diff --git a/cloud/apps/relay/src/control-close-reason-text.ts b/cloud/apps/relay/src/control-close-reason-text.ts
new file mode 100644
index 00000000000..19ac79ea648
--- /dev/null
+++ b/cloud/apps/relay/src/control-close-reason-text.ts
@@ -0,0 +1,7 @@
+// Peer-supplied close reasons are logged; keep them printable and short.
+export function printableCloseReason(reason: Buffer | string): string {
+  return reason
+    .toString()
+    .replace(/[^\x20-\x7e]/g, '')
+    .slice(0, 80)
+}
diff --git a/cloud/apps/relay/src/host-session-registry.test.ts b/cloud/apps/relay/src/host-session-registry.test.ts
index d58899e84b6..4a994c4b091 100644
--- a/cloud/apps/relay/src/host-session-registry.test.ts
+++ b/cloud/apps/relay/src/host-session-registry.test.ts
@@ -7,7 +7,7 @@ import {
   RELAY_HOST_CAPABILITY_IDLE_REGIONAL_REHOME,
   RELAY_PROTOCOL_LIMITS
 } from '@orca-cloud/relay-contract'
-import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi, type MockInstance } from 'vitest'
 import type WebSocket from 'ws'
 import type { RelayAssignmentStore } from './assignment-store.js'
 import type { RelayConfig } from './config.js'
@@ -130,6 +130,7 @@ function createRegistry(
   observer: {
     recordAuth: ReturnType<typeof vi.fn>
     recordControlClose: ReturnType<typeof vi.fn>
+    recordPostProofClose: ReturnType<typeof vi.fn>
     recordSpliceClose: ReturnType<typeof vi.fn>
   }
 } {
@@ -177,6 +178,7 @@ function createRegistry(
     recordReconnect: vi.fn(),
     recordSql: vi.fn(),
     recordControlClose: vi.fn(),
+    recordPostProofClose: vi.fn(),
     recordSpliceClose: vi.fn()
   } satisfies RelayRuntimeObserver
   const registry = new HostSessionRegistry(
@@ -2038,3 +2040,162 @@ describe('paced drain', () => {
     expect(sockets.map((socket) => socket.send.mock.calls.length)).toEqual(sendsAfterEmergency)
   })
 })
+
+describe('controls closed after host proof but before wiring', () => {
+  let warn: MockInstance<typeof console.warn>
+  beforeEach(() => {
+    vi.useFakeTimers()
+    warn = vi.spyOn(console, 'warn').mockImplementation(() => {})
+  })
+  afterEach(() => {
+    warn.mockRestore()
+    vi.clearAllTimers()
+    vi.useRealTimers()
+  })
+  const refusedLines = (): string[] =>
+    warn.mock.calls
+      .map((call) => String(call[0]))
+      .filter((line) => line.includes('control refused after proof'))
+
+  function expectRefusal(
+    observer: { recordPostProofClose: ReturnType<typeof vi.fn> },
+    code: number | null,
+    reason: string,
+    cause?: string
+  ): void {
+    expect(observer.recordPostProofClose).toHaveBeenCalledWith(reason)
+    const [line] = refusedLines()
+    expect(line).toContain(`host=${relayHostLogDigest(identity.relayHostId)} gen=1 app="1.4.173"`)
+    expect(line).toContain(`code=${code ?? 'none'} reason=${JSON.stringify(reason)}`)
+    if (cause) expect(line).toContain(`cause=${cause}`)
+    expect(line).not.toContain(identity.relayHostId)
+    expect(line).not.toContain(identity.sub)
+  }
+
+  it('logs an idle cutover refusal', async () => {
+    const h = createRegistry(vi.fn())
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: beginIdleWork only checks the host key's presence.
