diff --git a/.github/workflows/studio-windows-api-smoke.yml b/.github/workflows/studio-windows-api-smoke.yml
index 429627cc7d..c8c2192b2e 100644
--- a/.github/workflows/studio-windows-api-smoke.yml
+++ b/.github/workflows/studio-windows-api-smoke.yml
@@ -89,6 +89,12 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories. See
+          # studio-windows-update-smoke.yml for the full rationale --
+          # creating an empty studio/frontend/dist trips setup.ps1's
+          # mtime-based staleness check into "frontend up to date, skip
+          # rebuild" and Studio boots with an empty dist directory.
+          # Add-MpPreference accepts paths that do not yet exist.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -96,7 +102,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {
diff --git a/.github/workflows/studio-windows-inference-smoke.yml b/.github/workflows/studio-windows-inference-smoke.yml
index e81cf2944c..9a2fb46e62 100644
--- a/.github/workflows/studio-windows-inference-smoke.yml
+++ b/.github/workflows/studio-windows-inference-smoke.yml
@@ -99,6 +99,12 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories. See
+          # studio-windows-update-smoke.yml for the full rationale --
+          # creating an empty studio/frontend/dist trips setup.ps1's
+          # mtime-based staleness check into "frontend up to date, skip
+          # rebuild" and Studio boots with an empty dist directory.
+          # Add-MpPreference accepts paths that do not yet exist.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -106,7 +112,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {
@@ -390,6 +395,12 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories. See
+          # studio-windows-update-smoke.yml for the full rationale --
+          # creating an empty studio/frontend/dist trips setup.ps1's
+          # mtime-based staleness check into "frontend up to date, skip
+          # rebuild" and Studio boots with an empty dist directory.
+          # Add-MpPreference accepts paths that do not yet exist.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -397,7 +408,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {
@@ -763,6 +773,12 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories. See
+          # studio-windows-update-smoke.yml for the full rationale --
+          # creating an empty studio/frontend/dist trips setup.ps1's
+          # mtime-based staleness check into "frontend up to date, skip
+          # rebuild" and Studio boots with an empty dist directory.
+          # Add-MpPreference accepts paths that do not yet exist.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -770,7 +786,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {
diff --git a/.github/workflows/studio-windows-ui-smoke.yml b/.github/workflows/studio-windows-ui-smoke.yml
index fc62b2c5a8..1858cc7f8f 100644
--- a/.github/workflows/studio-windows-ui-smoke.yml
+++ b/.github/workflows/studio-windows-ui-smoke.yml
@@ -98,6 +98,12 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories. See
+          # studio-windows-update-smoke.yml for the full rationale --
+          # creating an empty studio/frontend/dist trips setup.ps1's
+          # mtime-based staleness check into "frontend up to date, skip
+          # rebuild" and Studio boots with an empty dist directory.
+          # Add-MpPreference accepts paths that do not yet exist.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -105,7 +111,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {
diff --git a/.github/workflows/studio-windows-update-smoke.yml b/.github/workflows/studio-windows-update-smoke.yml
index 209c7a540b..d06ea2a760 100644
--- a/.github/workflows/studio-windows-update-smoke.yml
+++ b/.github/workflows/studio-windows-update-smoke.yml
@@ -103,6 +103,17 @@ jobs:
           Write-Host "npm version before upgrade: $(npm -v)"
           npm install -g 'npm@^11' 2>&1 | Out-Host
           Write-Host "npm version after upgrade: $(npm -v)"
+          # NOTE: do NOT pre-create these directories before adding the
+          # exclusion -- creating an empty studio/frontend/dist trips
+          # setup.ps1 line 1281-1296's mtime-based "is the frontend
+          # stale?" check into "up to date, skip rebuild", because the
+          # newly-created dist's mtime is younger than every source
+          # file. Studio then boots with an empty dist and 500s on
+          # GET / with FileNotFoundError: dist\index.html. See run
+          # 25546676715 / job 74984469728.
+          # Add-MpPreference accepts paths that do not yet exist; the
+          # exclusion is registered and applies when the path
+          # materialises.
           foreach ($p in @(
             "$env:USERPROFILE\.unsloth",
             "$env:USERPROFILE\AppData\Local\uv",
@@ -110,7 +121,6 @@ jobs:
             "$env:GITHUB_WORKSPACE\studio\frontend\dist"
           )) {
             try {
-              if (-not (Test-Path $p)) { New-Item -ItemType Directory -Force -Path $p | Out-Null }
               Add-MpPreference -ExclusionPath $p -ErrorAction Stop
               Write-Host "Defender exclusion added: $p"
             } catch {