Plugin probe path starts in incorrect location?

@sheetalkamat is already working on this.

Since Oct 17, 2025.

The code to determine the global plugin search path is I think incorrect?

It joins the executing file path which includes the `typescript.js` or `tsserver.js` filename, with the `../../..` string which results in a path like: `X/node_modules/typescript/lib/tsserver.js/../../..` which means that the resultant path for this example is actually `X/node_modules` to which the resolve process appends a second `node_modules` folder resulting in looking for plugins in `X/node_modules/node_modules` so plugins never resolve.

```typescript
protected getGlobalPluginSearchPaths(): string[] {
// Search any globally-specified probe paths, then our peer node_modules
return [
...this.projectService.pluginProbeLocations,
// ../../.. to walk from X/node_modules/typescript/lib/tsserver.js to X/node_modules/
combinePaths(this.projectService.getExecutingFilePath(), "../../.."),
];
}
```
https://github.com/microsoft/TypeScript/blob/main/src/server/project.ts#L2110

The actual resolve then happens here and the `node_modules` folder is appended:

```typescript
public static importServicePluginSync(
pluginConfigEntry: PluginImport,
searchPaths: string[],
host: ServerHost,
log: (message: string) => void,
): PluginImportResult {
Debug.assertIsDefined(host.require);
let errorLogs: string[] | undefined;
let resolvedModule: T | undefined;
for (const initialDir of searchPaths) {
const resolvedPath = normalizeSlashes(host.resolvePath(combinePaths(initialDir, "node_modules")));
log(`Loading ${pluginConfigEntry.name} from ${initialDir} (resolved to ${resolvedPath})`);
const result = host.require(resolvedPath, pluginConfigEntry.name); // TODO: GH#18217
if (!result.error) {
resolvedModule = result.module as T;
break;
}
const err = result.error.stack || result.error.message || JSON.stringify(result.error);
(errorLogs ??= []).push(`Failed to load module '${pluginConfigEntry.name}' from ${resolvedPath}: ${err}`);
}
return { pluginConfigEntry, resolvedModule, errorLogs };
}
```
https://github.com/microsoft/TypeScript/blob/main/src/server/project.ts#L500

I believe this may be the root cause of a number of different issues raised here:
https://github.com/microsoft/TypeScript/issues/61584
https://github.com/microsoft/TypeScript/issues/44289