diff --git a/config/scripts/session-scan-cutoff-benchmark.mjs b/config/scripts/session-scan-cutoff-benchmark.mjs
new file mode 100644
index 00000000000..4353754199e
--- /dev/null
+++ b/config/scripts/session-scan-cutoff-benchmark.mjs
@@ -0,0 +1,197 @@
+#!/usr/bin/env node
+// git show <base>:src/main/ai-vault/session-scanner.ts | node config/scripts/session-scan-cutoff-benchmark.mjs
+import assert from 'node:assert/strict'
+import { readFileSync } from 'node:fs'
+import path from 'node:path'
+import { performance } from 'node:perf_hooks'
+import ts from 'typescript-api'
+import { build } from 'esbuild'
+import { buildCounterbalancedSchedule } from './counterbalanced-benchmark-schedule.mjs'
+
+const baselineSource = ts.createSourceFile(
+  'session-scanner.ts',
+  readFileSync(0, 'utf8'),
+  ts.ScriptTarget.Latest,
+  true,
+  ts.ScriptKind.TS
+)
+const baselineFunction = baselineSource.statements.find(
+  (node) => ts.isFunctionDeclaration(node) && node.name?.text === 'canStopParsingSessions'
+)
+assert(baselineFunction, 'Pipe the baseline session-scanner.ts on stdin')
+
+async function load(contents) {
+  const result = await build({
+    stdin: { contents, resolveDir: path.resolve('src/main/ai-vault'), loader: 'ts' },
+    platform: 'node',
+    format: 'esm',
+    bundle: true,
+    write: false
+  })
+  const encoded = Buffer.from(result.outputFiles[0].text).toString('base64')
+  return import(`data:text/javascript;base64,${encoded}`)
+}
+const [baselineModule, currentModule] = await Promise.all([
+  load(`import { sessionSortTime } from './session-scanner-accumulator';
+export ${baselineFunction.getText(baselineSource)}`),
+  load(`export { canStopParsingSessions } from './session-scan-cutoff';
+export { CodexSessionCollection } from './codex-session-root-dedup';`)
+])
+const baseline = baselineModule.canStopParsingSessions
+const current = currentModule.canStopParsingSessions
+const { CodexSessionCollection } = currentModule
+
+let randomState = 91114
+function random(bound) {
+  randomState = (Math.imul(randomState, 1664525) + 1013904223) >>> 0
+  return Math.floor((randomState / 2 ** 32) * bound)
+}
+function session(index, overrides = {}) {
+  return Object.freeze({
+    agent: 'claude',
+    executionHostId: 'local',
+    sessionId: `session-${index}`,
+    filePath: `/home/ada/.codex/sessions/rollout-${index}.jsonl`,
+    codexHome: null,
+    updatedAt: new Date(index).toISOString(),
+    modifiedAt: new Date(0).toISOString(),
+    ...overrides
+  })
+}
+function collection(rows) {
+  const result = new CodexSessionCollection()
+  for (const row of rows) {
+    result.add(row)
+  }
+  return result
+}
+function check(sessions, limit, next) {
+  const rows = [...sessions.values()]
+  assert.equal(current(sessions, limit, next), baseline(sessions, limit, next))
+  assert.deepEqual([...sessions.values()], rows)
+}
+
+const dates = [
+  null,
+  '',
+  'invalid',
+  '1970-01-01T00:00:00Z',
+  '1970-01-01T00:00:02+00:00',
+  '-000001-01-01T00:00:00Z',
+  '+010000-01-01T00:00:00Z',
+  '-271821-04-20T00:00:00.000Z'
+]
+const limits = [0, -1, -3, 0.5, 1.5, Number.NaN, Infinity, -Infinity]
+const nextTimes = [undefined, Number.NaN, Infinity, -Infinity, 0, 1, 2, 2000]
+let comparisons = 0
+for (let trial = 0; trial < 4_000; trial += 1) {
+  const sessions = new CodexSessionCollection()
+  const admitted = []
+  for (let batch = 0; batch < 10; batch += 1) {
+    const count = random(8)
+    for (let index = 0; index < count; index += 1) {
+      const id = random(12)
+      const row =
+        admitted.length && random(5) === 0
+          ? admitted[random(admitted.length)]
+          : session(id, {