+    const idle = h.registry as unknown as { idleAttempts: Map<string, unknown> }
+    idle.idleAttempts.set(identity.relayHostId, {})
+    const socket = new FakeSocket()
+    await h.activate(socket as unknown as WebSocket, identity, null, 1, false, 1)
+    expect(socket.close).toHaveBeenCalledWith(
+      RELAY_CLOSE_CODE.WRONG_CELL,
+      'idle cutover in progress'
+    )
+    expectRefusal(h.observer, RELAY_CLOSE_CODE.WRONG_CELL, 'idle cutover in progress')
+  })
+
+  it('logs a stalled activation queue once', async () => {
+    const stalled = deferred<string>()
+    const h = createRegistry(
+      vi.fn<RelayAssignmentStore['activateControl']>().mockReturnValueOnce(stalled.promise)
+    )
+    const first = h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    const waiting = new FakeSocket()
+    const second = h.activate(waiting as unknown as WebSocket, identity, null, 1, false, 1)
+    await Promise.resolve()
+    await Promise.resolve()
+    vi.advanceTimersByTime(30_000)
+    expectRefusal(h.observer, RELAY_CLOSE_CODE.LIMIT_EXCEEDED, 'control activation queue stalled')
+    stalled.resolve('control:production-gce-c3:1')
+    await Promise.all([first, second])
+    expect(h.observer.recordPostProofClose).toHaveBeenCalledOnce()
+  })
+
+  it('logs a superseded activation', async () => {
+    const h = createRegistry(vi.fn())
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: only compared by identity against the empty session map.
+    const stale = {} as HostSession
+    await h.activate(new FakeSocket() as unknown as WebSocket, identity, stale, 1, false, 1)
+    expectRefusal(h.observer, RELAY_CLOSE_CODE.PEER_DROPPED, 'control activation superseded')
+  })
+
+  it.each([
+    { error: new Error('wrong_assignment'), cause: 'wrong_assignment' },
+    { error: Object.assign(new Error('timeout'), { code: '57014' }), cause: 'database_transient' },
+    // Assembled at runtime so the secret scanner does not read the fixture as a real URL.
+    {
+      error: new Error(`connect ${['postgres', '//user:secret@db/relay'].join(':')}`),
+      cause: 'error'
+    }
+  ])('logs a failed host-proof assignment check as $cause', async ({ error, cause }) => {
+    const h = createRegistry(
+      vi.fn<RelayAssignmentStore['activateControl']>().mockRejectedValueOnce(error)
+    )
+    await h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    expectRefusal(
+      h.observer,
+      RELAY_CLOSE_CODE.WRONG_CELL,
+      'assignment changed during host proof',
+      cause
+    )
+    expect(refusedLines()[0]).not.toContain('secret')
+  })
+
+  it('logs a drain that lands during activation', async () => {
+    const h = createRegistry(vi.fn().mockResolvedValue('control:production-gce-c3:1'))
+    h.registry.drain(100)
+    await h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    expectRefusal(h.observer, RELAY_CLOSE_CODE.DRAINING, 'relay draining')
+  })
+
+  it('logs a host that hangs up during activation, with no cell close code', async () => {
+    const blocked = deferred<string>()
+    const h = createRegistry(
+      vi.fn<RelayAssignmentStore['activateControl']>().mockReturnValueOnce(blocked.promise)
+    )
+    const socket = new FakeSocket()
+    const activation = h.activate(socket as unknown as WebSocket, identity, null, 1, false, 1)
+    await vi.advanceTimersByTimeAsync(0)
+    socket.close()
+    blocked.resolve('control:production-gce-c3:1')
+    await activation
+    expectRefusal(h.observer, null, 'host closed during activation')
+  })
+
+  it('logs a host that hangs up while queued, with no cell close code', async () => {
+    const stalled = deferred<string>()
+    const h = createRegistry(
+      vi
+        .fn<RelayAssignmentStore['activateControl']>()
+        .mockReturnValueOnce(stalled.promise)
+        .mockResolvedValue('control:production-gce-c3:1')
+    )
+    const first = h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    const queued = new FakeSocket()
+    const second = h.activate(queued as unknown as WebSocket, identity, null, 1, false, 1)
+    queued.close()
