From ac8f70a16d38fa490f6eb806660705da00b56125 Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Sun, 6 Sep 2026 22:05:30 +0000
Subject: [PATCH 1/2] =?UTF-8?q?perf:=20O(N=20log=20N)=20Date.parse()=20?=
 =?UTF-8?q?=ED=98=B8=EC=B6=9C=EC=9D=84=20Map-Sort-Map=EC=9C=BC=EB=A1=9C=20?=
 =?UTF-8?q?=EC=B5=9C=EC=A0=81=ED=99=94?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .jules/bolt.md                                        |  6 ++++++
 .../components/dashboard/session-timeline-chart.tsx   | 11 +++++------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index 57daf471..12a0bb7d 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -3,3 +3,9 @@
 **Learning:** `Date.parse(value)` returns the timestamp primitive directly, while `new Date(value).getTime()` also constructs a `Date` object. Both use the same ECMAScript string-parsing semantics for these call sites.
 
 **Action:** In frequently executed paths that only need a timestamp primitive, prefer `Date.parse(value)`. Treat the allocation reduction as a bounded micro-optimization unless a committed benchmark establishes a larger runtime effect.
+
+## 2026-09-06 - Schwartzian transform for expensive sort comparators
+
+**Learning:** When sorting large arrays based on an expensive data transformation like `Date.parse()` on ISO strings, placing the transformation directly inside the `Array.prototype.sort()` comparator causes it to execute O(N log N) times. A Schwartzian transform (map-sort-map) pre-computes the values in O(N) time.
+
+**Action:** Wrap items in an object `{ original: item, parsedValue: expensiveOperation(item) }` prior to sorting when the comparator relies on computationally non-trivial operations.
diff --git a/packages/web/src/components/dashboard/session-timeline-chart.tsx b/packages/web/src/components/dashboard/session-timeline-chart.tsx
index 222d0b22..6e66ee21 100644
--- a/packages/web/src/components/dashboard/session-timeline-chart.tsx
+++ b/packages/web/src/components/dashboard/session-timeline-chart.tsx
@@ -67,9 +67,10 @@ function buildChartData(
   toolCalls: ToolCallPoint[],
   sessionStartedAt: string
 ): ChartDataItem[] {
-  const sortedUsage = [...usageTimeline].sort(
-    (a, b) => Date.parse(a.timestamp) - Date.parse(b.timestamp)
-  )
+  const sortedUsage = usageTimeline
+    .map((item) => ({ original: item, parsedValue: Date.parse(item.timestamp) }))
+    .sort((a, b) => a.parsedValue - b.parsedValue)
+
   const sortedTools = [...toolCalls].sort(
     (a, b) => a.parsedTimestamp - b.parsedTimestamp
   )
@@ -77,9 +78,7 @@ function buildChartData(
   let toolIndex = 0
   const cumulativeToolCounts = new Map<string, number>()
 
-  return sortedUsage.map((usage) => {
-    const currentTimestamp = Date.parse(usage.timestamp)
-
+  return sortedUsage.map(({ original: usage, parsedValue: currentTimestamp }) => {
     while (
       toolIndex < sortedTools.length &&
       sortedTools[toolIndex]!.parsedTimestamp <= currentTimestamp

From 1e1100f2224a94699fd66f94be573fc516db44cf Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Sun, 6 Sep 2026 22:44:38 +0000
Subject: [PATCH 2/2] =?UTF-8?q?perf:=20O(N=20log=20N)=20Date.parse()=20?=
 =?UTF-8?q?=ED=98=B8=EC=B6=9C=EC=9D=84=20Map-Sort-Map=EC=9C=BC=EB=A1=9C=20?=
 =?UTF-8?q?=EC=B5=9C=EC=A0=81=ED=99=94?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit