Isolate manual artifact validation without package publication

build/linux-toolchain/README.md

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+# Debian 12 Zig cross toolchain
+
+The production native-build path is the pinned Debian 12 image plus Zig 0.14.1,
+covering all nine GNU Linux, musl Linux, Windows and macOS targets. musl uses
+checksum-locked target sysroots inside the same Debian image.
+
+Read [CROSS-COMPILE.md](CROSS-COMPILE.md) for current build commands, exact local
+validation scope and remaining Docker/runtime/NativeAOT verification. Read
+[DAILY-RELEASE.md](../../DAILY-RELEASE.md) for daily 3/4 release configuration.
+
+`Dockerfile` pins the base digest, apt snapshot and source-preparation tools.
+`Dockerfile.cross-probe` adds Zig, macOS SDK, Windows headers, target Linux SDKs
+and .NET SDKs. The historical filename is retained for existing references.
+`zig-toolchain-image.yml` reuses recipe-tagged GHCR images and downstream jobs
+pull their immutable digest. Source locks and archive/link manifests provide
+traceability. No complete local Docker image build has been run.
+
+Legacy platform helper scripts are retained for reference; production graphics
+Actions now delegate to the common Zig cross-build workflow. SkiaSharp 2 remains
+outside the new daily tracks.