+              agent: random(3) ? 'codex' : 'claude',
+              executionHostId: random(4) ? 'local' : 'ssh:dev',
+              codexHome: random(2) ? null : '/custom',
+              updatedAt: random(3)
+                ? new Date(random(5000) - 2500).toISOString()
+                : dates[random(dates.length)],
+              modifiedAt: random(4) ? new Date(random(5000)).toISOString() : 'invalid'
+            })
+      admitted.push(row)
+      sessions.add(row)
+    }
+    const limit = random(3) ? 1 + random(40) : limits[random(limits.length)]
+    const next = random(2) ? random(5000) - 2500 : nextTimes[random(nextTimes.length)]
+    check(sessions, limit, next)
+    comparisons += 1
+  }
+}
+console.log(`${comparisons} differential batch cutoffs passed.`)
+
+function median(values) {
+  const sorted = values.toSorted((left, right) => left - right)
+  return (sorted[sorted.length / 2 - 1] + sorted[sorted.length / 2]) / 2
+}
+function measure(name, run, repeats) {
+  const expected = run(baseline)
+  assert.deepEqual(run(current), expected)
+  const sample = (cutoff) => {
+    let result
+    const start = performance.now()
+    for (let index = 0; index < repeats; index += 1) {
+      result = run(cutoff)
+    }
+    const elapsed = (performance.now() - start) / repeats
+    assert.deepEqual(result, expected)
+    return elapsed
+  }
+  sample(baseline)
+  sample(current)
+  const samples = { baseline: [], current: [] }
+  for (const pair of buildCounterbalancedSchedule(8, 'baseline', 'current')) {
+    for (const arm of pair) {
+      samples[arm].push(sample(arm === 'baseline' ? baseline : current))
+    }
+  }
+  return { name, beforeMs: median(samples.baseline), afterMs: median(samples.current) }
+}
+
+console.log(
+  JSON.stringify({ node: process.version, platform: process.platform, arch: process.arch })
+)
+const results = []
+for (const count of [8, 100, 1_000, 2_000, 10_000]) {
+  for (const order of ['ordered', 'shuffled']) {
+    const rows = Array.from({ length: count }, (_, index) => session(count - index))
+    if (order === 'shuffled') {
+      for (let index = count - 1; index > 0; index -= 1) {
+        const other = random(index + 1)
+        ;[rows[index], rows[other]] = [rows[other], rows[index]]
+      }
+    }
+    const sessions = collection(rows)
+    for (const next of [0, count]) {
+      results.push(
+        measure(
+          `${count} ${order} / ${next === 0 ? 'stop' : 'continue'}`,
+          (cutoff) => cutoff(sessions, Math.ceil(count / 2), next),
+          Math.max(20, Math.floor(30_000 / count))
+        )
+      )
+    }
+  }
+}
+for (const invalidIndex of [0, 999]) {
+  const sessions = collection(
+    Array.from({ length: 1_000 }, (_, index) =>
+      session(index, invalidIndex === index ? { updatedAt: 'invalid' } : {})
+    )
+  )
+  results.push(measure(`1000 invalid at ${invalidIndex}`, (cutoff) => cutoff(sessions, 500, 0), 50))
+}
+const rows = Array.from({ length: 2_000 }, () => session(random(2_000)))
+results.push(
+  measure(
+    '2000-candidate scan cutoff + admission / limit1000',
+    (cutoff) => {
+      const sessions = new CodexSessionCollection()
+      let index = 0
+      while (index < rows.length && !cutoff(sessions, 1_000, 10_000)) {
+        const end = Math.min(rows.length, index + Math.min(8, Math.max(1, 1_000 - sessions.size)))
+        while (index < end) {
+          sessions.add(rows[index++])
+        }
+      }
+      return { parsed: index, sessions: sessions.size }
+    },
+    2
+  )
+)
+console.table(results)
+console.log('Synthetic cutoff/admission CPU; excludes discovery, parsing, I/O and final sorting.')
