tests: restore the inheritance-before-guard ordering assertion (#7251)

The gguf order fix that landed on main dropped the only assertion
covering the prerequisite that llama_extra_args inheritance runs before
the GGUF branch: the inherited value (a carried --no-mmproj) shapes the
hub guard's require_mmproj, so a future reorder could reject a load
over an mmproj download the inherited arguments would disable. The
comment also misattributed the inheritance site to
_guard_chat_load_against_training.

The assertion is restored anchored on the call form
"= _resolve_inherited_extra_args(", which pins the endpoint's call site
(the bare name would match the function definition, which always
precedes the endpoint, making the check vacuous), and the comment now
names the real inheritance site. 32 tests pass.

studio/backend/tests/test_gguf_load_cache_reuse.py

@@ -789,9 +789,12 @@ class TestLoadHubDownloadExclusion:
 
         # The gguf_load_in_flight marker must be entered before the hub-download
         # guard and the unload so a concurrent load can't race the download
-        # manager. The llama_extra_args inheritance that used to sit between the
-        # marker and the guard now runs in _guard_chat_load_against_training, ahead
-        # of the GGUF branch, so it is no longer a landmark inside this slice.
+        # manager. The llama_extra_args inheritance moved out of the branch into
+        # _resolve_inherited_extra_args, which must still run BEFORE it: the
+        # inherited value (e.g. a carried --no-mmproj) shapes the guard's
+        # require_mmproj. Anchor on the call form so the assertion pins the
+        # endpoint's call site, not the function definition.
+        assert source.index("= _resolve_inherited_extra_args(") < source.index("if config.is_gguf:")
         assert (
             gguf_branch.index("enter_context(gguf_load_in_flight")
             < gguf_branch.index("_hub_download_blocks_gguf_load")