diff --git a/src/main/runtime/device-entry.ts b/src/main/runtime/device-entry.ts
index 41804c1163d..ac05b74f120 100644
--- a/src/main/runtime/device-entry.ts
+++ b/src/main/runtime/device-entry.ts
@@ -35,6 +35,8 @@ export type DeviceEntry = {
   devicePublicKeyB64?: string
   // The token row this installation migrated from; that row stays for its other holders.
   forkedFrom?: string
+  // Session-only browser key (memory only); the row is dropped on host restart and after idling.
+  ephemeral?: true
 }
 
 /** A row that authenticates by bearer token: every pairing offer and delegated child. */
diff --git a/src/main/runtime/device-key-fork.ts b/src/main/runtime/device-key-fork.ts
index 00099a31bdb..cfa95d464f0 100644
--- a/src/main/runtime/device-key-fork.ts
+++ b/src/main/runtime/device-key-fork.ts
@@ -29,7 +29,8 @@ export function planDeviceKeyFork(
   legacyDeviceId: string,
   devicePublicKeyB64: string,
   label: string,
-  now: number
+  now: number,
+  options: { ephemeral?: boolean } = {}
 ): DeviceKeyFork {
   const legacy = devices.find((device) => device.deviceId === legacyDeviceId)
   if (!legacy) {
@@ -70,6 +71,7 @@ export function planDeviceKeyFork(
     credentialKind: 'device-key',
     devicePublicKeyB64,
     forkedFrom: legacy.deviceId,
+    ...(options.ephemeral ? { ephemeral: true as const } : {}),
     // Why: orchestration work owned under the token keeps its owner after migration.
     callerFingerprint: devicePrincipalOf(legacy).callerFingerprint,
     pairedAt: now,
diff --git a/src/main/runtime/device-registry-file-read.ts b/src/main/runtime/device-registry-file-read.ts
new file mode 100644
index 00000000000..30bab126e83
--- /dev/null
+++ b/src/main/runtime/device-registry-file-read.ts
@@ -0,0 +1,41 @@
+import { readFileSync } from 'node:fs'
+import { hardenExistingSecureFile, isUnreadableError } from '../../shared/secure-file'
+import { corruptRegistryCopyExists, isMissingFileError } from './device-registry-corruption'
+import type { DeviceEntry } from './device-entry'
+import { normalizeLoadedDeviceRow } from './device-registry-row-validation'
+
+export type DeviceRegistryFileRead = {
+  devices: DeviceEntry[]
+  /** The registry exists but could not be read, which makes `devices` a lie to save from. */
+  unreadable: boolean
+  /** A parse failure, now or in an earlier run, means an unlisted device may still exist. */
+  doubtful: boolean
+  /** A corrupt file must be set aside before the first rewrite. */
+  corruptFilePending: boolean
+}
+
+export function readDeviceRegistryFile(registryPath: string): DeviceRegistryFileRead {
+  // Why: a set-aside corrupt copy keeps revocation verdicts off until the owner removes it, even
+  // when the rewrite after quarantine never landed and the registry file itself is missing.
+  const doubtful = corruptRegistryCopyExists(registryPath)
+  try {
+    hardenExistingSecureFile(registryPath)
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: normalizeLoadedDeviceRow re-validates every field; a non-array throws below and reads as corrupt.
+    const parsed = JSON.parse(readFileSync(registryPath, 'utf-8')) as DeviceEntry[]
+    return {
+      devices: parsed.map(normalizeLoadedDeviceRow),
+      unreadable: false,
+      doubtful,
+      corruptFilePending: false
+    }
+  } catch (error) {
+    if (isMissingFileError(error)) {
+      return { devices: [], unreadable: false, doubtful, corruptFilePending: false }
+    }
+    // "Cannot read" is not "is empty". Saving an empty list over a registry we were merely
+    // denied would erase every paired device's bearer token, and the write would succeed.
+    const unreadable = isUnreadableError(error)
+    // Why: a corrupt file is not evidence any device was revoked; never tell a keyed client so.
+    return { devices: [], unreadable, doubtful: true, corruptFilePending: !unreadable }
+  }
+}
diff --git a/src/main/runtime/device-registry-row-validation.ts b/src/main/runtime/device-registry-row-validation.ts
index 591732b98ca..04966feec63 100644
--- a/src/main/runtime/device-registry-row-validation.ts
+++ b/src/main/runtime/device-registry-row-validation.ts
@@ -76,15 +76,21 @@ export function normalizeLoadedDeviceRow(device: DeviceEntry): DeviceEntry {
 // Why: a malformed keyed row stays keyed (so it never falls back to a token) but cannot authenticate.
 function validDeviceKeyFields(
   device: DeviceEntry
-): Pick<DeviceEntry, 'credentialKind' | 'devicePublicKeyB64' | 'forkedFrom'> {
+): Pick<DeviceEntry, 'credentialKind' | 'devicePublicKeyB64' | 'forkedFrom' | 'ephemeral'> {
   if (device.credentialKind !== 'device-key') {
-    return { credentialKind: undefined, devicePublicKeyB64: undefined, forkedFrom: undefined }
+    return {
+      credentialKind: undefined,
+      devicePublicKeyB64: undefined,
+      forkedFrom: undefined,
+      ephemeral: undefined
+    }
   }
   return {
     credentialKind: 'device-key',
     devicePublicKeyB64: isDevicePublicKeyB64(device.devicePublicKeyB64)
       ? device.devicePublicKeyB64
       : undefined,
-    forkedFrom: typeof device.forkedFrom === 'string' ? device.forkedFrom : undefined
+    forkedFrom: typeof device.forkedFrom === 'string' ? device.forkedFrom : undefined,
+    ephemeral: device.ephemeral === true ? true : undefined
   }
 }
diff --git a/src/main/runtime/device-registry.ts b/src/main/runtime/device-registry.ts
index 677d5b189b7..cf312bc79d7 100644
--- a/src/main/runtime/device-registry.ts
+++ b/src/main/runtime/device-registry.ts
@@ -2,24 +2,16 @@
 // (mobile) connections. Each paired device gets its own revocable token so
 // compromising one device doesn't expose others. The registry is a simple
 // JSON file with hardened permissions matching the runtime metadata pattern.
-import { readFileSync } from 'node:fs'
 import { join } from 'node:path'
-import {
-  hardenExistingSecureFile,
-  isUnreadableError,
-  writeDurableSecureJsonFile,
-  writeSecureJsonFile
-} from '../../shared/secure-file'
+import { writeDurableSecureJsonFile, writeSecureJsonFile } from '../../shared/secure-file'
 import type { DeviceScope } from '../../shared/runtime-types'
 import { removeStaleDurableWriteTempFiles } from '../durable-file-write'
 import { DEVICE_REGISTRY_FILENAME } from './mobile-pairing-files'
 import { mintDeviceCredential } from './device-credential'
 import { planDeviceKeyFork } from './device-key-fork'
-import {
-  corruptRegistryCopyExists,
-  isMissingFileError,
-  quarantineCorruptRegistry
-} from './device-registry-corruption'
+import { planIdleEphemeralPrune, withoutEphemeralRows } from './ephemeral-device-rows'
+import { quarantineCorruptRegistry } from './device-registry-corruption'
+import { readDeviceRegistryFile } from './device-registry-file-read'
 import type { RelayDeviceBinding } from './relay/relay-revoke-outbox'
 import type { MobilePairingConnectionMode } from '../../shared/mobile-pairing-connection-mode'
 import type { RuntimePairingReach } from '../../shared/runtime-pairing-reach'
@@ -29,7 +21,7 @@ import {
   type DelegatedMobileDeviceEntry
 } from './delegated-mobile-devices'
 import type { RuntimeDeviceGrant } from './rpc/rpc-method-permission'
-import { normalizeLoadedDeviceRow, validGrants } from './device-registry-row-validation'
+import { validGrants } from './device-registry-row-validation'
 import {
   isPendingTokenRow,
   mobilePairingConnectionModeOf,
@@ -247,13 +239,19 @@ export class DeviceRegistry {
   }
 
   /** Forks `legacyDeviceId` into a keyed row; durable before it returns (security transition). */
-  forkDeviceKey(legacyDeviceId: string, devicePublicKeyB64: string, label: string): DeviceEntry {
+  forkDeviceKey(
+    legacyDeviceId: string,
+    devicePublicKeyB64: string,
+    label: string,
+    options: { ephemeral?: boolean } = {}
+  ): DeviceEntry {
     const fork = planDeviceKeyFork(
       this.devices,
       legacyDeviceId,
       devicePublicKeyB64,
       label,
-      Date.now()
+      Date.now(),
+      options
     )
     if (fork.created) {
       this.save(fork.nextDevices, { durable: true })
@@ -262,6 +260,16 @@ export class DeviceRegistry {
     return fork.entry
   }
 
