fix: v0.9.1 — clearer messages for exec/redeploy/check_image_updates

Three live-verified MCP weaknesses (update run 2026-06-22):

- exec_in_container: SYNO.Docker.Container/exec does not exist on this DSM
  firmware (code 103, like pause/unpause). Catch it and return a guiding
  "not supported on this firmware" message instead of the raw DSM error;
  the tool stays available for firmwares that do implement exec.
- redeploy_project: the failure hint suggested stop_project + start_project,
  but start_project does not recreate on a new image (it restarts the old
  one). Both failure hints now point back at redeploy_project and warn about
  parallel pull_image lock contention (DSM 2101/2202).
- check_image_updates: docstring and output now state it only reflects DSM
  digest drift on already-pulled tags and does NOT discover newer version
  tags (use list_image_tags + release notes for that).

Tests updated accordingly; CHANGELOG + version bumped to 0.9.1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_modules/test_projects.py

@@ -353,7 +353,7 @@ async def test_redeploy_large_image_returns_background_hint():
 
 @pytest.mark.asyncio
 async def test_redeploy_unknown_status_returns_error():
-    """Unknown status must return a clear error with a workaround hint."""
+    """Unknown status must return a clear error pointing back at redeploy_project."""
     client = AsyncMock()
 
     async def mock_request(api, method, **kwargs):
@@ -368,7 +368,8 @@ async def test_redeploy_unknown_status_returns_error():
     result = await tools["redeploy_project"]("myapp", confirmed=True)
 
     assert "UPDATING" in result
-    assert "Workaround" in result or "stop_project" in result
+    assert "redeploy_project" in result
+    assert "does NOT recreate" in result
 
 
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