Three foreground costs ran on every commit before the detached rebuild
launcher even started:
1. Interpreter probes imported the full package. Each probe executed
'import graphify' wholesale — measured 13s per probe cold on a Windows 11
dev box with AV-scanned site-packages — and up to four probes could run
synchronously. Probes now use importlib.util.find_spec, which locates the
package without executing it (interpreter startup cost only). A broken
install under the selected interpreter still fails loudly in the rebuild
log, as before.
2. The shebang probe read a binary. Git for Windows' command -v can return
the launcher path WITHOUT its .exe suffix, so the '*.exe)' guard missed
and head -1 read a PE binary: the shell warned 'ignored null byte in
input' on every commit and the garbage always fell through to the slow
python3/python fallbacks. The Windows pip layout is now resolved directly
(Scripts/graphify -> sibling ../python.exe, or ./python.exe for venvs),
and the remaining POSIX shebang read strips NULs first.
3. GIT_DIR was re-derived. git exports GIT_DIR to hooks; the unconditional
rev-parse added ~1.3s more on machines where every git exec is scanned.
Now reused from the environment with rev-parse as the manual-run fallback.
Measured on the affected machine: hook foreground drops from 26s+ (cold) to
~1.4s, warnings gone. Behavior is unchanged on healthy POSIX setups — probe
order and fallback semantics are preserved.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
JimandClaude Fable 5
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