Add workspace handoff shortcuts and file-backed inputs

Remove the remaining shell glue from the canonical CLI workspace flows so users can hand off IDs and host-authored text files directly.

Add --id-only on workspace create and shell open, plus --text-file and --patch-file for workspace file write and patch apply, while keeping the underlying SDK, MCP, and backend behavior unchanged.

Update the top walkthroughs, contract docs, roadmap status, and use-case smoke runner to use the new shortcuts, and verify the milestone with uv lock, make check, make dist-check, focused CLI tests, and a real guest-backed smoke for create, file write, patch apply, and shell open/read.

tests/test_workspace_use_case_smokes.py

@@ -478,6 +478,18 @@ def test_run_all_use_case_scenarios_with_fake_pyro(
     fake_pyro = _FakePyro(tmp_path / "fake-pyro")
     monkeypatch.setattr(smoke_module, "Pyro", lambda: fake_pyro)
     monkeypatch.setattr(time_module, "sleep", lambda _seconds: None)
+    monkeypatch.setattr(
+        smoke_module,
+        "_run_pyro_cli",
+        lambda *args, cwd: (
+            fake_pyro.write_workspace_file(
+                args[3],
+                "message.txt",
+                text="fixed\n",
+            ),
+            f"[workspace-patch] workspace_id={args[3]} total=1\n",
+        )[1],
+    )
 
     smoke_module.run_workspace_use_case_scenario("all")
 
@@ -493,6 +505,18 @@ def test_main_runs_selected_scenario(monkeypatch: pytest.MonkeyPatch, tmp_path:
     fake_pyro = _FakePyro(tmp_path / "fake-pyro-main")
     monkeypatch.setattr(smoke_module, "Pyro", lambda: fake_pyro)
     monkeypatch.setattr(time_module, "sleep", lambda _seconds: None)
+    monkeypatch.setattr(
+        smoke_module,
+        "_run_pyro_cli",
+        lambda *args, cwd: (
+            fake_pyro.write_workspace_file(
+                args[3],
+                "message.txt",
+                text="fixed\n",
+            ),
+            f"[workspace-patch] workspace_id={args[3]} total=1\n",
+        )[1],
+    )
     monkeypatch.setattr(
         "sys.argv",
         [