diff --git a/scripts/setup-linux.sh b/scripts/setup-linux.sh
index 8817364..689c880 100755
--- a/scripts/setup-linux.sh
+++ b/scripts/setup-linux.sh
@@ -18,7 +18,26 @@ if [ ${#MISSING[@]} -gt 0 ]; then
     exit 1
 fi
 
-# ── 1. System user for UID isolation ──
+# ── 1. Prerequisite check: Antigravity must be installed ──
+LS_BINARY="${ZEROGRAVITY_LS_PATH:-/usr/share/antigravity/resources/app/extensions/antigravity/bin/language_server_linux_x64}"
+echo "→ Checking for Antigravity installation…"
+if [ ! -f "$LS_BINARY" ]; then
+    echo ""
+    echo "✗ Antigravity is not installed (or the LS binary is missing)."
+    echo "  ZeroGravity requires a working Antigravity installation."
+    echo "  The Language Server binary is bundled with the Antigravity app"
+    echo "  and cannot be downloaded separately."
+    echo ""
+    echo "  Expected path:"
+    echo "    $LS_BINARY"
+    echo ""
+    echo "  Install Antigravity first, then re-run this script."
+    echo "  Alternatively, set ZEROGRAVITY_LS_PATH to a custom LS binary location."
+    exit 1
+fi
+echo "  Found: $LS_BINARY"
+
+# ── 2. System user for UID isolation ──
 echo "→ Creating zerogravity-ls system user…"
 if id -u zerogravity-ls &>/dev/null; then
     echo "  Already exists."
@@ -27,7 +46,7 @@ else
     echo "  Created."
 fi
 
-# ── 2. Sudoers rule (run commands as zerogravity-ls without password) ──
+# ── 3. Sudoers rule (run commands as zerogravity-ls without password) ──
 SUDOERS="/etc/sudoers.d/zerogravity"
 echo "→ Installing sudoers rule…"
 if [ -f "$SUDOERS" ]; then
@@ -38,16 +57,16 @@ else
     echo "  Installed: $SUDOERS"
 fi
 
-# ── 3. Data directory permissions ──
+# ── 4. Data directory permissions ──
 echo "→ Setting up /tmp/zerogravity-standalone…"
 sudo mkdir -p /tmp/zerogravity-standalone
 sudo chmod 1777 /tmp/zerogravity-standalone
 
-# ── 4. Config directory ──
+# ── 5. Config directory ──
 echo "→ Setting up ~/.config/zerogravity…"
 mkdir -p "$HOME/.config/zerogravity"
 
-# ── 5. Systemd user service ──
+# ── 6. Systemd user service ──
 echo "→ Installing systemd user service…"
 UNIT_DIR="$HOME/.config/systemd/user"
 mkdir -p "$UNIT_DIR"
@@ -73,7 +92,7 @@ systemctl --user daemon-reload
 echo "  Installed: $UNIT_DIR/zerogravity.service"
 echo "  Enable with: systemctl --user enable zerogravity"
 
-# ── 6. Build ──
+# ── 7. Build ──
 echo "→ Building release binary…"
 cd "$PROJECT_DIR"
 cargo build --release 2>&1 | tail -1
diff --git a/scripts/setup-macos.sh b/scripts/setup-macos.sh
index c6ea782..7697049 100755
--- a/scripts/setup-macos.sh
+++ b/scripts/setup-macos.sh
@@ -16,7 +16,35 @@ mkdir -p "$CONFIG_DIR"
 echo "→ Setting up /tmp/zerogravity-standalone…"
 mkdir -p /tmp/zerogravity-standalone
 
-# ── 3. Launchd plist ──
+# ── 3. Prerequisite check: Antigravity must be installed ──
+LS_BINARY="${ZEROGRAVITY_LS_PATH:-}"
+if [ -z "$LS_BINARY" ]; then
+    # Check both /Applications and ~/Applications
+    for base in "/Applications/Antigravity.app" "$HOME/Applications/Antigravity.app"; do
+        candidate="$base/Contents/Resources/app/extensions/antigravity/bin/language_server_darwin_arm64"
+        if [ -f "$candidate" ]; then
+            LS_BINARY="$candidate"
+            break
+        fi
+    done
+fi
+echo "→ Checking for Antigravity installation…"
+if [ -z "$LS_BINARY" ] || [ ! -f "$LS_BINARY" ]; then
+    echo ""
+    echo "✗ Antigravity is not installed (or the LS binary is missing)."
+    echo "  ZeroGravity requires a working Antigravity installation."
+    echo "  The Language Server binary is bundled with the Antigravity app"
+    echo "  and cannot be downloaded separately."
+    echo ""
+    echo "  Expected in: /Applications/Antigravity.app or ~/Applications/Antigravity.app"
+    echo ""
+    echo "  Install Antigravity first, then re-run this script."
+    echo "  Alternatively, set ZEROGRAVITY_LS_PATH to a custom LS binary location."
+    exit 1
+fi
+echo "  Found: $LS_BINARY"
+
+# ── 4. Launchd plist ──
 echo "→ Installing launchd plist…"
 PLIST_DIR="$HOME/Library/LaunchAgents"
 PLIST="$PLIST_DIR/com.zerogravity.proxy.plist"
@@ -55,7 +83,7 @@ echo "  Installed: $PLIST"
 echo "  Start with: launchctl load $PLIST"
 echo "  Stop with:  launchctl unload $PLIST"
 
-# ── 4. Build ──
+# ── 5. Build ──
 echo "→ Building release binary…"
 cd "$PROJECT_DIR"
 cargo build --release 2>&1 | tail -1
diff --git a/scripts/setup-windows.ps1 b/scripts/setup-windows.ps1
index 89da62e..cf1cfcb 100644
--- a/scripts/setup-windows.ps1
+++ b/scripts/setup-windows.ps1
@@ -19,7 +19,26 @@ $DataDir = Join-Path $env:TEMP "zerogravity-standalone"
 New-Item -ItemType Directory -Force -Path $DataDir | Out-Null
 Write-Host "  $DataDir"
 
-# ── 3. Build ──
+# ── 3. Prerequisite check: Antigravity must be installed ──
+Write-Host "→ Checking for Antigravity installation…"
+$LsBinary = Join-Path $env:LOCALAPPDATA "Programs\Antigravity\resources\app\extensions\antigravity\bin\language_server_windows_x64.exe"
+if (-not (Test-Path $LsBinary)) {
+    Write-Host ""
+    Write-Host "✗ Antigravity is not installed (or the LS binary is missing)." -ForegroundColor Red
+    Write-Host "  ZeroGravity requires a working Antigravity installation."
+    Write-Host "  The Language Server binary is bundled with the Antigravity app"
+    Write-Host "  and cannot be downloaded separately."
+    Write-Host ""
+    Write-Host "  Expected path:"
+    Write-Host "    $LsBinary"
+    Write-Host ""
+    Write-Host "  Install Antigravity first, then re-run this script."
+    Write-Host "  Alternatively, set ZEROGRAVITY_LS_PATH to a custom LS binary location."
+    exit 1
+}
+Write-Host "  Found: $LsBinary"
+
+# ── 4. Build ──
 Write-Host "→ Building release binary…"
 Push-Location $ProjectDir
 cargo build --release
@@ -32,7 +51,7 @@ if (-not (Test-Path $Binary)) {
 }
 Write-Host "  Built: $Binary"
 
-# ── 4. Scheduled task (optional) ──
+# ── 5. Scheduled task (optional) ──
 $TaskName = "ZeroGravity Proxy"
 $Existing = Get-ScheduledTask -TaskName $TaskName -ErrorAction SilentlyContinue