diff --git a/src/main/ai-vault/remote-session-scanner.ts b/src/main/ai-vault/remote-session-scanner.ts
index b3fcc56ec9d..259c84d66ef 100644
--- a/src/main/ai-vault/remote-session-scanner.ts
+++ b/src/main/ai-vault/remote-session-scanner.ts
@@ -31,6 +31,7 @@ import { errorMessage } from './session-scanner-values'
 import { mapRemoteScanBatches } from './remote-session-scan-batching'
 import { throwIfAiVaultScanCancelled } from './ai-vault-scan-cancellation'
 import { recordSessionScanIssue } from './session-scan-issues'
+import { canStopParsingSessions } from './session-scan-cutoff'
 import { refreshCodexTitleFromIndex } from './session-scanner-codex-cached-title'
 import { limitRemoteScanFilesystemConcurrency } from './remote-session-scan-concurrency'
 import { aiVaultScanLimit } from '../../shared/ai-vault-session-depth'
@@ -145,7 +146,7 @@ async function parseRemoteSessionCandidates(args: {
   let index = 0
 
   while (index < args.candidates.length) {
-    if (canStopParsingRemoteSessions(sessions, args.limit, args.candidates[index]?.file.mtimeMs)) {
+    if (canStopParsingSessions(sessions, args.limit, args.candidates[index]?.file.mtimeMs)) {
       break
     }
 
@@ -311,23 +312,6 @@ function normalizeRemoteScopePaths(scopePaths: readonly string[]): string[] {
   return scopePaths.map((scopePath) => scopePath.trim()).filter(Boolean)
 }
 
-function canStopParsingRemoteSessions(
-  sessions: CodexSessionCollection,
-  limit: number,
-  nextCandidateMtimeMs: number | undefined
-): boolean {
-  if (sessions.size < limit || typeof nextCandidateMtimeMs !== 'number') {
-    return false
-  }
-  const visibleCutoff = Array.from(sessions.values(), sessionSortTime)
-    .sort((left, right) => right - left)
-    .at(limit - 1)
-
-  // Transcript mtimes bound the remaining candidate order; once the visible
-  // cutoff is newer, older files cannot enter the unscoped top-N result.
-  return typeof visibleCutoff === 'number' && nextCandidateMtimeMs < visibleCutoff
-}
-
 function isAiVaultSession(session: AiVaultSession | null): session is AiVaultSession {
   return Boolean(session)
 }
diff --git a/src/main/ai-vault/session-scan-cutoff.test.ts b/src/main/ai-vault/session-scan-cutoff.test.ts
new file mode 100644
index 00000000000..53ddd0a019b
--- /dev/null
+++ b/src/main/ai-vault/session-scan-cutoff.test.ts
@@ -0,0 +1,121 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import type { AiVaultSession } from '../../shared/ai-vault-types'
+import { CodexSessionCollection } from './codex-session-root-dedup'
+import { canStopParsingSessions } from './session-scan-cutoff'
+import { createAccumulator, finalizeSession, sessionSortTime } from './session-scanner-accumulator'
+
+function session(time: number | string, overrides: Partial<AiVaultSession> = {}): AiVaultSession {
+  const parsed = finalizeSession(
+    createAccumulator({
+      agent: 'claude',
+      sessionId: 'session',
+      file: { path: '/sessions/session.jsonl', mtimeMs: 0, modifiedAt: new Date(0).toISOString() }
+    }),
+    'linux'
+  )
+  if (!parsed) {
+    throw new Error('Expected a session fixture')
+  }
+  return Object.freeze({
+    ...parsed,
+    updatedAt: typeof time === 'number' ? new Date(time).toISOString() : time,
+    ...overrides
+  })
+}
+
+function collection(rows: AiVaultSession[]): CodexSessionCollection {
+  const result = new CodexSessionCollection()
