diff --git a/src/main/browser/browser-cookie-clear-store.test.ts b/src/main/browser/browser-cookie-clear-store.test.ts
new file mode 100644
index 00000000000..e44d71c15dc
--- /dev/null
+++ b/src/main/browser/browser-cookie-clear-store.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, it } from 'vitest'
+import type { Cookie } from 'electron'
+import {
+  cdpRestoreParamsFromIdentity,
+  cookieClearIdentitiesFromCdp
+} from './browser-cookie-clear-store'
+
+const chipsCookie: Cookie = {
+  domain: 'app.acme-chips.test',
+  name: 'chips-auth',
+  path: '/',
+  secure: true,
+  sameSite: 'no_restriction',
+  value: 'keep-me'
+}
+
+describe('cookie clear CDP identities', () => {
+  it('captures a CHIPS partition key for restore and never invents one', () => {
+    const identities = cookieClearIdentitiesFromCdp(
+      [{ cookie: chipsCookie, url: 'https://app.acme-chips.test/' }],
+      [
+        {
+          name: 'chips-auth',
+          value: 'keep-me',
+          domain: 'app.acme-chips.test',
+          path: '/',
+          secure: true,
+          sameSite: 'None',
+          partitionKey: { topLevelSite: 'https://top.example', hasCrossSiteAncestor: true }
+        }
+      ]
+    )
+
+    expect(identities).toEqual([
+      expect.objectContaining({
+        name: 'chips-auth',
+        partitionKey: { topLevelSite: 'https://top.example', hasCrossSiteAncestor: true }
+      })
+    ])
+    expect(cdpRestoreParamsFromIdentity(identities[0])).toEqual(
+      expect.objectContaining({
+        name: 'chips-auth',
+        sameSite: 'None',
+        partitionKey: { topLevelSite: 'https://top.example', hasCrossSiteAncestor: true }
+      })
+    )
+  })
+
+  it('fails closed when CDP cannot identify a removable cookie', () => {
+    expect(() =>
+      cookieClearIdentitiesFromCdp(
+        [{ cookie: chipsCookie, url: 'https://app.acme-chips.test/' }],
+        []
+      )
+    ).toThrow(/Could not snapshot cookie identity/)
+  })
+})
diff --git a/src/main/browser/browser-cookie-clear-store.ts b/src/main/browser/browser-cookie-clear-store.ts
new file mode 100644
index 00000000000..f0817cb5830
--- /dev/null
+++ b/src/main/browser/browser-cookie-clear-store.ts
@@ -0,0 +1,255 @@
+import { BrowserWindow, webContents, type Cookie, type Session } from 'electron'
+import { acquireElectronDebugger } from './electron-debugger-lease'
+import { normalizeCookieDomain } from './browser-cookie-import-policy'
+import type {
+  CookieClearIdentity,
+  CookieClearPartitionKey,
+  CookieClearStore
+} from './browser-cookie-import-clear'
+
+type CdpCookiePartitionKey = {
+  topLevelSite?: string
+  hasCrossSiteAncestor?: boolean
+}
+
+type CdpCookie = {
+  name: string
+  value: string
+  domain?: string
+  path?: string
+  secure?: boolean
+  httpOnly?: boolean
+  session?: boolean
+  expires?: number
+  sameSite?: string
+  partitionKey?: CdpCookiePartitionKey
+}
+
+type CookieClearDebugger = {
+  sendCommand: (method: string, params?: Record<string, unknown>) => Promise<unknown>
+}
+
+type CookieClearSession = {
+  debugger: CookieClearDebugger
+  dispose: () => void
+}
+
+function findPartitionWebContents(targetSession: Session) {
+  return webContents
+    .getAllWebContents()
+    .find((contents) => !contents.isDestroyed() && contents.session === targetSession)
+}
+
+function cdpSameSite(sameSite: Cookie['sameSite']): 'Strict' | 'Lax' | 'None' {
+  if (sameSite === 'strict') {
+    return 'Strict'
+  }
+  if (sameSite === 'no_restriction') {
+    return 'None'
+  }
+  return 'Lax'
+}
+
+function electronSameSite(sameSite: string | undefined): Cookie['sameSite'] {
+  if (sameSite === 'Strict') {
+    return 'strict'
+  }
+  if (sameSite === 'None') {
+    return 'no_restriction'
+  }
+  return sameSite === 'Lax' ? 'lax' : 'unspecified'
+}
+
+function partitionKeyFromCdp(
+  partitionKey: CdpCookiePartitionKey | undefined
+): CookieClearPartitionKey | undefined {
+  const topLevelSite = partitionKey?.topLevelSite
+  if (!topLevelSite) {
+    return undefined
+  }
+  return {
+    topLevelSite,
+    hasCrossSiteAncestor: partitionKey.hasCrossSiteAncestor === true
+  }
+}
+
+function sameCookieScope(cookie: Cookie, cdpCookie: CdpCookie): boolean {
+  const cookieDomain = cookie.domain ? normalizeCookieDomain(cookie.domain) : null
+  const cdpDomain = cdpCookie.domain ? normalizeCookieDomain(cdpCookie.domain) : null
+  return (
+    cookie.name === cdpCookie.name &&
+    cookieDomain !== null &&
+    cookieDomain === cdpDomain &&
+    (cookie.path || '/') === (cdpCookie.path || '/')
+  )
+}
+
+function identityFromCdpCookie(
+  url: string,
+  cookie: Cookie,
+  cdpCookie: CdpCookie
+): CookieClearIdentity {
+  const partitionKey = partitionKeyFromCdp(cdpCookie.partitionKey)
+  return {
+    url,
+    name: cdpCookie.name,
+    value: cdpCookie.value,
+    domain: cdpCookie.domain,
+    hostOnly: cookie.hostOnly,
+    path: cdpCookie.path,
+    secure: cdpCookie.secure,
+    httpOnly: cdpCookie.httpOnly,
+    sameSite: electronSameSite(cdpCookie.sameSite),
+    ...(cdpCookie.session === true || cdpCookie.expires == null
+      ? {}
+      : { expirationDate: cdpCookie.expires }),
+    ...(partitionKey ? { partitionKey } : {})
+  }
+}
+
+async function attachCookieClearSession(targetSession: Session): Promise<CookieClearSession> {
+  const existing = findPartitionWebContents(targetSession)
+  const window = existing
+    ? null
+    : new BrowserWindow({
+        show: false,
+        webPreferences: {
+          session: targetSession,
+          sandbox: true,
+          contextIsolation: true,
+          nodeIntegration: false
+        }
+      })
+  try {
+    if (window) {
+      await window.loadURL('data:text/html,<!doctype html><title>cookie-clear</title>')
+    }
+    const contents = existing ?? window?.webContents
+    if (!contents || contents.isDestroyed()) {
+      throw new Error('Could not attach to the cookie session for an atomic clear')
+    }
+    const lease = acquireElectronDebugger(contents)
+    try {
+      await contents.debugger.sendCommand('Network.enable')
+    } catch (error) {
+      lease.release()
+      throw error
+    }
+    return {
+      debugger: contents.debugger,
+      dispose: () => {
+        lease.release()
+        window?.destroy()
+      }
+    }
+  } catch (error) {
+    window?.destroy()
+    throw error
+  }
+}
+
+export function cookieClearIdentitiesFromCdp(
+  cookies: readonly { cookie: Cookie; url: string }[],
+  cdpCookies: readonly CdpCookie[]
+): CookieClearIdentity[] {
+  const identities: CookieClearIdentity[] = []
+  const seen = new Set<string>()
+  for (const item of cookies) {
+    const matches = cdpCookies.filter((cdpCookie) => sameCookieScope(item.cookie, cdpCookie))
+    if (matches.length === 0) {
+      throw new Error('Could not snapshot cookie identity for an atomic clear')
+    }
+    for (const match of matches) {
+      const key = JSON.stringify([
+        item.url,
+        match.name,
+        match.domain,
+        match.path,
+        partitionKeyFromCdp(match.partitionKey) ?? null
+      ])
+      if (seen.has(key)) {
+        continue
+      }
+      seen.add(key)
+      identities.push(identityFromCdpCookie(item.url, item.cookie, match))
+    }
+  }
+  return identities
+}
+
+export function cdpRestoreParamsFromIdentity(
+  identity: CookieClearIdentity
+): Record<string, unknown> {
+  return {
+    url: identity.url,
+    name: identity.name,
+    value: identity.value,
+    ...(identity.hostOnly ? {} : { domain: identity.domain }),
+    ...(identity.path ? { path: identity.path } : {}),
+    secure: identity.secure,
+    httpOnly: identity.httpOnly,
+    sameSite: cdpSameSite(identity.sameSite),
+    ...(identity.expirationDate ? { expires: identity.expirationDate } : {}),
+    ...(identity.partitionKey ? { partitionKey: identity.partitionKey } : {})
+  }
+}
+
+function cdpCookiesFromCommand(value: unknown): CdpCookie[] {
+  if (typeof value !== 'object' || value === null || !('cookies' in value)) {
+    return []
+  }
+  const cookies = value.cookies
+  return Array.isArray(cookies) ? cookies : []
+}
+
+function cdpSetCookieSucceeded(value: unknown): boolean {
+  if (typeof value !== 'object' || value === null || !('success' in value)) {
+    return true
+  }
+  return value.success !== false
+}
+
+async function snapshotClearIdentitiesFromCdp(
