feat: add archive_session and unarchive_session to SessionService

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_sessions.py

@@ -2170,3 +2170,43 @@ async def test_list_sessions_archived_filter(service, db, tmux):
 
     archived = await service.list_sessions(project_id=1, archived=True)
     assert [i.session.id for i in archived] == [arch_id]
+
+
+@pytest.mark.asyncio
+async def test_archive_session_kills_window_and_keeps_row(service, db, tmux):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    await service.archive_session(1)
+
+    tmux.kill.assert_called_once_with("hqt-1")
+    db.expire_all()
+    row = db.get(Session, 1)
+    assert row is not None
+    assert row.archived is True
+    # Excluded from the default (active) listing.
+    assert await service.list_sessions(project_id=1) == []
+
+
+@pytest.mark.asyncio
+async def test_archive_session_no_kill_when_window_missing(service, db, tmux):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    tmux.window_exists = AsyncMock(return_value=False)
+    tmux.kill.reset_mock()
+
+    await service.archive_session(1)
+
+    tmux.kill.assert_not_called()
+    db.expire_all()
+    assert db.get(Session, 1).archived is True
+
+
+@pytest.mark.asyncio
+async def test_unarchive_session_restores_to_active_list(service, db, tmux):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    await service.archive_session(1)
+
+    await service.unarchive_session(1)
+
+    db.expire_all()
+    assert db.get(Session, 1).archived is False
+    active = await service.list_sessions(project_id=1)
+    assert [i.session.id for i in active] == [1]