test(e2e): an inherited subos comes with the ledger that registers its assets

_inherit_toolchain.sh linked the user's subos into the test home but not the
version ledger that registers the assets its workspace projects. xlings
checks those before it changes the sysroot, so every install that touched it
was refused ("Scrt1.o@glibc-2.44.3: installed asset registration missing"):
e2e 32, 33 and 40 on a runner whose ~/.mcpp held no mcpplibs.cmdline.

Author: Sunrisepeak

tests/e2e/_inherit_toolchain.sh

@@ -83,6 +83,13 @@ if [[ "${MCPP_INHERIT_SUBOS:-1}" != "0" && -d "$USER_MCPP/registry/subos" ]]; th
     [[ -e "$MCPP_HOME/registry/subos" ]] \
         || ln -sf "$USER_MCPP/registry/subos" "$MCPP_HOME/registry/subos" 2>/dev/null \
         || cp -r "$USER_MCPP/registry/subos" "$MCPP_HOME/registry/subos"
+    # The subos's workspace names the assets it projects (glibc's Scrt1.o,
+    # ...), and xlings checks each one against the home's version ledger
+    # before it changes the sysroot. A ledger without them refuses every
+    # install that touches the sysroot ("installed asset registration
+    # missing"), so the inherited subos comes with a copy of the ledger.
+    [[ -e "$MCPP_HOME/registry/.xlings.json" || ! -f "$USER_MCPP/registry/.xlings.json" ]] \
+        || cp -f "$USER_MCPP/registry/.xlings.json" "$MCPP_HOME/registry/.xlings.json"
 fi
 if [[ "${MCPP_INHERIT_CONFIG:-1}" != "0" && -f "$USER_MCPP/config.toml" ]]; then
     cp -f "$USER_MCPP/config.toml" "$MCPP_HOME/config.toml" 2>/dev/null || true