diff --git a/frontend/src/components/FacetGroups.jsx b/frontend/src/components/FacetGroups.jsx
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+++ b/frontend/src/components/FacetGroups.jsx
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+// FacetGroups.jsx — §22.4a SLICE-3 faceted left-pane filters (§5.1).
+//
+// Renders one collapsible group per facet field returned by the API, each with
+// per-value result counts and multi-select checkboxes. A `tags`-type field gets
+// a "filter values…" search box so it stays usable at 30+ values. Selection
+// state + the malformed toggle are owned by the parent (Catalog), which
+// re-fetches server-side on change.
+
+import { useState } from 'react'
+
+// Human label for the built-in state facet; declared fields use their own name
+// (or the schema `label` when the API supplies it on `fields`).
+function groupLabel(field, fields) {
+  if (field === 'state') return 'State'
+  const def = fields?.[field]
+  return def?.label || field.charAt(0).toUpperCase() + field.slice(1)
+}
+
+function FacetGroup({ field, fields, counts, selected, onToggle, isTags }) {
+  const [open, setOpen] = useState(true)
+  const [valueSearch, setValueSearch] = useState('')
+  const entries = Object.entries(counts).sort((a, b) => b[1] - a[1])
+  const needle = valueSearch.trim().toLowerCase()
+  const shown = isTags && needle
+    ? entries.filter(([v]) => v.toLowerCase().includes(needle))
+    : entries
+  return (
+    <div className="facet-group">
+      <button className="facet-header" onClick={() => setOpen(o => !o)}>
+        <span>{open ? '▾' : '▸'} {groupLabel(field, fields)}</span>
+      </button>
+      {open && (
+        <div className="facet-values">
+          {isTags && entries.length > 8 && (
+            <input
+              className="facet-value-search"
+              placeholder="filter values…"
+              value={valueSearch}
+              onChange={e => setValueSearch(e.target.value)}
+            />
+          )}
+          {shown.length === 0 && (
+            <div className="facet-empty">No values.</div>
+          )}
+          {shown.map(([value, count]) => (
+            <label key={value} className="facet-value">
+              <input
+                type="checkbox"
+                checked={selected.has(value)}
+                onChange={() => onToggle(field, value)}
+              />
+              <span className="facet-value-label">{value}</span>
+              <span className="facet-count">{count}</span>
+            </label>
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}
+
+export default function FacetGroups({
+  facets, fields, selections, onToggle, malformedOnly, onToggleMalformed,
+  onClear, hasActiveFilters,
+}) {
+  // The API returns facets in field order with `state` last; render in that
+  // order. `selections` is { field: Set<string> }.
+  const fieldOrder = Object.keys(facets || {})
+  // A `tags`-type field renders the value-search box.
+  const isTags = (field) => fields?.[field]?.type === 'tags'
+  return (
+    <div className="facets">
+      {hasActiveFilters && (
+        <button className="facet-clear" onClick={onClear}>Clear filters</button>
+      )}
+      {fieldOrder.map(field => (
+        <FacetGroup
+          key={field}
+          field={field}
+          fields={fields}
+          counts={facets[field]}
+          selected={selections[field] || new Set()}
+          onToggle={onToggle}
+          isTags={isTags(field)}
+        />
+      ))}
+      <label className="facet-malformed">
+        <input
+          type="checkbox"
+          checked={malformedOnly}
+          onChange={onToggleMalformed}
+        />
+        <span>Malformed metadata only</span>
+      </label>
+    </div>
+  )
+}