Provide independent source tree references for the sandbox P1 checks

flake.nix

@@ -162,6 +162,7 @@
         checks.tests = craneLib.mkCargoDerivation (common // wasiCcEnv // {
           inherit cargoArtifacts;
           pnameSuffix = "-test";
+          nativeBuildInputs = common.nativeBuildInputs ++ [ pkgs.git ];
           doCheck = true;
           buildPhaseCargoCommand = "";
           # Keep the same sandbox-compatible modules in the shared host test executable.
@@ -175,6 +176,15 @@
           preCheck = ''
             export SAUSAGE_CACHE="$TMPDIR/sausage-cache"
             export CARGO_TARGET_DIR="$PWD/target"
+            export RUST_BACKTRACE=1
+            # Flake sources omit Git history. Map the recorded revision to independently
+            # staged source trees for P1's directory-hash comparison.
+            cp -r ${userlandSrc}/agents ${userlandSrc}/skills ${userlandSrc}/extensions .
+            git init --quiet
+            git add agents skills extensions
+            git -c user.name=Sausage -c user.email=sausage@localhost \
+              commit --no-gpg-sign --quiet -m 'Flake source trees'
+            git update-ref refs/replace/${revision} HEAD
             mkdir -p target/userland
             ln -s ${userland} target/bundle
             ln -s ${userland} target/userland/bundle