+    stalled.resolve('control:production-gce-c3:1')
+    await Promise.all([first, second])
+    expectRefusal(h.observer, null, 'host closed while queued')
+  })
+
+  it('logs the hang-up, not a stall, when the queued host left before the deadline', async () => {
+    const stalled = deferred<string>()
+    const h = createRegistry(
+      vi.fn<RelayAssignmentStore['activateControl']>().mockReturnValueOnce(stalled.promise)
+    )
+    const first = h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    const queued = new FakeSocket()
+    const second = h.activate(queued as unknown as WebSocket, identity, null, 1, false, 1)
+    await Promise.resolve()
+    await Promise.resolve()
+    queued.readyState = queued.CLOSED
+    vi.advanceTimersByTime(30_000)
+    expect(queued.close).toHaveBeenCalledWith(
+      RELAY_CLOSE_CODE.LIMIT_EXCEEDED,
+      'control activation queue stalled'
+    )
+    expectRefusal(h.observer, null, 'host closed while queued')
+    stalled.resolve('control:production-gce-c3:1')
+    await Promise.all([first, second])
+  })
+
+  it('does not log a control that was wired', async () => {
+    const h = createRegistry(vi.fn().mockResolvedValue('control:production-gce-c3:1'))
+    await h.activate(new FakeSocket() as unknown as WebSocket, identity, null, 1, false, 1)
+    expect(h.observer.recordPostProofClose).not.toHaveBeenCalled()
+    expect(refusedLines()).toEqual([])
+  })
+})
diff --git a/cloud/apps/relay/src/host-session-registry.ts b/cloud/apps/relay/src/host-session-registry.ts
index 4bbbf896830..6bf30e9a60d 100644
--- a/cloud/apps/relay/src/host-session-registry.ts
+++ b/cloud/apps/relay/src/host-session-registry.ts
@@ -35,9 +35,15 @@ import type { CellAdmitMode, CellReserveBook } from './cell-reserve-book.js'
 import type { DemoteRequest, ReserveOutcome, ReserveRequest } from './cell-reserve-contract.js'
 import { CellSeatLog, type CellSeatChange, type CellSeatFeedPage } from './cell-seat-log.js'
 import { isRelayDatabaseTransientError } from './database.js'
+import { printableCloseReason } from './control-close-reason-text.js'
 import { ControlRenewalBatch } from './control-renewal-batch.js'
 import { RelayCredentialStore, type CredentialReservation } from './credential-store.js'
 import { HostCloseReasonMemory } from './host-close-reason-memory.js'
+import {
+  postProofCloseCause,
+  PostProofCloseLog,
+  type PostProofCloseCause
+} from './post-proof-close-log.js'
 import { relayHostLogDigest } from './relay-host-log-digest.js'
 import type { RelayTokenClaims } from './relay-token-verifier.js'
 import {
@@ -52,14 +58,6 @@ import type { PendingHostDataReservation } from './relay-connection-ledger.js'
 import { closeRelayWebSocket } from './relay-websocket-close.js'
 import { ProcessQueuedByteBudget, wireSplice } from './splice-forwarder.js'
 
-// Peer-supplied close reasons are logged; keep them printable and short.
-function printableCloseReason(reason: Buffer | string): string {
-  return reason
-    .toString()
-    .replace(/[^\x20-\x7e]/g, '')
-    .slice(0, 80)
-}
-
 type VerifyRelayToken = (token: string) => Promise<RelayTokenClaims | null>
 type HostState = 'proving' | 'active' | 'orphaned' | 'drain-only' | 'closed'
 
@@ -299,6 +297,7 @@ export class HostSessionRegistry {
   // draining" is not the same question as "this host has been told to leave".
   private readonly drainSentHosts = new Set<string>()
   private readonly seatLog: CellSeatLog
+  private readonly postProofCloses: PostProofCloseLog
   // Seat key -> the demoted control socket. Its own set, not drainSentHosts: it ends with
   // that socket (close, rebind or a new join), so a later booking here is a fresh seat.
   private readonly demotedSeats = new Map<string, WebSocket>()
@@ -442,6 +441,7 @@ export class HostSessionRegistry {
     private readonly reserveAdmission?: CellReserveAdmission
   ) {
     this.seatLog = new CellSeatLog(undefined, now)
+    this.postProofCloses = new PostProofCloseLog(observer)
   }
 
   // Reserve mode is only ever a cell's, and only while its applied switch says so.
