[mhegazy]

Before: nothing in the plugin's metrics says whether the Python that runs its hooks sits behind a symbolic link or junction on Windows. anthropics/claude-code#96870 reports that inside the packaged Claude Desktop app Windows leaks kernel memory on every file opened through such a link under AppData (a uv-managed Python is one), and every hook starts an interpreter, so the plugin's hooks add to that leak. How many users are in that situation is unknown.

After: the SessionStart row carries one more key on Windows, interp_reparse, that says so. No behaviour changes.

Measurement only: no hook does anything different, no process is started, and no other row changes.

How

• interp_reparse_metric() in hooks/_base.py walks the folders of sys.executable and sys.base_prefix with one lstat each, up to the first symbolic link or junction, and reports bits: 1 executable path through a link, 2 standard library path through a link, 4 that path is under %APPDATA% or %LOCALAPPDATA% as spelled, 8 a path could not be checked (including Python older than 3.8, which has no reparse tag).
• App execution aliases (...\Microsoft\WindowsApps) and volumes mounted at a folder are not counted as links.
• 0 is sent too, so a Windows row without the key is a row that lost it, not a "no".
• ensure_agent_sdk.py appends it as the last key of the SessionStart row, so it is the first key a row over the key cap loses and never displaces another. A healthy row stays within 10 keys.
• Other systems return before looking at anything.

Implications

• One more key on each Windows SessionStart row, and about 10 extra lstat calls once per session on Windows.
• It sizes sessions and users, not hook starts: only rows the plugin already sends carry metrics, and most hook runs send none.
• Not covered: where a link points (a link outside AppData whose target is inside reads as "not AppData"), 8.3 short path spellings, and links on the plugin's own folders.

Tests

• tests/test_interp_reparse_metric.py: 21 tests with the interpreter paths and file attributes passed in (regular install, junction and symlink under AppData, link elsewhere, only the standard library or only the executable behind a link, AppData itself moved by a link, app execution alias, mounted volume, unreadable folders, failures on one path, other systems, the SessionStart row and its key order).
• GitHub-hosted Windows runners (Server 2025 x64 and Windows 11 ARM64, Python 3.12), running the function from this branch under real interpreters:

interpreter	value
regular install	0
junction under %APPDATA% to that install	7
directory symlink under %LOCALAPPDATA%	7
junction outside AppData	3
venv of a regular install	0
venv of the junctioned install	6
uv-managed Python through uv's minor-version junction (cpython-3.12-windows-...-none)	7
the same uv Python through its real folder	0
venv made by uv from that junction	6

• Not run: a real Claude Code session on Windows carrying the key end to end (the function was called directly), a mounted volume on real Windows, Python 3.7 on Windows, and anything inside the packaged Desktop app.

No version bump.

Human: @mhegazy

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