docs(notes): the surfaces say WHEN a note earns a check, and a guard keeps them saying it (#3168, milestone 317 step 5)

The step that decides whether steps 1-4 were worth building. `verify_with` is
a free-text field on the highest-volume record kind in the product; described
only as "how to verify this note" it gets filled in on every note within a
week, and at that point the sweep returns the whole corpus and means nothing.
The signal is not "has a check" — it is "has a check AND almost nothing else
does".

Rule 119 puts this in the app's own instruction surfaces, never in a Scribe
rule. So:

- the using-scribe skill gains the reflex, next to "state updates in place;
  chronicles don't" — its other half, since supersession only fires once
  somebody has read a note and disagreed, which is the case where it was
  already believed;
- update_note's docstring now states the DEFAULT rather than only deferring
  to create_note for the test. Found by the new guard on its first run;
- plugin 0.1.48.

THE _INSTRUCTIONS BUDGET, decided rather than skipped. The payload is ~1980 of
the client's ~2048-char cap, so everything in it competes for the last ~68
characters. The operator declined a line for this milestone: the map's own
closing sentence says each tool's description carries the full contract, and
the sweep is a curation act rather than a session-start reflex like
enter_project or list_always_on_rules. That reasoning is now a comment beside
the constant, with the accepted cost named — an agent that never opens
create_note's docstring never learns the field exists — so the question is not
re-litigated blind.

The guard pins STRUCTURE, never wording, for the disambiguator's reason (a
test that punishes rewriting is a test that gets deleted): each write surface
must still draw the norm-vs-constraint distinction, say the empty case is
normal, and name where NOT to reach for it — plus that the skill carries the
one-question form, because the docstrings only reach a caller who already
opened the tool.

`_doc` moves to tests/helpers as `tool_doc`; it had been written twice.

plugin/skills/using-scribe/SKILL.md

@@ -106,6 +106,30 @@ Two constraints on *how* that's achieved:
    re-measurement, a reversed decision), pass the old id in `supersedes` so the
    stale record is demoted and labelled rather than left competing.
 
+9. **A few notes assert a FACT, and those can carry their own check.**
+   Supersession only fires once somebody has read a note and disagreed — which
+   is the case where it was already believed. A note asserting something about
+   *someone else's* software — what a service does on a duplicate upload, how a
+   forge numbers its CI runs, what an updater compares — can instead carry
+   `verify_with` (how to check it) and `expires_when` (the STATE that ends it:
+   "when the forge numbers runs per workflow", never "in six months").
+   `notes_due_for_verification` lists them least-recently-confirmed first, with
+   never-checked at the top; `mark_note_verified` records what you found, and
+   `still_true=False` deliberately writes nothing — a note whose check failed
+   is wrong rather than in a state worth recording, so it keeps its place.
+
+   **The test is one question: could this note become false without anyone
+   editing it?** If no, leave both fields empty. That is the normal case, and
+   an empty `verify_with` is the positive marker for "this is a decision, there
+   is nothing to go and check" — not an unfinished record. The sweep is only
+   worth reading while almost nothing is on it, so a check added out of
+   tidiness costs the whole surface, not just that note.
+
+   Not for tasks — a task's decay is its status, and a done issue records what
+   happened rather than asserting something that can go false. Not for snippets
+   either: `verify_snippet` compares the recorded location and code against the
+   repo, which is richer and already wired to drift detection.
+
 ## Stay inside the active project's scope
 
 Once a project is in scope — you called `enter_project`, or the working repo is