Problems when installing packages with `yarn`

Using VS Code 1.26.1 and reason-vscode 1.0.3 on macOS. It keeps insisting that I run bsb. It was fine yesterday. Since then I installed yarn via Homebrew, and deleted the `package-lock.json` file. Out of pure superstition, I ran `npm i` to get the `package-lock.json` back, but that didn't help. So how do I clean this thing ("thing" being whatever needs cleaning) so it works again?

The project in question is reductive, which has bsb 3.1.1 installed locally, if that matters. I happen to have bsb 4.0.5 installed globally via npm.

The last chunk of the `.lsp/debug.log` file:

```
Read message ^M
{"jsonrpc":"2.0","id":5,"method":"textDocument/codeLens","params":{"textDocument":{"uri":"file:///Users/nfiedler/proje\
cts/reductive/examples/react/TodoApp.re"}}}
Got a method textDocument/codeLens
>> Build system: /Users/nfiedler/projects/reductive/node_modules/bs-platform/lib/bsb.exe -make-world
ninja: no work to do.
ninja: no work to do.
ninja: Entering directory `lib/bs'
ninja: no work to do.
>> Error
Duplicated package: bs-platform /Users/nfiedler/projects/reductive/node_modules/bs-platform (chosen) vs /Users/nfiedle\
r/projects/reductive/node_modules/immutable-re/node_modules/bs-platform in /Users/nfiedler/projects/reductive/node_mod\
ules/immutable-re
Affected files
Cleaning bsconfig.json
Sending notification {"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": {"uri": "file:///Users/\
nfiedler/projects/reductive/bsconfig.json", "diagnostics": []}}
Deps reason-react
Dep loc /Users/nfiedler/projects/reductive/node_modules/reason-react/bsconfig.json
Compiled base: /Users/nfiedler/projects/reductive/node_modules/reason-react/lib/ocaml
Source directories: /Users/nfiedler/projects/reductive/node_modules/reason-react/src
Source files found: /Users/nfiedler/projects/reductive/node_modules/reason-react/src/ReasonReactOptimizedCreateClass.r\
e : /Users/nfiedler/projects/reductive/node_modules/reason-react/src/ReactEventRe.rei : /Users/nfiedler/projects/reduc\
tive/node_modules/reason-react/src/ReactDOMRe.re : /Users/nfiedler/projects/reductive/node_modules/reason-react/src/Re\
actDOMServerRe.re : /Users/nfiedler/projects/reductive/node_modules/reason-react/src/ReactEventRe.re : /Users/nfiedler\
/projects/reductive/node_modules/reason-react/src/ReasonReact.rei : /Users/nfiedler/projects/reductive/node_modules/re\
ason-react/src/ReasonReact.re
With compiled base:
Sending response {"id": 5, "jsonrpc": "2.0", "result": [{"range": {"start": {"line": 0, "character": 0}, "end": {"line\
": 0, "character": 0}}, "command": {"title": "Unable to load compilation data: You need to run bsb first so that reaso\
n-language-server can access the compiled artifacts.\nOnce you've run bsb, restart the language server.", "command": "\
"}}]}
```

Thanks for this extension, it's been really nice so far.

Start with the duplicated bs-platform error and the build-system output in .lsp/debug.log, then inspect the referenced bsconfig.json and node_modules paths. Reproduce the package installation state described for reductive and verify that the language server no longer prompts for bsb or reports duplicated packages.

Written by the indexing model from the issue text.