prep stage 4: assert on n_hub, not on the log-capped missing list

kernels/phase4_prep.py

@@ -269,10 +269,13 @@ with open(p, "r+b") as fh:
     fh.write(b)
 assert hubckpt.verify_checkpoint(REPO, local, SUB, repo_type="dataset")["ok"], "restoring did not help"
 
-# 2. A path that is not on the Hub at all: nothing listed means nothing verified.
+# 2. A path that is not on the Hub at all: nothing listed means nothing verified. `missing` is capped at
+# ten entries because it is a log field, so the uncapped fact (`n_hub`) is what the assertion uses --
+# rehearsing this stage caught that, not a defect in the verifier.
 v3 = hubckpt.verify_checkpoint(REPO, local, "ckpt/checkpoint-99999999", repo_type="dataset")
-print("VERIFY_ABSENT ok", v3["ok"], "missing", len(v3["missing"]), "of", v3["n_local"], flush=True)
-assert not v3["ok"] and len(v3["missing"]) == v3["n_local"], v3["missing"][:3]
+print("VERIFY_ABSENT ok", v3["ok"], "n_hub", v3["n_hub"], "missing(shown)", len(v3["missing"]),
+      "of n_local", v3["n_local"], flush=True)
+assert not v3["ok"] and v3["n_hub"] == 0 and v3["missing"], v3
 
 # 3. A server that ignores Range and streams the whole object: the read-back must fail rather than pay
 #    for 850 MB, because a silent full download is the thing this change exists to prevent.