+  cookieDebugger: CookieClearDebugger,
+  cookies: readonly { cookie: Cookie; url: string }[]
+): Promise<CookieClearIdentity[]> {
+  const result = await cookieDebugger.sendCommand('Network.getAllCookies')
+  return cookieClearIdentitiesFromCdp(cookies, cdpCookiesFromCommand(result))
+}
+
+async function restoreClearIdentitiesWithCdp(
+  cookieDebugger: CookieClearDebugger,
+  identities: readonly CookieClearIdentity[]
+): Promise<void> {
+  for (const identity of identities) {
+    const result = await cookieDebugger.sendCommand(
+      'Network.setCookie',
+      cdpRestoreParamsFromIdentity(identity)
+    )
+    if (!cdpSetCookieSucceeded(result)) {
+      throw new Error(`Could not restore cookie ${identity.name}`)
+    }
+  }
+}
+
+export function openCookieClearStore(
+  targetSession: Session
+): CookieClearStore & { dispose: () => void } {
+  let attached: CookieClearSession | null = null
+  const attach = async () => {
+    attached ??= await attachCookieClearSession(targetSession)
+    return attached
+  }
+  return {
+    get: (filter) => targetSession.cookies.get(filter),
+    remove: (url, name) => targetSession.cookies.remove(url, name),
+    snapshotClearIdentities: async (cookies) =>
+      snapshotClearIdentitiesFromCdp((await attach()).debugger, cookies),
+    restoreClearIdentities: async (identities) =>
+      restoreClearIdentitiesWithCdp((await attach()).debugger, identities),
+    dispose: () => {
+      attached?.dispose()
+      attached = null
+    }
+  }
+}
diff --git a/src/main/browser/browser-cookie-import-clear-atomicity.test.ts b/src/main/browser/browser-cookie-import-clear-atomicity.test.ts
new file mode 100644
index 00000000000..927df9b145b
--- /dev/null
+++ b/src/main/browser/browser-cookie-import-clear-atomicity.test.ts
@@ -0,0 +1,179 @@
+import { describe, expect, it, vi } from 'vitest'
+import type { Cookie } from 'electron'
+import {
+  identitiesFromClearCookies,
+  removeTransplantableCookies,
+  type CookieClearIdentity,
+  type CookieClearSession
+} from './browser-cookie-import-clear'
+
+function cookie(domain: string, name: string, path = '/', secure = true): Cookie {
+  return {
+    domain,
+    name,
+    path,
+    secure,
+    sameSite: 'unspecified',
+    value: `${name}-value`
+  }
+}
+
+function createJarSession(
+  initial: Cookie[],
+  options: {
+    failOn?: string
+    restoreError?: Error
+    snapshot?: CookieClearSession['snapshotClearIdentities']
+  } = {}
+) {
+  let jar = [...initial]
+  const removedNames: string[] = []
+  const session: CookieClearSession & {
+    names: () => string[]
+    removedNames: () => string[]
+  } = {
+    cookies: {
+      get: async () => [...jar],
+      remove: async (_url, name) => {
+        if (name === (options.failOn ?? 'stale')) {
+          throw new Error('cookie store unavailable')
+        }
+        removedNames.push(name)
+        jar = jar.filter((entry) => entry.name !== name)
+      }
+    },
+    clearData: async () => {
+      throw new Error('storage busy')
+    },
+    snapshotClearIdentities:
+      options.snapshot ?? (async (items) => identitiesFromClearCookies(items)),
+    restoreClearIdentities: async (identities) => {
+      if (options.restoreError) {
+        throw options.restoreError
+      }
+      for (const identity of identities) {
+        if (jar.some((entry) => entry.name === identity.name)) {
+          continue
+        }
+        jar.push(cookie(identity.domain ?? '', identity.name, identity.path, identity.secure))
+      }
+    },
+    names: () => jar.map((entry) => entry.name).sort(),
+    removedNames: () => [...removedNames]
+  }
+  return session
+}
+
+describe('STA-4090 failed full cookie clear', () => {
+  it('does not permanently delete a cookie removed before another removal rejects', async () => {
+    const session = createJarSession([
+      cookie('.google.com', 'SID'),
+      cookie('.example.com', 'removed-first', '/one'),
+      cookie('.other.test', 'stale', '/two')
+    ])
+
+    await expect(removeTransplantableCookies(session)).rejects.toThrow(
+      /existing cookies were restored/
+    )
+
+    expect(session.removedNames()).toEqual(['removed-first'])
+    expect(session.names()).toEqual(['SID', 'removed-first', 'stale'])
+  })
+
+  it('does not start removing when a cookie identity cannot be snapshotted', async () => {
+    const session = createJarSession(
+      [cookie('.example.com', 'removed-first'), cookie('.other.test', 'stale')],
+      {
+        snapshot: async (items) =>
+          identitiesFromClearCookies(items.filter(({ cookie: entry }) => entry.name !== 'stale'))
+      }
+    )
+
+    await expect(removeTransplantableCookies(session)).rejects.toThrow(
+      /the session was left unchanged/
+    )
+    expect(session.removedNames()).toEqual([])
+    expect(session.names()).toEqual(['removed-first', 'stale'])
+  })
+
+  it('reports a partial clear only when restore also fails', async () => {
+    const session = createJarSession(
+      [cookie('.example.com', 'removed-first'), cookie('.other.test', 'stale')],
+      { restoreError: new Error('restore rejected') }
+    )
+
+    await expect(removeTransplantableCookies(session)).rejects.toThrow(
+      /the session was left partially cleared/
+    )
+    expect(session.names()).toEqual(['stale'])
+  })
+
+  it('never restores through cookies.set for a partitioned identity', async () => {
+    const set = vi.fn()
+    const identities: CookieClearIdentity[] = []
+    const session: CookieClearSession = {
+      cookies: {
+        get: async () => [cookie('.example.com', 'removed-first'), cookie('.other.test', 'stale')],
+        remove: async (_url, name) => {
+          if (name === 'stale') {
+            throw new Error('cookie store unavailable')
+          }
+        }
+      },
+      clearData: async () => {
+        throw new Error('storage busy')
+      },
+      snapshotClearIdentities: async (items) =>
+        identitiesFromClearCookies(items).map((identity) =>
+          identity.name === 'removed-first'
+            ? {
+                ...identity,
+                partitionKey: { topLevelSite: 'https://top.example', hasCrossSiteAncestor: true }
+              }
+            : identity
+        ),
+      restoreClearIdentities: async (restored) => {
+        identities.push(...restored)
+      }
+    }
+
+    await expect(removeTransplantableCookies(session)).rejects.toThrow(
+      /existing cookies were restored/
+    )
+    expect(set).not.toHaveBeenCalled()
+    expect(identities).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({
+          name: 'removed-first',
+          partitionKey: { topLevelSite: 'https://top.example', hasCrossSiteAncestor: true }
+        }),
+        expect.objectContaining({ name: 'stale' })
+      ])
+    )
+  })
+
+  it('serializes concurrent clears on the same session', async () => {
+    const activeClears: number[] = []
+    let inClear = 0
+    const session: CookieClearSession = {
+      cookies: {
+        get: async () => [cookie('.example.com', 'session')],
+        remove: async () => {
+          inClear += 1
+          activeClears.push(inClear)
+          await Promise.resolve()
+          inClear -= 1
+        }
+      },
+      clearData: async () => {
+        throw new Error('storage busy')
+      },
+      snapshotClearIdentities: async (items) => identitiesFromClearCookies(items),
+      restoreClearIdentities: async () => undefined
+    }
+
+    await Promise.all([removeTransplantableCookies(session), removeTransplantableCookies(session)])
+
+    expect(activeClears).toEqual([1, 1])
+  })
+})
diff --git a/src/main/browser/browser-cookie-import-clear.ts b/src/main/browser/browser-cookie-import-clear.ts
new file mode 100644
index 00000000000..369ad5d432d
--- /dev/null
+++ b/src/main/browser/browser-cookie-import-clear.ts
@@ -0,0 +1,192 @@
+import type { Cookie, Cookies, Session } from 'electron'
+import { mapSettledWithConcurrency } from '../../shared/map-with-concurrency'
+import {
+  cookieRemovalUrl,
+  isNonTransplantableCookieDomain,
+  NON_TRANSPLANTABLE_CLEAR_EXCLUDED_ORIGINS,
+  normalizeCookieDomain
+} from './browser-cookie-import-policy'
+
+const COOKIE_CLEAR_CONCURRENCY = 8
+
+export type CookieClearPartitionKey = {
+  topLevelSite: string
+  hasCrossSiteAncestor: boolean
+}
+
+export type CookieClearIdentity = {