+  rows.forEach((row) => result.add(row))
+  return result
+}
+
+function sortedReference(rows: AiVaultSession[], limit: number, next: number | undefined): boolean {
+  if (rows.length < limit || typeof next !== 'number') {
+    return false
+  }
+  const cutoff = rows
+    .map(sessionSortTime)
+    .sort((left, right) => right - left)
+    .at(limit - 1)
+  return typeof cutoff === 'number' && next < cutoff
+}
+
+afterEach(() => vi.restoreAllMocks())
+
+describe('canStopParsingSessions', () => {
+  it('counts strictly newer rows without sorting or mutating their order', () => {
+    const rows = [session(8), session(2), session(6), session(4)]
+    const sessions = collection(rows)
+    const sort = vi.spyOn(Array.prototype, 'sort')
+    expect(canStopParsingSessions(sessions, 2, 5)).toBe(true)
+    expect(canStopParsingSessions(sessions, 2, 6)).toBe(false)
+    expect(canStopParsingSessions(sessions, 4, 1)).toBe(true)
+    expect(canStopParsingSessions(sessions, 4, 2)).toBe(false)
+    expect(sort).not.toHaveBeenCalled()
+    expect([...sessions.values()]).toEqual(rows)
+  })
+
+  it('does not visit rows before the unique-session budget is met', () => {
+    const sessions = collection([session(5)])
+    const values = vi.spyOn(sessions, 'values')
+    expect(canStopParsingSessions(sessions, 2, 0)).toBe(false)
+    expect(canStopParsingSessions(sessions, Number.POSITIVE_INFINITY, 0)).toBe(false)
+    expect(canStopParsingSessions(sessions, 1, undefined)).toBe(false)
+    expect(values).not.toHaveBeenCalled()
+  })
+
+  it('recounts a preferred alias even when replacement lowers its timestamp', () => {
+    const alias = {
+      agent: 'codex' as const,
+      sessionId: 'same',
+      filePath: '/sessions/rollout-same.jsonl'
+    }
+    const sessions = collection([session(100, { ...alias, codexHome: '/custom' }), session(100)])
+    expect(canStopParsingSessions(sessions, 2, 50)).toBe(true)
+    const preferred = session(10, { ...alias, codexHome: null })
+    sessions.add(preferred)
+    expect(sessions.size).toBe(2)
+    expect(canStopParsingSessions(sessions, 2, 50)).toBe(false)
+    sessions.add(preferred)
+    expect(sessions.size).toBe(3)
+    expect(canStopParsingSessions(sessions, 3, 9)).toBe(true)
+  })
+
+  it('preserves the legacy sort result when a later timestamp is invalid', () => {
+    const rows = [session(0), session('invalid'), session(20)]
+    const sessions = collection(rows)
+    expect(canStopParsingSessions(sessions, 1, 10)).toBe(false)
+    for (const candidate of [rows, rows.toReversed(), [rows[2], rows[0], rows[1]]]) {
+      for (const limit of [1, 2, 3]) {
+        for (const next of [-1, 0, 10, 20]) {
+          expect(canStopParsingSessions(collection(candidate), limit, next)).toBe(
+            sortedReference(candidate, limit, next)
+          )
+        }
+      }
+    }
+  })
+
+  it('parses timestamps only once when an invalid date appears at the end', () => {
+    const sessions = collection([session(10), session(5), session('invalid')])
+    const parse = vi.spyOn(Date, 'parse')
+    canStopParsingSessions(sessions, 1, 0)
+    expect(parse).toHaveBeenCalledTimes(3)
+  })
+
+  it('uses the same nullish modified-time fallback and numeric limit semantics', () => {
+    const rows = [
+      session('', { updatedAt: null, modifiedAt: '1970-01-01T00:00:02+00:00' }),
+      session('-000001-01-01T00:00:00Z'),
