Distribution.files drops entries whose paths no longer exist, which is
precisely the set the last change looked for, so on 3.13 (what both
desktop installers pick) the check could never fire. Verified against a
dist-info whose RECORD names a deleted file: files returned 3 of 4
entries and the damaged package read as complete. RECORD is parsed
directly now, and the test builds a real dist-info rather than a stub so
it would have caught this.
The marker is also not always ours. A retry after an interrupted install
finds the earlier one still there, and a repair that then fails to spawn
was deleting it, losing the classification the next launch depends on.
Creation reports whether it created the file; the pre-spawn and elevation
paths clear only then, and success still clears unconditionally.
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