+  url: string
+  name: string
+  value: string
+  domain?: string
+  hostOnly?: boolean
+  path?: string
+  secure?: boolean
+  httpOnly?: boolean
+  sameSite: Cookie['sameSite']
+  expirationDate?: number
+  partitionKey?: CookieClearPartitionKey
+}
+
+export type CookieClearStore = Pick<Cookies, 'get' | 'remove'> & {
+  snapshotClearIdentities(
+    cookies: readonly { cookie: Cookie; url: string }[]
+  ): Promise<CookieClearIdentity[]>
+  restoreClearIdentities(identities: readonly CookieClearIdentity[]): Promise<void>
+}
+
+// Why (STA-4061): 'set' stays out so the lossy partition-dropping reconstruction cannot return.
+export type CookieClearSession = {
+  cookies: Pick<Cookies, 'get' | 'remove'>
+  clearData: Session['clearData']
+  snapshotClearIdentities: CookieClearStore['snapshotClearIdentities']
+  restoreClearIdentities: CookieClearStore['restoreClearIdentities']
+}
+
+const clearLocks = new WeakMap<object, Promise<void>>()
+
+function cookieClearKey(url: string, name: string): string {
+  return JSON.stringify([url, name])
+}
+
+export function identitiesFromClearCookies(
+  cookies: readonly { cookie: Cookie; url: string }[]
+): CookieClearIdentity[] {
+  return cookies.map(({ cookie, url }) => ({
+    url,
+    name: cookie.name,
+    value: cookie.value,
+    domain: cookie.domain,
+    hostOnly: cookie.hostOnly,
+    path: cookie.path,
+    secure: cookie.secure,
+    httpOnly: cookie.httpOnly,
+    sameSite: cookie.sameSite,
+    expirationDate: cookie.expirationDate
+  }))
+}
+
+export async function withCookieClearLock<T>(owner: object, run: () => Promise<T>): Promise<T> {
+  const previous = clearLocks.get(owner) ?? Promise.resolve()
+  let release!: () => void
+  const current = new Promise<void>((resolve) => {
+    release = resolve
+  })
+  clearLocks.set(
+    owner,
+    previous.then(() => current)
+  )
+  await previous
+  try {
+    return await run()
+  } finally {
+    release()
+  }
+}
+
+function removableCookieEntries(cookies: readonly Cookie[]): { cookie: Cookie; url: string }[] {
+  const removable: { cookie: Cookie; url: string }[] = []
+  for (const cookie of cookies) {
+    if (isNonTransplantableCookieDomain(cookie.domain ?? '')) {
+      continue
+    }
+    const domain = cookie.domain ? normalizeCookieDomain(cookie.domain) : null
+    const url = domain ? cookieRemovalUrl(cookie, domain) : null
+    if (!url) {
+      continue
+    }
+    removable.push({ cookie, url })
+  }
+  return removable
+}
+
+function assertClearIdentitiesCoverRemovable(
+  removable: readonly { cookie: Cookie; url: string }[],
+  identities: readonly CookieClearIdentity[]
+): void {
+  const covered = new Set(identities.map((identity) => cookieClearKey(identity.url, identity.name)))
+  for (const item of removable) {
+    if (!covered.has(cookieClearKey(item.url, item.cookie.name))) {
+      throw new Error('Could not clear existing cookies; the session was left unchanged')
+    }
+  }
+}
+
+function groupRemovableCookies(
+  removable: readonly { cookie: Cookie; url: string }[]
+): Map<string, { cookie: Cookie; url: string }[]> {
+  const groups = new Map<string, { cookie: Cookie; url: string }[]>()
+  for (const item of removable) {
+    const key = cookieClearKey(item.url, item.cookie.name)
+    const group = groups.get(key) ?? []
+    group.push(item)
+    groups.set(key, group)
+  }
+  return groups
+}
+
+async function restoreClearedCookies(
+  targetSession: CookieClearSession,
+  identities: readonly CookieClearIdentity[],
+  failures: unknown[]
+): Promise<never> {
+  try {
+    await targetSession.restoreClearIdentities(identities.toReversed())
+  } catch (restoreError) {
+    throw new AggregateError(
+      [...failures, restoreError],
+      'Could not clear existing cookies; the session was left partially cleared'
+    )
+  }
+  throw new AggregateError(
+    failures,
+    'Could not clear existing cookies; existing cookies were restored'
+  )
+}
+
+export async function removeTransplantableCookies(
+  targetSession: CookieClearSession
+): Promise<void> {
+  return withCookieClearLock(targetSession, async () => {
+    const store = targetSession.cookies
+    const initialCookies = await store.get({})
+    if (initialCookies.length === 0) {
+      return
+    }
+
+    const initialRemovable = removableCookieEntries(initialCookies)
+    const identities = await targetSession.snapshotClearIdentities(initialRemovable)
+    assertClearIdentitiesCoverRemovable(initialRemovable, identities)
+
+    try {
+      // Why (STA-4065): excludeOrigins keeps the google.com family, including partitioned
+      // cookies, so one call replaces a remove() per cookie on the ordinary import path.
+      await targetSession.clearData({
+        dataTypes: ['cookies'],
+        excludeOrigins: NON_TRANSPLANTABLE_CLEAR_EXCLUDED_ORIGINS
+      })
+      return
+    } catch {
+      // Why: a rejected bulk clear can still have emptied part of the jar.
+    }
+
+    const existingCookies = await store.get({})
+    const removableGroups = groupRemovableCookies(removableCookieEntries(existingCookies))
+    const results = await mapSettledWithConcurrency(
+      [...removableGroups.values()],
+      COOKIE_CLEAR_CONCURRENCY,
+      async (group) => {
+        // Why: identical removal coordinates must stay ordered instead of racing.
+        for (const { cookie, url } of group) {
+          await store.remove(url, cookie.name)
+        }
+      }
+    )
+    const failures = results.flatMap((result) =>
+      result.status === 'rejected' ? [result.reason] : []
+    )
+    if (failures.length > 0) {
+      await restoreClearedCookies(targetSession, identities, failures)
+    }
+  })
+}
diff --git a/src/main/browser/browser-cookie-import-google-exclusion.test.ts b/src/main/browser/browser-cookie-import-google-exclusion.test.ts
index 431ca758f2f..a213d42f16a 100644
--- a/src/main/browser/browser-cookie-import-google-exclusion.test.ts
+++ b/src/main/browser/browser-cookie-import-google-exclusion.test.ts
@@ -30,6 +30,78 @@ vi.mock('electron', () => ({
   dialog: { showOpenDialog: vi.fn() },
   session: { fromPartition: sessionFromPartitionMock }
 }))
+vi.mock('./browser-cookie-clear-store', () => ({
+  openCookieClearStore: (targetSession: {
+    cookies: {
+      get: (filter: object) => Promise<unknown>
+      remove: (url: string, name: string) => Promise<void>
+      set?: (details: Record<string, unknown>) => Promise<void>
+    }
+  }) => ({
+    get: (filter: object) => targetSession.cookies.get(filter),
+    remove: (url: string, name: string) => targetSession.cookies.remove(url, name),
+    snapshotClearIdentities: async (
+      items: {
+        cookie: {
+          name: string
+          value: string
+          domain?: string
+          path?: string
+          secure?: boolean
+          httpOnly?: boolean
+          sameSite: string
+          expirationDate?: number
+          hostOnly?: boolean
+        }
+        url: string
+      }[]
+    ) =>
+      items.map(({ cookie, url }) => ({
+        url,
+        name: cookie.name,
+        value: cookie.value,
+        domain: cookie.domain,
+        hostOnly: cookie.hostOnly,
+        path: cookie.path,
+        secure: cookie.secure,
+        httpOnly: cookie.httpOnly,
+        sameSite: cookie.sameSite,
+        expirationDate: cookie.expirationDate
+      })),
+    restoreClearIdentities: async (
+      identities: {
+        url: string
+        name: string
+        value: string
+        domain?: string
+        path?: string
+        secure?: boolean
+        httpOnly?: boolean
+        sameSite: string
+        expirationDate?: number
+        hostOnly?: boolean
+      }[]
+    ) => {
+      if (!targetSession.cookies.set) {
+        return
+      }
+      for (const identity of identities.toReversed()) {
+        await targetSession.cookies.set({
+          url: identity.url,
+          name: identity.name,
+          value: identity.value,
+          ...(identity.hostOnly ? {} : { domain: identity.domain }),
+          ...(identity.path ? { path: identity.path } : {}),
+          secure: identity.secure,
+          httpOnly: identity.httpOnly,
+          sameSite: identity.sameSite,
+          ...(identity.expirationDate ? { expirationDate: identity.expirationDate } : {})
+        })
+      }
+    },
+    dispose: () => undefined
+  })
+}))
 
