Add task sync push milestone

Tasks could start from host content in 2.2.0, but there was still no post-create path to update a live workspace from the host. This change adds the next host-to-task step so repeated fix or review loops do not require recreating the task for every local change.

Add task sync push across the CLI, Python SDK, and MCP server, reusing the existing safe archive import path from seeded task creation instead of introducing a second transfer stack. The implementation keeps sync separate from workspace_seed metadata, validates destinations under /workspace, and documents the current non-atomic recovery path as delete-and-recreate.

Validation:
- uv lock
- UV_CACHE_DIR=.uv-cache uv run pytest --no-cov tests/test_cli.py tests/test_vm_manager.py tests/test_api.py tests/test_server.py tests/test_public_contract.py
- UV_CACHE_DIR=.uv-cache make check
- UV_CACHE_DIR=.uv-cache make dist-check
- real guest-backed smoke: task create --source-path, task sync push, task exec to verify both files, task delete

tests/test_vm_manager.py

@@ -363,6 +363,90 @@ def test_task_create_seeds_tar_archive_into_workspace(tmp_path: Path) -> None:
     assert executed["stdout"] == "archive\n"
 
 
+def test_task_sync_push_updates_started_workspace(tmp_path: Path) -> None:
+    source_dir = tmp_path / "seed"
+    source_dir.mkdir()
+    (source_dir / "note.txt").write_text("hello\n", encoding="utf-8")
+    update_dir = tmp_path / "update"
+    update_dir.mkdir()
+    (update_dir / "more.txt").write_text("more\n", encoding="utf-8")
+
+    manager = VmManager(
+        backend_name="mock",
+        base_dir=tmp_path / "vms",
+        network_manager=TapNetworkManager(enabled=False),
+    )
+
+    created = manager.create_task(
+        environment="debian:12-base",
+        allow_host_compat=True,
+        source_path=source_dir,
+    )
+    task_id = str(created["task_id"])
+    synced = manager.push_task_sync(task_id, source_path=update_dir, dest="subdir")
+
+    assert synced["workspace_sync"]["mode"] == "directory"
+    assert synced["workspace_sync"]["destination"] == "/workspace/subdir"
+
+    executed = manager.exec_task(task_id, command="cat subdir/more.txt", timeout_seconds=30)
+    assert executed["stdout"] == "more\n"
+
+    status = manager.status_task(task_id)
+    assert status["command_count"] == 1
+    assert status["workspace_seed"]["mode"] == "directory"
+
+
+def test_task_sync_push_requires_started_task(tmp_path: Path) -> None:
+    source_dir = tmp_path / "seed"
+    source_dir.mkdir()
+    (source_dir / "note.txt").write_text("hello\n", encoding="utf-8")
+    update_dir = tmp_path / "update"
+    update_dir.mkdir()
+    (update_dir / "more.txt").write_text("more\n", encoding="utf-8")
+
+    manager = VmManager(
+        backend_name="mock",
+        base_dir=tmp_path / "vms",
+        network_manager=TapNetworkManager(enabled=False),
+    )
+
+    created = manager.create_task(
+        environment="debian:12-base",
+        allow_host_compat=True,
+        source_path=source_dir,
+    )
+    task_id = str(created["task_id"])
+    task_path = tmp_path / "vms" / "tasks" / task_id / "task.json"
+    payload = json.loads(task_path.read_text(encoding="utf-8"))
+    payload["state"] = "stopped"
+    task_path.write_text(json.dumps(payload, indent=2, sort_keys=True), encoding="utf-8")
+
+    with pytest.raises(RuntimeError, match="must be in 'started' state before task_sync_push"):
+        manager.push_task_sync(task_id, source_path=update_dir)
+
+
+def test_task_sync_push_rejects_destination_outside_workspace(tmp_path: Path) -> None:
+    source_dir = tmp_path / "seed"
+    source_dir.mkdir()
+    (source_dir / "note.txt").write_text("hello\n", encoding="utf-8")
+
+    manager = VmManager(
+        backend_name="mock",
+        base_dir=tmp_path / "vms",
+        network_manager=TapNetworkManager(enabled=False),
+    )
+
+    task_id = str(
+        manager.create_task(
+            environment="debian:12-base",
+            allow_host_compat=True,
+        )["task_id"]
+    )
+
+    with pytest.raises(ValueError, match="workspace destination must stay inside /workspace"):
+        manager.push_task_sync(task_id, source_path=source_dir, dest="../escape")
+
+
 def test_task_create_rejects_unsafe_seed_archive(tmp_path: Path) -> None:
     archive_path = tmp_path / "bad.tgz"
     with tarfile.open(archive_path, "w:gz") as archive: