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.

tests/helpers.py

@@ -38,6 +38,27 @@ async def drive_update_note(note, **kwargs):
         return await update_note(user_id=7, note_id=note.id, **kwargs)
 
 
+def tool_doc(module: str, name: str) -> str:
+    """An MCP tool's docstring, whitespace-flattened.
+
+    Flattened because these are hard-wrapped at ~76 characters, so any phrase
+    worth asserting on is liable to straddle a line break — a property of the
+    formatter, not of the guidance. The disambiguator guard (#3123) learned
+    that on its own first run, matching raw text and reporting a phrase absent
+    that was plainly there.
+
+    Used by every test that pins the docstring CONTRACT rather than its
+    wording. The tool docstring is the agent-facing contract (rule 119), so
+    these guards exist to catch it being tidied down to a parameter list.
+    """
+    import importlib
+    import re as _re
+
+    fn = getattr(importlib.import_module(module), name)
+    assert fn.__doc__, f"{name} has no docstring at all"
+    return _re.sub(r"\s+", " ", fn.__doc__)
+
+
 def compiled_sql(element) -> str:
     """A SQLAlchemy clause or statement rendered as literal SQL text.