diff --git a/packages/web/src/lib/server/daily-rollup.own-properties.test.ts b/packages/web/src/lib/server/daily-rollup.own-properties.test.ts
new file mode 100644
index 00000000..2f33841e
--- /dev/null
+++ b/packages/web/src/lib/server/daily-rollup.own-properties.test.ts
@@ -0,0 +1,75 @@
+import { describe, expect, it } from 'vitest'
+import { aggregateSummary, type DailyRollup } from './daily-rollup'
+
+function rollup(overrides: Partial<DailyRollup> = {}): DailyRollup {
+  return {
+    date: '2026-09-05',
+    sessionCount: 0,
+    turnCount: 0,
+    activeUserCount: 0,
+    activeUserIds: [],
+    inputTokens: 0,
+    outputTokens: 0,
+    cacheReadTokens: 0,
+    cacheCreationTokens: 0,
+    estimatedCostUsd: 0,
+    skillCounts: {},
+    agentCounts: {},
+    modelTokens: {},
+    userStats: [],
+    ...overrides,
+  }
+}
+
+function recordWithInheritedEntry(ownKey: string, ownValue: number): Record<string, number> {
+  const values = Object.create({ inherited: 999 }) as Record<string, number>
+  values[ownKey] = ownValue
+  return values
+}
+
+describe('aggregateSummary own-property contract', () => {
+  it('aggregates ordinary own keys and preserves empty-map behavior', () => {
+    const summary = aggregateSummary([
+      rollup({
+        skillCounts: { review: 2 },
+        agentCounts: { worker: 3 },
+        modelTokens: { modelA: 5 },
+      }),
+      rollup({
+        skillCounts: { review: 4 },
+        agentCounts: { worker: 1 },
+        modelTokens: { modelA: 7 },
+      }),
+      rollup(),
+    ])
+
+    expect(summary.topSkills).toEqual([{ skillName: 'review', callCount: 6 }])
+    expect(summary.topAgents).toEqual([{ agentType: 'worker', callCount: 4 }])
+    expect(summary.modelShare).toEqual([{ model: 'modelA', totalTokens: 12 }])
+  })
+
+  it('does not aggregate inherited enumerable properties', () => {
+    const summary = aggregateSummary([
+      rollup({
+        skillCounts: recordWithInheritedEntry('ownSkill', 2),
+        agentCounts: recordWithInheritedEntry('ownAgent', 3),
+        modelTokens: recordWithInheritedEntry('ownModel', 5),
+      }),
+    ])
+
+    expect(summary.topSkills).toEqual([{ skillName: 'ownSkill', callCount: 2 }])
+    expect(summary.topAgents).toEqual([{ agentType: 'ownAgent', callCount: 3 }])
+    expect(summary.modelShare).toEqual([{ model: 'ownModel', totalTokens: 5 }])
+    expect(summary.topSkills.some(({ skillName }) => skillName === 'inherited')).toBe(false)
+    expect(summary.topAgents.some(({ agentType }) => agentType === 'inherited')).toBe(false)
+    expect(summary.modelShare.some(({ model }) => model === 'inherited')).toBe(false)
+  })
+
+  it('returns empty aggregate lists when every count map is empty', () => {
+    const summary = aggregateSummary([rollup()])
+
+    expect(summary.topSkills).toEqual([])
+    expect(summary.topAgents).toEqual([])
+    expect(summary.modelShare).toEqual([])
+  })
+})
diff --git a/packages/web/src/lib/server/daily-rollup.ts b/packages/web/src/lib/server/daily-rollup.ts
index 44fb4e5c..75a2bb60 100644
--- a/packages/web/src/lib/server/daily-rollup.ts
+++ b/packages/web/src/lib/server/daily-rollup.ts
@@ -438,16 +438,22 @@ export async function getDailyRollupsForProjects(
         const userSet = userSetsByDate.get(r.date)!
         for (const u of r.activeUserIds) userSet.add(u)
 
