Apply adversarial-review fixes to the merged page and API route

- Source narrower: 'All sources (merged)' now clears the ?source
pre-highlight instead of being a dead option.
- eval-summary route: merged lookup failures degrade to the per-source
lookup/404 instead of a 500 (connection-reset race on the optional
merged table).
- hasMergedEvalsView: only cache the positive probe, so a transient
init failure of the optional parquet can't pin merged pages to
'absent' for the process lifetime.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/api/eval-summary/route.ts

@@ -20,9 +20,16 @@ export async function GET(request: Request) {
   if (isMergedEvalId(id)) {
     const metricId = searchParams.get("metric")?.trim() || undefined
     const sliceId = searchParams.get("slice")?.trim() || undefined
-    const merged = await getMergedBenchmarkSummary(routeIdFromSegments(id), metricId, sliceId)
-    if (merged) {
-      return NextResponse.json(merged)
+    try {
+      const merged = await getMergedBenchmarkSummary(routeIdFromSegments(id), metricId, sliceId)
+      if (merged) {
+        return NextResponse.json(merged)
+      }
+    } catch (error) {
+      // A connection reset can drop the optional merged table between
+      // the presence probe and the query — degrade to the per-source
+      // lookup/404 instead of a 500.
+      console.warn(`[eval-summary] merged lookup failed for ${id}:`, error)
     }
   }
 

components/merged-benchmark-view.tsx

@@ -221,7 +221,14 @@ export function MergedBenchmarkView({ benchmarkId }: { benchmarkId: string }) {
             value={preselectedSource}
             onChange={(e) => {
               const slug = e.target.value
-              if (!slug) return
+              if (!slug) {
+                // Back to "All sources": clear the pre-highlight param.
+                const params = new URLSearchParams(searchParams.toString())
+                params.delete("source")
+                const qs = params.toString()
+                router.replace(qs ? `${pathname}?${qs}` : pathname)
+                return
+              }
               const source = summary.aggregate_sources.find((s) => s.composite_slug === slug)
               if (source?.evaluation_id) {
                 // Navigate-on-select to the per-source page (spec Q5).

lib/view-data.ts

@@ -1144,7 +1144,12 @@ async function hasMergedEvalsView(): Promise<boolean> {
       const rows = await readRows<{ n: number }>(
         "SELECT COUNT(*) AS n FROM information_schema.tables WHERE table_name = 'merged_evals_view'"
       )
-      mergedEvalsViewPresenceCache = asNumber(rows[0]?.n) > 0
+      const present = asNumber(rows[0]?.n) > 0
+      // Cache only the positive: a transient init failure of the
+      // optional parquet must not pin merged pages to "absent" for the
+      // process lifetime — absent-table probes are trivial to repeat.
+      if (present) mergedEvalsViewPresenceCache = true
+      return present
     } catch {
       // Probe failed (connection blip) — don't cache; retry next request.
       return false