fix(tests): deflake custom-nodes uninstall test (global shutil.rmtree patch)

[lstein]

Summary

TestUninstallPackNameValidation::test_rejects_invalid_pack_names_before_filesystem_side_effects (added in #9256) fails intermittently in CI:

FAILED tests/app/routers/test_custom_nodes.py::TestUninstallPackNameValidation::test_rejects_invalid_pack_names_before_filesystem_side_effects
  AssertionError: Expected 'rmtree' to not have been called. Called 1 times.
  Calls: [call('/var/folders/g3/.../T/tmp7n0m81lc', onerror=<function TemporaryDirectory._rmtree.<locals>.onerror at 0x164d5e480>)]

Seen on py3.11 macos-default in this run on PR #9367 (which doesn't touch this code); the same run passed on re-run.

Root cause

The test patches invokeai.app.api.routers.custom_nodes.shutil.rmtree. Since custom_nodes.py does a plain import shutil, that target resolves to the global shutil module — the patch affects every caller in the process, not just the router.

Several tests in the suite leak TemporaryDirectory objects inside reference cycles (the CI log shows many ResourceWarning: Implicitly cleaning up <TemporaryDirectory ...>). Whenever the cyclic GC happens to run while the patch is active, tempfile's finalizer calls shutil.rmtree — i.e. the mock — and assert_not_called() fails. The recorded call's onerror=<TemporaryDirectory._rmtree...> argument shows it is tempdir cleanup, not the router. Whether it fires is pure GC-timing luck, hence one platform failing while five pass.

Reproducible deterministically:

import gc, tempfile
from unittest.mock import patch
gc.disable()

td = tempfile.TemporaryDirectory()
class H: pass
h = H(); h.td = td; h.self = h   # cycle: only the cyclic GC can free it
del td, h

with patch("invokeai.app.api.routers.custom_nodes.shutil.rmtree") as m:
    gc.collect()                  # stands in for CI's unlucky GC pass
    m.assert_not_called()         # AssertionError: Called 1 times

Fix

Patch the router module's shutil attribute (patch("...custom_nodes.shutil")) instead of the global shutil.rmtree, and assert on mock_shutil.rmtree. Only lookups through custom_nodes.shutil hit the mock; tempdir finalizers keep the real shutil.

Verified both properties:

• the repro above no longer trips the narrowed mock;
• a valid pack name still drives the router's real shutil.rmtree(target_dir) call into the mock, so the test still catches a broken validator.

QA Instructions

uv run pytest tests/app/routers/test_custom_nodes.py — 39 passed.

Merge Plan

Squash-merge whenever; test-only change.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

🤖 Generated with Claude Code

[Pfannkuchensack]

Good fix.