fix: treat empty git branch as undefined in detectGit

In CI detached HEAD, git branch --show-current returns an empty
string. Convert empty string to undefined so callers get a clean
undefined instead of "".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: anandgupta42

packages/altimate-code/src/tool/project-scan.ts

@@ -56,7 +56,7 @@ export async function detectGit(): Promise<GitInfo> {
     stdout: "pipe",
     stderr: "pipe",
   })
-  const branch = branchResult.exitCode === 0 ? branchResult.stdout.toString().trim() : undefined
+  const branch = branchResult.exitCode === 0 ? branchResult.stdout.toString().trim() || undefined : undefined
 
   let remoteUrl: string | undefined
   const remoteResult = Bun.spawnSync(["git", "remote", "get-url", "origin"], {

packages/altimate-code/test/tool/project-scan.test.ts

@@ -48,10 +48,12 @@ describe("detectGit", () => {
     expect(typeof result.branch).toBe("string")
   })
 
-  test("returns a branch name or undefined in detached HEAD", async () => {
+  test("branch is a non-empty string or undefined (detached HEAD)", async () => {
     const result = await detectGit()
-    // In CI, GitHub Actions checks out in detached HEAD, so branch may be undefined
+    // In CI, GitHub Actions checks out in detached HEAD → branch is undefined
+    // Locally, branch is a non-empty string
     if (result.branch !== undefined) {
+      expect(typeof result.branch).toBe("string")
       expect(result.branch.length).toBeGreaterThan(0)
     }
   })