fix plugins reinstalling too often

packages/opencode/src/npm/index.ts

@@ -1,6 +1,7 @@
 export * as Npm from "."
 
 import path from "path"
+import npa from "npm-package-arg"
 import semver from "semver"
 import { Effect, Schema, Context, Layer, Option, FileSystem } from "effect"
 import { NodeFileSystem } from "@effect/platform-node"
@@ -135,6 +136,17 @@ export const layer = Layer.effect(
 
     const add = Effect.fn("Npm.add")(function* (pkg: string) {
       const dir = directory(pkg)
+      const name = (() => {
+        try {
+          return npa(pkg).name ?? pkg
+        } catch {
+          return pkg
+        }
+      })()
+
+      if (yield* afs.existsSafe(dir)) {
+        return resolveEntryPoint(name, path.join(dir, "node_modules", name))
+      }
 
       const tree = yield* reify({ dir, add: [pkg] })
       const first = tree.edgesOut.values().next().value?.to