@@ -1627,9 +1627,15 @@ export class HostSessionRegistry {
     // Present when the hello was admitted from memory: no database registration.
     reserved?: { reservedBy?: string }
   ): Promise<void> {
+    const refused = { relayHostId: identity.relayHostId, generation, appVersion }
     const release = this.beginIdleWork(identity.relayHostId)
     if (!release) {
-      socket.close(RELAY_CLOSE_CODE.WRONG_CELL, 'idle cutover in progress')
+      this.refuseProvenControl(
+        socket,
+        refused,
+        RELAY_CLOSE_CODE.WRONG_CELL,
+        'idle cutover in progress'
+      )
       return Promise.resolve()
     }
     const key = this.key(identity.sub, identity.relayHostId)
@@ -1639,16 +1645,36 @@ export class HostSessionRegistry {
     let queueWaitExpired = false
     const queueWaitTimer = setTimeout(() => {
       queueWaitExpired = true
-      socket.close(RELAY_CLOSE_CODE.LIMIT_EXCEEDED, 'control activation queue stalled')
+      this.refuseProvenControl(
+        socket,
+        refused,
+        RELAY_CLOSE_CODE.LIMIT_EXCEEDED,
+        'control activation queue stalled',
+        undefined,
+        'host closed while queued'
+      )
     }, ACTIVATION_QUEUE_WAIT_MS)
     queueWaitTimer.unref?.()
     const activation = previous
       .catch(() => undefined)
       .then(async () => {
         clearTimeout(queueWaitTimer)
-        if (queueWaitExpired || socket.readyState !== socket.OPEN) return
+        if (queueWaitExpired) return
+        if (socket.readyState !== socket.OPEN) {
+          this.postProofCloses.record({
+            ...refused,
+            code: null,
+            reason: 'host closed while queued'
+          })
+          return
+        }
         if ((this.sessions.get(key) ?? null) !== existing) {
-          socket.close(RELAY_CLOSE_CODE.PEER_DROPPED, 'control activation superseded')
+          this.refuseProvenControl(
+            socket,
+            refused,
+            RELAY_CLOSE_CODE.PEER_DROPPED,
+            'control activation superseded'
+          )
           return
         }
         await this.activateCurrent(
@@ -1683,6 +1709,7 @@ export class HostSessionRegistry {
     connectionInclusionWatermark?: number,
     reserved?: { reservedBy?: string }
   ): Promise<void> {
+    const refused = { relayHostId: identity.relayHostId, generation, appVersion }
     let controlActivityId: string | null = null
     // Admitted from memory, but the cell left reserve mode before the proof landed: lease now.
     if (this.config.role === 'cell' && !(reserved && this.reserveMode())) {
@@ -1704,7 +1731,7 @@ export class HostSessionRegistry {
           { userId: identity.sub, relayHostId: identity.relayHostId },
           { cellId: this.config.cellId, assignmentEpoch }
         )
-      } catch {
+      } catch (error) {
         // A failure after activateControl succeeded must not strand the
         // acquired control activity until lease expiry.
         if (controlActivityId) {
@@ -1713,7 +1740,13 @@ export class HostSessionRegistry {
             controlActivityId
           )
         }
-        socket.close(RELAY_CLOSE_CODE.WRONG_CELL, 'assignment changed during host proof')
+        this.refuseProvenControl(
+          socket,
+          refused,
+          RELAY_CLOSE_CODE.WRONG_CELL,
+          'assignment changed during host proof',
+          postProofCloseCause(error, isRelayDatabaseTransientError)
+        )
         return
       }
     }
@@ -1725,7 +1758,13 @@ export class HostSessionRegistry {
         )
       }
       if (socket.readyState === socket.OPEN) {
-        socket.close(RELAY_CLOSE_CODE.DRAINING, 'relay draining')
+        this.refuseProvenControl(socket, refused, RELAY_CLOSE_CODE.DRAINING, 'relay draining')
+      } else {
+        this.postProofCloses.record({
+          ...refused,
+          code: null,
+          reason: 'host closed during activation'
+        })
       }
       return
     }
@@ -1828,6 +1867,22 @@ export class HostSessionRegistry {
     this.appendSeatChange(session, 'join', undefined, reserved?.reservedBy)
   }
 
+  private refuseProvenControl(
+    socket: WebSocket,
+    refused: { relayHostId: string; generation: number; appVersion: string },
+    code: number,
+    reason: string,
+    cause?: PostProofCloseCause,
+    hungUpReason = 'host closed during activation'
+  ): void {
+    // A host that already hung up got no close frame from us; log what happened instead.
