Hermit's rustup package sets CARGO_HOME to ${HERMIT_ENV}/.hermit/rust.
Swatinem/rust-cache keeps only target/ outputs for packages whose manifest
is outside the workspace root, so every registry crate looked like a
workspace member and each root-workspace cache saved an empty target/
(1303 B on main for unit-tests, rust-lint, cross, relay-e2e, and mesh
lifecycle). The exact-key hit then blocked every later save.
Set CARGO_HOME to ${HOME}/.cargo-hermit (and its bin/ on PATH) in
bin/hermit.hcl. Hermit applies that env whenever it execs cargo, so a
workflow-level CARGO_HOME export cannot do this; the environment config
fixes CI and local alike. The rust-cache contract pins it, and
bin/hermit.hcl now selects the Rust CI lanes.
Consolidate the default-feature just test-unit nextest runs into one
invocation with per-package filter clauses, so shared dependencies compile
once. Feature-flagged runs and doctests stay separate.
Signed-off-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
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