+      session('+010000-01-01T00:00:00Z'),
+      session(0)
+    ]
+    for (const limit of [0, -1, -5, 0.5, 1.5, Number.NaN, Infinity, -Infinity, 1, 2, 4, 5]) {
+      for (const next of [undefined, Number.NaN, -Infinity, Infinity, -1, 0, 1, 2000]) {
+        expect(canStopParsingSessions(collection(rows), limit, next)).toBe(
+          sortedReference(rows, limit, next)
+        )
+      }
+    }
+  })
+})
diff --git a/src/main/ai-vault/session-scan-cutoff.ts b/src/main/ai-vault/session-scan-cutoff.ts
new file mode 100644
index 00000000000..e93d25bc985
--- /dev/null
+++ b/src/main/ai-vault/session-scan-cutoff.ts
@@ -0,0 +1,41 @@
+import type { CodexSessionCollection } from './codex-session-root-dedup'
+import { sessionSortTime } from './session-scanner-accumulator'
+
+type ScanSessions = Pick<CodexSessionCollection, 'size' | 'values'>
+
+function sortedCutoffIsNewer(
+  times: number[],
+  limit: number,
+  nextCandidateMtimeMs: number
+): boolean {
+  const visibleCutoff = times.sort((left, right) => right - left).at(limit - 1)
+  return typeof visibleCutoff === 'number' && nextCandidateMtimeMs < visibleCutoff
+}
+
+export function canStopParsingSessions(
+  sessions: ScanSessions,
+  limit: number,
+  nextCandidateMtimeMs: number | undefined
+): boolean {
+  if (sessions.size < limit || typeof nextCandidateMtimeMs !== 'number') {
+    return false
+  }
+  const times = Array.from(sessions.values(), sessionSortTime)
+  if (!Number.isInteger(limit) || limit <= 0) {
+    return sortedCutoffIsNewer(times, limit, nextCandidateMtimeMs)
+  }
+
+  // The top-N cutoff is newer exactly when N retained sessions beat the next mtime.
+  let newerCount = 0
+  for (const time of times) {
+    if (Number.isNaN(time)) {
+      // NaN makes the old comparator inconsistent; preserve its ordering verbatim.
+      return sortedCutoffIsNewer(times, limit, nextCandidateMtimeMs)
+    }
+    if (time > nextCandidateMtimeMs) {
+      newerCount += 1
+    }
+  }
+  // Check every timestamp before deciding: a later NaN requires the legacy sort.
+  return newerCount >= limit
+}
diff --git a/src/main/ai-vault/session-scanner-cutoff.test.ts b/src/main/ai-vault/session-scanner-cutoff.test.ts
new file mode 100644
index 00000000000..76488ddabbe
--- /dev/null
+++ b/src/main/ai-vault/session-scanner-cutoff.test.ts
@@ -0,0 +1,77 @@
+import { mkdtemp, mkdir, rm, utimes, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { getRemoteHostPlatform } from '../ssh/ssh-remote-platform'
+import { scanRemoteAiVaultSessions } from './remote-session-scanner'
+import { MemoryRemoteProvider } from './remote-session-scanner-test-fixtures'
+import { scanAiVaultSessions } from './session-scanner'
+import { isolatedScanRoots, jsonLines } from './session-scanner-test-fixtures'
+
+const tempRoots: string[] = []
+afterEach(async () => {
+  vi.restoreAllMocks()
+  await Promise.all(tempRoots.splice(0).map((root) => rm(root, { recursive: true, force: true })))
+})
+
+describe('session scanner cutoff', () => {
+  it.each(['native', 'remote'] as const)(
+    '%s does not sort timestamps at every post-limit candidate',
+    async (host) => {
+      const count = 128
+      const limit = count / 2
+      const provider = new MemoryRemoteProvider()
+      const root = await mkdtemp(join(tmpdir(), 'orca-session-cutoff-'))
+      tempRoots.push(root)
+      const roots = isolatedScanRoots(root)
