test: tachyon workload generation

.cargo/config.toml

@@ -4,6 +4,12 @@
 xtask = "run --package xtask --"
 
 [build]
+# An explicit RUSTFLAGS environment variable replaces these flags, so callers that set it must
+# also enable the NuTachyon cfg.
+rustflags = [
+    '--cfg',
+    'zcash_unstable="nutachyon"',
+]
 rustdocflags = [
     # Keep shared rustdoc lint levels synchronized with the book and lint
     # workflows.

.github/workflows/lint.yml

@@ -134,6 +134,10 @@ jobs:
       # coverage. `zakura-watchdog` is excluded: it depends on `sentry`, which
       # requires a newer rustc than the workspace library MSRV.
       - run: cargo check --workspace --bins --exclude zakura-watchdog
+        env:
+          # NuTachyon's Tachyon dependency requires Rust 1.97. Clear the repository-level
+          # opt-in cfg so this job continues to check the supported cfg-off build on 1.91.
+          RUSTFLAGS: ""
 
   docs:
     name: docs

.github/workflows/semver-checks.yml

@@ -269,7 +269,7 @@ jobs:
         run: |
           # cargo-public-api builds both the current and published crate with
           # nightly. Nightly-only warnings are evidence, not the lint gate.
-          RUSTFLAGS='' cargo public-api diff latest -p "$PACKAGE" -sss
+          RUSTFLAGS='--cfg zcash_unstable="nutachyon"' cargo public-api diff latest -p "$PACKAGE" -sss
 
   warm-baselines:
     name: Warm semver baselines

.github/workflows/test-crates.yml

@@ -101,8 +101,8 @@ jobs:
           cargo hack check --workspace
           cargo hack check --workspace --no-default-features
         env:
-          # Treat warnings as errors, preserving the old `features` job behavior.
-          RUSTFLAGS: -D warnings
+          # Treat warnings as errors while preserving the workspace NuTachyon cfg.
+          RUSTFLAGS: '--cfg zcash_unstable="nutachyon" -D warnings'
 
       - name: Check publishable crate packaging
         run: ./scripts/check-crate-packaging.sh