diff --git a/sdk/prototype_state.py b/sdk/prototype_state.py
new file mode 100644
index 0000000..4682bd9
--- /dev/null
+++ b/sdk/prototype_state.py
@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+from datetime import UTC, datetime
+from typing import Any
+
+from sdk.interface import User, UserSettings
+
+# Keep the prototype backend self-contained; do not import these from sdk.mock.
+DEFAULT_SKILLS: dict[str, bool] = {
+    "web-search": True,
+    "fetch-url": True,
+    "email": False,
+    "browser": False,
+    "image-gen": False,
+    "files": True,
+}
+DEFAULT_SAFETY: dict[str, bool] = {
+    "email-send": True,
+    "file-delete": True,
+    "social-post": True,
+}
+DEFAULT_SOUL: dict[str, str] = {"name": "Лямбда", "instructions": ""}
+DEFAULT_PLAN: dict[str, Any] = {
+    "name": "Beta",
+    "tokens_used": 0,
+    "tokens_limit": 1000,
+}
+
+
+class PrototypeStateStore:
+    def __init__(self) -> None:
+        self._users: dict[str, User] = {}
+        self._settings: dict[str, dict[str, Any]] = {}
+
+    async def get_or_create_user(
+        self,
+        *,
+        external_id: str,
+        platform: str,
+        display_name: str | None = None,
+    ) -> User:
+        key = f"{platform}:{external_id}"
+        existing = self._users.get(key)
+        if existing is not None:
+            return existing.model_copy(update={"is_new": False})
+
+        user = User(
+            user_id=f"usr-{platform}-{external_id}",
+            external_id=external_id,
+            platform=platform,
+            display_name=display_name,
+            created_at=datetime.now(UTC),
+            is_new=True,
+        )
+        self._users[key] = user
+        return user
+
+    async def get_settings(self, user_id: str) -> UserSettings:
+        stored = self._settings.get(user_id, {})
+        return UserSettings(
+            skills={**DEFAULT_SKILLS, **stored.get("skills", {})},
+            connectors=stored.get("connectors", {}),
+            soul={**DEFAULT_SOUL, **stored.get("soul", {})},
+            safety={**DEFAULT_SAFETY, **stored.get("safety", {})},
+            plan={**DEFAULT_PLAN, **stored.get("plan", {})},
+        )
+
+    async def update_settings(self, user_id: str, action: Any) -> None:
+        settings = self._settings.setdefault(user_id, {})
+
+        if action.action == "toggle_skill":
+            skills = settings.setdefault("skills", DEFAULT_SKILLS.copy())
+            skills[action.payload["skill"]] = action.payload.get("enabled", True)
+        elif action.action == "set_soul":
+            soul = settings.setdefault("soul", DEFAULT_SOUL.copy())
+            soul[action.payload["field"]] = action.payload["value"]
+        elif action.action == "set_safety":
+            safety = settings.setdefault("safety", DEFAULT_SAFETY.copy())
+            safety[action.payload["trigger"]] = action.payload.get("enabled", True)
diff --git a/tests/platform/test_prototype_state.py b/tests/platform/test_prototype_state.py
new file mode 100644
index 0000000..2a49375
--- /dev/null
+++ b/tests/platform/test_prototype_state.py
@@ -0,0 +1,75 @@
+import pytest
+
+from core.protocol import SettingsAction
+from sdk.interface import UserSettings
+from sdk.prototype_state import PrototypeStateStore
+
+
+@pytest.mark.asyncio
+async def test_get_or_create_user_is_stable_per_surface_identity():
+    store = PrototypeStateStore()
+
+    first = await store.get_or_create_user(
+        external_id="@alice:example.org",
+        platform="matrix",
+        display_name="Alice",
+    )
+    second = await store.get_or_create_user(
+        external_id="@alice:example.org",
+        platform="matrix",
+    )
+
+    assert first.user_id == "usr-matrix-@alice:example.org"
+    assert first.is_new is True
+    assert second.user_id == first.user_id
+    assert second.is_new is False
+    assert second.display_name == "Alice"
+
+
+@pytest.mark.asyncio
+async def test_settings_defaults_match_existing_mock_shape():
+    store = PrototypeStateStore()
+
+    settings = await store.get_settings("usr-matrix-@alice:example.org")
+
+    assert isinstance(settings, UserSettings)
+    assert settings.skills == {
+        "web-search": True,
+        "fetch-url": True,
+        "email": False,
+        "browser": False,
+        "image-gen": False,
+        "files": True,
+    }
+    assert settings.safety == {
+        "email-send": True,
+        "file-delete": True,
+        "social-post": True,
+    }
+    assert settings.soul == {"name": "Лямбда", "instructions": ""}
+    assert settings.plan == {"name": "Beta", "tokens_used": 0, "tokens_limit": 1000}
+
+
+@pytest.mark.asyncio
+async def test_update_settings_supports_toggle_skill_and_setters():
+    store = PrototypeStateStore()
+
+    await store.update_settings(
+        "usr-matrix-@alice:example.org",
+        SettingsAction(action="toggle_skill", payload={"skill": "browser", "enabled": True}),
+    )
+    await store.update_settings(
+        "usr-matrix-@alice:example.org",
+        SettingsAction(action="set_soul", payload={"field": "instructions", "value": "Be concise"}),
+    )
+    await store.update_settings(
+        "usr-matrix-@alice:example.org",
+        SettingsAction(action="set_safety", payload={"trigger": "social-post", "enabled": False}),
+    )
+
+    settings = await store.get_settings("usr-matrix-@alice:example.org")
+
+    assert settings.skills["browser"] is True
+    assert settings.skills["web-search"] is True
+    assert settings.soul["instructions"] == "Be concise"
+    assert settings.safety["social-post"] is False