diff --git a/scripts/build-module-runtime.sh b/scripts/build-module-runtime.sh
index 17a9192..53f57a5 100755
--- a/scripts/build-module-runtime.sh
+++ b/scripts/build-module-runtime.sh
@@ -33,7 +33,16 @@ SRCS=(); for f in \
   pg.d.ts; do
   [ -f "$MOD/$f" ] && SRCS+=("$f")
 done
-TSC="$MESH_SDK/node_modules/.bin/tsc"; ( cd "$MOD" && "$TSC" "${SRCS[@]}" --module NodeNext --moduleResolution NodeNext --target ES2022 --outDir dist >/dev/null )
+# The module compiles against the SDK, which its package.json names and nothing installs: a module
+# never built on this workstation has no node_modules, and tsc fails on the first import. Installed
+# as a package copy from the sibling checkout (never a link) when absent — the compile needs only
+# the types; the image takes the SDK from MESH_SDK below.
+if [ ! -e "$MOD/node_modules/@novox/mesh-sdk" ]; then
+  ( cd "$MOD" && npm install --no-save --install-links --no-package-lock --ignore-scripts --silent "$MESH_SDK" ) \
+    || { echo "cannot install the SDK into $MOD for the compile" >&2; exit 1; }
+fi
+# Output kept: a compile error hidden behind /dev/null is a build that fails saying nothing.
+TSC="$MESH_SDK/node_modules/.bin/tsc"; ( cd "$MOD" && "$TSC" "${SRCS[@]}" --module NodeNext --moduleResolution NodeNext --target ES2022 --outDir dist 1>&2 )
 
 STAGE="$(mktemp -d)"; trap 'rm -rf "$STAGE"' EXIT
 cp -r "$MESH_TOOLS/dist" "$STAGE/dist"
diff --git a/src/rebuild.ts b/src/rebuild.ts
index e20dda8..d6276f3 100644
--- a/src/rebuild.ts
+++ b/src/rebuild.ts
@@ -134,7 +134,7 @@ export function rebuild(env: NodeJS.ProcessEnv = process.env, testFiles: string[
       // the code in front of you, which is the whole of 005.
       throw new Error(
         `could not build the ${build.what}: ${build.argv.join(" ")} in ${build.in}\n\n` +
-          `${(ran.stderr || ran.stdout || String(ran.error)).trim()}`,
+          `${(ran.stderr || ran.stdout || (ran.error ? String(ran.error) : `exit status ${ran.status}, and it said nothing`)).trim()}`,
       );
     }
     built.push(build.what);