Add seeded task workspace creation

Current persistent tasks started with an empty workspace, which blocked the first useful host-to-task workflow in the task roadmap. This change lets task creation start from a host directory or tar archive without changing the one-shot VM surfaces.

Expose source_path on task create across the CLI, SDK, and MCP, add safe archive upload and extraction support for guest and host-compat backends, persist workspace_seed metadata, and patch the per-task rootfs with the bundled guest agent before boot so seeded guest tasks work without republishing environments. Also switch post--- command reconstruction to shlex.join() so documented sh -lc task examples preserve argument boundaries.

Validation:
- uv lock
- UV_CACHE_DIR=.uv-cache uv run pytest --no-cov tests/test_vm_guest.py tests/test_vm_manager.py tests/test_cli.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 exec -- cat note.txt, task delete

tests/test_vm_guest.py

@@ -1,6 +1,10 @@
 from __future__ import annotations
 
+import io
+import json
 import socket
+import tarfile
+from pathlib import Path
 
 import pytest
 
@@ -62,6 +66,45 @@ def test_vsock_exec_client_round_trip(monkeypatch: pytest.MonkeyPatch) -> None:
     assert stub.closed is True
 
 
+def test_vsock_exec_client_upload_archive_round_trip(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+) -> None:
+    monkeypatch.setattr(socket, "AF_VSOCK", 40, raising=False)
+    archive_path = tmp_path / "seed.tgz"
+    with tarfile.open(archive_path, "w:gz") as archive:
+        payload = b"hello\n"
+        info = tarfile.TarInfo(name="note.txt")
+        info.size = len(payload)
+        archive.addfile(info, io.BytesIO(payload))
+    stub = StubSocket(
+        b'{"destination":"/workspace","entry_count":1,"bytes_written":6}'
+    )
+
+    def socket_factory(family: int, sock_type: int) -> StubSocket:
+        assert family == socket.AF_VSOCK
+        assert sock_type == socket.SOCK_STREAM
+        return stub
+
+    client = VsockExecClient(socket_factory=socket_factory)
+    response = client.upload_archive(
+        1234,
+        5005,
+        archive_path,
+        destination="/workspace",
+        timeout_seconds=60,
+    )
+
+    request_payload, archive_payload = stub.sent.split(b"\n", 1)
+    request = json.loads(request_payload.decode("utf-8"))
+    assert request["action"] == "extract_archive"
+    assert request["destination"] == "/workspace"
+    assert int(request["archive_size"]) == archive_path.stat().st_size
+    assert archive_payload == archive_path.read_bytes()
+    assert response.entry_count == 1
+    assert response.bytes_written == 6
+    assert stub.closed is True
+
+
 def test_vsock_exec_client_rejects_bad_json(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(socket, "AF_VSOCK", 40, raising=False)
     stub = StubSocket(b"[]")