diff --git a/install.sh b/install.sh
index 4435ed1..6b0eec1 100755
--- a/install.sh
+++ b/install.sh
@@ -234,8 +234,13 @@ if [[ -d "$KIT_DIR/skills" ]]; then
 fi
 
 # --- build assembler -------------------------------------------------------
-say "building Rust assembler (cargo build --release)"
-( cd "$AGENTS_DIR/_assembler" && cargo build --release )
+# Prefer offline build (fresh-clone on a no-network machine should still work
+# if the registry cache is warm). Fall back to online fetch on failure.
+say "building Rust assembler (cargo build --release, offline first)"
+if ! ( cd "$AGENTS_DIR/_assembler" && cargo build --release --offline ) 2>/tmp/keiseikit-cargo-offline.log; then
+  say "offline build failed — fetching deps from crates.io"
+  ( cd "$AGENTS_DIR/_assembler" && cargo build --release )
+fi
 if [[ ! -x "$AGENTS_DIR/_assembler/target/release/assemble" ]]; then
   err "build succeeded but binary not found at $AGENTS_DIR/_assembler/target/release/assemble"
   exit 2