test(claude-code-plugin-loader): cover plugin path nullish resolution

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/claude-code-plugin-loader/plugin-path-resolver.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, test } from "bun:test"
+
+import { resolvePluginPath, resolvePluginPaths } from "./plugin-path-resolver"
+
+describe("resolvePluginPath", () => {
+  test("#given a plugin root placeholder #when resolving the path #then it replaces the placeholder", () => {
+    // given
+    const path = "${CLAUDE_PLUGIN_ROOT}/dist/index.js"
+
+    // when
+    const result = resolvePluginPath(path, "/tmp/plugin-root")
+
+    // then
+    expect(result).toBe("/tmp/plugin-root/dist/index.js")
+  })
+})
+
+describe("resolvePluginPaths", () => {
+  test("#given a nested object #when resolving paths #then it rewrites every nested string path", () => {
+    // given
+    const value = {
+      command: "node",
+      args: ["${CLAUDE_PLUGIN_ROOT}/server.js"],
+      nested: {
+        config: "${CLAUDE_PLUGIN_ROOT}/config.json",
+      },
+    }
+
+    // when
+    const result = resolvePluginPaths(value, "/tmp/plugin-root")
+
+    // then
+    expect(result).toEqual({
+      command: "node",
+      args: ["/tmp/plugin-root/server.js"],
+      nested: {
+        config: "/tmp/plugin-root/config.json",
+      },
+    })
+  })
+
+  test("#given nullish input #when resolving paths #then it returns the same nullish value", () => {
+    // given
+    const nullValue = null
+    const undefinedValue = undefined
+
+    // when
+    const nullResult = resolvePluginPaths(nullValue, "/tmp/plugin-root")
+    const undefinedResult = resolvePluginPaths(undefinedValue, "/tmp/plugin-root")
+
+    // then
+    expect(nullResult).toBeNull()
+    expect(undefinedResult).toBeUndefined()
+  })
+})

src/features/claude-code-plugin-loader/plugin-path-resolver.ts

@@ -5,7 +5,7 @@ export function resolvePluginPath(path: string, pluginRoot: string): string {
 }
 
 export function resolvePluginPaths<T>(obj: T, pluginRoot: string): T {
-  if (obj === null || obj === undefined) return obj
+  if (obj == null) return obj
   if (typeof obj === "string") {
     return resolvePluginPath(obj, pluginRoot) as T
   }