+    const open = socket.readyState === socket.OPEN
+    socket.close(code, reason)
+    this.postProofCloses.record(
+      open ? { ...refused, code, reason, cause } : { ...refused, code: null, reason: hungUpReason }
+    )
+  }
+
   seatFeed(sinceSeq: number | null): CellSeatFeedPage {
     return { ...this.seatLog.read(sinceSeq), seats: this.seatLog.seatCount() }
   }
diff --git a/cloud/apps/relay/src/post-proof-close-log.test.ts b/cloud/apps/relay/src/post-proof-close-log.test.ts
new file mode 100644
index 00000000000..6113c8d72a8
--- /dev/null
+++ b/cloud/apps/relay/src/post-proof-close-log.test.ts
@@ -0,0 +1,63 @@
+import { describe, expect, it, vi } from 'vitest'
+import { POST_PROOF_CLOSE_LOG_WINDOW_MS, PostProofCloseLog } from './post-proof-close-log.js'
+
+const close = {
+  relayHostId: 'abcdefghijklmnop',
+  generation: 7,
+  appVersion: '1.4.150',
+  code: 4409,
+  reason: 'assignment changed during host proof',
+  cause: 'wrong_assignment' as const
+}
+
+function createLog() {
+  const lines: string[] = []
+  const scheduled: Array<{ callback: () => void; delayMs: number }> = []
+  const observer = {
+    recordAuth: vi.fn(),
+    recordForwardedBytes: vi.fn(),
+    recordHttp: vi.fn(),
+    recordReconnect: vi.fn(),
+    recordSql: vi.fn(),
+    recordPostProofClose: vi.fn()
+  }
+  const log = new PostProofCloseLog(
+    observer,
+    (line) => lines.push(line),
+    (callback, delayMs) => {
+      scheduled.push({ callback, delayMs })
+      return () => undefined
+    }
+  )
+  return { log, lines, scheduled, observer }
+}
+
+describe('post-proof close log', () => {
+  it('counts every close but writes one line per reason and cause per window', () => {
+    const { log, lines, scheduled, observer } = createLog()
+    for (let index = 0; index < 1_000; index++) log.record({ ...close, generation: index })
+    log.record({ ...close, cause: 'database_transient' })
+    log.record({ ...close, code: 4400, reason: 'relay draining', cause: undefined })
+
+    expect(observer.recordPostProofClose).toHaveBeenCalledTimes(1_002)
+    expect(lines).toHaveLength(3)
+    expect(scheduled.map((entry) => entry.delayMs)).toEqual(
+      Array.from({ length: 3 }, () => POST_PROOF_CLOSE_LOG_WINDOW_MS)
+    )
+
+    for (const { callback } of scheduled) callback()
+    // Only the window that held closes back writes a closing line, naming the latest.
