What
The native installer is the standalone way of installing Claude Code, where Claude Code updates its own program file. When it replaces that file, it keeps a backup copy of the old one. Backup copies are now named <exe>.old.<ms>.<pid>:
<exe>is the program's file name.<ms>is a timestamp.<pid>is the process ID, the number the operating system gives each running program.
A new name parser recognises two kinds of leftover file: these backups (.old.), and staged copies of a new version waiting to be put in place (.new.).
Why
If you look in the folder where Claude Code is installed, backup files now have a longer name with an extra number at the end. Because Claude Code can now read these names, it can identify its own leftover files when it cleans up after an update.
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The finding suggests the process ID lets cleanup tell which running process owns a file, but the evidence does not confirm how cleanup uses…