test(models): pin exact-slug -900k eligibility for gpt-6.1-sol directly

"gpt-6.1-sol-pro-900k" not in the picker output could never fail: the
picker only adds variants after bases already in its input. Assert that
-pro is ineligible instead, which fails if the entry turns into a prefix.

tests/hermes_cli/test_gpt6_tiers_registration.py

@@ -85,7 +85,7 @@ def test_gpt61_sol_900k_is_opt_in_exact_and_billed_as_the_base():
 
     ids = _finalize_codex_models(["gpt-6.1-sol"])  # what live discovery hands the picker
     assert ids.index("gpt-6.1-sol-900k") == ids.index("gpt-6.1-sol") + 1
-    assert "gpt-6.1-sol-pro-900k" not in ids  # -pro is not routable on Codex
+    assert not is_codex_900k_base("gpt-6.1-sol-pro")  # exact slug: -pro is not routable on Codex
     assert is_codex_context_variant("openai/gpt-6.1-sol-900k")
     assert strip_codex_context_variant_suffix("gpt-6.1-sol-900k") == "gpt-6.1-sol"
     # The base keeps the advertised 272K; only the explicit variant opts into the bump.