 import { importCookiesFromBrowser, importCookiesFromFile } from './browser-cookie-import'
 import { createChromiumCookieTestDatabase } from './browser-cookie-import-test-database'
@@ -268,22 +340,29 @@ describe('native Chromium import excludes the Google cookie family', () => {
     ])
   })
 
-  // Why (STA-4061): reconstruction drops partition keys, so a rejected removal must not rebuild
-  // anything — not the excluded Google rows, and not the non-Google rows that were already gone.
-  it('fails the import without reconstructing any cookie when selective removal rejects', async () => {
+  // Why (STA-4090): a rejected removal must restore cookies already deleted in the same clear
+  // without writing imported rows or touching the live Google session.
+  it('fails the import without permanently deleting a cookie removed before a later rejection', async () => {
     const sourceCookiesPath = seedSource([
       { domain: '.example.com', name: 'session', value: 'new' }
     ])
     seedTarget([{ domain: '.example.com', name: 'stale', value: 'stale' }])
-    cookiesGetMock.mockResolvedValue([
+    let jar = [
       existingCookie('.google.com', 'SID'),
       existingCookie('.example.com', 'removed-first'),
       existingCookie('.other.test', 'stale')
-    ])
+    ]
+    cookiesGetMock.mockImplementation(async () => [...jar])
     cookiesRemoveMock.mockImplementation(async (_url: string, name: string) => {
       if (name === 'stale') {
         throw new Error('cookie store unavailable')
       }
+      jar = jar.filter((entry) => entry.name !== name)
+    })
+    cookiesSetMock.mockImplementation(async (details: { domain?: string; name: string }) => {
+      if (!jar.some((entry) => entry.name === details.name)) {
+        jar.push(existingCookie(details.domain ?? '.example.com', details.name))
+      }
     })
     clearDataMock.mockRejectedValue(new Error('storage busy'))
 