+      await mkdir(roots.codexSessionsDir, { recursive: true })
+      for (let index = 0; index < count; index++) {
+        const name = `rollout-session-${index}.jsonl`
+        const content = jsonLines([
+          { type: 'session_meta', payload: { id: `session-${index}`, cwd: '/repo/folder' } },
+          {
+            type: 'event_msg',
+            timestamp: new Date(index).toISOString(),
+            payload: { type: 'user_message', message: 'Check this session' }
+          }
+        ])
+        const mtime = 10_000 - index
+        if (host === 'native') {
+          const filePath = join(roots.codexSessionsDir, name)
+          await writeFile(filePath, content)
+          await utimes(filePath, new Date(mtime), new Date(mtime))
+        } else {
+          provider.addFile(`/home/ada/.codex/sessions/${name}`, content, mtime)
+        }
+      }
+      let numericSorts = 0
+      const originalSort = Array.prototype.sort
+      vi.spyOn(Array.prototype, 'sort').mockImplementation(function (this: unknown[], compare) {
+        if (typeof this[0] === 'number') {
+          numericSorts++
+        }
+        return originalSort.call(this, compare)
+      })
+      const scan = () =>
+        host === 'native'
+          ? scanAiVaultSessions({ ...roots, limit })
+          : scanRemoteAiVaultSessions({
+              provider,
+              remoteHome: '/home/ada',
+              hostPlatform: getRemoteHostPlatform('linux-x64'),
+              executionHostId: 'ssh:scan-cutoff',
+              limit
+            })
+
+      for (let pass = 0; pass < 2; pass++) {
+        numericSorts = 0
+        const result = await scan()
+        expect(result.issues).toEqual([])
+        expect(result.sessions.map((row) => row.sessionId)).toEqual(
+          Array.from({ length: limit }, (_, index) => `session-${count - index - 1}`)
+        )
+        expect(numericSorts).toBe(0)
+      }
+    }
+  )
+})
diff --git a/src/main/ai-vault/session-scanner.ts b/src/main/ai-vault/session-scanner.ts
index 9461fef6525..94c69258d59 100644
--- a/src/main/ai-vault/session-scanner.ts
+++ b/src/main/ai-vault/session-scanner.ts
@@ -23,6 +23,7 @@ import {
   type SessionParseStats
 } from './session-scanner-parse-cache'
 import { recordSessionScanIssue } from './session-scan-issues'
+import { canStopParsingSessions } from './session-scan-cutoff'
 import { discoverInScopeClaudeFiles } from './session-scanner-scope-discovery'
 import { discoverAiVaultSessionSources } from './session-scanner-source-discovery'
 import { cursorChatMetaRefusals, withCursorChatMetaScan } from './session-scanner-cursor-chat-meta'
@@ -296,20 +297,3 @@ function withSessionExecutionHost(
     id: `${executionHostId}:${session.agent}:${session.sessionId}:${session.filePath}`
   }
 }
-
-function canStopParsingSessions(
-  sessions: CodexSessionCollection,
-  limit: number,
-  nextCandidateMtimeMs: number | undefined
-): boolean {
-  if (sessions.size < limit || typeof nextCandidateMtimeMs !== 'number') {
-    return false
-  }
-  const visibleCutoff = Array.from(sessions.values(), sessionSortTime)
-    .sort((left, right) => right - left)
-    .at(limit - 1)
-
-  // Transcript mtime is already our discovery bound and fallback sort key; older
-  // files cannot displace the current visible set once the cutoff is newer.
-  return typeof visibleCutoff === 'number' && nextCandidateMtimeMs < visibleCutoff
-}