Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Deleting the last active heap item removes its position entry, then immediately recreates that same entry while recording the moved item. A subsequent deletion of the supposedly absent key can remove a newly inserted, unrelated item:

h = Heap()
h.insert_item(1, 10)
h.delete_item(1)
h.insert_item(2, 20)
h.delete_item(1)  # should be a no-op
print(h.get_top())  # before: None; after: [2, 20]

Remove the deleted key after updating the moved item's position. This preserves the index map for both last-slot and interior deletions without changing the heap's storage or ordering behavior.

Validation on free-threaded CPython 3.15.0rc2:

• All 24 existing doctest examples pass; module pytest run: 2 passed.
• 200 seeded max/min-heap scenarios (100,000 operations) pass dictionary-oracle checks of membership, positions, size, priorities, and heap ordering. All 200 scenarios fail on the original code.
• Independent review verified direct last/interior/root deletion, repeated absent operations, reinsertion, and a separate randomized oracle.
• Full configured pre-commit run --all-files --show-diff-on-failure: passed.

Existing tests are unchanged, following the instruction against changing algorithm code and doctests together. This original change was prepared with AI assistance and independently reviewed.

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized. (AI assistance is disclosed above.)
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory. (No new file.)
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints. (Existing signatures are unchanged.)
• All functions have doctests that pass the automated testing. (All existing doctests pass; no new function or doctest.)
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation. (No new algorithm.)
• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a closing keyword. (No issue claimed.)