-        // [Bolt: Performance Optimization] Use Object.keys() instead of Object.entries() in hot paths.
-        // Impact: Avoids array allocation for each key-value pair, significantly reducing GC overhead when aggregating large daily rollups.
-        for (const k of Object.keys(r.skillCounts)) {
-          prev.skillCounts[k] = (prev.skillCounts[k] ?? 0) + r.skillCounts[k]!
+        // [Bolt: Performance Optimization] Use for...in instead of Object.keys() in hot paths.
+        // Impact: Completely avoids array allocation for keys, significantly reducing GC overhead when aggregating large daily rollups.
+        for (const k in r.skillCounts) {
+          if (Object.hasOwn(r.skillCounts, k)) {
+            prev.skillCounts[k] = (prev.skillCounts[k] ?? 0) + r.skillCounts[k]!
+          }
         }
-        for (const k of Object.keys(r.agentCounts)) {
-          prev.agentCounts[k] = (prev.agentCounts[k] ?? 0) + r.agentCounts[k]!
+        for (const k in r.agentCounts) {
+          if (Object.hasOwn(r.agentCounts, k)) {
+            prev.agentCounts[k] = (prev.agentCounts[k] ?? 0) + r.agentCounts[k]!
+          }
         }
-        for (const k of Object.keys(r.modelTokens)) {
-          prev.modelTokens[k] = (prev.modelTokens[k] ?? 0) + r.modelTokens[k]!
+        for (const k in r.modelTokens) {
+          if (Object.hasOwn(r.modelTokens, k)) {
+            prev.modelTokens[k] = (prev.modelTokens[k] ?? 0) + r.modelTokens[k]!
+          }
         }
 
         // userStats: userId 기준 sum (지연된 Map 변환)
@@ -622,10 +628,10 @@ export function aggregateSummary(
     totals.cacheCreationTokens += r.cacheCreationTokens
     totals.estimatedCostUsd += r.estimatedCostUsd
     for (const u of r.activeUserIds) activeUsers.add(u)
-    // [Bolt: Performance Optimization] Object.keys() iterations avoid internal array tuples, reducing heap thrashing
-    for (const k of Object.keys(r.skillCounts)) skillCounts[k] = (skillCounts[k] ?? 0) + r.skillCounts[k]!
-    for (const k of Object.keys(r.agentCounts)) agentCounts[k] = (agentCounts[k] ?? 0) + r.agentCounts[k]!
-    for (const k of Object.keys(r.modelTokens)) modelTokens[k] = (modelTokens[k] ?? 0) + r.modelTokens[k]!
+    // [Bolt: Performance Optimization] for...in iterations avoid array allocations entirely, reducing heap thrashing
+    for (const k in r.skillCounts) if (Object.hasOwn(r.skillCounts, k)) skillCounts[k] = (skillCounts[k] ?? 0) + r.skillCounts[k]!
+    for (const k in r.agentCounts) if (Object.hasOwn(r.agentCounts, k)) agentCounts[k] = (agentCounts[k] ?? 0) + r.agentCounts[k]!
+    for (const k in r.modelTokens) if (Object.hasOwn(r.modelTokens, k)) modelTokens[k] = (modelTokens[k] ?? 0) + r.modelTokens[k]!
   }
 
   // Deterministic tie-break: callCount DESC, skillName ASC (codepoint binary —
diff --git a/packages/web/src/lib/server/weekly-report.ts b/packages/web/src/lib/server/weekly-report.ts
index eb95d36f..710b03dc 100644
--- a/packages/web/src/lib/server/weekly-report.ts
+++ b/packages/web/src/lib/server/weekly-report.ts
@@ -401,12 +401,16 @@ export async function getWeeklyReport(
   const distinctSkillsThisWeek = new Set<string>()
 
   for (const r of thisWeekRollups) {
-    for (const k of Object.keys(r.agentCounts)) {
-      totalAgentCalls += r.agentCounts[k]
+    for (const k in r.agentCounts) {
+      if (Object.hasOwn(r.agentCounts, k)) {
+        totalAgentCalls += r.agentCounts[k]
+      }
     }
-    for (const k of Object.keys(r.skillCounts)) {
-      totalSkillCalls += r.skillCounts[k]
-      distinctSkillsThisWeek.add(k)
+    for (const k in r.skillCounts) {
+      if (Object.hasOwn(r.skillCounts, k)) {
+        totalSkillCalls += r.skillCounts[k]
+        distinctSkillsThisWeek.add(k)
+      }
     }
   }