fix(next-version): only trust ls-remote when origin is actually configured

Without the guard, git DWIMs the literal 'origin' as an ssh host/path; on
hosts whose transport launders exit codes the probe 'succeeds' with zero
branches and the allocator silently sees an empty queue — the exact
duplicate-allocation failure (#2545) fetchGitClaimed exists to prevent.
git remote get-url origin gates the probe; absence falls through to the
existing local-refs path with its staleness warning.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/gstack-next-version

@@ -499,12 +499,26 @@ function fetchGitClaimed(
   //    claim set and pushed the allocation further than the real queue.
   //    GIT_TERMINAL_PROMPT=0 + a 5s timeout keep a dead/credential-prompting
   //    remote from hanging the allocator.
-  const lsRemote = spawnSync("git", ["ls-remote", "--heads", "origin"], {
-    encoding: "utf8",
-    timeout: 5000,
-    env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
-  });
-  const lsOk = lsRemote.status === 0 && !lsRemote.error;
+  //    Guard: only consult ls-remote when a remote named `origin` is actually
+  //    CONFIGURED. Without the guard, git DWIMs the literal `origin` as an
+  //    ssh host/path — and on hosts whose ssh launders exit codes (observed:
+  //    Vercel sandboxes' ssh exits 0 on "Could not resolve hostname"), the
+  //    probe "succeeds" with zero branches and the allocator silently sees an
+  //    empty queue: the exact duplicate-allocation failure (#2545) this
+  //    function exists to prevent.
+  const originConfigured =
+    spawnSync("git", ["remote", "get-url", "origin"], {
+      encoding: "utf8",
+      timeout: 5000,
+    }).status === 0;
+  const lsRemote = originConfigured
+    ? spawnSync("git", ["ls-remote", "--heads", "origin"], {
+        encoding: "utf8",
+        timeout: 5000,
+        env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
+      })
+    : null;
+  const lsOk = lsRemote !== null && lsRemote.status === 0 && !lsRemote.error;
 
   // Each candidate carries the LIVE tip sha when it came from ls-remote, so
   // the VERSION read prefers the fresh commit (present locally after any