+  /** Drops idle session-only rows; durable, since a removed row is a revocation. */
+  pruneIdleEphemeralDevices(now: number, isLive: (deviceId: string) => boolean): string[] {
+    const plan = planIdleEphemeralPrune(this.devices, now, isLive)
+    if (plan.removed.length > 0) {
+      this.save(plan.nextDevices, { durable: true })
+      this.devices = plan.nextDevices
+    }
+    return plan.removed
+  }
+
   /** The row an authenticated socket is still entitled to, or null once revoked or re-credentialed. */
   resolveAuthenticatedPrincipal(principal: AuthenticatedPrincipalBinding): DeviceEntry | null {
     const device = this.getDevice(principal.deviceId)
@@ -306,11 +314,15 @@ export class DeviceRegistry {
       return
     }
     this.cancelPendingLastSeenFlush()
+    // Why: matches the async hardening path — a failed bookkeeping write must not take down the runtime.
+    this.saveOrLog({}, 'persist device lastSeen')
+  }
+
+  private saveOrLog(options: { durable?: boolean }, action: string): void {
     try {
-      this.save(this.devices)
+      this.save(this.devices, options)
     } catch (error) {
-      // Why: matches the async hardening path — a failed bookkeeping write must not take down the runtime.
-      console.error('[mobile] Failed to persist device lastSeen:', error)
+      console.error(`[runtime] Failed to ${action}:`, error)
     }
   }
 
@@ -322,25 +334,14 @@ export class DeviceRegistry {
   }
 
   private load(): void {
-    // Why: a set-aside corrupt copy keeps revocation verdicts off until the owner removes it, even
-    // when the rewrite after quarantine never landed and the registry file itself is missing.
-    this.registryDoubtful = corruptRegistryCopyExists(this.registryPath)
-    try {
-      hardenExistingSecureFile(this.registryPath)
-      const parsed = JSON.parse(readFileSync(this.registryPath, 'utf-8')) as DeviceEntry[]
-      this.devices = parsed.map(normalizeLoadedDeviceRow)
-      this.registryUnreadable = false
-    } catch (error) {
-      this.devices = []
-      if (isMissingFileError(error)) {
-        return
-      }
-      // "Cannot read" is not "is empty". Saving an empty list over a registry we were merely
-      // denied would erase every paired device's bearer token, and the write would succeed.
-      this.registryUnreadable = isUnreadableError(error)
-      // Why: a corrupt file is not evidence any device was revoked; never tell a keyed client so.
-      this.registryDoubtful = true
-      this.corruptFilePending = !this.registryUnreadable
+    const read = readDeviceRegistryFile(this.registryPath)
+    this.registryUnreadable = read.unreadable
+    this.registryDoubtful = read.doubtful
+    this.corruptFilePending = read.corruptFilePending
+    this.devices = withoutEphemeralRows(read.devices)
+    // Why: a session-only browser's key died with the last host process; its row must not outlive it.
+    if (this.devices.length !== read.devices.length) {
+      this.saveOrLog({ durable: true }, 'drop session-only devices after restart')
     }
   }
 
diff --git a/src/main/runtime/ephemeral-device-rows.test.ts b/src/main/runtime/ephemeral-device-rows.test.ts
new file mode 100644
index 00000000000..d213a73aba0
--- /dev/null
+++ b/src/main/runtime/ephemeral-device-rows.test.ts
@@ -0,0 +1,107 @@
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import { planDeviceKeyFork } from './device-key-fork'
+import { DeviceRegistry, type DeviceEntry } from './device-registry'
+import { EPHEMERAL_DEVICE_IDLE_MS, planIdleEphemeralPrune } from './ephemeral-device-rows'
+import { DEVICE_REGISTRY_FILENAME } from './mobile-pairing-files'
+
+const KEY_A = Buffer.alloc(32, 1).toString('base64')
+const dirs: string[] = []
+
+afterEach(() => {
+  for (const dir of dirs.splice(0)) {
+    rmSync(dir, { recursive: true, force: true })
+  }
+})
+
+function tokenRow(overrides: Partial<DeviceEntry> = {}): DeviceEntry {
+  return {
+    deviceId: 'legacy',
+    name: 'Browser',
+    token: 'token',
+    scope: 'runtime',
+    pairedAt: 1,
+    lastSeenAt: 2,
+    ...overrides
+  }
+}
+
+function keyedRow(overrides: Partial<DeviceEntry> = {}): DeviceEntry {
+  return {
+    deviceId: 'keyed',
+    name: 'Browser',
+    scope: 'runtime',
+    pairedAt: 1,
+    lastSeenAt: 1_000,
+    credentialKind: 'device-key',
+    devicePublicKeyB64: KEY_A,
+    forkedFrom: 'legacy',
+    ephemeral: true,
+    ...overrides
+  }
+}
+
+function registryWith(rows: DeviceEntry[]): { dir: string; registry: DeviceRegistry } {
+  const dir = mkdtempSync(join(tmpdir(), 'orca-ephemeral-rows-'))
+  dirs.push(dir)
+  writeFileSync(join(dir, DEVICE_REGISTRY_FILENAME), JSON.stringify(rows))
+  return { dir, registry: new DeviceRegistry(dir) }
+}
+
+describe('ephemeral device rows', () => {
+  it('marks a session-only fork ephemeral and keeps persistent forks unmarked', () => {
+    const session = planDeviceKeyFork([tokenRow()], 'legacy', KEY_A, 'Tab', 9, {
+      ephemeral: true
+    })
+    expect(session.entry.ephemeral).toBe(true)
+    expect(planDeviceKeyFork([tokenRow()], 'legacy', KEY_A, 'Tab', 9).entry.ephemeral).toBe(
+      undefined
+    )
+  })
+
+  it('drops ephemeral rows when the host restarts and persists that', () => {
+    const { dir, registry } = registryWith([tokenRow(), keyedRow()])
+    expect(registry.getDevice('keyed')).toBeNull()
+    expect(registry.lookupDeviceKey('keyed')).toEqual({ kind: 'unknown' })
+    expect(registry.getDevice('legacy')).not.toBeNull()
+    const onDisk = JSON.parse(readFileSync(join(dir, DEVICE_REGISTRY_FILENAME), 'utf8'))
+    expect(onDisk.map((row: DeviceEntry) => row.deviceId)).toEqual(['legacy'])
+  })
+
+  it('ignores an ephemeral flag on a token row', () => {
+    const { registry } = registryWith([tokenRow({ ephemeral: true })])
+    expect(registry.getDevice('legacy')?.ephemeral).toBeUndefined()
+  })
+
+  it('prunes only idle, disconnected ephemeral rows', () => {
+    const rows = [
+      tokenRow(),
+      keyedRow(),
+      keyedRow({ deviceId: 'live', lastSeenAt: 1_000 }),
+      keyedRow({ deviceId: 'recent', lastSeenAt: 1_000 + EPHEMERAL_DEVICE_IDLE_MS }),
+      keyedRow({ deviceId: 'persistent', ephemeral: undefined })
+    ]
+    const now = 2_000 + EPHEMERAL_DEVICE_IDLE_MS
+    const plan = planIdleEphemeralPrune(rows, now, (deviceId) => deviceId === 'live')
+    expect(plan.removed).toEqual(['keyed'])
+    expect(plan.nextDevices.map((row) => row.deviceId)).toEqual([
+      'legacy',
+      'live',
+      'recent',
+      'persistent'
+    ])
+  })
+
+  it('removes idle rows from the registry durably', () => {
+    const { registry } = registryWith([tokenRow()])
+    const fork = registry.forkDeviceKey('legacy', KEY_A, 'Tab', { ephemeral: true })
+    const removed = registry.pruneIdleEphemeralDevices(
+      fork.lastSeenAt + EPHEMERAL_DEVICE_IDLE_MS + 1,
+      () => false
+    )
+    expect(removed).toEqual([fork.deviceId])
+    expect(registry.lookupDeviceKey(fork.deviceId)).toEqual({ kind: 'unknown' })
+  })
+})
diff --git a/src/main/runtime/ephemeral-device-rows.ts b/src/main/runtime/ephemeral-device-rows.ts
new file mode 100644
index 00000000000..4249a44493c
--- /dev/null
+++ b/src/main/runtime/ephemeral-device-rows.ts
@@ -0,0 +1,30 @@
+import type { DeviceEntry } from './device-entry'
+
+// Why: a session-only browser keeps its key in memory; an idle row is an abandoned tab, not a device.
+export const EPHEMERAL_DEVICE_IDLE_MS = 12 * 60 * 60 * 1000
+export const EPHEMERAL_DEVICE_SWEEP_INTERVAL_MS = 5 * 60 * 1000
+
+/** Rows that survive a host restart: a session-only browser's key did not. */
+export function withoutEphemeralRows(devices: readonly DeviceEntry[]): DeviceEntry[] {
+  return devices.filter((device) => device.ephemeral !== true)
+}
+
+/** Idle is measured from the last connect or disconnect; a row with a live socket never expires. */
+export function planIdleEphemeralPrune(
+  devices: readonly DeviceEntry[],
+  now: number,
+  isLive: (deviceId: string) => boolean
+): { nextDevices: DeviceEntry[]; removed: string[] } {
+  const removed = devices
+    .filter(
+      (device) =>
+        device.ephemeral === true &&
+        now - device.lastSeenAt > EPHEMERAL_DEVICE_IDLE_MS &&
+        !isLive(device.deviceId)
+    )
+    .map((device) => device.deviceId)
+  return {
+    nextDevices: devices.filter((device) => !removed.includes(device.deviceId)),
+    removed
+  }
+}
diff --git a/src/main/runtime/rpc/e2ee-channel.ts b/src/main/runtime/rpc/e2ee-channel.ts
index b7c3506d1f9..4bf7c1d0e7d 100644
--- a/src/main/runtime/rpc/e2ee-channel.ts
+++ b/src/main/runtime/rpc/e2ee-channel.ts
@@ -11,7 +11,8 @@ import {
   authenticateMobileE2EE,
   decodeMobileE2EEPublicKey,
   describeMobileE2EEAuthFailure,
-  type DeviceKeyResolution
+  type DeviceKeyResolution,
+  type DeviceTokenRefusal
 } from './mobile-e2ee-auth-validation'
 import { isMobileE2EEOutboundItemWithinLimit } from './mobile-e2ee-outbound-admission'
 import { parseRemoteRuntimeJsonText } from '../../../shared/remote-runtime-request-frames'
@@ -36,7 +37,7 @@ const MAX_CONSECUTIVE_DECRYPT_FAILURES = 5
 