@@ -293,7 +372,10 @@ describe('native Chromium import excludes the Google cookie family', () => {
     expect(result.ok || result.reason).toContain('Could not clear existing cookies')
     expect(clearDataMock).toHaveBeenCalledOnce()
     expect(cookiesRemoveMock.mock.calls.map(([, name]) => name)).toEqual(['removed-first', 'stale'])
-    expect(cookiesSetMock).not.toHaveBeenCalled()
+    expect(cookiesSetMock.mock.calls.map(([details]) => details.name)).toEqual(
+      expect.arrayContaining(['removed-first'])
+    )
+    expect(jar.map((entry) => entry.name).sort()).toEqual(['SID', 'removed-first', 'stale'])
     expect(setPendingCookieImportMock).not.toHaveBeenCalled()
   })
 })
diff --git a/src/main/browser/browser-cookie-import-partition-rollback.electron.test.ts b/src/main/browser/browser-cookie-import-partition-rollback.electron.test.ts
index bbd0d9a8a25..574e27fbfc5 100644
--- a/src/main/browser/browser-cookie-import-partition-rollback.electron.test.ts
+++ b/src/main/browser/browser-cookie-import-partition-rollback.electron.test.ts
@@ -31,11 +31,11 @@ const EXPECTED_PARTITION_KEY = {
   hasCrossSiteAncestor: true
 }
 
