feat(gateway): notify users when session auto-resets (#2519)

When a session expires (daily schedule or idle timeout) and is
automatically reset, send a notification to the user explaining
what happened:

  ◐ Session automatically reset (inactive for 24h).
    Conversation history cleared.
  Use /resume to browse and restore a previous session.
  Adjust reset timing in config.yaml under session_reset.

Notifications are suppressed when:
- The expired session had no activity (no tokens used)
- The platform is excluded (api_server, webhook by default)
- notify: false in config

Changes:
- session.py: _should_reset() returns reason string ('idle'/'daily')
  instead of bool; SessionEntry gains auto_reset_reason and
  reset_had_activity fields; old entry's total_tokens checked
- config.py: SessionResetPolicy gains notify (bool, default: true)
  and notify_exclude_platforms (default: api_server, webhook)
- run.py: sends notification via adapter.send() before processing
  the user's message, with activity + platform checks
- 13 new tests

Config (config.yaml):

  session_reset:
    notify: true
    notify_exclude_platforms: [api_server, webhook]

tests/gateway/test_session_reset_notify.py

@@ -0,0 +1,207 @@
+"""Tests for session auto-reset notifications.
+
+Verifies that:
+- _should_reset() returns a reason string ("idle" or "daily") instead of bool
+- SessionEntry captures auto_reset_reason
+- SessionResetPolicy.notify controls whether notifications are sent
+- notify_exclude_platforms skips notifications for excluded platforms
+"""
+
+from datetime import datetime, timedelta
+from unittest.mock import MagicMock
+
+import pytest
+
+from gateway.config import (
+    GatewayConfig,
+    Platform,
+    PlatformConfig,
+    SessionResetPolicy,
+)
+from gateway.session import SessionEntry, SessionSource, SessionStore
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _make_source(platform=Platform.TELEGRAM, chat_id="123", user_id="u1"):
+    return SessionSource(
+        platform=platform,
+        chat_id=chat_id,
+        user_id=user_id,
+    )
+
+
+def _make_store(policy=None, tmp_path=None):
+    config = GatewayConfig()
+    if policy:
+        config.default_reset_policy = policy
+    store = SessionStore(sessions_dir=tmp_path or "/tmp/test-sessions", config=config)
+    return store
+
+
+# ---------------------------------------------------------------------------
+# _should_reset returns reason string
+# ---------------------------------------------------------------------------
+
+class TestShouldResetReason:
+    def test_returns_none_when_not_expired(self, tmp_path):
+        store = _make_store(
+            SessionResetPolicy(mode="both", idle_minutes=60, at_hour=4),
+            tmp_path,
+        )
+        entry = SessionEntry(
+            session_key="test",
+            session_id="s1",
+            created_at=datetime.now(),
+            updated_at=datetime.now(),  # just updated
+        )
+        source = _make_source()
+        assert store._should_reset(entry, source) is None
+
+    def test_returns_idle_when_idle_expired(self, tmp_path):
+        store = _make_store(
+            SessionResetPolicy(mode="idle", idle_minutes=30),
+            tmp_path,
+        )
+        entry = SessionEntry(
+            session_key="test",
+            session_id="s1",
+            created_at=datetime.now() - timedelta(hours=2),
+            updated_at=datetime.now() - timedelta(hours=1),  # 60min ago > 30min threshold
+        )
+        source = _make_source()
+        assert store._should_reset(entry, source) == "idle"
+
+    def test_returns_daily_when_daily_boundary_crossed(self, tmp_path):
+        now = datetime.now()
+        store = _make_store(
+            SessionResetPolicy(mode="daily", at_hour=now.hour),
+            tmp_path,
+        )
+        entry = SessionEntry(
+            session_key="test",
+            session_id="s1",
+            created_at=now - timedelta(days=2),
+            updated_at=now - timedelta(days=1),  # last active yesterday
+        )
+        source = _make_source()
+        assert store._should_reset(entry, source) == "daily"
+
+    def test_returns_none_when_mode_is_none(self, tmp_path):
+        store = _make_store(
+            SessionResetPolicy(mode="none"),
+            tmp_path,