 export type E2EEChannelOptions = {
   serverSecretKey: Uint8Array
-  resolveAuthenticatedDevice: (token: string) => E2EEAuthenticatedDevice | null
+  resolveAuthenticatedDevice: (token: string) => E2EEAuthenticatedDevice | DeviceTokenRefusal | null
   // Absent: key auth is refused as bad_auth, the same as before device keys existed.
   resolveAuthenticatedDeviceKey?: (deviceId: string) => DeviceKeyResolution<E2EEAuthenticatedDevice>
   onReady: (channel: E2EEChannel, device: E2EEAuthenticatedDevice) => void
diff --git a/src/main/runtime/rpc/mobile-e2ee-auth-validation.ts b/src/main/runtime/rpc/mobile-e2ee-auth-validation.ts
index 18e15fa6281..cb2c4b2bb28 100644
--- a/src/main/runtime/rpc/mobile-e2ee-auth-validation.ts
+++ b/src/main/runtime/rpc/mobile-e2ee-auth-validation.ts
@@ -2,6 +2,7 @@ import type { DesktopMobileE2EEV2Session } from './mobile-e2ee-v2-desktop-sessio
 import { publicKeyFromBase64 } from './e2ee-crypto'
 import { parseRemoteRuntimeJsonText } from '../../../shared/remote-runtime-request-frames'
 import { isDeviceProofB64, verifyDeviceProof } from '../../../shared/device-key-proof'
+import { INSECURE_WEB_ORIGIN_AUTH_CODE } from '../../../shared/web-origin-security'
 
 export type ClassifiedE2EEAuth =
   | { kind: 'token'; deviceToken: string; clientCapabilities?: unknown }
@@ -80,6 +81,10 @@ export type MobileE2EEAuthFailureCode =
   | 'device_revoked'
   | 'registry_unavailable'
   | 'bad_proof'
+  | typeof INSECURE_WEB_ORIGIN_AUTH_CODE
+
+// The token matched, but this transport may not claim it (e.g. a first pairing from an insecure page).
+export type DeviceTokenRefusal = { refused: typeof INSECURE_WEB_ORIGIN_AUTH_CODE }
 
 export type DeviceKeyResolution<TDevice> =
   | { kind: 'found'; device: TDevice; devicePublicKeyB64: string }
@@ -92,7 +97,7 @@ export type DeviceKeyResolution<TDevice> =
 export function authenticateMobileE2EE<TDevice extends { deviceToken?: string }>(args: {
   plaintext: string
   v2Session: DesktopMobileE2EEV2Session | null
-  resolveDevice: (token: string) => TDevice | null
+  resolveDevice: (token: string) => TDevice | DeviceTokenRefusal | null
   // Absent on a host that does not accept device keys: key auth is then bad_auth, as before.
   resolveDeviceKey?: (deviceId: string) => DeviceKeyResolution<TDevice>
 }):
@@ -101,6 +106,9 @@ export function authenticateMobileE2EE<TDevice extends { deviceToken?: string }>
   const auth = classifyE2EEAuth(args.plaintext, args.v2Session)
   if (auth.kind === 'token') {
     const device = args.resolveDevice(auth.deviceToken)
+    if (device && 'refused' in device) {
+      return { ok: false, code: device.refused }
+    }
     // Why: a keyed row has no token, so presenting one can never match it.
     return device?.deviceToken === auth.deviceToken
       ? { ok: true, device, clientCapabilities: auth.clientCapabilities }
@@ -144,7 +152,9 @@ export function describeMobileE2EEAuthFailure(failure: {
       ? 'Unauthorized'
       : failure.code === 'registry_unavailable'
         ? 'Device registry unavailable'
-        : 'Invalid e2ee_auth'
+        : failure.code === INSECURE_WEB_ORIGIN_AUTH_CODE
+          ? 'Insecure web origin'
+          : 'Invalid e2ee_auth'
   return {
     sealedError: {
       type: 'e2ee_error',
diff --git a/src/main/runtime/rpc/mobile-socket-wiring.ts b/src/main/runtime/rpc/mobile-socket-wiring.ts
index 009a35c9363..4305a73c89b 100644
--- a/src/main/runtime/rpc/mobile-socket-wiring.ts
+++ b/src/main/runtime/rpc/mobile-socket-wiring.ts
@@ -1,6 +1,12 @@
 import { randomBytes } from 'node:crypto'
 import type { WebSocket } from 'ws'
 import type { DeviceEntry, DeviceRegistry } from '../device-registry'
+import { isPendingTokenRow } from '../device-entry'
+import { EPHEMERAL_DEVICE_SWEEP_INTERVAL_MS } from '../ephemeral-device-rows'
+import {
+  INSECURE_WEB_ORIGIN_AUTH_CODE,
+  isInsecureRemoteWebOrigin
+} from '../../../shared/web-origin-security'
 import { devicePrincipalOf } from '../device-principal'
 import type { E2EEKeypair } from '../e2ee-keypair'
 import { E2EEChannel, type E2EEAuthenticatedDevice } from './e2ee-channel'
@@ -11,7 +17,8 @@ import type { RpcBinarySender } from './rpc-binary-sender'
 type MobileSocketPayload = string | Uint8Array<ArrayBufferLike>
 
 export type MobileSocketTransportMetadata =
-  | { transport: 'direct' }
+  // webClient: the Orca web bundle marked its upgrade; webOrigin: that page's origin.
+  | { transport: 'direct'; webOrigin?: string; webClient?: true }
   | {
       transport: 'relay'
       relayHostId: string
@@ -59,6 +66,8 @@ type MobileSocketWiringOptions = {
   onReady?: (socket: AuthenticatedMobileSocket) => void
   // Why: stale keys and missing registry entries both fail before RPC can explain the re-pair action.
   onUnpairedDeviceAuthFailure?: (metadata: MobileSocketTransportMetadata) => void
+  // Operator opt-in for first pairings from a plain-http page on another machine.
+  allowInsecureWebPairing?: () => boolean
 }
 
