Add regression test for ~/.npmrc not being read during bun install

This test demonstrates that bun install does not read configuration from
~/.npmrc, only from local .npmrc files. The bug is caused by incorrect
path construction when trying to load the user's npmrc file.

The test covers:
- Registry configuration from ~/.npmrc
- Cache directory configuration from ~/.npmrc
- Local .npmrc properly overriding ~/.npmrc (once fixed)

Co-Authored-By: Claude <noreply@anthropic.com>

test/regression/issue/issue-22592-home-npmrc.test.ts

@@ -0,0 +1,146 @@
+import { test, expect } from "bun:test";
+import { bunEnv, bunExe, tempDir, isWindows } from "harness";
+import { join } from "path";
+
+test("bun install should read registry from ~/.npmrc", async () => {
+  // Skip on Windows as npmrc path is different
+  if (isWindows) {
+    test.skip();
+    return;
+  }
+
+  using testDir = tempDir("npmrc-home", {
+    "package.json": JSON.stringify({
+      name: "test-npmrc-home",
+      version: "1.0.0",
+      dependencies: {
+        "fake-package": "1.0.0"
+      }
+    }),
+    "home": {
+      ".npmrc": "registry=https://custom.registry.example.com/\n"
+    }
+  });
+  
+  const fakeHome = join(String(testDir), "home");
+
+  // Run bun install with HOME pointing to our fake home
+  // The install should fail trying to reach the custom registry
+  const result = await Bun.spawn({
+    cmd: [bunExe(), "install"],
+    env: {
+      ...bunEnv,
+      HOME: fakeHome,
+      // Clear XDG_CONFIG_HOME to ensure HOME is used
+      XDG_CONFIG_HOME: undefined,
+    },
+    cwd: String(testDir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr] = await Promise.all([
+    result.stdout.text(),
+    result.stderr.text(),
+  ]);
+
+  const exitCode = await result.exited;
+
+  // The install should fail because it tries to reach our custom registry
+  // If ~/.npmrc was properly read, it would try to fetch from custom.registry.example.com
+  // and fail with a network error
+  expect(stderr).toContain("custom.registry.example.com");
+  
+  // Currently this test will FAIL because bun doesn't read ~/.npmrc
+  // Once the bug is fixed, this test should PASS
+});
+
+test("bun install should read cache directory from ~/.npmrc", async () => {
+  // Skip on Windows as npmrc path is different
+  if (isWindows) {
+    test.skip();
+    return;
+  }
+
+  using testDir = tempDir("npmrc-cache", {
+    "package.json": JSON.stringify({
+      name: "test-npmrc-cache",
+      version: "1.0.0"
+    }),
+    "home": {
+      ".npmrc": ""  // Will be written after we know the path
+    },
+    "custom-cache": {}  // Create empty dir
+  });
+  
+  const fakeHome = join(String(testDir), "home");
+  const customCache = join(String(testDir), "custom-cache");
+  
+  // Write the npmrc with the actual cache path
+  await Bun.write(join(fakeHome, ".npmrc"), `cache=${customCache}\n`);
+
+  // Run bun install with HOME pointing to our fake home and verbose mode
+  const result = await Bun.spawn({
+    cmd: [bunExe(), "install"],
+    env: {
+      ...bunEnv,
+      HOME: fakeHome,
+      XDG_CONFIG_HOME: undefined,
+      BUN_INSTALL_VERBOSE: "1",
+    },
+    cwd: String(testDir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const stderr = await result.stderr.text();
+  await result.exited;
+
+  // Check if the custom cache directory from ~/.npmrc is being used
+  // Currently this will FAIL because bun doesn't read ~/.npmrc
+  expect(stderr).toContain(`Cache Dir: ${customCache}`);
+});
+
+test("local .npmrc should override ~/.npmrc", async () => {
+  // Skip on Windows as npmrc path is different  
+  if (isWindows) {
+    test.skip();
+    return;
+  }
+
+  using testDir = tempDir("npmrc-override", {
+    "package.json": JSON.stringify({
+      name: "test-npmrc-override",
+      version: "1.0.0",
+      dependencies: {
+        "fake-package": "1.0.0"
+      }
+    }),
+    ".npmrc": "registry=https://local.registry.example.com/\n",
+    "home": {
+      ".npmrc": "registry=https://home.registry.example.com/\n"
+    }
+  });
+  
+  const fakeHome = join(String(testDir), "home");
+
+  // Run bun install
+  const result = await Bun.spawn({
+    cmd: [bunExe(), "install"],
+    env: {
+      ...bunEnv,
+      HOME: fakeHome,
+      XDG_CONFIG_HOME: undefined,
+    },
+    cwd: String(testDir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const stderr = await result.stderr.text();
+  await result.exited;
+
+  // The local .npmrc should take precedence
+  expect(stderr).toContain("local.registry.example.com");
+  expect(stderr).not.toContain("home.registry.example.com");
+});