-function buildFixtureMain(policyPath: string, resultPath: string): string {
+function buildFixtureMain(clearPath: string, resultPath: string): string {
   return `
 const { app, BrowserWindow, session } = require('electron')
 const { writeFileSync } = require('node:fs')
-const { removeTransplantableCookies } = require(${JSON.stringify(policyPath)})
+const { removeTransplantableCookies } = require(${JSON.stringify(clearPath)})
 const resultPath = ${JSON.stringify(resultPath)}
 let currentStep = 'starting'
 const mark = (step) => {
@@ -83,24 +83,54 @@ async function run() {
   await targetSession.cookies.set({ url: 'https://accounts.google.com/', name: 'SID', value: 'live', secure: true })
   mark('removable cookies set')
 
-  const store = {
-    get: (filter) => targetSession.cookies.get(filter),
-    set: (details) => targetSession.cookies.set(details),
-    // Why: one rejecting removal is what drove the old rollback; the rest still succeed.
-    remove: async (url, name) => {
-      if (name === 'victim') throw new Error('forced victim removal failure')
-      return targetSession.cookies.remove(url, name)
-    }
-  }
-
-  // Why: the bulk clear is the ordinary path now, so rejecting it is what routes this fixture onto
-  // the per-cookie fallback where a partial failure — and the old rollback — could happen at all.
+  // Why: the bulk clear is the ordinary path now, so rejecting it routes this fixture onto
+  // the per-cookie fallback where a later removal can fail after earlier ones succeeded.
   let bulkClearCalls = 0
   const clearSession = {
-    cookies: store,
+    cookies: {
+      get: (filter) => targetSession.cookies.get(filter),
+      remove: async (url, name) => {
+        if (name === 'victim') throw new Error('forced victim removal failure')
+        return targetSession.cookies.remove(url, name)
+      }
+    },
     clearData: async () => {
       bulkClearCalls++
       throw new Error('forced bulk clear failure')
+    },
+    snapshotClearIdentities: async (cookies) => {
+      const { cookies: cdpCookies } = await debug.sendCommand('Network.getAllCookies')
+      return cookies.flatMap((item) => {
+        const matches = cdpCookies.filter((cdpCookie) => cdpCookie.name === item.cookie.name)
+        if (matches.length === 0) throw new Error('Could not snapshot cookie identity for an atomic clear')
+        return matches.map((cdpCookie) => ({
+          url: item.url,
+          name: cdpCookie.name,
+          value: cdpCookie.value,
+          domain: cdpCookie.domain,
+          path: cdpCookie.path,
+          secure: cdpCookie.secure,
+          httpOnly: cdpCookie.httpOnly,
+          sameSite: cdpCookie.sameSite === 'None' ? 'no_restriction' : 'lax',
+          partitionKey: cdpCookie.partitionKey
+        }))
+      })
+    },
+    restoreClearIdentities: async (identities) => {
+      for (const identity of identities) {
+        const result = await debug.sendCommand('Network.setCookie', {
+          url: identity.url,
+          name: identity.name,
+          value: identity.value,
+          domain: identity.domain,
+          path: identity.path,
+          secure: identity.secure,
+          httpOnly: identity.httpOnly,
+          sameSite: identity.sameSite === 'no_restriction' ? 'None' : 'Lax',
+          partitionKey: identity.partitionKey
+        })
+        if (result && result.success === false) throw new Error('CDP restore rejected ' + identity.name)
+      }
     }
   }
 
@@ -140,7 +170,7 @@ run().catch((error) => {
 async function runFixture(): Promise<FixtureResult> {
   const root = mkdtempSync(join(tmpdir(), 'orca-partition-rollback-'))
   fixtureRoots.push(root)
-  const policyPath = join(root, 'browser-cookie-import-policy.cjs')
+  const clearPath = join(root, 'browser-cookie-import-clear.cjs')
   const resultPath = join(root, 'result.json')
   const fixturePath = join(root, 'main.cjs')
   await buildVite({
@@ -149,16 +179,16 @@ async function runFixture(): Promise<FixtureResult> {
     build: {
       emptyOutDir: false,
       lib: {
-        entry: join(process.cwd(), 'src/main/browser/browser-cookie-import-policy.ts'),
+        entry: join(process.cwd(), 'src/main/browser/browser-cookie-import-clear.ts'),
         formats: ['cjs'],
-        fileName: () => 'browser-cookie-import-policy.cjs'
+        fileName: () => 'browser-cookie-import-clear.cjs'
       },
       outDir: root,
       target: 'node20',
       rollupOptions: { external: ['electron', /^node:/] }
     }
   })
-  writeFileSync(fixturePath, buildFixtureMain(policyPath, resultPath))
+  writeFileSync(fixturePath, buildFixtureMain(clearPath, resultPath))
   const { ELECTRON_RUN_AS_NODE: _electronRunAsNode, ...env } = process.env
   const electronArgs = [fixturePath, `--user-data-dir=${join(root, 'profile')}`]
   const executable = process.platform === 'linux' ? 'xvfb-run' : electronBinary
@@ -178,20 +208,18 @@ async function runFixture(): Promise<FixtureResult> {
 }
 
 describe('non-Google partitioned cookie under a failed Electron cookie clear', () => {
-  it('never resurrects a removed partitioned cookie', async () => {
+  // Why (STA-4090): a later fallback rejection must not permanently drop cookies already
+  // removed in the same clear — including CHIPS cookies cookies.set() cannot round-trip.
+  it('keeps already-removed CHIPS and ordinary cookies after a later removal rejects', async () => {
     const result = await runFixture()
 
     expect(result.beforePartitionKey).toEqual(EXPECTED_PARTITION_KEY)
-    // Why (STA-4065): the fallback is only reachable once the bulk clear has been tried and failed;
-    // if it ever succeeded here the partial-failure assertions below would be vacuous.
     expect(result.bulkClearCalls).toBe(1)
     expect(result.remainingExcluded.map(({ name }) => name)).toEqual(['SID'])
     expect(result.clearError).toContain('Could not clear existing cookies')
-    // STA-4061: rollback rebuilt this cookie through cookies.set, which drops partitionKey.
-    expect(
-      result.remainingChips,
-      `chips-auth survived: ${JSON.stringify(result.remainingChips)}`
-    ).toEqual([])
-    expect(result.remainingPlain).toEqual([])
+    expect(result.remainingChips).toEqual([
+      { name: 'chips-auth', value: 'keep-me', partitionKey: EXPECTED_PARTITION_KEY }
+    ])
+    expect(result.remainingPlain).toEqual([{ name: 'plain', value: 'stale' }])
   }, 90_000)
 })
diff --git a/src/main/browser/browser-cookie-import-policy.test.ts b/src/main/browser/browser-cookie-import-policy.test.ts
index 51a1a6107d5..ad83fd75950 100644
--- a/src/main/browser/browser-cookie-import-policy.test.ts
+++ b/src/main/browser/browser-cookie-import-policy.test.ts
@@ -1,12 +1,15 @@
 import { describe, expect, it, vi, type Mock } from 'vitest'
 import { DatabaseSync } from 'node:sqlite'
 import type { Cookie } from 'electron'
+import {
+  identitiesFromClearCookies,
+  removeTransplantableCookies
+} from './browser-cookie-import-clear'
 import {
   isGoogleSourceBoundCookie,
   isNonTransplantableCookieDomain,
   NON_TRANSPLANTABLE_HOST_KEY_SQL,
   normalizeCookieDomain,
-  removeTransplantableCookies,
   replaceCookiesForImportedDomains
 } from './browser-cookie-import-policy'
 