 function toAuthenticatedDevice(device: DeviceEntry): E2EEAuthenticatedDevice {
@@ -76,6 +85,8 @@ export class MobileSocketWiring {
   private readonly onClose: MobileSocketWiringOptions['onClose']
   private readonly onReady: MobileSocketWiringOptions['onReady']
   private readonly onUnpairedDeviceAuthFailure: MobileSocketWiringOptions['onUnpairedDeviceAuthFailure']
+  private readonly allowInsecureWebPairing: () => boolean
+  private readonly ephemeralSweep: ReturnType<typeof setInterval>
   private readonly channels = new Map<WebSocket, E2EEChannel>()
   private readonly connectionIds = new Map<WebSocket, string>()
   private readonly authenticatedSockets = new Map<WebSocket, AuthenticatedMobileSocket>()
@@ -90,6 +101,39 @@ export class MobileSocketWiring {
     this.onClose = options.onClose
     this.onReady = options.onReady
     this.onUnpairedDeviceAuthFailure = options.onUnpairedDeviceAuthFailure
+    this.allowInsecureWebPairing = options.allowInsecureWebPairing ?? (() => false)
+    this.ephemeralSweep = setInterval(
+      () => this.sweepIdleEphemeralDevices(Date.now()),
+      EPHEMERAL_DEVICE_SWEEP_INTERVAL_MS
+    )
+    // Why: bookkeeping must never hold the process open.
+    this.ephemeralSweep.unref?.()
+  }
+
+  dispose(): void {
+    clearInterval(this.ephemeralSweep)
+  }
+
+  /** Removes idle session-only browser rows and cuts any socket still bound to them. */
+  sweepIdleEphemeralDevices(now: number): string[] {
+    let removed: string[] = []
+    try {
+      removed = this.deviceRegistry.pruneIdleEphemeralDevices(now, (deviceId) =>
+        this.hasAuthenticatedSocket(deviceId)
+      )
+    } catch (error) {
+      console.error('[mobile] Failed to prune idle browser-session devices:', error)
+    }
+    for (const deviceId of removed) {
+      this.terminateDeviceConnections(deviceId)
+    }
+    return removed
+  }
+
+  private hasAuthenticatedSocket(deviceId: string): boolean {
+    return Array.from(this.authenticatedSockets.values()).some(
+      (socket) => socket.device.deviceId === deviceId
+    )
   }
 
