How do I Properly run NPM Install in Visual Studio

I'm having trouble setting up an NPM task for an automated build in Visual Studio Team Services (previously Visual Studio Online). There are two problems:

Cache locking errors (shown below).
It is painfully slow -- 45+ minutes for a dozen or so packages.

I added the --cache argument but that did not seem to help.

npm install --dev --cache $(Agent.BuildDirectory)\b

The binaries folder seems like the right spot for the cache, but honestly, I'm not sure. Some documentation here:

https://msdn.microsoft.com/Library/vs/alm/Build/scripts/variables#AgentVariables

I appreciate any advice...

Current Config:

Build console output:

Set workingFolder to default: C:\LR\MMS\Services\Mms\TaskAgentProvisioner\Tools\agents\1.97.1\tasks\Npm\0.2.7
##[debug]check path : C:\LR\MMS\Services\Mms\TaskAgentProvisioner\Tools\agents\1.97.1\tasks\Npm\0.2.7\task.json
##[debug]set resource file to: C:\LR\MMS\Services\Mms\TaskAgentProvisioner\Tools\agents\1.97.1\tasks\Npm\0.2.7\task.json
##[debug]system.culture=en-US
##[debug]check path : C:\Program Files\nodejs\npm.cmd
##[debug]npm=C:\Program Files\nodejs\npm.cmd
##[debug]cwd=C:\a\1\s\com.example.web
##[debug]path exists: C:\a\1\s\com.example.web
##[debug]command=install
##[debug]C:\Program Files\nodejs\npm.cmd arg: install
##[debug]arguments=--dev --cache C:\a\1\b
##[debug]C:\Program Files\nodejs\npm.cmd arg: --dev --cache C:\a\1\b
##[debug]exec tool: C:\Program Files\nodejs\npm.cmd
##[debug]Arguments:
##[debug]   install
##[debug]   --dev
##[debug]   --cache
##[debug]   C:\a\1\b
[command]C:\Program Files\nodejs\npm.cmd install --dev --cache C:\a\1\b
npm WARN deprecated graceful-fs@3.0.8: graceful-fs version 3 and before will fail on newer node releases. Please update to graceful-fs@^4.0.0 as soon as possible.
npm WARN deprecated sf-lint@1.0.2: Use eslint-config-simplifield instead.
npm WARN deprecated lodash@2.4.1: lodash@<3.0.0 is no longer maintained. Upgrade to lodash@^4.0.0.
npm WARN deprecated lodash@0.9.2: Grunt needs your help! See https://github.com/gruntjs/grunt/issues/1403.
npm ERR! addLocal Could not install C:\a\1\s\com.example.web\@shinnn\eslint-config@>=0.0.5 <0.0.6\fixtures
npm WARN deprecated phantomjs@2.1.3: Package renamed to phantomjs-prebuilt. Please update 'phantomjs' package references to 'phantomjs-prebuilt'
npm WARN peerDependencies The peer dependency qunitjs@^1.14.0 included from karma-qunit will no
npm WARN peerDependencies longer be automatically installed to fulfill the peerDependency 
npm WARN peerDependencies in npm 3+. Your application will need to depend on it explicitly.
npm WARN package.json Dependency 'mocha' exists in both dependencies and devDependencies, using 'mocha@*' from dependencies
npm WARN package.json Dependency 'mocha' exists in both dependencies and devDependencies, using 'mocha@*' from dependencies
npm ERR! addLocal Could not install C:\a\1\s\com.example.web\@shinnn\eslint-config@>=0.0.4 <0.0.5\fixtures
> cson@1.6.2 preinstall C:\a\1\s\com.example.web\node_modules\gulp-uglify\node_modules\uglify-save-license\node_modules\grunt-replace\node_modules\applause\node_modules\cson
> node ./cyclic.js
npm WARN locking Error: EMFILE, open 'C:\a\1\b\_locks\strip-ansi-0bb45da2369f5768.lock.STALE.STALE.STALE'
npm WARN locking     at Error (native)
npm WARN locking  C:\a\1\b\_locks\strip-ansi-0bb45da2369f5768.lock failed { [Error: EMFILE, open 'C:\a\1\b\_locks\strip-ansi-0bb45da2369f5768.lock.STALE.STALE.STALE']
npm WARN locking   errno: -4066,
npm WARN locking   code: 'EMFILE',
npm WARN locking   path: 'C:\\a\\1\\b\\_locks\\strip-ansi-0bb45da2369f5768.lock.STALE.STALE.STALE' }
npm ERR! Windows_NT 6.3.9600
npm ERR! argv "C:\\Program Files\\nodejs\\\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install" "--dev" "--cache" "C:\\a\\1\\b"
npm ERR! node v0.12.7
npm ERR! npm  v2.11.3
2016-03-30T14:15:17.4509244Z npm ERR! Attempt to unlock C:\a\1\s\com.example.web\node_modules\gulp-imagemin\node_modules\imagemin-pngquant\node_modules\pngquant-bin\node_modules\compare-size\node_modules\ava\node_modules\chalk\node_modules\strip-ansi, which hasn't been locked
npm ERR! 
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>
npm WARN locking Error: EMFILE, open 'C:\a\1\b\_locks\ansi-styles-cedcc1e1e4774cd0.lock.STALE.STALE.STALE'
npm WARN locking     at Error (native)
npm WARN locking  C:\a\1\b\_locks\ansi-styles-cedcc1e1e4774cd0.lock failed { [Error: EMFILE, open 'C:\a\1\b\_locks\ansi-styles-cedcc1e1e4774cd0.lock.STALE.STALE.STALE']
npm WARN locking   errno: -4066,
npm WARN locking   code: 'EMFILE',
npm WARN locking   path: 'C:\\a\\1\\b\\_locks\\ansi-styles-cedcc1e1e4774cd0.lock.STALE.STALE.STALE' }
npm ERR! Windows_NT 6.3.9600
npm ERR! argv "C:\\Program Files\\nodejs\\\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install" "--dev" "--cache" "C:\\a\\1\\b"
npm ERR! node v0.12.7
npm ERR! npm  v2.11.3
npm ERR! Attempt to unlock C:\a\1\s\com.example.web\node_modules\gulp-imagemin\node_modules\imagemin-pngquant\node_modules\pngquant-bin\node_modules\compare-size\node_modules\ava\node_modules\chalk\node_modules\ansi-styles, which hasn't been locked
npm ERR! 
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>
npm WARN locking Error: EMFILE, open 'C:\a\1\b\_locks\has-ansi-819c7cca16ab7ac8.lock.STALE.STALE.STALE'
npm WARN locking     at Error (native)
2016-03-30T14:15:17.5709240Z npm WARN locking  C:\a\1\b\_locks\has-ansi-819c7cca16ab7ac8.lock failed { [Error: EMFILE, open 'C:\a\1\b\_locks\has-ansi-819c7cca16ab7ac8.lock.STALE.STALE.STALE']

Re-installing NPM solved my issue:

npm install npm -g

Specifically, I added the circled task to my build: