diff --git a/studio/setup.ps1 b/studio/setup.ps1
index 2420448deb..1046304c46 100644
--- a/studio/setup.ps1
+++ b/studio/setup.ps1
@@ -748,9 +748,39 @@ Write-Host ""
 # ==========================================================================
 #  PHASE 2: Frontend build (skip if pip-installed -- already bundled)
 # ==========================================================================
+$DistDir = Join-Path $FrontendDir "dist"
+# Skip build if dist/ exists and no tracked input is newer than dist/.
+# Checks src/, public/, package.json, config files -- not just src/.
+$NeedFrontendBuild = $true
 if ($IsPipInstall) {
+    $NeedFrontendBuild = $false
     Write-Host "[OK] Running from pip install - frontend already bundled, skipping build" -ForegroundColor Green
-} else {
+} elseif (Test-Path $DistDir) {
+    $DistTime = (Get-Item $DistDir).LastWriteTime
+    # Check src/ and public/ recursively using explicit paths
+    $TrackedDirs = @("src", "public") |
+        ForEach-Object { Join-Path $FrontendDir $_ } |
+        Where-Object { Test-Path $_ }
+    $NewerFile = $null
+    if ($TrackedDirs.Count -gt 0) {
+        $NewerFile = $TrackedDirs |
+            ForEach-Object { Get-ChildItem -Path $_ -Recurse -File -ErrorAction SilentlyContinue } |
+            Where-Object { $_.LastWriteTime -gt $DistTime } | Select-Object -First 1
+    }
+    # Also check top-level config and entry files (package.json, vite.config.ts, index.html, etc.)
+    if (-not $NewerFile) {
+        $NewerFile = Get-ChildItem -Path $FrontendDir -File -ErrorAction SilentlyContinue |
+            Where-Object { $_.Name -match '\.(json|ts|js|mjs|html)$' -and $_.LastWriteTime -gt $DistTime } |
+            Select-Object -First 1
+    }
+    if (-not $NewerFile) {
+        $NeedFrontendBuild = $false
+        Write-Host "[OK] Frontend already built and up to date -- skipping build" -ForegroundColor Green
+    } else {
+        Write-Host "[INFO] Frontend source changed since last build -- rebuilding..." -ForegroundColor Yellow
+    }
+}
+if ($NeedFrontendBuild -and -not $IsPipInstall) {
     Write-Host ""
     Write-Host "Building frontend..." -ForegroundColor Cyan
     # npm writes warnings to stderr; lower ErrorActionPreference so PS doesn't
@@ -758,9 +788,6 @@ if ($IsPipInstall) {
     $prevEAP_npm = $ErrorActionPreference
     $ErrorActionPreference = "Continue"
     Push-Location $FrontendDir
-    # Remove stale node_modules and package-lock.json to avoid version conflicts
-    if (Test-Path "node_modules") { Remove-Item -Recurse -Force "node_modules" }
-    if (Test-Path "package-lock.json") { Remove-Item -Force "package-lock.json" }
     npm install 2>&1 | Out-Null
     if ($LASTEXITCODE -ne 0) {
         Pop-Location
diff --git a/studio/setup.sh b/studio/setup.sh
index 4c8a6c7dde..98d6d4b8f4 100755
--- a/studio/setup.sh
+++ b/studio/setup.sh
@@ -41,13 +41,27 @@ if [[ "$keynames" == *$'\nCOLAB_'* ]]; then
 fi
 
 # ── Detect whether frontend needs building ──
-# Only skip when BOTH conditions are true:
-#   1. We're inside site-packages (PyPI / pip install, not editable)
-#   2. dist/ already exists (pre-built in the wheel)
-# Otherwise always (re)build — handles upgrades, editable installs, and
-# pip-from-source where dist/ was never built.
-if [[ "$SCRIPT_DIR" == */site-packages/* ]] && [ -d "$SCRIPT_DIR/frontend/dist" ]; then
-    echo "✅ Frontend pre-built (PyPI) — skipping Node/npm check."
+# Skip if dist/ exists AND no tracked input is newer than dist/.
+# Checks top-level config/entry files and src/, public/ recursively.
+# This handles: PyPI installs (dist/ bundled), repeat runs (no changes),
+# and upgrades/pulls (source newer than dist/ triggers rebuild).
+_NEED_FRONTEND_BUILD=true
+if [ -d "$SCRIPT_DIR/frontend/dist" ]; then
+    # Check top-level config and entry files (package.json, vite.config.ts, index.html, etc.)
+    _changed=$(find "$SCRIPT_DIR/frontend" -maxdepth 1 \
+        \( -name "*.json" -o -name "*.ts" -o -name "*.js" -o -name "*.mjs" -o -name "*.html" \) \
+        -newer "$SCRIPT_DIR/frontend/dist" -print -quit 2>/dev/null)
+    # Check src/ and public/ recursively
+    if [ -z "$_changed" ]; then
+        _changed=$(find "$SCRIPT_DIR/frontend/src" "$SCRIPT_DIR/frontend/public" \
+            -type f -newer "$SCRIPT_DIR/frontend/dist" -print -quit 2>/dev/null)
+    fi
+    if [ -z "$_changed" ]; then
+        _NEED_FRONTEND_BUILD=false
+    fi
+fi
+if [ "$_NEED_FRONTEND_BUILD" = false ]; then
+    echo "✅ Frontend already built and up to date -- skipping Node/npm check."
 else
 NEED_NODE=true
 if command -v node &>/dev/null && command -v npm &>/dev/null; then
@@ -146,12 +160,17 @@ run_quiet "npm run build" npm run build
 
 _restore_gitignores
 trap - EXIT
-cd "$SCRIPT_DIR/backend/core/data_recipe/oxc-validator"
-run_quiet "npm install (oxc validator runtime)" npm install
 cd "$SCRIPT_DIR"
 echo "✅ Frontend built to frontend/dist"
 
-fi  # end frontend dist check
+fi  # end frontend build check
+
+# ── oxc-validator runtime (always install, independent of frontend build) ──
+if [ -d "$SCRIPT_DIR/backend/core/data_recipe/oxc-validator" ] && command -v npm &>/dev/null; then
+    cd "$SCRIPT_DIR/backend/core/data_recipe/oxc-validator"
+    run_quiet "npm install (oxc validator runtime)" npm install
+    cd "$SCRIPT_DIR"
+fi
 
 # ── 6. Python venv + deps ──