   attachTransport(
@@ -156,6 +200,16 @@ export class MobileSocketWiring {
           if (!device) {
             return null
           }
+          if (
+            isPendingTokenRow(device) &&
+            metadata.transport === 'direct' &&
+            // Why the marker too: phones send an http Origin as well, and must never be gated.
+            metadata.webClient === true &&
+            isInsecureRemoteWebOrigin(metadata.webOrigin) &&
+            !this.allowInsecureWebPairing()
+          ) {
+            return { refused: INSECURE_WEB_ORIGIN_AUTH_CODE }
+          }
           // Why: outer relay authorization cannot choose the local Orca
           // identity; E2EE must resolve the same device before readiness.
           if (metadata.transport === 'relay' && metadata.relayDeviceId !== device.deviceId) {
@@ -251,6 +305,10 @@ export class MobileSocketWiring {
       Array.from(this.authenticatedSockets.values()).some(
         (candidate) => candidate.device.deviceId === socket.device.deviceId
       )
+    // Why: a session-only row idles from its last disconnect, not from when it connected.
+    if (socket && !hasOtherConnections && socket.device.deviceToken === undefined) {
+      this.deviceRegistry.updateLastSeenDeferred(socket.device.deviceId)
+    }
     this.onClose(socket, hasOtherConnections)
   }
 }
diff --git a/src/main/runtime/rpc/web-session-pairing.test.ts b/src/main/runtime/rpc/web-session-pairing.test.ts
new file mode 100644
index 00000000000..0965e4971f3
--- /dev/null
+++ b/src/main/runtime/rpc/web-session-pairing.test.ts
@@ -0,0 +1,239 @@
+import { mkdtempSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import nacl from 'tweetnacl'
+import type { WebSocket } from 'ws'
+import { describe, expect, it, vi } from 'vitest'
+import { encodeDeviceProofMessage } from '../../../shared/device-key-proof'
+import { DeviceRegistry } from '../device-registry'
+import { EPHEMERAL_DEVICE_IDLE_MS } from '../ephemeral-device-rows'
+import { SimulatedMobileE2EEV2Peer } from '../relay/simulated-mobile-e2ee-v2-peer'
+import { registerSocketDeviceKey } from '../runtime-rpc/runtime-rpc-device-key-registration'
+import { generateKeyPair } from './e2ee-crypto'
+import {
+  MobileSocketWiring,
+  type AuthenticatedMobileSocket,
+  type MobileSocketTransport,
+  type MobileSocketTransportMetadata
+} from './mobile-socket-wiring'
+
+class FakeSocket {
+  readonly OPEN = 1
+  readyState = this.OPEN
+  bufferedAmount = 0
+  readonly sent: (string | Buffer)[] = []
+  readonly send = vi.fn((data: string | Buffer) => this.sent.push(data))
+  readonly close = vi.fn()
+}
+
+class FakeTransport implements MobileSocketTransport {
+  private messageHandler: Parameters<MobileSocketTransport['onMessage']>[0] | null = null
+  readonly setClientId = vi.fn()
+  readonly terminateClientConnections = vi.fn(() => 0)
+  onMessage(handler: Parameters<MobileSocketTransport['onMessage']>[0]): void {
+    this.messageHandler = handler
+  }
+  onConnectionClose(): void {}
+  receive(ws: FakeSocket, message: string): void {
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the wiring only sends, closes and reads OPEN/readyState/bufferedAmount.
+    this.messageHandler?.(message, vi.fn(), ws as unknown as WebSocket)
+  }
+}
+
+const desktop = generateKeyPair()
+const LAN_PAGE = 'http://192.168.1.20:6768'
+const RELAY_HOST_ID = 'AbCdEf0123_-xyZ9'
+
+// The new web bundle marks its upgrade; phones (React Native) send an http Origin but no marker.
+const WEB_CLIENT = { webOrigin: LAN_PAGE, webClient: true as const }
+
+function harness(
+  page: { webOrigin?: string; webClient?: true } | undefined,
+  allowInsecureWebPairing = false,
+  relay?: (deviceId: string) => MobileSocketTransportMetadata
+) {
+  const registry = new DeviceRegistry(mkdtempSync(join(tmpdir(), 'orca-web-session-')))
+  const transport = new FakeTransport()
+  const ready: AuthenticatedMobileSocket[] = []
+  const wiring = new MobileSocketWiring({
+    deviceRegistry: registry,
+    e2eeKeypair: {
+      publicKey: desktop.publicKey,
+      secretKey: desktop.secretKey,
+      publicKeyB64: Buffer.from(desktop.publicKey).toString('base64')
+    },
+    onText: vi.fn(),
+    onBinary: vi.fn(),
+    onClose: vi.fn(),
+    onReady: (socket) => ready.push(socket),
+    allowInsecureWebPairing: () => allowInsecureWebPairing
+  })
+  let relayDeviceId = ''
+  wiring.attachTransport(transport, () =>
+    relay ? relay(relayDeviceId) : { transport: 'direct', ...page }
+  )
+
+  function connect(auth: (transcriptHashB64: string) => Record<string, unknown>) {
+    const ws = new FakeSocket()
+    const peer = new SimulatedMobileE2EEV2Peer(
+      nacl.box.keyPair(),
+      desktop.publicKey,
+      relay ? RELAY_HOST_ID : null
+    )
+    transport.receive(ws, JSON.stringify(peer.hello))
+    expect(peer.acceptReady(JSON.parse(String(ws.sent[0])))).toBe(true)
+    const transcriptHashB64 = peer.transcriptHashB64
+    const before = ready.length
+    transport.receive(
+      ws,
+      peer.sealText(
+        JSON.stringify({ type: 'e2ee_auth', v: 2, transcriptHashB64, ...auth(transcriptHashB64) })
+      )
+    )
+    const reply = ws.sent[1] ? JSON.parse(peer.openText(String(ws.sent[1]))!) : null
+    return { ws, transcriptHashB64, reply, socket: ready.length > before ? ready.at(-1) : null }
+  }
+  return {
+    registry,
+    wiring,
+    transport,
+    connect,
+    bindRelay: (deviceId: string) => (relayDeviceId = deviceId)
+  }
+}
+
+function sign(key: nacl.SignKeyPair, purpose: 'auth' | 'register', transcriptHashB64: string) {
+  const message = encodeDeviceProofMessage(purpose, Buffer.from(transcriptHashB64, 'base64'))
+  return Buffer.from(nacl.sign.detached(message, key.secretKey)).toString('base64')
+}
+
+describe('pairing from a plain-http page on another machine', () => {
+  it('refuses a first pairing without operator opt-in, with a sealed reason', () => {
+    const { registry, connect } = harness(WEB_CLIENT)
+    const pending = registry.getOrCreatePendingDevice('Browser', 'runtime')
+    const attempt = connect(() => ({ deviceToken: pending.token }))
+    expect(attempt.reply).toEqual({ type: 'e2ee_error', error: { code: 'insecure_origin' } })
+    expect(attempt.socket).toBeNull()
+    expect(attempt.ws.close).toHaveBeenCalledWith(4001, 'Insecure web origin')
+    expect(registry.getDevice(pending.deviceId)?.lastSeenAt).toBe(0)
+  })
+
+  it('pairs when the operator opted in', () => {
+    const { registry, connect } = harness(WEB_CLIENT, true)
+    const pending = registry.getOrCreatePendingDevice('Browser', 'runtime')
+    expect(connect(() => ({ deviceToken: pending.token })).reply).toMatchObject({
+      type: 'e2ee_authenticated'
+    })
+  })
+
+  it('never cuts a browser that was already paired', () => {
+    const { registry, connect } = harness(WEB_CLIENT)
+    const paired = registry.addDevice('Browser', 'runtime')
+    registry.updateLastSeen(paired.deviceId)
+    expect(connect(() => ({ deviceToken: paired.token })).reply).toMatchObject({
+      type: 'e2ee_authenticated'
+    })
+  })
+
+  it('lets https, loopback and native clients pair as before', () => {
+    for (const page of [
+      { webOrigin: 'https://desk.example.com', webClient: true as const },
+      { webOrigin: 'http://localhost:6768', webClient: true as const },
+      undefined
+    ]) {
+      const { registry, connect } = harness(page)
+      const pending = registry.getOrCreatePendingDevice('Client', 'runtime')
+      expect(connect(() => ({ deviceToken: pending.token })).reply).toMatchObject({
+        type: 'e2ee_authenticated'
+      })
+    }
+  })
+})
+
+describe('phones over direct LAN are never gated by their Origin', () => {
+  it('pairs a released phone whose socket sends an http LAN Origin but no web marker', () => {
+    for (const scope of ['mobile', 'runtime'] as const) {
+      const { registry, connect } = harness({ webOrigin: LAN_PAGE })
+      const pending = registry.getOrCreatePendingDevice('Phone', scope)
+      expect(connect(() => ({ deviceToken: pending.token })).reply).toMatchObject({
+        type: 'e2ee_authenticated'
+      })
+    }
+  })
+})
+
+describe('relayed phones are never gated', () => {
+  it('pairs over Relay whatever the page marker says', () => {
+    const { registry, connect, bindRelay } = harness(WEB_CLIENT, false, (relayDeviceId) => ({
+      transport: 'relay',
+      relayHostId: RELAY_HOST_ID,
+      relayDeviceId,
+      basisConnId: 'conn',
+      credentialKind: 'invite'
+    }))
+    const pending = registry.getOrCreatePendingDevice('Phone', 'mobile')
+    bindRelay(pending.deviceId)
+    expect(connect(() => ({ deviceToken: pending.token })).reply).toMatchObject({
+      type: 'e2ee_authenticated'
+    })
+  })
+})
+
+describe('session-only browser keys', () => {
+  it('registers an ephemeral row, sweeps it once idle and disconnected, and then revokes it', () => {
+    const { registry, wiring, transport, connect } = harness({
+      webOrigin: 'https://desk.example.com',
+      webClient: true as const
+    })
+    const paired = registry.addDevice('Browser', 'runtime')
+    registry.updateLastSeen(paired.deviceId)
+    const migrating = connect(() => ({ deviceToken: paired.token }))
+    const key = nacl.sign.keyPair()
+    const fork = registerSocketDeviceKey(registry, migrating.socket!, {
+      devicePublicKeyB64: Buffer.from(key.publicKey).toString('base64'),
+      deviceProofB64: sign(key, 'register', migrating.transcriptHashB64),
+      ephemeral: true
+    })
+    expect(registry.getDevice(fork.deviceId)?.ephemeral).toBe(true)
+
+    const keyed = connect((hash) => ({
+      deviceId: fork.deviceId,
+      deviceProofB64: sign(key, 'auth', hash)
+    }))
+    expect(keyed.reply).toMatchObject({ type: 'e2ee_authenticated' })
+    const idle = registry.getDevice(fork.deviceId)!.lastSeenAt + EPHEMERAL_DEVICE_IDLE_MS + 1
+    // A live socket keeps the row however long the tab stays open.
+    expect(wiring.sweepIdleEphemeralDevices(idle)).toEqual([])
+
+    transport.receive(keyed.ws, 'ignored')
+    wiring.dispose()
+    expect(registry.pruneIdleEphemeralDevices(idle, () => false)).toEqual([fork.deviceId])
+    const after = connect((hash) => ({
+      deviceId: fork.deviceId,
+      deviceProofB64: sign(key, 'auth', hash)
+    }))
+    expect(after.reply).toEqual({
+      type: 'e2ee_error',
+      error: { code: 'device_revoked', deviceId: fork.deviceId }
+    })
+  })
+
+  it('cuts sockets bound to a swept row', () => {
+    const { registry, wiring, transport } = harness(undefined)
+    const paired = registry.addDevice('Browser', 'runtime')
+    registry.updateLastSeen(paired.deviceId)
+    const key = nacl.sign.keyPair()
+    const fork = registry.forkDeviceKey(
+      paired.deviceId,
+      Buffer.from(key.publicKey).toString('base64'),
+      'Tab',
+      { ephemeral: true }
+    )
+    expect(
+      wiring.sweepIdleEphemeralDevices(fork.lastSeenAt + EPHEMERAL_DEVICE_IDLE_MS + 1)
+    ).toEqual([fork.deviceId])
+    expect(transport.terminateClientConnections).toHaveBeenCalledWith(fork.deviceId)
+    expect(registry.getDevice(paired.deviceId)).not.toBeNull()
+    wiring.dispose()
+  })
+})
diff --git a/src/main/runtime/rpc/ws-transport.ts b/src/main/runtime/rpc/ws-transport.ts
index 29a6aa4b854..06d943faddf 100644
--- a/src/main/runtime/rpc/ws-transport.ts
+++ b/src/main/runtime/rpc/ws-transport.ts
@@ -4,6 +4,7 @@ import { createServer as createHttpServer, type Server as HttpServer } from 'nod
 import { WebSocketServer, type WebSocket } from 'ws'
 import type { RpcTransport } from './transport'
 import { createStaticWebClientHandler } from './static-web-client-handler'
+import { hasWebClientUpgradeMarker } from '../../../shared/web-origin-security'
 import {
   attachNodeWebSocketLifecycle,
   clearNodeWebSocketPreAuthTimer,
@@ -59,6 +60,7 @@ export class WebSocketTransport implements RpcTransport {
   private readonly fallbackLadder: readonly number[]
   private persistedFallbackBindFailed = false
   private httpServer: HttpsServer | HttpServer | null = null
+  private readonly webPages = new WeakMap<WebSocket, { webOrigin?: string; webClient: true }>()
   private wss: WebSocketServer | null = null
   private messageHandler: WebSocketMessageHandler | null = null
   private connectionCloseHandler: WebSocketConnectionCloseHandler | null = null
@@ -110,6 +112,11 @@ export class WebSocketTransport implements RpcTransport {
     this.connectionCloseHandler = handler
   }
 
+  /** The Orca web bundle that opened `ws` (it marks its upgrade), with its page origin. */
+  webPageOf(ws: WebSocket): { webOrigin?: string; webClient: true } | undefined {
+    return this.webPages.get(ws)
+  }
+
   setClientId(ws: WebSocket, clientId: string): void {
     this.wsClientIds.set(ws, clientId)
     clearNodeWebSocketPreAuthTimer(ws, this.preAuthTimers)
@@ -213,11 +220,18 @@ export class WebSocketTransport implements RpcTransport {
       maxPayload: WEBSOCKET_TRANSPORT_MAX_MESSAGE_BYTES
     })
 
