Replaced buildctl CLI shell-out with direct gRPC communication via
buildkit-client crate. Connects to buildkitd daemon over Unix socket
or TCP with optional TLS.
Implementation:
- connect() with custom tonic UnixStream connector
- execute_build() implementing the solve protocol directly against
ControlClient (session setup, file sync, frontend attributes)
- Extracts digest from containerimage.digest in solve response
Added custom lima template (test/lima/wfe-test.yaml) that provides
both buildkitd and containerd with host-forwarded Unix sockets for
reproducible integration testing.
E2E tests against real buildkitd daemon via WFE_BUILDKIT_ADDR env var.
54 tests total. 89% line coverage (cargo-llvm-cov with E2E).
