pypotrace is an sdist that compiles at install time, so every machine
and every CI runner resolving it needs these headers first. That makes
it a recurring per-box action rather than the one-off it arrived as.
Two things learned installing it on nh3-dev are recorded here rather
than left in an althing thread, at forseti's suggestion, because a
thread is not where the next person looks:
Only libagg is a pkg-config consumer. potrace ships no .pc file and is
found via potracelib.h directly, so `pkg-config --exists potrace`
returns false on a correctly configured box. It looks exactly like the
cause and never is.
libagg's pkg-config modversion is 2.7.0 while its Debian package version
is 1:2.6.1-r134. Comparing those two numbers convinces you the wrong
package is installed.
The verify phase asserts the geometry, not the import: a square must
come back as one curve of four CornerSegments. An extension linked
against the wrong thing can import cleanly and return nonsense, so a
successful build is not evidence the module works.
Getting the build probe to run took three passes and the reason is worth
keeping. uv is not on a non-interactive ssh PATH; it is in a different
place on each box; and on nh3-dev it sits inside a 0700 home, so even
the correct absolute path fails `test -x` for the ssh user because the
directory cannot be traversed. The headers are system-wide and root's
business, but the build check is a developer action and has to run as
the user who owns the toolchain.