-    wss.on('connection', (ws) => {
+    wss.on('connection', (ws, request) => {
       if (wss.clients.size > WEBSOCKET_TRANSPORT_MAX_CONNECTIONS) {
         rejectNodeWebSocketOverCapacity(ws)
         return
       }
+      if (hasWebClientUpgradeMarker(request.url)) {
+        const origin = request.headers.origin
+        this.webPages.set(ws, {
+          ...(typeof origin === 'string' ? { webOrigin: origin } : {}),
+          webClient: true
+        })
+      }
       this.handleConnection(ws)
     })
 
diff --git a/src/main/runtime/runtime-rpc-browser-host-admission.test.ts b/src/main/runtime/runtime-rpc-browser-host-admission.test.ts
index b9187315478..24b94ee4fe4 100644
--- a/src/main/runtime/runtime-rpc-browser-host-admission.test.ts
+++ b/src/main/runtime/runtime-rpc-browser-host-admission.test.ts
@@ -55,7 +55,9 @@ describe('runtime RPC browser-host admission', () => {
     })
     server['deviceRegistry'] = new DeviceRegistry(userDataPath)
     const device = server['deviceRegistry'].addDevice('runtime-test', 'runtime')
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the server reads only these wiring members in this test.
     server['mobileSocketWiring'] = {
+      dispose: () => {},
       getConnectionId: () => 'connection-a'
     } as unknown as NonNullable<(typeof server)['mobileSocketWiring']>
     const socket = new FakeWebSocket()
@@ -125,7 +127,9 @@ describe('runtime RPC browser-host admission', () => {
       [socketB, 'connection-b'],
       [socketAReplacement, 'connection-a-replacement']
     ])
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the server reads only these wiring members in this test.
     server['mobileSocketWiring'] = {
+      dispose: () => {},
       getConnectionId: (socket) => connectionIds.get(socket as unknown as FakeWebSocket)
     } as unknown as NonNullable<(typeof server)['mobileSocketWiring']>
     const repliesA: Record<string, unknown>[] = []
diff --git a/src/main/runtime/runtime-rpc-websocket-long-poll-caps.test.ts b/src/main/runtime/runtime-rpc-websocket-long-poll-caps.test.ts
index ea8837c01c9..2054fa23de8 100644
--- a/src/main/runtime/runtime-rpc-websocket-long-poll-caps.test.ts
+++ b/src/main/runtime/runtime-rpc-websocket-long-poll-caps.test.ts
@@ -54,7 +54,9 @@ describe('OrcaRuntimeRpcServer', () => {
     server['deviceRegistry'] = new DeviceRegistry(userDataPath)
     const entry = server['deviceRegistry']!.addDevice('runtime-test', 'runtime')
     const ws = new FakeWebSocket()
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the server reads only these wiring members in this test.
     server['mobileSocketWiring'] = {
+      dispose: () => {},
       getConnectionId: () => 'conn-test'
     } as unknown as NonNullable<(typeof server)['mobileSocketWiring']>
     const replies: Record<string, unknown>[] = []
@@ -132,7 +134,9 @@ describe('OrcaRuntimeRpcServer', () => {
     // Why: 'runtime' scope, not 'mobile' — orchestration.ask is absent from the mobile allowlist.
     const entry = server['deviceRegistry']!.addDevice('runtime-test', 'runtime')
     const ws = new FakeWebSocket()
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the server reads only these wiring members in this test.
     server['mobileSocketWiring'] = {
+      dispose: () => {},
       getConnectionId: () => 'conn-test'
     } as unknown as NonNullable<(typeof server)['mobileSocketWiring']>
     const replies: Record<string, unknown>[] = []
@@ -214,7 +218,9 @@ describe('OrcaRuntimeRpcServer', () => {
     server['deviceRegistry'] = new DeviceRegistry(userDataPath)
     const entry = server['deviceRegistry']!.addDevice('runtime-test', 'runtime')
     const ws = new FakeWebSocket()
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the server reads only these wiring members in this test.
     server['mobileSocketWiring'] = {
+      dispose: () => {},
       getConnectionId: () => 'conn-test'
     } as unknown as NonNullable<(typeof server)['mobileSocketWiring']>
     let activeDispatches = 0
diff --git a/src/main/runtime/runtime-rpc/runtime-rpc-device-key-registration.ts b/src/main/runtime/runtime-rpc/runtime-rpc-device-key-registration.ts
index e63b2d7f38c..7c566e7c407 100644
--- a/src/main/runtime/runtime-rpc/runtime-rpc-device-key-registration.ts
+++ b/src/main/runtime/runtime-rpc/runtime-rpc-device-key-registration.ts
@@ -35,7 +35,8 @@ export function registerSocketDeviceKey(
   const entry = registry.forkDeviceKey(
     legacy.deviceId,
     params.devicePublicKeyB64,
-    sanitizeDeviceLabel(params.deviceLabel, legacy.name)
+    sanitizeDeviceLabel(params.deviceLabel, legacy.name),
+    { ephemeral: params.ephemeral === true }
   )
   return { deviceId: entry.deviceId, credentialRevision: entry.credentialRevision ?? 0 }
 }
diff --git a/src/main/runtime/runtime-rpc/runtime-rpc-lifecycle.ts b/src/main/runtime/runtime-rpc/runtime-rpc-lifecycle.ts
index 3159f9f6286..188ce1318e4 100644
--- a/src/main/runtime/runtime-rpc/runtime-rpc-lifecycle.ts
+++ b/src/main/runtime/runtime-rpc/runtime-rpc-lifecycle.ts
@@ -1,3 +1,4 @@
+import { ALLOW_INSECURE_WEB_PAIRING_ENV } from '../../../shared/web-origin-security'
 import { AGENT_LAUNCH_RUNTIME_CAPABILITY } from '../../../shared/agent-launch-runtime-capability'
 import type { RuntimeTransportMetadata } from '../../../shared/runtime-bootstrap'
 import { watchRuntimeMetadataOwnership } from '../runtime-metadata-ownership-watch'
@@ -112,6 +113,7 @@ export class RuntimeRpcLifecycle extends RuntimeRpcWebSocketDispatch {
         } catch (error) {
           // Why: WebSocket transport is supplementary; on failure (e.g. port in use) continue with Unix socket only.
           console.error('[runtime] Failed to start WebSocket transport:', error)
+          this.mobileSocketWiring?.dispose()
           this.mobileSocketWiring = null
         }
       }
@@ -191,7 +193,10 @@ export class RuntimeRpcLifecycle extends RuntimeRpcWebSocketDispatch {
       fallbackLadder: wsFallbackPortLadder(this.wsPort)
     })
     const mobileSocketWiring = this.ensureMobileSocketWiring(deviceRegistry, e2eeKeypair)
-    this.detachWebSocketWiring = mobileSocketWiring.attachTransport(wsTransport)
+    this.detachWebSocketWiring = mobileSocketWiring.attachTransport(wsTransport, (ws) => ({
+      transport: 'direct',
+      ...wsTransport.webPageOf(ws)
+    }))
 
     try {
       await wsTransport.start()
@@ -270,6 +275,7 @@ export class RuntimeRpcLifecycle extends RuntimeRpcWebSocketDispatch {
           this.runtime.onClientDisconnected(socket.device.clientId)
         }
       },
+      allowInsecureWebPairing: () => process.env[ALLOW_INSECURE_WEB_PAIRING_ENV] === '1',
       // Why: relay attempts are authorized upstream; only direct failures should prompt local re-pairing.
       onUnpairedDeviceAuthFailure: (metadata) => {
         if (metadata.transport === 'direct') {
diff --git a/src/main/runtime/runtime-rpc/runtime-rpc-shutdown.ts b/src/main/runtime/runtime-rpc/runtime-rpc-shutdown.ts
index 2efd9bc7678..d5e5b8610dd 100644
--- a/src/main/runtime/runtime-rpc/runtime-rpc-shutdown.ts
+++ b/src/main/runtime/runtime-rpc/runtime-rpc-shutdown.ts
@@ -41,6 +41,7 @@ export class RuntimeRpcShutdown extends RuntimeRpcMobilePairing {
     if (this.hostDescriptor) {
       publishHostDescriptor(this.runtime.getRuntimeId(), null)
     }
+    this.mobileSocketWiring?.dispose()
     this.mobileSocketWiring = null
     this.detachWebSocketWiring = null
     const stopResults = await Promise.allSettled(
diff --git a/src/shared/device-key-capability.ts b/src/shared/device-key-capability.ts
index 62bc1a8810a..48a8d4b8a9f 100644
--- a/src/shared/device-key-capability.ts
+++ b/src/shared/device-key-capability.ts
@@ -5,4 +5,12 @@
 // pairing.registerDeviceKey; clients migrate or present a key only when this is advertised.
 export const DEVICE_KEY_RUNTIME_CAPABILITY = 'pairing.device-key.v1' as const
 
