docs(plugin-detail): README teaches a detail tab whose `content.type` is `activity-timeline`, which nothing registers — a reader gets the OBJUI-001 panel

[baozhoutao]

Filed by the domain:devx @ objectui execution seat (PM session session_01FhBNJcLRZLe8M87VcUgpKr, R46) from the objectui#7896 census (PR #8111). ⛔ Filed finding only; grading and domain:* are the triage seat's. Left unassigned. Dedupe: one MCP semantic search on activity-timeline plugin-detail README returned three unrelated cards (#6170, #6932, #6907), so the channel is live and this is not filed already.

The defect, measured on origin/main 59a3a233d

packages/plugin-detail/README.md:163-171 teaches a detail tab:

{
  key: 'activity',
  label: 'Activity',
  badge: '12',
  content: {
    type: 'activity-timeline',
    data: activityData,
  },
},

packages/plugin-detail/src/DetailTabs.tsx:72 renders a tab's content through SchemaRenderer with toRenderableSchema(tab.content), so content.type is an SDUI node position judged by the component registry. Nothing registers activity-timeline: packages/plugin-detail/src/index.tsx registers detail-view, detail-section, related-list, detail, and details under the record namespace, and DetailView.tsx:1460 knows a tab key activity, not a component type. A reader copying the example renders the registry's Unknown component type panel (OBJUI-001).

This is the same shape as the line-chart widget objectui#7896 recorded in packages/plugin-dashboard/README.md (fixed on the docs side by PR #7951). It is the ONE real defect among the 26 unregistered type literals the census found across the 39 package READMEs; the other 25 are non-component vocabularies proposed as DOC_TYPE_EXEMPTIONS entries in PR #8111's body.

Why no gate caught it

check:doc-types does not walk packages/NAME/README.md (objectui#7896). check:doc-snippets compiles the block but its own header names schema-key validity as the question it does not answer.

Acceptance

The README example names a component type that is registered on main (the seat that takes this decides which — record:activity per the registry, or a different tab content shape — by reading DetailTabs.tsx and the registry, not by guessing). No gate change in this card: the widening that would make this class fail loudly is objectui#7896's, and that card is blocked by this one.

Back-links

objectui#7896 (the census and the widening, Blocked-by: this card), PR #8111 (the census PR), objectui#7866 and objectui#7440 (earlier instances of the same shape), PR #7951 (the line-chart fix).