title: `Extension Development Host` fails with `Cannot find module 'vscode-languageclient' `
body: <p>Writing a VSCode Extension which fails with <code>Cannot find module 'vscode-languageclient' </code> in <code>Extension Development Host</code> Mode ( <code>F5</code> Key ). Not sure how to fix that. If I package the Extension and install the <code>vsix</code> File, everything works fine.</p>
  <p>Thank's a lot!</p>
  <p><a href="https://i.stack.imgur.com/GUWeN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GUWeN.png" alt="enter image description here" /></a></p>
  <p>Here is the Output from the <code>vcse</code> Tool.</p>
  <pre><code>D:\Work\Coding\VSCode\Extensions\BDD Recorder\bdd-recorder&gt;vsce ls
  Executing prepublish script 'npm run vscode:prepublish'...
  
  &gt; bdd-recorder@0.0.1 vscode:prepublish D:\Work\Coding\VSCode\Extensions\BDD Recorder\bdd-recorder
  &gt; npm run compile
  
  
  &gt; bdd-recorder@0.0.1 compile D:\Work\Coding\VSCode\Extensions\BDD Recorder\bdd-recorder
  &gt; tsc -p ./
  
  build_extension.cmd
  CHANGELOG.md
  out/extension.js
  package.json
  README.md
  node_modules/vscode-languageclient/.eslintignore
  node_modules/vscode-languageclient/lib/callHierarchy.proposed.js
  node_modules/vscode-languageclient/lib/client.js
  node_modules/vscode-languageclient/lib/codeConverter.js
  node_modules/vscode-languageclient/lib/colorProvider.js
  node_modules/vscode-languageclient/lib/configuration.js
  node_modules/vscode-languageclient/lib/declaration.js
  node_modules/vscode-languageclient/lib/foldingRange.js
  node_modules/vscode-languageclient/lib/implementation.js
  node_modules/vscode-languageclient/lib/main.js
  node_modules/vscode-languageclient/lib/progress.js
  node_modules/vscode-languageclient/lib/progressPart.js
  node_modules/vscode-languageclient/lib/protocolCodeLens.js
  node_modules/vscode-languageclient/lib/protocolCompletionItem.js
  node_modules/vscode-languageclient/lib/protocolConverter.js
  node_modules/vscode-languageclient/lib/protocolDocumentLink.js
  node_modules/vscode-languageclient/lib/selectionRange.js
  node_modules/vscode-languageclient/lib/semanticTokens.proposed.js
  node_modules/vscode-languageclient/lib/typeDefinition.js
  node_modules/vscode-languageclient/lib/utils/async.js
  node_modules/vscode-languageclient/lib/utils/is.js
  node_modules/vscode-languageclient/lib/utils/processes.js
  node_modules/vscode-languageclient/lib/utils/terminateProcess.sh
  node_modules/vscode-languageclient/lib/utils/uuid.js
  node_modules/vscode-languageclient/lib/workspaceFolders.js
  node_modules/vscode-languageclient/License.txt
  node_modules/vscode-languageclient/package.json
  node_modules/vscode-languageclient/README.md
  node_modules/vscode-languageclient/thirdpartynotices.txt
  node_modules/vscode-languageclient/node_modules/semver/bin/semver.js
  node_modules/vscode-languageclient/node_modules/semver/CHANGELOG.md
  node_modules/vscode-languageclient/node_modules/semver/LICENSE
  node_modules/vscode-languageclient/node_modules/semver/package.json
  node_modules/vscode-languageclient/node_modules/semver/range.bnf
  node_modules/vscode-languageclient/node_modules/semver/README.md
  node_modules/vscode-languageclient/node_modules/semver/semver.js
  node_modules/vscode-languageserver-protocol/.eslintignore
  node_modules/vscode-languageserver-protocol/lib/main.js
  node_modules/vscode-languageserver-protocol/lib/messages.js
  node_modules/vscode-languageserver-protocol/lib/protocol.callHierarchy.proposed.js
  node_modules/vscode-languageserver-protocol/lib/protocol.colorProvider.js
  node_modules/vscode-languageserver-protocol/lib/protocol.configuration.js
  node_modules/vscode-languageserver-protocol/lib/protocol.declaration.js
  node_modules/vscode-languageserver-protocol/lib/protocol.foldingRange.js
  node_modules/vscode-languageserver-protocol/lib/protocol.implementation.js
  node_modules/vscode-languageserver-protocol/lib/protocol.js
  node_modules/vscode-languageserver-protocol/lib/protocol.progress.js
  node_modules/vscode-languageserver-protocol/lib/protocol.selectionRange.js
  node_modules/vscode-languageserver-protocol/lib/protocol.sematicTokens.proposed.js
  node_modules/vscode-languageserver-protocol/lib/protocol.typeDefinition.js
  node_modules/vscode-languageserver-protocol/lib/protocol.workspaceFolders.js
  node_modules/vscode-languageserver-protocol/lib/utils/is.js
  node_modules/vscode-languageserver-protocol/License.txt
  node_modules/vscode-languageserver-protocol/package.json
  node_modules/vscode-languageserver-protocol/README.md
  node_modules/vscode-languageserver-protocol/thirdpartynotices.txt
  node_modules/vscode-jsonrpc/.eslintignore
  node_modules/vscode-jsonrpc/lib/cancellation.js
  node_modules/vscode-jsonrpc/lib/events.js
  node_modules/vscode-jsonrpc/lib/is.js
  node_modules/vscode-jsonrpc/lib/linkedMap.js
  node_modules/vscode-jsonrpc/lib/main.js
  node_modules/vscode-jsonrpc/lib/messageReader.js
  node_modules/vscode-jsonrpc/lib/messages.js
  node_modules/vscode-jsonrpc/lib/messageWriter.js
  node_modules/vscode-jsonrpc/lib/pipeSupport.js
  node_modules/vscode-jsonrpc/lib/socketSupport.js
  node_modules/vscode-jsonrpc/License.txt
  node_modules/vscode-jsonrpc/package.json
  node_modules/vscode-jsonrpc/README.md
  node_modules/vscode-jsonrpc/thirdpartynotices.txt
  node_modules/vscode-languageserver-types/.eslintignore
  node_modules/vscode-languageserver-types/lib/esm/main.js
  node_modules/vscode-languageserver-types/lib/tsconfig.esm.tsbuildInfo
  node_modules/vscode-languageserver-types/lib/umd/main.js
  node_modules/vscode-languageserver-types/License.txt
  node_modules/vscode-languageserver-types/package.json
  node_modules/vscode-languageserver-types/README.md
  node_modules/vscode-languageserver-types/tsconfig.esm.json
  
  D:\Work\Coding\VSCode\Extensions\BDD Recorder\bdd-recorder&gt;
  </code></pre>