diff --git a/scripts/perf/metrics.mjs b/scripts/perf/metrics.mjs
index adcf72d2..1b50b64e 100644
--- a/scripts/perf/metrics.mjs
+++ b/scripts/perf/metrics.mjs
@@ -37,6 +37,36 @@ export const percentile = (values, fraction) => {
   return round(sorted[rank])
 }
 
+// `RunTask` and `RunMicrotasks` are containers: their duration already
+// includes the work below them, so counting them would double-count.
+const CONTAINER_TRACE_EVENTS = new Set(["RunTask", "RunMicrotasks", "ProfileChunk", "Profile"])
+
+/**
+ * Breaks recorded time down by trace event.
+ *
+ * A CPU sampling profile attributes native work to `(program)`, which hides
+ * whether time went to HTML parsing, style recalculation, layout, or paint.
+ * The timeline trace names that work explicitly, so this is what turns "76% of
+ * busy time is native" into an actionable list.
+ */
+export const summarizeTraceEvents = (traceEvents, topCount = 15) => {
+  const totals = new Map()
+  for (const event of traceEvents) {
+    if (event.ph !== "X" || !(Number(event.dur) > 0)) continue
+    if (CONTAINER_TRACE_EVENTS.has(event.name)) continue
+    const entry = totals.get(event.name) ?? { name: event.name, count: 0, totalMs: 0, maxMs: 0 }
+    const durationMs = Number(event.dur) / 1000
+    entry.count += 1
+    entry.totalMs += durationMs
+    if (durationMs > entry.maxMs) entry.maxMs = durationMs
+    totals.set(event.name, entry)
+  }
+  return [...totals.values()]
+    .sort((left, right) => right.totalMs - left.totalMs)
+    .slice(0, topCount)
+    .map((entry) => ({ ...entry, totalMs: round(entry.totalMs), maxMs: round(entry.maxMs) }))
+}
+
 /**
  * Long tasks block input and animation, so a streaming capture is judged by
  * its task-duration distribution rather than by an average frame rate.
diff --git a/scripts/profile-session.mjs b/scripts/profile-session.mjs
index f7c0e11e..e9483c40 100644
--- a/scripts/profile-session.mjs
+++ b/scripts/profile-session.mjs
@@ -29,7 +29,7 @@ import process from "node:process"
 import { CdpClient, createPageTarget, evaluateValue, launchChrome, reservePort, resolveChrome, wait } from "./perf/cdp.mjs"
 import { buildIdleProbeSource, IDLE_PROBE_GLOBAL } from "./perf/idle-probe.mjs"
 import { summarizeCpuProfile } from "./perf/cpu-profile.mjs"
-import { growthPerSecond, metricMap, round, summarizeLongTasks } from "./perf/metrics.mjs"
+import { growthPerSecond, metricMap, round, summarizeLongTasks, summarizeTraceEvents } from "./perf/metrics.mjs"
 
 const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..")
 const cliPath = join(repoRoot, "packages/web/bin/cli.js")
@@ -224,6 +224,11 @@ const printReport = (summary, baseline) => {
     console.log(`  ${String(entry.selfMs).padStart(9)} ms  ${String(entry.percentOfBusy).padStart(5)}%  ${entry.function}`)
   }
 
+  console.log("\nWhere recorded time went (timeline trace):")
+  for (const entry of summary.traceBreakdown?.slice(0, 14) ?? []) {
+    console.log(`  ${String(entry.totalMs).padStart(9)} ms  ${String(entry.count).padStart(6)}x  max ${String(entry.maxMs).padStart(7)} ms  ${entry.name}`)
+  }
+
   const streamEntries = summary.streamPerformance?.entries ?? []
   if (streamEntries.length > 0) {
     console.log("\nApplication stream counters (total ms / count):")
@@ -435,6 +440,7 @@ const main = async () => {
     const renderedCharacterGrowth = renderedAfter.characters - renderedBefore.characters
 
     const tasks = summarizeLongTasks(traceEvents)
+    const traceBreakdown = summarizeTraceEvents(traceEvents)
     const delta = (name) => Number(after[name] ?? 0) - Number(before[name] ?? 0)
     const perSecond = (name) => round(delta(name) / elapsedSeconds)
     const heapSamples = samples.map((sample) => sample.jsHeapUsedMb)
@@ -488,6 +494,7 @@ const main = async () => {
       },
       frameLiveness,
       cpuProfile: summarizeCpuProfile(profile),
+      traceBreakdown,
       streamPerformance,
       syncCounters,
       scheduledWork: probe,