Studio: harden marker handling and tighten the data-center routing gate

Follow-up hardening from review:

- check_prebuilt_freshness: guard a non-dict marker and a non-string
  source the same way effective_published_repo does, so a corrupt
  on-disk UNSLOTH_PREBUILT_INFO.json cannot crash update-status polling.
- Data-center lemonade gate: skip on macOS explicitly. macOS never has
  AMD ROCm, so a stray forwarded gfx must keep the macOS bundle path.
- Tests: Windows data-center routing (windows-hip + windows asset),
  draft/prerelease filtering in the release scan, and a direct
  effective_published_repo matrix including corrupt-marker fail-safes.

studio/backend/tests/test_llama_cpp_freshness.py

@@ -362,6 +362,32 @@ def test_is_behind(installed, latest, expected):
     assert fr.is_behind(installed, latest) is expected
 
 
+_FORK = fr.DEFAULT_PUBLISHED_REPO
+_LEM = fr.LEMONADE_ROCM_REPO
+_GGML = "ggml-org/llama.cpp"
+
+
+@pytest.mark.parametrize(
+    "marker, expected",
+    [
+        # consumer lemonade recorded a non-fork repo -> migrate to the fork
+        ({"source": "lemonade", "published_repo": _GGML}, _FORK),
+        ({"source": "lemonade", "published_repo": _FORK}, _FORK),
+        # data-center lemonade already on the lemonade repo -> keep it
+        ({"source": "lemonade", "published_repo": _LEM}, _LEM),
+        # non-lemonade markers keep their own repo
+        ({"source": "published", "published_repo": _FORK}, _FORK),
+        ({"source": "upstream", "published_repo": _GGML}, _GGML),
+        # defensive: corrupt markers fail safe instead of crashing the poller
+        (None, None),
+        ([1, 2], None),
+        ({"source": ["lemonade"], "published_repo": _GGML}, _GGML),
+    ],
+)
+def test_effective_published_repo(marker, expected):
+    assert fr.effective_published_repo(marker) == expected
+
+
 def test_check_prebuilt_freshness_not_behind_on_mix_latest(monkeypatch, tmp_path):
     # Installed the mix latest: marker base tag b9596, full release_tag with sha,
     # GitHub latest is that same full tag. Must not report behind (sticky bug).

studio/backend/utils/llama_cpp_freshness.py

@@ -275,14 +275,15 @@ def check_prebuilt_freshness(
         "threshold_days": int(threshold_days),
     }
     marker = read_install_marker(binary_path)
-    if not marker:
+    if not marker or not isinstance(marker, dict):
         return out
     out["has_marker"] = True
     # Display prefers the normalized base ("tag"); comparison below prefers the
     # full "release_tag" -- deliberately opposite fallbacks. A lemonade install's
     # "tag" is the upstream build it was made from, but it tracks lemonade's own
     # release counter, so show release_tag to keep installed/latest one series.
-    if (marker.get("source") or "").lower() == "lemonade":
+    source = marker.get("source")
+    if isinstance(source, str) and source.lower() == "lemonade":
         out["installed_tag"] = marker.get("release_tag") or marker.get("tag")
     else:
         out["installed_tag"] = marker.get("tag") or marker.get("release_tag")

studio/install_llama_prebuilt.py

@@ -1717,9 +1717,11 @@ def resolve_simple_install_release_plans(
     repo = published_repo or DEFAULT_PUBLISHED_REPO
     # Data-center AMD GPUs (gfx908/gfx90a) are not in the fork's per-gfx bundles;
     # serve them from lemonade. Catches the fork-routed fresh install and the
-    # lemonade-repo update re-install alike.
+    # lemonade-repo update re-install alike. macOS never has AMD ROCm, so a
+    # stray forwarded gfx there must not divert off the macOS bundle path.
     if (
         host.is_x86_64
+        and not host.is_macos
         and not host.has_usable_nvidia
         and (repo == LEMONADE_ROCM_REPO or _lemonade_datacenter_gfx(host.rocm_gfx_target))
     ):

tests/studio/install/test_rocm_support.py

@@ -460,6 +460,34 @@ class TestDataCenterLemonadeRouting:
         assert plans[0].release_tag == "b1295"
         assert plans[0].llama_tag == "b9637"
 
+    @patch.object(prebuilt_mod, "fetch_json", side_effect = _fetch_router)
+    def test_datacenter_windows_routes_to_windows_hip(self, _mock):
+        # Windows data-center host: lemonade "windows" asset, windows-hip kind.
+        host = rocm_host(
+            system = "Windows",
+            machine = "AMD64",
+            is_windows = True,
+            is_linux = False,
+            rocm_gfx_target = "gfx908",
+        )
+        _tag, plans = prebuilt_mod.resolve_simple_install_release_plans(
+            "latest", host, prebuilt_mod.DEFAULT_PUBLISHED_REPO, ""
+        )
+        choice = plans[0].attempts[0]
+        assert choice.install_kind == "windows-hip"
+        assert choice.name == "llama-b1300-windows-rocm-gfx908-x64.zip"
+
+    @patch.object(prebuilt_mod, "fetch_json")
+    def test_draft_and_prerelease_releases_skipped(self, mock_fetch):
+        # The newest list entry is a draft + prerelease; fall back to the real one.
+        newest = _lemonade_release(tag = "b1310", published_at = "2026-03-01T00:00:00Z")
+        newest["draft"], newest["prerelease"] = True, True
+        stable = _lemonade_release(tag = "b1300", published_at = "2026-01-15T00:00:00Z")
+        mock_fetch.return_value = [newest, stable]
+        host = rocm_host(rocm_gfx_target = "gfx908")
+        choice = prebuilt_mod.resolve_lemonade_rocm_choice(host, "ubuntu", "linux-rocm")
+        assert choice is not None and choice.tag == "b1300"
+
 
 # TEST: install_llama_prebuilt.py -- runtime_patterns_for_choice