diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index c808b80..2ca1852 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -196,10 +196,23 @@ jobs:
           mkdir -p "$fixture" "$install_dir"
           cp "$ARCHIVE" "$fixture/aas-$TARGET.tar.gz"
           cp "$CHECKSUM" "$fixture/aas-$TARGET.sha256"
-          python3 -m http.server 18765 --bind 127.0.0.1 --directory "$fixture" >/dev/null 2>&1 &
+          server_log="$RUNNER_TEMP/aas-installer-fixture.log"
+          python3 -m http.server 18765 --bind 127.0.0.1 --directory "$fixture" >"$server_log" 2>&1 &
           server_pid=$!
           trap 'kill "$server_pid" 2>/dev/null || true' EXIT
-          sleep 1
+          # Wait for the port to accept. A fixed sleep raced the interpreter's startup, and a
+          # server that never came up was indistinguishable from the installer being broken.
+          ready=0
+          for _ in $(seq 1 150); do
+            if ! kill -0 "$server_pid" 2>/dev/null; then break; fi
+            if curl -fsS -o /dev/null "http://127.0.0.1:18765/aas-$TARGET.sha256"; then ready=1; break; fi
+            sleep 0.2
+          done
+          if [ "$ready" != 1 ]; then
+            echo "installer fixture server never served on 127.0.0.1:18765" >&2
+            cat "$server_log" >&2 || true
+            exit 1
+          fi
           AAS_DOWNLOAD_BASE=http://127.0.0.1:18765 \
             AAS_BIN_DIR="$install_dir" \
             AAS_SKIP_ATTESTATION=1 \
@@ -227,12 +240,42 @@ jobs:
           New-Item -ItemType Directory -Force -Path $fixture, $installDir | Out-Null
           Copy-Item $env:ARCHIVE (Join-Path $fixture "aas-$env:TARGET.zip")
           Copy-Item $env:CHECKSUM (Join-Path $fixture "aas-$env:TARGET.sha256")
-          $server = Start-Process python -ArgumentList @(
+          # The Microsoft Store alias stub is named `python` and on PATH: it starts, so
+          # `Start-Process` succeeds, and then serves nothing.
+          $python = $null
+          foreach ($candidate in @("python", "python3")) {
+            $resolved = Get-Command $candidate -ErrorAction SilentlyContinue
+            if ($resolved -and $resolved.Source -notlike "*WindowsApps*") {
+              $python = $resolved.Source
+              break
+            }
+          }
+          if (-not $python) { throw "no usable python on PATH to serve the installer fixture" }
+          $serverLog = Join-Path $env:RUNNER_TEMP "aas-installer-fixture.log"
+          $server = Start-Process $python -ArgumentList @(
             "-m", "http.server", "18766", "--bind", "127.0.0.1", "--directory", $fixture
-          ) -PassThru -WindowStyle Hidden
+          ) -PassThru -NoNewWindow -RedirectStandardError $serverLog
           $originalUserPath = [Environment]::GetEnvironmentVariable("Path", "User")
           try {
-            Start-Sleep -Seconds 1
+            # Wait for the port to accept. A fixed sleep raced the interpreter's startup, and a
+            # server that never came up was indistinguishable from the installer being broken.
+            $ready = $false
+            foreach ($attempt in 1..150) {
+              if ($server.HasExited) { break }
+              try {
+                $probe = New-Object System.Net.Sockets.TcpClient
+                $probe.Connect("127.0.0.1", 18766)
+                $probe.Close()
+                $ready = $true
+                break
+              } catch {
+                Start-Sleep -Milliseconds 200
+              }
+            }
+            if (-not $ready) {
+              $detail = if (Test-Path $serverLog) { Get-Content $serverLog -Raw } else { "(no output)" }
+              throw "installer fixture server never accepted on 127.0.0.1:18766. $detail"
+            }
             $env:AAS_DOWNLOAD_BASE = "http://127.0.0.1:18766"
             $env:AAS_BIN_DIR = $installDir
             $env:AAS_SKIP_ATTESTATION = "1"