revert: restore _poll_task and dir_size/get_md5 to 0.2.2 state

All changes since 0.2.2 to _poll_task, dir_size, and get_md5 (window_timeout,
_poll_oneshot, start_and_poll_immediately) are reverted. The 0.2.2 behaviour
worked reliably for small directories and is the last known-good baseline.

The remaining known limitation (occasional 599 on large directories) is
documented in SPEC.md. Retry the operation as a workaround.

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

tests/test_tools_filestation.py

@@ -22,24 +22,8 @@ def config() -> AppConfig:
 
 def _make_mcp_and_tools(config: AppConfig, client: MagicMock) -> dict:
     """Register FileStation tools on a mock FastMCP and collect them by name."""
-    from mcp_synology_filestation.client import FileStationClient
     from mcp_synology_filestation.tools.filestation import register_filestation
 
-    # Bind the real start_and_poll_immediately so it delegates into the
-    # already-mocked client.request — no separate mock needed per test.
-    async def _start_and_poll_immediately(
-        api: str,
-        start_params: dict,
-        poll_version: int,
-        *,
-        start_version: int | None = None,
-    ):
-        return await FileStationClient.start_and_poll_immediately(
-            client, api, start_params, poll_version, start_version=start_version
-        )
-
-    client.start_and_poll_immediately = _start_and_poll_immediately
-
     registered: dict[str, object] = {}
 
     mcp = MagicMock()
@@ -1651,12 +1635,8 @@ async def test_dir_size_retries_on_transient_599(config: AppConfig) -> None:
 
 
 @pytest.mark.asyncio
-async def test_dir_size_times_out_on_persistent_599(config: AppConfig) -> None:
-    """dir_size times out after 60 s when DSM returns only 599s for every poll.
-
-    The immediate poll + burst both return 599; Phase 2 keeps polling (large
-    directories eventually surface) until the 60 s timeout fires.
-    """
+async def test_dir_size_fails_after_5_consecutive_599(config: AppConfig) -> None:
+    """dir_size gives up and returns Error: after 5 consecutive 599 responses."""
     client = MagicMock()
 
     async def _request(api, method, version=None, params=None, **kwargs):
@@ -1671,7 +1651,6 @@ async def test_dir_size_times_out_on_persistent_599(config: AppConfig) -> None:
         result = await tools["dir_size"](path="/dead")
 
     assert result.startswith("Error:")
-    assert "timed out" in result.lower() or "60 seconds" in result
 
 
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