+// Why: registerDeviceKey's params are strict on older hosts, so `ephemeral` is sent only when advertised.
+export const DEVICE_KEY_EPHEMERAL_RUNTIME_CAPABILITY = 'pairing.device-key-ephemeral.v1' as const
+
+export const DEVICE_KEY_RUNTIME_CAPABILITIES = [
+  DEVICE_KEY_RUNTIME_CAPABILITY,
+  DEVICE_KEY_EPHEMERAL_RUNTIME_CAPABILITY
+] as const
+
 export const REGISTER_DEVICE_KEY_METHOD = 'pairing.registerDeviceKey' as const
diff --git a/src/shared/device-key-registration-contract.ts b/src/shared/device-key-registration-contract.ts
index 8655cc67acb..d02e326bc4e 100644
--- a/src/shared/device-key-registration-contract.ts
+++ b/src/shared/device-key-registration-contract.ts
@@ -6,7 +6,10 @@ export const RegisterDeviceKeyParamsSchema = z
     devicePublicKeyB64: z.string().refine(isDevicePublicKeyB64, 'expected a 32-byte Ed25519 key'),
     // Ed25519 over encodeDeviceProofMessage('register', this connection's v2 transcript hash).
     deviceProofB64: z.string().refine(isDeviceProofB64, 'expected a 64-byte signature'),
-    deviceLabel: z.string().max(256).optional()
+    deviceLabel: z.string().max(256).optional(),
+    // Session-only browser key: the host drops the row on restart and after idling.
+    // Sent only to hosts advertising DEVICE_KEY_EPHEMERAL_RUNTIME_CAPABILITY (older hosts are strict).
+    ephemeral: z.literal(true).optional()
   })
   .strict()
 
diff --git a/src/shared/protocol-version.ts b/src/shared/protocol-version.ts
index a24fd1ef1be..b71bdce3726 100644
--- a/src/shared/protocol-version.ts
+++ b/src/shared/protocol-version.ts
@@ -45,7 +45,7 @@ import { AGENT_SESSION_RESUME_RUNTIME_CAPABILITIES } from './agent-session-resum
 import { QODER_OWNED_TERMINAL_CREATE_CAPABILITY } from './qoder-terminal-create-capability'
 import { AGENT_SESSION_CONTINUE_INTERRUPTED_RUNTIME_CAPABILITY } from './agent-session-continue-interrupted-capability'
 import { ORCAD_RUNTIME_CAPABILITIES } from './orcad-runtime-capabilities'
-import { DEVICE_KEY_RUNTIME_CAPABILITY } from './device-key-capability'
+import { DEVICE_KEY_RUNTIME_CAPABILITIES } from './device-key-capability'
 // Why a star: every resume capability is part of the runtime contract this module re-exports.
 export * from './agent-session-resume-runtime-capabilities'
 import { AGENT_SESSION_BACKGROUND_TASK_CHILD_VIEWS_CAPABILITY } from './agent-session-background-task-child-views-capability'
@@ -356,7 +356,7 @@ export const ANTIGRAVITY_CONFIGURED_MODEL_RUNTIME_CAPABILITY =
 
