ci: fix Windows npm cache corruption (ECOMPROMISED error)

Fix fundamental issue causing "npm error code ECOMPROMISED" in Windows CI.

Root Cause Analysis:
--------------------
1. Environment Variable Timing Issue:
   - Writing to $env:GITHUB_ENV only affects FUTURE steps, not current step
   - Previous workflow: Set NPM_CONFIG_CACHE in GITHUB_ENV, then ran
     "npm cache clean" in SAME step
   - Result: Cache clean ran against DEFAULT cache, not configured cache

2. Configuration Order Issue:
   - NPM_CONFIG_PREFIX was set AFTER installing promptfoo globally
   - npm install used default prefix, then config pointed to different location
   - Created mismatch between package location and npm expectations
   - Caused cache lock file integrity errors (ECOMPROMISED)

3. Cache Clean Timing:
   - Cache was cleaned before configuring where cache should be located
   - Wrong cache was cleaned, leaving actual cache potentially corrupted

The Fix:
--------
- Use "npm config set" to configure cache/prefix IMMEDIATELY (not GITHUB_ENV)
- Configure cache location FIRST
- Configure prefix location SECOND
- Clean and verify cache THIRD (now cleans correctly-configured cache)
- Only THEN export to GITHUB_ENV for future steps
- Consolidated "Add npm global bin to PATH" into single configuration step

Changes Applied to Both Jobs:
- test: Uses global promptfoo install
- test-npx-fallback: Uses npx fallback (no global install)

This ensures npm configuration is consistent and cache integrity is maintained
across all Windows CI runs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: mldangelo

.github/workflows/test.yml

@@ -79,31 +79,46 @@ jobs:
         with:
           node-version: "24"
 
-      - name: Configure npm cache on Windows
+      - name: Configure npm on Windows
         if: matrix.os == 'windows-latest'
+        shell: pwsh
         run: |
-          "NPM_CONFIG_CACHE=$env:RUNNER_TEMP\\npm-cache" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
-          npm cache clean --force
-
-      - name: Install promptfoo globally
-        run: npm install -g promptfoo@latest
-        env:
-          NODE_OPTIONS: --max-old-space-size=4096
-
-      - name: Add npm global bin to PATH (Windows)
-        if: matrix.os == 'windows-latest'
-        run: |
-          $globalPrefix = (npm config get prefix).Trim()
-          if (-not $globalPrefix) {
+          # Configure cache location (applies immediately to this step)
+          $cacheDir = Join-Path $env:RUNNER_TEMP "npm-cache"
+          New-Item -ItemType Directory -Force -Path $cacheDir | Out-Null
+          npm config set cache $cacheDir --location=user
+
+          # Configure prefix location (applies immediately to this step)
+          $globalPrefix = npm config get prefix
+          if (-not $globalPrefix -or $globalPrefix -eq "undefined") {
             $globalPrefix = Join-Path $env:APPDATA "npm"
           }
+          $globalPrefix = $globalPrefix.Trim()
+          npm config set prefix $globalPrefix --location=user
+
+          # NOW clean and verify cache (cleans the correctly-configured cache)
+          npm cache clean --force
+          npm cache verify
+
+          # Export settings for future steps
+          "NPM_CONFIG_CACHE=$cacheDir" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
           "NPM_CONFIG_PREFIX=$globalPrefix" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
           "npm_config_prefix=$globalPrefix" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+
+          # Add global bin directories to PATH
           $binPaths = @($globalPrefix, (Join-Path $globalPrefix "bin")) | Where-Object { Test-Path $_ }
           foreach ($binPath in $binPaths) {
             $binPath | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           }
 
+          Write-Host "npm cache: $cacheDir"
+          Write-Host "npm prefix: $globalPrefix"
+
+      - name: Install promptfoo globally
+        run: npm install -g promptfoo@latest
+        env:
+          NODE_OPTIONS: --max-old-space-size=4096
+
       - uses: astral-sh/setup-uv@v7
         with:
           enable-cache: true
@@ -138,11 +153,34 @@ jobs:
         with:
           node-version: "24"
 
-      - name: Configure npm cache on Windows
+      - name: Configure npm on Windows
         if: matrix.os == 'windows-latest'
+        shell: pwsh
         run: |
-          "NPM_CONFIG_CACHE=$env:RUNNER_TEMP\\npm-cache" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+          # Configure cache location (applies immediately to this step)
+          $cacheDir = Join-Path $env:RUNNER_TEMP "npm-cache"
+          New-Item -ItemType Directory -Force -Path $cacheDir | Out-Null
+          npm config set cache $cacheDir --location=user
+
+          # Configure prefix location (applies immediately to this step)
+          $globalPrefix = npm config get prefix
+          if (-not $globalPrefix -or $globalPrefix -eq "undefined") {
+            $globalPrefix = Join-Path $env:APPDATA "npm"
+          }
+          $globalPrefix = $globalPrefix.Trim()
+          npm config set prefix $globalPrefix --location=user
+
+          # NOW clean and verify cache (cleans the correctly-configured cache)
           npm cache clean --force
+          npm cache verify
+
+          # Export settings for future steps
+          "NPM_CONFIG_CACHE=$cacheDir" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+          "NPM_CONFIG_PREFIX=$globalPrefix" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+          "npm_config_prefix=$globalPrefix" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+
+          Write-Host "npm cache: $cacheDir"
+          Write-Host "npm prefix: $globalPrefix"
 
       # Intentionally skip installing promptfoo globally
       # This tests the npx fallback path