feat(lessons): the kind whose whole question is "is this trigger right" was the one kind that could not see its own counts (#4196)

The lesson slot has recorded surfaced-vs-opened since it shipped. Nothing
showed it. `get_lesson`'s REST door attached `usage` to the payload and no
view rendered it; the listing did not attach it at all, and neither MCP door
did.

#4196 asks when a lesson that keeps getting followed should become a rule, and
names the trap in the same breath: raw frequency cannot separate "this should
bind" from "this trigger is too broad", and the second is the commoner reading
by a wide margin. Surfaced-AND-opened can separate them. Neither question is
answerable by a reader who cannot see the numbers, which is why this is the
first step and not the threshold.

NO THRESHOLD IS PROPOSED HERE, deliberately. The corpus today is 10 lessons
with 7 recorded surfacings and 3 opens, over about fifteen hours of usage
data. A promotion rule fitted to that would be fitting noise — #3311's failure,
and the warning lesson #4228 was written to carry. `UsageBadge` already
declines to render a verdict under three surfacings for the same reason. So
#4196 stays open: its subject, the promotion path, is still unbuilt. What
lands is the evidence it needs.

  - REST `GET /api/lessons` and MCP `list_lessons` attach `usage` to every
    row, from one aggregate per page rather than a per-row read, which would
    be N+1 by construction. Every row carries the key zero-filled, so "never
    surfaced" is a state a reader can see rather than a missing field they
    have to interpret.
  - MCP `get_lesson` attaches it too, and reads it BEFORE recording its own
    pull. That door records a pull on every open — it has to, or the kind sits
    permanently at zero — which makes the order load-bearing in a way it is
    not for a kind that only counts. The REST detail door already ordered it
    this way; the two now agree about what the number means.
  - `LessonDetailView` renders `UsageBadge` (snippet #3460) rather than
    re-spelling the chip, with the advice keyed to this kind: a lesson that is
    repeatedly offered and never opened is usually keyed to a situation nobody
    is in, so it points at re-keying `when_to_apply`, not at deleting the
    claim.

Guards, in the two styles this pair of doors already uses: the MCP side driven
behaviourally through mocks, including the call ORDER for `get_lesson`; the
REST side on structure like its siblings in test_lesson_rest_door.py, because
the route is decorated and returns a Quart response. Rule 167's falsifier is
included.

KNOWN GAP, not fixed here: `KnowledgeView` is the only lesson LIST in the UI
and it reads `/knowledge`, not `/lessons` — so the REST listing change reaches
`frontend/src/api/lessons.ts::listLessons`, which currently has no consumer.
The agent-facing listing does reach a reader today.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

frontend/src/api/lessons.ts

@@ -65,6 +65,10 @@ export interface LessonListRow {
   tags: string[];
   when_to_apply?: string;
   snippet?: string;
+  /** Surfaced-vs-opened for this lesson. Always present on a listing from
+   *  this door, zero-filled where nothing has been recorded — absent only
+   *  when a row came from somewhere else. */
+  usage?: RecordUsage;
   shared?: boolean;
   owner?: string | null;
 }

frontend/src/views/LessonDetailView.vue

@@ -24,6 +24,7 @@ import { apiErrorMessage } from "@/api/client";
 import { deleteLesson, getLesson, type Lesson } from "@/api/lessons";
 import ConfirmDialog from "@/components/ConfirmDialog.vue";
 import TagPill from "@/components/TagPill.vue";
+import UsageBadge from "@/components/UsageBadge.vue";
 import { useToastStore } from "@/stores/toast";
 import { renderMarkdown } from "@/utils/markdown";
 
@@ -99,7 +100,19 @@ onMounted(load);
         <p class="ld-trigger-text">{{ lesson.when_to_apply }}</p>
       </section>
 
-      <h1 class="ld-what">{{ lesson.what }}</h1>
+      <div class="ld-what-row">
+        <h1 class="ld-what">{{ lesson.what }}</h1>
+        <!-- Lessons collected surfaced-vs-opened from the day the slot shipped
+             and showed it nowhere (#4196). It belongs here above anywhere
+             else: the reading that matters is almost never "delete this", it
+             is "the trigger is keyed to a situation nobody is in", and the
+             place to act on that is the lesson you are already looking at. -->
+        <UsageBadge
+          :usage="lesson.usage"
+          noun="lesson"
+          dead-weight-advice="Repeatedly offered and never opened usually means the trigger fires on the wrong situation — re-key `when_to_apply` rather than deleting the claim."
+        />
+      </div>
 
       <div
         v-if="insightHtml"
@@ -210,6 +223,13 @@ onMounted(load);
 }
 .ld-trigger-text { margin: 0; font-size: 0.98rem; line-height: 1.5; }
 
+.ld-what-row {
+  display: flex;
+  align-items: baseline;
+  gap: var(--fs-space-2);
+  flex-wrap: wrap;
+}
+
 .ld-what {
   margin: 0 0 1.25rem;
   font-size: 1.25rem;