@@ -225,12 +228,20 @@ describe('removeTransplantableCookies', () => {
       ...overrides
     }
     const clearData = overrides.clearData ?? vi.fn().mockResolvedValue(undefined)
+    const restoreClearIdentities = vi.fn().mockResolvedValue(undefined)
     return {
-      session: { cookies: store, clearData },
+      session: {
+        cookies: store,
+        clearData,
+        snapshotClearIdentities: async (items: Parameters<typeof identitiesFromClearCookies>[0]) =>
+          identitiesFromClearCookies(items),
+        restoreClearIdentities
+      },
       get: store.get,
       remove: store.remove,
       set: store.set,
-      clearData
+      clearData,
+      restoreClearIdentities
     }
   }
 
@@ -343,10 +354,9 @@ describe('removeTransplantableCookies', () => {
     expect(set).not.toHaveBeenCalled()
   })
 
-  // Why (STA-4061): reconstructing a removed cookie loses its partition key, and the snapshot
-  // cannot say which cookies had one, so a failed clear must stay failed.
-  it('never reconstructs removed cookies when another removal fails', async () => {
-    const { session, remove, set } = clearSession(
+  // Why (STA-4090): a failed fallback must restore through captured identities, never cookies.set.
+  it('restores removed cookies through captured identities when another removal fails', async () => {
+    const { session, remove, set, restoreClearIdentities } = clearSession(
       [
         cookie('.google.com', 'SID'),
         cookie('.example.com', 'first', '/one'),
@@ -364,10 +374,14 @@ describe('removeTransplantableCookies', () => {
     )
 
     await expect(removeTransplantableCookies(session)).rejects.toThrow(
-      'the session was left partially cleared'
+      'existing cookies were restored'
     )
     expect(remove).toHaveBeenCalledTimes(3)
     expect(set).not.toHaveBeenCalled()
+    expect(restoreClearIdentities).toHaveBeenCalledOnce()
+    expect(
+      restoreClearIdentities.mock.calls[0][0].map((identity: { name: string }) => identity.name)
+    ).toEqual(expect.arrayContaining(['first', 'second', 'third']))
   })
 
   it('bounds parallel removals so large cookie jars do not clear serially or fan out', async () => {
diff --git a/src/main/browser/browser-cookie-import-policy.ts b/src/main/browser/browser-cookie-import-policy.ts
index 6f81407f4a9..9fa3bc5f9b7 100644
--- a/src/main/browser/browser-cookie-import-policy.ts
+++ b/src/main/browser/browser-cookie-import-policy.ts
@@ -1,6 +1,5 @@
-import type { Cookie, Cookies, Session } from 'electron'
+import type { Cookie, Cookies } from 'electron'
 import { parse as parseDomain } from 'psl'
-import { mapSettledWithConcurrency } from '../../shared/map-with-concurrency'
 
 const GOOGLE_SOURCE_BOUND_COOKIE_NAMES = new Set([
   'SIDCC',
@@ -66,10 +65,9 @@ export function normalizeCookieImportDomain(domain: string): string | null {
 // its cookies via the accounts.youtube.com relay, so excluding it would silently drop imports
 // users actually asked for.
 const NON_TRANSPLANTABLE_DOMAINS = ['google.com'] as const
-const NON_TRANSPLANTABLE_CLEAR_EXCLUDED_ORIGINS = NON_TRANSPLANTABLE_DOMAINS.map(
+export const NON_TRANSPLANTABLE_CLEAR_EXCLUDED_ORIGINS = NON_TRANSPLANTABLE_DOMAINS.map(
   (root) => `https://${root}`
 )
-const COOKIE_CLEAR_CONCURRENCY = 8
 
 export function isNonTransplantableCookieDomain(domain: string): boolean {
   const normalized = normalizeCookieDomain(domain)
@@ -159,7 +157,7 @@ function overlapsImportedDomain(
   return domainSuffixes(domain).some((suffix) => scopes.descendantRoots.has(suffix))
 }
 
-function cookieRemovalUrl(cookie: Cookie, domain: string): string | null {
+export function cookieRemovalUrl(cookie: Cookie, domain: string): string | null {
   try {
     const url = new URL(`${cookie.secure ? 'https' : 'http'}://${domain}/`)
     url.pathname = cookie.path?.startsWith('/') ? cookie.path : '/'
@@ -201,83 +199,6 @@ export async function restoreImportedDomainCookies(
   }
 }
 