+        )
+        entry = SessionEntry(
+            session_key="test",
+            session_id="s1",
+            created_at=datetime.now() - timedelta(days=30),
+            updated_at=datetime.now() - timedelta(days=30),
+        )
+        source = _make_source()
+        assert store._should_reset(entry, source) is None
+
+
+# ---------------------------------------------------------------------------
+# SessionEntry captures reason
+# ---------------------------------------------------------------------------
+
+class TestSessionEntryReason:
+    def test_auto_reset_reason_stored(self, tmp_path):
+        store = _make_store(
+            SessionResetPolicy(mode="idle", idle_minutes=1),
+            tmp_path,
+        )
+        source = _make_source()
+
+        # Create initial session
+        entry1 = store.get_or_create_session(source)
+        assert not entry1.was_auto_reset
+
+        # Age it past the idle threshold
+        entry1.updated_at = datetime.now() - timedelta(minutes=5)
+        store._save()
+
+        # Next call should create a new session with reason
+        entry2 = store.get_or_create_session(source)
+        assert entry2.was_auto_reset is True
+        assert entry2.auto_reset_reason == "idle"
+        assert entry2.session_id != entry1.session_id
+
+    def test_reset_had_activity_false_when_no_tokens(self, tmp_path):
+        """Expired session with no tokens → reset_had_activity=False."""
+        store = _make_store(
+            SessionResetPolicy(mode="idle", idle_minutes=1),
+            tmp_path,
+        )
+        source = _make_source()
+
+        entry1 = store.get_or_create_session(source)
+        # No tokens used — session was idle with no conversation
+        entry1.updated_at = datetime.now() - timedelta(minutes=5)
+        store._save()
+
+        entry2 = store.get_or_create_session(source)
+        assert entry2.was_auto_reset is True
+        assert entry2.reset_had_activity is False
+
+    def test_reset_had_activity_true_when_tokens_used(self, tmp_path):
+        """Expired session with tokens → reset_had_activity=True."""
+        store = _make_store(
+            SessionResetPolicy(mode="idle", idle_minutes=1),
+            tmp_path,
+        )
+        source = _make_source()
+
+        entry1 = store.get_or_create_session(source)
+        # Simulate some conversation happened
+        entry1.total_tokens = 5000
+        entry1.updated_at = datetime.now() - timedelta(minutes=5)
+        store._save()
+
+        entry2 = store.get_or_create_session(source)
+        assert entry2.was_auto_reset is True
+        assert entry2.reset_had_activity is True
+
+
+# ---------------------------------------------------------------------------
+# SessionResetPolicy notify config
+# ---------------------------------------------------------------------------
+
+class TestResetPolicyNotify:
+    def test_notify_defaults_true(self):
+        policy = SessionResetPolicy()
+        assert policy.notify is True
+
+    def test_notify_exclude_defaults(self):
+        policy = SessionResetPolicy()
+        assert "api_server" in policy.notify_exclude_platforms
+        assert "webhook" in policy.notify_exclude_platforms
+
+    def test_from_dict_with_notify_false(self):
+        policy = SessionResetPolicy.from_dict({"notify": False})
+        assert policy.notify is False
+
+    def test_from_dict_with_custom_excludes(self):
+        policy = SessionResetPolicy.from_dict({
+            "notify_exclude_platforms": ["api_server", "webhook", "homeassistant"],
+        })
+        assert "homeassistant" in policy.notify_exclude_platforms
+
+    def test_from_dict_preserves_defaults_on_missing_keys(self):
+        policy = SessionResetPolicy.from_dict({})
+        assert policy.notify is True
+        assert "api_server" in policy.notify_exclude_platforms
+
+    def test_to_dict_roundtrip(self):
+        original = SessionResetPolicy(
+            mode="idle",
+            notify=False,
+            notify_exclude_platforms=("api_server",),
+        )
+        restored = SessionResetPolicy.from_dict(original.to_dict())
+        assert restored.notify == original.notify
+        assert restored.notify_exclude_platforms == original.notify_exclude_platforms
+        assert restored.mode == original.mode