The generated post-commit / post-checkout block is appended to whatever
hook a repo already has, and other tools chain their logic after it. Every
skip condition in the block was a bare `exit 0`, which in a flat sh script
ends the ENTIRE hook process — so anything after graphify's end marker
was silently dropped on every root commit (HEAD~1 does not exist), every
rebase/merge/cherry-pick, every linked worktree, every GRAPHIFY_SKIP_HOOK=1
and whenever no graphify-capable python could be found.
Both bodies now run inside a subshell `( ... )`, so an `exit` ends only
graphify's section: no rewriting of the seventeen skip sites, no
`return`-outside-a-function hazard for the _PYTHON_DETECT fragment that
tests run standalone, the detached rebuild launch unaffected, and the
hook's own exit status 0 as before. The markers stay outside the subshell
so reinstall/uninstall/status keep finding the block.
(cherry picked from commit 6f09919f10)
