fix: compute z-context per-round in edition-mode rankings rollup

Previously the edition-level branch of analytics.getProjectRankings
(programId mode) pooled every juror's evaluations across every round
into a single z-normalization context. A juror's mean and stddev are
not stable across round types — quick intake screening produces a
very different grading profile than a deep evaluation round, and
mixing them yields a meaningless personal calibration.

The rollup now groups points by roundId, computes one balance context
per round, and aggregates per-project as the unweighted mean of the
per-round balanced averages. roundId mode is unchanged.

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

src/server/services/juror-balance.ts

@@ -118,3 +118,71 @@ export function computeBalancedProjectScores(
 
   return results
 }
+
+/**
+ * Per-round balanced rollup: groups points by roundId, computes a balance
+ * context per round, then averages the per-round balanced averages for each
+ * project. Use when surfacing edition-level rankings — never pool z-contexts
+ * across rounds, because a juror's grading profile differs by round type.
+ */
+export type RoundScopedScorePoint = ScorePoint & { roundId: string }
+
+export type EditionRollupResult = {
+  projectId: string
+  rawAverage: number | null
+  balancedAverage: number | null
+  count: number
+  roundCount: number
+}
+
+export function computePerRoundBalanced(
+  points: RoundScopedScorePoint[],
+): Map<string, EditionRollupResult> {
+  const byRound = new Map<string, ScorePoint[]>()
+  for (const p of points) {
+    const arr = byRound.get(p.roundId) ?? []
+    arr.push({ projectId: p.projectId, userId: p.userId, rawScore: p.rawScore })
+    byRound.set(p.roundId, arr)
+  }
+
+  const perRoundResults: Array<Map<string, BalancedProjectResult>> = []
+  for (const roundPoints of byRound.values()) {
+    const ctx = computeBalanceContext(roundPoints)
+    perRoundResults.push(computeBalancedProjectScores(roundPoints, ctx))
+  }
+
+  const accumulator = new Map<
+    string,
+    { rawSum: number; rawCount: number; balancedSum: number; balancedCount: number; count: number; roundCount: number }
+  >()
+  for (const roundMap of perRoundResults) {
+    for (const [projectId, result] of roundMap.entries()) {
+      const acc = accumulator.get(projectId) ?? {
+        rawSum: 0, rawCount: 0, balancedSum: 0, balancedCount: 0, count: 0, roundCount: 0,
+      }
+      if (result.rawAverage != null) {
+        acc.rawSum += result.rawAverage
+        acc.rawCount += 1
+      }
+      if (result.balancedAverage != null) {
+        acc.balancedSum += result.balancedAverage
+        acc.balancedCount += 1
+      }
+      acc.count += result.count
+      acc.roundCount += 1
+      accumulator.set(projectId, acc)
+    }
+  }
+
+  const out = new Map<string, EditionRollupResult>()
+  for (const [projectId, acc] of accumulator.entries()) {
+    out.set(projectId, {
+      projectId,
+      rawAverage: acc.rawCount > 0 ? acc.rawSum / acc.rawCount : null,
+      balancedAverage: acc.balancedCount > 0 ? acc.balancedSum / acc.balancedCount : null,
+      count: acc.count,
+      roundCount: acc.roundCount,
+    })
+  }
+  return out
+}