range(11):
+            r = await client.post("/api/signal", json=payload, headers=ip_hdrs)
+            statuses.append(r.status_code)
+
+    assert statuses[-1] == 429, (
+        f"Expected 429 on 11th signal with same X-Real-IP, got: {statuses}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_x_forwarded_for_header_is_used_for_rate_counting():
+    """Rate counter keys are derived from X-Forwarded-For (first IP) when
+    X-Real-IP is absent: requests sharing the same forwarded IP hit the limit.
+    """
+    async with make_app_client() as client:
+        await client.post(
+            "/api/register", json={"uuid": _UUID_XFWD, "name": "FwdUser"}
+        )
+
+        # Chain: first IP is the original client (only that one is used)
+        fwd_hdrs = {"X-Forwarded-For": "198.51.100.5, 10.0.0.1, 172.16.0.1"}
+        payload = {"user_id": _UUID_XFWD, "timestamp": 1742478000000}
+
+        statuses = []
+        for _ in range(11):
+            r = await client.post("/api/signal", json=payload, headers=fwd_hdrs)
+            statuses.append(r.status_code)
+
+    assert statuses[-1] == 429, (
+        f"Expected 429 on 11th request with same X-Forwarded-For first IP, got: {statuses}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_different_x_real_ip_values_have_independent_counters():
+    """Exhausting the rate limit for IP-A must not block IP-B.
+
+    Verifies that rate-limit keys are truly per-IP.
+    """
+    async with make_app_client() as client:
+        await client.post(
+            "/api/register", json={"uuid": _UUID_XREALIP_A, "name": "IPA"}
+        )
+        await client.post(
+            "/api/register", json={"uuid": _UUID_XREALIP_B, "name": "IPB"}
+        )
+
+        # Exhaust limit for IP-A
+        for _ in range(11):
+            await client.post(
+                "/api/signal",
+                json={"user_id": _UUID_XREALIP_A, "timestamp": 1742478000000},
+                headers={"X-Real-IP": "198.51.100.100"},
+            )
+
+        # IP-B has its own independent counter — must not be blocked
+        r = await client.post(
+            "/api/signal",
+            json={"user_id": _UUID_XREALIP_B, "timestamp": 1742478000000},
+            headers={"X-Real-IP": "198.51.100.200"},
+        )
+
+    assert r.status_code == 200, (
+        f"IP-B was incorrectly blocked after IP-A exhausted its counter: {r.status_code}"
+    )