-// Why (STA-4061): 'set' stays out so the lossy partition-dropping reconstruction cannot return.
-export type CookieClearSession = {
-  cookies: Pick<Cookies, 'get' | 'remove'>
-  clearData: Session['clearData']
-}
-
-// Why: Electron cannot round-trip partition identity, so excluded cookies must never be removed.
-// Why (STA-4061): the same gap forbids rolling a partial clear back. cookies.get() omits
-// partitionKey and cookies.set() silently drops it, so every reconstruction is a coin flip that
-// can downgrade a partitioned (CHIPS) cookie into an unpartitioned one — and nothing in the
-// snapshot says which cookies are at risk. A partially cleared jar is a retryable import failure;
-// a downgraded cookie is unrecoverable auth-state corruption that survives restart.
-// Why (STA-4065): the exclusion is module state rather than a parameter so the predicate and the
-// origins the bulk clear preserves cannot drift apart — a caller-supplied predicate that disagreed
-// with NON_TRANSPLANTABLE_DOMAINS would silently delete a cookie the bulk call is meant to keep.
-export async function removeTransplantableCookies(
-  targetSession: CookieClearSession
-): Promise<void> {
-  const store = targetSession.cookies
-  const initialCookies = await store.get({})
-  if (initialCookies.length === 0) {
-    return
-  }
-
-  // Why (STA-4065): measured on Electron 43, excludeOrigins preserves the whole registrable
-  // family — host, leading-dot, subdomain, and partitioned Google cookies — so one call replaces a
-  // remove() per cookie even when the jar holds cookies to keep. That is the ordinary case here:
-  // this import exists for Google, so a Google cookie is usually present.
-  try {
-    await targetSession.clearData({
-      dataTypes: ['cookies'],
-      excludeOrigins: NON_TRANSPLANTABLE_CLEAR_EXCLUDED_ORIGINS
-    })
-    return
-  } catch {
-    // Why: a rejected bulk clear can still have changed the jar, so the fallback must act on the
-    // survivors rather than stale removal coordinates from before the attempt.
-  }
-
-  const existingCookies = await store.get({})
-  const removableGroups = new Map<string, { cookie: Cookie; url: string }[]>()
-  for (const cookie of existingCookies) {
-    if (isNonTransplantableCookieDomain(cookie.domain ?? '')) {
-      continue
-    }
-    const domain = cookie.domain ? normalizeCookieDomain(cookie.domain) : null
-    const url = domain ? cookieRemovalUrl(cookie, domain) : null
-    if (!url) {
-      continue
-    }
-    const key = JSON.stringify([url, cookie.name])
-    const group = removableGroups.get(key) ?? []
-    group.push({ cookie, url })
-    removableGroups.set(key, group)
-  }
-
-  const results = await mapSettledWithConcurrency(
-    [...removableGroups.values()],
-    COOKIE_CLEAR_CONCURRENCY,
-    async (group) => {
-      // Why: identical removal coordinates must stay ordered instead of racing.
-      for (const { cookie, url } of group) {
-        await store.remove(url, cookie.name)
-      }
-    }
-  )
-  const failures = results.flatMap((result) =>
-    result.status === 'rejected' ? [result.reason] : []
-  )
-  if (failures.length > 0) {
-    throw new AggregateError(
-      failures,
-      'Could not clear existing cookies; the session was left partially cleared'
-    )
-  }
-}
-
 export async function replaceCookiesForImportedDomains(
   store: Pick<Cookies, 'get' | 'remove' | 'set'>,
   importedDomains: readonly string[]
diff --git a/src/main/browser/browser-cookie-import-replacement.test.ts b/src/main/browser/browser-cookie-import-replacement.test.ts
index db70922ccb5..a727a8275f5 100644
--- a/src/main/browser/browser-cookie-import-replacement.test.ts
+++ b/src/main/browser/browser-cookie-import-replacement.test.ts
@@ -26,6 +26,21 @@ vi.mock('electron', () => ({
   dialog: { showOpenDialog: vi.fn() },
   session: { fromPartition: sessionFromPartitionMock }
 }))
+vi.mock('./browser-cookie-clear-store', () => ({
+  openCookieClearStore: (targetSession: {
+    cookies: {
+      get: (filter: object) => Promise<unknown>
+      remove: (url: string, name: string) => Promise<void>
+    }
+  }) => ({
+    get: (filter: object) => targetSession.cookies.get(filter),
+    remove: (url: string, name: string) => targetSession.cookies.remove(url, name),
+    snapshotClearIdentities: async (items: { cookie: Record<string, unknown>; url: string }[]) =>
+      items.map(({ cookie, url }) => ({ url, ...cookie })),
+    restoreClearIdentities: async () => undefined,
+    dispose: () => undefined
+  })
+}))
 
 import { importCookiesFromBrowser, importCookiesFromFile } from './browser-cookie-import'
 import { createChromiumCookieTestDatabase } from './browser-cookie-import-test-database'
diff --git a/src/main/browser/browser-cookie-import.test.ts b/src/main/browser/browser-cookie-import.test.ts
index 90514321d54..6ec09edf8aa 100644
--- a/src/main/browser/browser-cookie-import.test.ts
+++ b/src/main/browser/browser-cookie-import.test.ts
@@ -44,6 +44,21 @@ vi.mock('electron', () => ({
   dialog: { showOpenDialog: dialogShowOpenDialogMock },
   session: { fromPartition: sessionFromPartitionMock }
 }))
+vi.mock('./browser-cookie-clear-store', () => ({
+  openCookieClearStore: (targetSession: {
+    cookies: {
+      get: (filter: object) => Promise<unknown>
+      remove: (url: string, name: string) => Promise<void>
+    }
+  }) => ({
+    get: (filter: object) => targetSession.cookies.get(filter),
+    remove: (url: string, name: string) => targetSession.cookies.remove(url, name),
+    snapshotClearIdentities: async (items: { cookie: Record<string, unknown>; url: string }[]) =>
+      items.map(({ cookie, url }) => ({ url, ...cookie })),
+    restoreClearIdentities: async () => undefined,
+    dispose: () => undefined
+  })
+}))
 
 import {
   buildChromiumCookieInsertParams,
diff --git a/src/main/browser/browser-cookie-import.ts b/src/main/browser/browser-cookie-import.ts
index 3c3a701f953..e841f3168d8 100644
--- a/src/main/browser/browser-cookie-import.ts
+++ b/src/main/browser/browser-cookie-import.ts
@@ -80,11 +80,12 @@ import {
   NON_TRANSPLANTABLE_HOST_KEY_SQL,
   normalizeCookieDomain,
   normalizeCookieImportDomain,
-  removeTransplantableCookies,
   replaceCookiesForImportedDomains,
   restoreImportedDomainCookies,
   type CookieImportMode
 } from './browser-cookie-import-policy'
+import { removeTransplantableCookies, withCookieClearLock } from './browser-cookie-import-clear'
+import { openCookieClearStore } from './browser-cookie-clear-store'
 import {
   createChromiumCookieSnapshot,
   type ChromiumCookieSnapshot
@@ -1780,7 +1781,20 @@ export async function importCookiesFromBrowser(
     // Why: clear stale cookies first; mixing them with the imported set makes sites reject the
     // session. Non-transplantable families are exempt — nothing was imported for them, and their
     // live session is the only one that works.
-    await removeTransplantableCookies(targetSession)
+    const cookieClearStore = openCookieClearStore(targetSession)
+    try {
+      await withCookieClearLock(targetSession, () =>
+        removeTransplantableCookies({
+          cookies: cookieClearStore,
+          clearData: (options) => targetSession.clearData(options),
+          snapshotClearIdentities: (cookies) => cookieClearStore.snapshotClearIdentities(cookies),
+          restoreClearIdentities: (identities) =>
+            cookieClearStore.restoreClearIdentities(identities)
+        })
+      )
+    } finally {
+      cookieClearStore.dispose()
+    }
     diag(
       `  cleared existing session cookies before loading ${decryptedCookies.length} imported cookies`
     )