 export const RUNTIME_CAPABILITIES = [
   ...ORCAD_RUNTIME_CAPABILITIES,
-  DEVICE_KEY_RUNTIME_CAPABILITY,
+  ...DEVICE_KEY_RUNTIME_CAPABILITIES,
   QODER_OWNED_TERMINAL_CREATE_CAPABILITY,
   ...AGENT_SESSION_STOP_RUNTIME_CAPABILITIES,
   ...AGENT_SESSION_CREATE_RUNTIME_CAPABILITIES,
diff --git a/src/shared/web-origin-security.test.ts b/src/shared/web-origin-security.test.ts
new file mode 100644
index 00000000000..a7fdeb6821d
--- /dev/null
+++ b/src/shared/web-origin-security.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest'
+import {
+  hasWebClientUpgradeMarker,
+  isInsecureRemoteWebOrigin,
+  withWebClientUpgradeMarker
+} from './web-origin-security'
+
+describe('isInsecureRemoteWebOrigin', () => {
+  it('flags plain http pages served to other machines', () => {
+    expect(isInsecureRemoteWebOrigin('http://192.168.1.20:6768')).toBe(true)
+    expect(isInsecureRemoteWebOrigin('http://desk.local')).toBe(true)
+    expect(isInsecureRemoteWebOrigin('http://[fe80::1]:6768')).toBe(true)
+  })
+
+  it('treats https and loopback pages as secure', () => {
+    expect(isInsecureRemoteWebOrigin('https://desk.example.com')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('http://localhost:6768')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('http://app.localhost')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('http://127.0.0.1:6768')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('http://127.8.0.1')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('http://[::1]:6768')).toBe(false)
+  })
+
+  it('leaves non-browser and unparseable origins to token auth', () => {
+    expect(isInsecureRemoteWebOrigin(undefined)).toBe(false)
+    expect(isInsecureRemoteWebOrigin('null')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('file://')).toBe(false)
+    expect(isInsecureRemoteWebOrigin('not a url')).toBe(false)
+  })
+})
+
+describe('web client upgrade marker', () => {
+  it('round-trips through the endpoint the web bundle dials', () => {
+    const marked = withWebClientUpgradeMarker('ws://192.168.1.20:6768')
+    expect(marked).toBe('ws://192.168.1.20:6768/?orca-client=web')
+    expect(hasWebClientUpgradeMarker(new URL(marked).pathname + new URL(marked).search)).toBe(true)
+    expect(withWebClientUpgradeMarker('wss://desk.example.com/orca?x=1')).toBe(
+      'wss://desk.example.com/orca?x=1&orca-client=web'
+    )
+  })
+
+  it('is absent for phones, CLIs and other paths', () => {
+    expect(hasWebClientUpgradeMarker('/')).toBe(false)
+    expect(hasWebClientUpgradeMarker(undefined)).toBe(false)
+    expect(hasWebClientUpgradeMarker('/?orca-client=phone')).toBe(false)
+  })
+})
diff --git a/src/shared/web-origin-security.ts b/src/shared/web-origin-security.ts
new file mode 100644
index 00000000000..a6a6bae1f12
--- /dev/null
+++ b/src/shared/web-origin-security.ts
@@ -0,0 +1,61 @@
+// Why: a plain-http page on another machine can be swapped by anyone on the LAN path, so a
+// pairing code typed into it is exposed. Browsers treat loopback http as a secure context.
+export function isInsecureRemoteWebOrigin(origin: string | undefined): boolean {
+  if (!origin) {
+    return false
+  }
+  let url: URL
+  try {
+    url = new URL(origin)
+  } catch {
+    return false
+  }
+  return url.protocol === 'http:' && !isLoopbackHostname(url.hostname)
+}
+
+function isLoopbackHostname(hostname: string): boolean {
+  const host = hostname.toLowerCase()
+  return (
+    host === 'localhost' ||
+    host.endsWith('.localhost') ||
+    host === '[::1]' ||
+    /^127(?:\.\d{1,3}){3}$/.test(host)
+  )
+}
+
+/** Sealed auth error for a first pairing from such a page without operator opt-in. */
+export const INSECURE_WEB_ORIGIN_AUTH_CODE = 'insecure_origin' as const
+
+// Operator opt-in, read by the host serving the page (desktop or `orca serve`).
+export const ALLOW_INSECURE_WEB_PAIRING_ENV = 'ORCA_ALLOW_INSECURE_WEB_PAIRING' as const
+
+// Why a marker: React Native phones also send an http Origin on LAN sockets, so the Origin alone
+// cannot say "browser". Only the web bundle adds this query to its upgrade URL; hosts that predate
+// it ignore the query string, so the marked upgrade still connects to them.
+export const WEB_CLIENT_UPGRADE_PARAM = 'orca-client' as const
+export const WEB_CLIENT_UPGRADE_VALUE = 'web' as const
+
+export function withWebClientUpgradeMarker(endpoint: string): string {
+  try {
+    const url = new URL(endpoint)
+    url.searchParams.set(WEB_CLIENT_UPGRADE_PARAM, WEB_CLIENT_UPGRADE_VALUE)
+    return url.toString()
+  } catch {
+    return endpoint
+  }
+}
+
+/** True when an upgrade request path (`/path?query`) carries the web bundle's marker. */
+export function hasWebClientUpgradeMarker(requestUrl: string | undefined): boolean {
+  if (!requestUrl) {
+    return false
+  }
+  try {
+    return (
+      new URL(requestUrl, 'http://upgrade.invalid').searchParams.get(WEB_CLIENT_UPGRADE_PARAM) ===
+      WEB_CLIENT_UPGRADE_VALUE
+    )
+  } catch {
+    return false
+  }
+}
diff --git a/tests/e2e/cross-version-wire/cross-version-web-session-pairing.unit.test.ts b/tests/e2e/cross-version-wire/cross-version-web-session-pairing.unit.test.ts
new file mode 100644
index 00000000000..508efdcb94b
--- /dev/null
+++ b/tests/e2e/cross-version-wire/cross-version-web-session-pairing.unit.test.ts
@@ -0,0 +1,71 @@
+import { mkdtempSync, readFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import nacl from 'tweetnacl'
+import { beforeAll, describe, expect, it } from 'vitest'
+import { DeviceRegistry, type DeviceEntry } from '../../../src/main/runtime/device-registry'
+import { DEVICE_REGISTRY_FILENAME } from '../../../src/main/runtime/mobile-pairing-files'
+import { DEVICE_KEY_EPHEMERAL_RUNTIME_CAPABILITY } from '../../../src/shared/device-key-capability'
+import {
+  importReleaseCheckoutModule,
+  materializeReleaseCheckout,
+  resolveBaselineReleaseRef
+} from './release-checkout'
+
+/**
+ * Session-only browser keys add an `ephemeral` flag to keyed rows. A released host (desktop
+ * downgrade) must keep such rows, keep token rows authenticating, and never advertise the
+ * capability that makes a browser send `ephemeral` to it.
+ */
+const SUITE_TIMEOUT_MS = 180_000
+
+type RegistryLike = {
+  validateToken(token: string): { deviceId: string } | null
+  updateLastSeen(deviceId: string): void
+}
+
+let ReleasedRegistry: new (userDataPath: string) => RegistryLike
+let releasedCapabilities: readonly string[]
+
+beforeAll(async () => {
+  const checkout = await materializeReleaseCheckout(resolveBaselineReleaseRef())
+  const [registryModule, protocolModule] = await Promise.all([
+    importReleaseCheckoutModule(checkout, 'src/main/runtime/device-registry.ts'),
+    importReleaseCheckoutModule(checkout, 'src/shared/protocol-version.ts')
+  ])
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the pinned release's DeviceRegistry class; a changed shape fails the assertions below.
+  ReleasedRegistry = registryModule.DeviceRegistry as typeof ReleasedRegistry
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the pinned release's capability list; a changed shape fails the assertion below.
+  releasedCapabilities = protocolModule.RUNTIME_CAPABILITIES as readonly string[]
+}, SUITE_TIMEOUT_MS)
+
+describe('cross-version: session-only browser rows', () => {
+  it('a released host never invites a browser to send ephemeral', () => {
+    expect(releasedCapabilities).not.toContain(DEVICE_KEY_EPHEMERAL_RUNTIME_CAPABILITY)
+  })
+
+  it('a released registry keeps the session row and token rows; this host drops it on restart', () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-xv-web-session-'))
+    const current = new DeviceRegistry(userDataPath)
+    const legacy = current.addDevice('Browser', 'runtime')
+    current.updateLastSeen(legacy.deviceId)
+    const keyB64 = Buffer.from(nacl.sign.keyPair().publicKey).toString('base64')
+    const session = current.forkDeviceKey(legacy.deviceId, keyB64, 'Tab', { ephemeral: true })
+
+    const released = new ReleasedRegistry(userDataPath)
+    expect(released.validateToken(legacy.token)?.deviceId).toBe(legacy.deviceId)
+    released.updateLastSeen(legacy.deviceId)
+    const rows: DeviceEntry[] = JSON.parse(
+      readFileSync(join(userDataPath, DEVICE_REGISTRY_FILENAME), 'utf8')
+    )
+    expect(rows.find((row) => row.deviceId === session.deviceId)).toMatchObject({
+      ephemeral: true,
+      devicePublicKeyB64: keyB64
+    })
+    expect(rows.find((row) => row.deviceId === session.deviceId)?.token).toBeUndefined()
+
+    const restarted = new DeviceRegistry(userDataPath)
+    expect(restarted.getDevice(session.deviceId)).toBeNull()
+    expect(restarted.validateToken(legacy.token)?.deviceId).toBe(legacy.deviceId)
+  })
+})
diff --git a/tests/e2e/cross-version-wire/cross-version-web-upgrade-marker.unit.test.ts b/tests/e2e/cross-version-wire/cross-version-web-upgrade-marker.unit.test.ts
new file mode 100644
index 00000000000..7d148b3df2f
--- /dev/null
+++ b/tests/e2e/cross-version-wire/cross-version-web-upgrade-marker.unit.test.ts
@@ -0,0 +1,85 @@
+import WebSocket from 'ws'
+import { afterEach, beforeAll, describe, expect, it } from 'vitest'
+import { WebSocketTransport } from '../../../src/main/runtime/rpc/ws-transport'
+import { withWebClientUpgradeMarker } from '../../../src/shared/web-origin-security'
+import {
+  importReleaseCheckoutModule,
+  materializeReleaseCheckout,
+  resolveBaselineReleaseRef
+} from './release-checkout'
+
+/**
+ * The updated web client marks its WebSocket upgrade with `?orca-client=web` so a host can tell
+ * it from a phone (React Native also sends an http Origin). A released host must still accept the
+ * marked upgrade, and this host must record the marker only when it is present.
+ */
+const SUITE_TIMEOUT_MS = 180_000
+const LAN_PAGE = 'http://192.168.1.20:6768'
+
+type TransportLike = {
+  start(): Promise<void>
+  stop(): Promise<void>
+  readonly resolvedPort: number
+  onMessage(handler: (message: unknown, reply: unknown, ws: WebSocket) => void): void
+}
+type TransportConstructor = new (options: Record<string, unknown>) => TransportLike
+
+let ReleasedTransport: TransportConstructor
+const running: TransportLike[] = []
+
+beforeAll(async () => {
+  const checkout = await materializeReleaseCheckout(resolveBaselineReleaseRef())
+  const module = await importReleaseCheckoutModule(checkout, 'src/main/runtime/rpc/ws-transport.ts')
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the pinned release's WebSocketTransport; a changed shape fails the assertions below.
+  ReleasedTransport = module.WebSocketTransport as TransportConstructor
+}, SUITE_TIMEOUT_MS)
+
+afterEach(async () => {
+  await Promise.all(running.splice(0).map((transport) => transport.stop()))
+})
+
+async function dial(transport: TransportLike, marked: boolean): Promise<WebSocket> {
+  const received = new Promise<WebSocket>((resolve) =>
+    transport.onMessage((_message, _reply, ws) => resolve(ws))
+  )
+  const base = `ws://127.0.0.1:${transport.resolvedPort}`
+  const client = new WebSocket(marked ? withWebClientUpgradeMarker(base) : base, {
+    headers: { Origin: LAN_PAGE }
+  })
+  await new Promise<void>((resolve, reject) => {
+    client.once('open', resolve)
+    client.once('error', reject)
+  })
+  client.send('{"type":"e2ee_hello"}')
+  const serverSide = await received
+  client.close()
+  return serverSide
+}
+
+async function started(Transport: TransportConstructor): Promise<TransportLike> {
+  const transport = new Transport({ host: '127.0.0.1', port: 0, preAuthTimeoutMs: 60_000 })
+  await transport.start()
+  running.push(transport)
+  return transport
+}
+
+describe('cross-version: web client upgrade marker', () => {
+  it('a released host accepts the marked upgrade and receives its frames', async () => {
+    const transport = await started(ReleasedTransport)
+    await expect(dial(transport, true)).resolves.toBeDefined()
+  })
+
+  it('this host records the marker for the web bundle only, never for a phone', async () => {
+    const transport = new WebSocketTransport({
+      host: '127.0.0.1',
+      port: 0,
+      preAuthTimeoutMs: 60_000
+    })
+    await transport.start()
+    running.push(transport)
+    const web = await dial(transport, true)
+    expect(transport.webPageOf(web)).toEqual({ webOrigin: LAN_PAGE, webClient: true })
+    const phone = await dial(transport, false)
+    expect(transport.webPageOf(phone)).toBeUndefined()
+  })
+})