feat: reset to system-calculated ranking order

Adds a 'Reset to system order' button per category (Startups and
Business Concepts). The button only appears when admins have
drag-reordered that category — otherwise there's nothing to reset.
Clicking it wipes that category's reorder history from the snapshot's
reordersJson via a new ranking.clearReorders mutation, after which
the dashboard re-initializes and falls back to the live composite
ranking (balanced/raw score, optionally blended with balanced pass
rate per the toggles).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/admin/round/ranking-dashboard.tsx

@@ -350,6 +350,15 @@ export function RankingDashboard({ competitionId: _competitionId, roundId }: Ran
     // Do NOT invalidate getSnapshot — would reset localOrder
   })
 
+  const clearReordersMutation = trpc.ranking.clearReorders.useMutation({
+    onSuccess: () => {
+      toast.success('Reverted to system-calculated order')
+      initialized.current = false // allow re-init on next snapshot load
+      void utils.ranking.getSnapshot.invalidate()
+    },
+    onError: (err) => toast.error(`Failed to reset: ${err.message}`),
+  })
+
   const updateRoundMutation = trpc.round.update.useMutation({
     onSuccess: () => {
       toast.success('Ranking config saved')
@@ -953,7 +962,7 @@ export function RankingDashboard({ competitionId: _competitionId, roundId }: Ran
         {/* Per-category sections */}
         {(['STARTUP', 'BUSINESS_CONCEPT'] as const).map((category) => (
           <Card key={category}>
-            <CardHeader>
+            <CardHeader className="flex-row items-center justify-between space-y-0">
               <CardTitle className="text-sm font-semibold uppercase tracking-wide text-muted-foreground">
                 {categoryLabels[category]}
                 {evalConfig && evalConfig.advanceMode === 'threshold' && evalConfig.advanceScoreThreshold != null ? (
@@ -966,6 +975,26 @@ export function RankingDashboard({ competitionId: _competitionId, roundId }: Ran
                   </span>
                 ) : null}
               </CardTitle>
+              {(() => {
+                const reorders = (snapshot?.reordersJson as Array<{
+                  category: 'STARTUP' | 'BUSINESS_CONCEPT'
+                }> | null) ?? []
+                const hasManualOrder = reorders.some((r) => r.category === category)
+                if (!hasManualOrder || !latestSnapshotId) return null
+                return (
+                  <Button
+                    variant="outline"
+                    size="sm"
+                    className="h-7 text-xs"
+                    disabled={clearReordersMutation.isPending}
+                    onClick={() => clearReordersMutation.mutate({ snapshotId: latestSnapshotId, category })}
+                    title="Discard manual drag-reorder for this category and revert to system-calculated order"
+                  >
+                    <RefreshCw className="h-3 w-3 mr-1" />
+                    Reset to system order
+                  </Button>
+                )
+              })()}
             </CardHeader>
             <CardContent>
               {localOrder[category].length === 0 ? (

src/server/routers/ranking.ts

@@ -264,6 +264,32 @@ export const rankingRouter = router({
       return { ok: true }
     }),
 
+  /** Clear all manual drag-reorders for a snapshot, optionally filtered by
+   * category. The next dashboard render falls back to the system-computed
+   * order. Append-only history of reorders is wiped — that's the point. */
+  clearReorders: adminProcedure
+    .input(
+      z.object({
+        snapshotId: z.string(),
+        category: z.enum(['STARTUP', 'BUSINESS_CONCEPT']).optional(),
+      }),
+    )
+    .mutation(async ({ ctx, input }) => {
+      const snapshot = await ctx.prisma.rankingSnapshot.findUniqueOrThrow({
+        where: { id: input.snapshotId },
+        select: { reordersJson: true },
+      })
+      const existing = (snapshot.reordersJson as ReorderEvent[] | null) ?? []
+      const next = input.category
+        ? existing.filter((r) => r.category !== input.category)
+        : []
+      await ctx.prisma.rankingSnapshot.update({
+        where: { id: input.snapshotId },
+        data: { reordersJson: next as unknown as Prisma.InputJsonValue },
+      })
+      return { ok: true, cleared: existing.length - next.length }
+    }),
+
   /**
    * RANK-09 — Manual trigger for auto-rank (admin button on round detail page).
    * Reads ranking criteria from round configJson and executes quickRank.