feat(slice4): schema-driven metadata edit panel in RFCView (§22.4a PUC-1 §5.2)

MetadataFieldsPanel renders one control per declared field (enum→select,
tags→chips, text→input), read-only without contribute access, saving changed
values via saveEntryMeta (direct sidecar commit). Wired into the canonical
main view, gated on the collection declaring fields (INV-5). saveEntryMeta
API client added.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/RFCView.jsx

@@ -46,7 +46,9 @@ import GraduateDialog from './GraduateDialog.jsx'
 import InvitationsModal from './InvitationsModal.jsx'
 import { claimOwnership, retireRFC, unretireRFC } from '../api'
 import { EVENTS, track } from '../lib/analytics'
-import { entryPath, entryPrPath, useProjectId } from '../lib/entryPaths'
+import { entryPath, entryPrPath, useProjectId, useCollectionId } from '../lib/entryPaths'
+import { getCollection } from '../api'
+import MetadataFieldsPanel from './MetadataFieldsPanel.jsx'
 
 const MANUAL_IDLE_MS = 5 * 60 * 1000   // §8.6 idle window; exact value is impl detail.
 const MANUAL_DEBOUNCE_MS = 800
@@ -70,10 +72,14 @@ export default function RFCView({ viewer }) {
   const [searchParams, setSearchParams] = useSearchParams()
   const navigate = useNavigate()
   const pid = useProjectId()
+  const cid = useCollectionId()
 
   const branchParam = searchParams.get('branch') || 'main'
 
   const [entry, setEntry] = useState(null)
+  // §22.4a SLICE-4: the collection's metadata field schema (null when the
+  // collection declares none — the panel then renders nothing, INV-5).
+  const [collectionFields, setCollectionFields] = useState(null)
   const [mainView, setMainView] = useState(null)
   const [branchView, setBranchView] = useState(null)
   const [error, setError] = useState(null)
@@ -142,6 +148,15 @@ export default function RFCView({ viewer }) {
       .catch(() => {})
   }, [slug, pid])
 
+  // §22.4a SLICE-4: load the collection's metadata field schema for the
+  // detail panel. Independent of the entry load; the panel reads the entry's
+  // own `meta` values + `can_edit_meta` capability.
+  useEffect(() => {
+    getCollection(pid, cid)
+      .then(c => setCollectionFields(c?.fields || null))
+      .catch(() => setCollectionFields(null))
+  }, [pid, cid])
+
   // Per §9.4 / §17's routing-collapse rule, super-drafts render through
   // the same surface as active RFCs — the bot, the chat, the change
   // panel, and the PR flow all dispatch on the entry's state internally.
@@ -747,6 +762,19 @@ export default function RFCView({ viewer }) {
                 : <span style={{ color: '#999', fontStyle: 'italic' }}>Left blank by the proposer.</span>}
             </div>
           )}
+          {/* §22.4a SLICE-4 (PUC-1, UX §5.2): schema-driven metadata panel on
+              the canonical (main) view. Renders nothing when the collection
+              declares no `fields` (INV-5). */}
+          {branchParam === 'main' && collectionFields && (
+            <MetadataFieldsPanel
+              projectId={pid}
+              collectionId={cid}
+              slug={slug}
+              fields={collectionFields}
+              meta={entry.meta || {}}
+              canEdit={!!entry.can_edit_meta}
+            />
+          )}
           {inDiscuss && branchParam !== 'main' && (
             <div className="discuss-mode-banner">
               Discuss mode on <strong>{branchParam}</strong> — chat freely;