fix(lessons): a lesson's name is one claim on one line (#4797)

#4797 "A lesson's what takes a whole narrative, and the narrative becomes
its name". `what` is the title every listing and menu prints. Nothing
enforced its documented "one line", so lessons written with the incident
in `what` printed up to ~1,500 characters as a menu line, buried the
claim, and diluted the trigger in the embedded title. That was 14 of the
39 lessons on this install.

- lessons.require_claim refuses a `what` over WHAT_MAX_CHARS (240) or
  running over several lines. The refusal says the story goes in
  `insight`.
- Both doors call it before writing:
  - MCP create_lesson / update_lesson;
  - REST create / update.
  An update checks only a NEW name, so a lesson stored with a long one can
  still take the edit that repairs it.
- lessons.claim_line is the display half. _menu_name shows an over-long
  stored name as its first sentence marked " …", because a door guard
  does not undo rows already stored and an unrepaired install would keep
  printing them.
- The tool docstrings state the bound.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/mcp/tools/lessons.py

@@ -167,7 +167,9 @@ async def create_lesson(
 
     Args:
         what: The insight in one line — the claim itself, as you would say it.
-            This becomes the title, joined with the trigger.
+            This becomes the title, joined with the trigger. At most 240
+            characters and no line breaks; a longer one is refused — the
+            story goes in `insight`.
         when_to_apply: The situation this applies in, as a symptom. Required.
         insight: The body — what to do, and the incident that taught it.
             Write the story here for the reader; it costs the ranking nothing,
@@ -208,6 +210,7 @@ async def create_lesson(
             "record saves, reads correctly, and never surfaces."
         )
 
+    lessons_svc.require_claim(what)
     sources = lessons_svc.normalize_sources(learned_from)
     # Validated before anything is written, so a lesson naming a rule the
     # caller cannot read fails whole rather than saving half-linked.
@@ -334,7 +337,8 @@ async def update_lesson(
 
     Args:
         lesson_id: Lesson to update.
-        what: New one-line claim. Empty leaves unchanged.
+        what: New one-line claim, at most 240 characters. Empty leaves
+            unchanged.
         when_to_apply: New trigger, as a symptom. Empty leaves unchanged.
         insight: New body. Empty leaves unchanged.
         learned_from: Replace the source ids. None leaves unchanged; pass the
@@ -362,6 +366,10 @@ async def update_lesson(
             `convergence`: the group, and the rule it may be missing.
     """
     uid = current_user_id()
+    # Only a NEW name is checked: a lesson stored with a long one must still
+    # take a new trigger or a rule link — and the fix for it is this call.
+    if what:
+        lessons_svc.require_claim(what)
     linked = (
         await lesson_rules_svc.require_rules(uid, rule_ids)
         if rule_ids is not None else None