refactor(agent): gate sustained goals behind explicit /goal

Replace the legacy long-goal skill contract with command-scoped goal tools and runtime guidance. Keep goal state durable across continuations while restricting create and replace mutations to explicit user /goal turns.

tests/command/test_skill_command.py

@@ -126,6 +126,14 @@ async def test_skill_command_no_render_as_text(tmp_path: Path) -> None:
     assert out.metadata.get("render_as") != "text"
 
 
+@pytest.mark.asyncio
+async def test_skill_command_does_not_list_goal_runtime_protocol(tmp_path: Path) -> None:
+    loop = _make_loop(tmp_path)
+    out = await cmd_skill(_ctx(loop))
+
+    assert "long-goal" not in out.content
+
+
 @pytest.mark.asyncio
 async def test_skill_command_registered_on_router(tmp_path: Path) -> None:
     router = CommandRouter()