Windows: a path on another drive is outside the repository, not an error (0.1.11)

[swapnilpaliwal-sd]

Why

#1948's Windows release gate failed in GitHub Actions (run 38516660285, e2e on win32-x64) on what my Windows VM
could not show: GitHub's runner keeps the repository on D: and the user cache on C:.

File "axiomcode-index", line 57, in rel
    r = os.path.relpath(a, REPO).replace(os.sep, '/')
ValueError: path is on mount 'C:', start on mount 'D:'

relpath raises across drives on Windows, so --library (its compiled IR is in the user cache) failed the whole index
for any repository off C:. 0.1.11 is on main without this, so its release push would fail the same gate and draft
nothing.

What changes

• axiomcode-index, axiomcode-graph: a path on another drive is outside the repository, as a .. path is, and is
  kept as written (with /).
• ax_links (link), axiomcode-changed: an absolute path on another drive is kept as given rather than raising.
• tests/no_exec.py: its control starts Git Bash (AXIOMCODE_BASH), not a bare bash, which is WSL's on GitHub's image.

POSIX is unchanged: relpath never raises there.

Verified

• the other 1,841 of 1,844 checks, windows_argv and no_symlink already passed in that run; this is the remainder
• full CI on this head (every platform's engines and e2e, the Windows gate included): run 38527702390
• locally: no_exec 7/7; Java cases unchanged

🤖 Generated with Claude Code