fix(update): resolve Bun global directories before changing cwd

src/application/Update.test.ts

@@ -1,4 +1,4 @@
-import { join } from "node:path";
+import { join, resolve } from "node:path";
 
 import { describe, expect, it } from "vitest";
 
@@ -413,17 +413,17 @@ describe("Bun installation ownership", () => {
   it("follows Bun's global directory precedence", () => {
     const home = { HOME: "/home/user" };
     expect(bunGlobalDirectory(home, "linux")).toBe(
-      join("/home/user", ".bun", "install", "global"),
+      resolve("/home/user", ".bun", "install", "global"),
     );
     expect(
       bunGlobalDirectory({ ...home, XDG_CACHE_HOME: "/cache" }, "linux"),
-    ).toBe(join("/cache", ".bun", "install", "global"));
+    ).toBe(resolve("/cache", ".bun", "install", "global"));
     expect(
       bunGlobalDirectory(
         { ...home, XDG_CACHE_HOME: "/cache", BUN_INSTALL: "/opt/bun" },
         "linux",
       ),
-    ).toBe(join("/opt/bun", "install", "global"));
+    ).toBe(resolve("/opt/bun", "install", "global"));
     expect(
       bunGlobalDirectory(
         {
@@ -433,12 +433,22 @@ describe("Bun installation ownership", () => {
         },
         "linux",
       ),
-    ).toBe("/srv/bun-global");
+    ).toBe(resolve("/srv/bun-global"));
+    const profile = resolve("profile");
     expect(
       bunGlobalDirectory(
-        { USERPROFILE: "C:\\Users\\user", HOME: "/c/Users/user" },
+        { USERPROFILE: profile, HOME: resolve("other-home") },
         "win32",
       ),
-    ).toBe(join("C:\\Users\\user", ".bun", "install", "global"));
+    ).toBe(join(profile, ".bun", "install", "global"));
+  });
+
+  it("resolves relative installation and cache roots before appending the global layout", () => {
+    expect(bunGlobalDirectory({ BUN_INSTALL: "bun" }, "linux")).toBe(
+      resolve("bun", "install", "global"),
+    );
+    expect(bunGlobalDirectory({ XDG_CACHE_HOME: "cache" }, "linux")).toBe(
+      resolve("cache", ".bun", "install", "global"),
+    );
   });
 });

src/application/UpdateRuntime.ts

@@ -141,19 +141,21 @@ const nonemptyEnvironment = (value: string | undefined): string | undefined =>
  * Bun's global project directory for the selected environment, in Bun's precedence:
  * BUN_INSTALL_GLOBAL_DIR, then $BUN_INSTALL/install/global, then
  * $XDG_CACHE_HOME/.bun/install/global, then ~/.bun/install/global.
+ * Resolve against the caller's cwd before reusing the path as a subprocess cwd.
  */
 export const bunGlobalDirectory = (
   environment: Readonly<NodeJS.ProcessEnv>,
   platform: NodeJS.Platform,
 ): string => {
   const explicit = nonemptyEnvironment(environment.BUN_INSTALL_GLOBAL_DIR);
-  if (explicit !== undefined) return explicit;
+  if (explicit !== undefined) return resolve(explicit);
   const installRoot = nonemptyEnvironment(environment.BUN_INSTALL);
-  if (installRoot !== undefined) return join(installRoot, "install", "global");
+  if (installRoot !== undefined)
+    return resolve(installRoot, "install", "global");
   const cacheRoot =
     nonemptyEnvironment(environment.XDG_CACHE_HOME) ??
     homeDirectoryFromEnvironment(environment, platform);
-  return join(cacheRoot, ".bun", "install", "global");
+  return resolve(cacheRoot, ".bun", "install", "global");
 };
 
 /**

tests/process-global/updateMaintenance.test.ts

@@ -1,9 +1,9 @@
 import { mkdir, readFile, rm, writeFile, access } from "node:fs/promises";
-import { delimiter, dirname, join, resolve } from "node:path";
+import { delimiter, dirname, join, relative, resolve } from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 import { err, ok } from "../../src/domain/result.js";
-import { runUpdate } from "../../src/application/Update.js";
+import { runUpdate, type UpdateResult } from "../../src/application/Update.js";
 import { PRODUCT_IDENTITY } from "../../src/identity.js";
 import { supportedClients } from "../../src/application/SupportedClients.js";
 import {
@@ -375,14 +375,15 @@ describe("update subprocess boundaries", () => {
 
 describe("Bun global installation update", () => {
   it.each([
-    ["1.4.2", "updated"],
-    ["1.2.17", "updated"],
-    ["1.2.14", "failed"],
-    ["1.2.17-canary.1", "failed"],
-    ["unknown", "failed"],
+    ["1.4.2", "updated", "absolute"],
+    ["1.2.17", "updated", "absolute"],
+    ["1.2.17", "updated", "relative"],
+    ["1.2.14", "failed", "absolute"],
+    ["1.2.17-canary.1", "failed", "absolute"],
+    ["unknown", "failed", "absolute"],
   ])(
-    "handles Bun %s with outcome %s inside its global project",
-    async (bunVersion, status) => {
+    "handles Bun %s with outcome %s using %s global-directory configuration",
+    async (bunVersion, status, directoryMode) => {
       // A recording `bun` on PATH crosses the real subprocess boundary without registry access.
       const root = await createTestTempDirectory("rea-update-bun-");
       const globalDirectory = join(root, "bun", "install", "global");
@@ -440,12 +441,21 @@ describe("Bun global installation update", () => {
         BUN_INSTALL: join(root, "bun"),
       };
       delete environment.BUN_INSTALL_GLOBAL_DIR;
+      if (directoryMode === "relative")
+        environment.BUN_INSTALL_GLOBAL_DIR = relative(root, globalDirectory);
 
-      const result = await runUpdate(
-        "3.2.1",
-        systemUpdateHost(packageRoot, home, environment),
-        "structured",
-      );
+      const callerDirectory = process.cwd();
+      let result: UpdateResult;
+      try {
+        process.chdir(root);
+        result = await runUpdate(
+          "3.2.1",
+          systemUpdateHost(packageRoot, home, environment),
+          "structured",
+        );
+      } finally {
+        process.chdir(callerDirectory);
+      }
 
       const invocations = (await readFile(logPath, "utf8"))
         .trim()