Key the Rust cargo cache on the toolchain that built it
The cache key was rust-<Cargo.lock hash> with a bare rust- restore prefix, so
one seaweed-volume/target survived across runner images. cargo tracks its own
inputs but not the runner's C toolchain, so build-script output for C
dependencies is reused even when the system libc underneath it changed.
That is how the Rust jobs got wedged: the cached aws-lc-sys objects reference
__isoc23_sscanf and __isoc23_strtol, symbols glibc only grew in 2.38, while the
jobs link on ubuntu-22.04 with glibc 2.35. Every job died at
rust-lld: error: undefined symbol: __isoc23_sscanf
>>> referenced by bcm.c in archive libaws_lc_sys-*.rlib
with nothing in the tree to explain it, and no amount of re-running helped
because the poisoned entry was hit every time.
Fold the glibc and rustc versions into the key so a toolchain change misses the
cache and rebuilds instead of producing an unlinkable target/.
Chris LuandGitHub
50464702d2