+    expect(lines).toHaveLength(4)
+    expect(lines[3]).toContain('gen=999')
+    expect(lines[3]).toContain('suppressed=999')
+  })
+
+  it('names the host by digest and keeps peer-supplied versions printable', () => {
+    const { log, lines } = createLog()
+    log.record({ ...close, appVersion: '1.4.150\n\u0007injected' })
+    expect(lines[0]).toMatch(
+      /^\[orca-relay\] control refused after proof host=\S+ gen=7 app="1\.4\.150injected" code=4409 reason="assignment changed during host proof" cause=wrong_assignment$/
+    )
+    expect(lines[0]).not.toContain(close.relayHostId)
+  })
+})
diff --git a/cloud/apps/relay/src/post-proof-close-log.ts b/cloud/apps/relay/src/post-proof-close-log.ts
new file mode 100644
index 00000000000..8385509309d
--- /dev/null
+++ b/cloud/apps/relay/src/post-proof-close-log.ts
@@ -0,0 +1,65 @@
+import { AssignmentRejectionLogWindow } from './assignment-rejection-log-window.js'
+import { printableCloseReason } from './control-close-reason-text.js'
+import { relayHostLogDigest } from './relay-host-log-digest.js'
+import type { RelayRuntimeObserver } from './relay-observability.js'
+
+// A looping host hits a post-proof close about once a second; per reason and
+// cause, one line opens the window and one closing line carries the rest.
+export const POST_PROOF_CLOSE_LOG_WINDOW_MS = 60_000
+
+// Why the assignment check failed: the close reason alone cannot tell a moved
+// assignment from a database timeout. Never the raw message (pg errors carry URLs).
+export type PostProofCloseCause = 'wrong_assignment' | 'database_transient' | 'error'
+
+export type PostProofClose = {
+  relayHostId: string
+  generation: number
+  appVersion: string
+  // Null when the host hung up itself: the cell sent no close frame.
+  code: number | null
+  reason: string
+  cause?: PostProofCloseCause
+}
+
+// Controls closed between host proof and wiring never reach the 'control closed' listener.
+export class PostProofCloseLog {
+  private readonly window: AssignmentRejectionLogWindow<PostProofClose>
+
+  constructor(
+    private readonly observer: RelayRuntimeObserver,
+    private readonly warn: (line: string) => void = (line) => console.warn(line),
+    schedule?: (callback: () => void, delayMs: number) => () => void
+  ) {
+    this.window = new AssignmentRejectionLogWindow<PostProofClose>({
+      windowMs: POST_PROOF_CLOSE_LOG_WINDOW_MS,
+      onWindowClosed: ({ suppressed, sample }) => this.warn(formatLine(sample, suppressed)),
+      schedule
+    })
+  }
+
+  record(close: PostProofClose): void {
+    this.observer.recordPostProofClose?.(close.reason)
+    if (!this.window.admit(`${close.reason}:${close.cause ?? ''}`, close)) return
+    this.warn(formatLine(close, 0))
+  }
+}
+
+export function postProofCloseCause(
+  error: unknown,
+  isTransient: (error: unknown) => boolean
+): PostProofCloseCause {
+  if (error instanceof Error && error.message === 'wrong_assignment') return 'wrong_assignment'
+  return isTransient(error) ? 'database_transient' : 'error'
+}
+
+function formatLine(close: PostProofClose, suppressed: number): string {
+  return (
+    `[orca-relay] control refused after proof host=${relayHostLogDigest(close.relayHostId)}` +
+    ` gen=${close.generation}` +
+    ` app=${JSON.stringify(printableCloseReason(close.appVersion))}` +
+    ` code=${close.code ?? 'none'} reason=${JSON.stringify(close.reason)}` +
+    (close.cause ? ` cause=${close.cause}` : '') +
+    // Closing line only: how many more closes the window held back; the fields name the latest.
+    (suppressed > 0 ? ` suppressed=${suppressed}` : '')
+  )
+}
diff --git a/cloud/apps/relay/src/relay-observability.test.ts b/cloud/apps/relay/src/relay-observability.test.ts
index 8e0e209cdf8..bb4ae848383 100644
--- a/cloud/apps/relay/src/relay-observability.test.ts
+++ b/cloud/apps/relay/src/relay-observability.test.ts
@@ -508,6 +508,8 @@ describe('relay observability', () => {
     observability.recordControlClose(1006)
     observability.recordControlClose(1006)
     observability.recordControlClose(4402)
+    observability.recordPostProofClose('relay draining')
+    observability.recordPostProofClose('relay draining')
     observability.recordSpliceClose('host-oversize-frame')
     observability.recordSpliceClose('queue-limit')
     observability.recordClientAcceptAbandoned('activity', 14_250.4)
@@ -518,12 +520,14 @@ describe('relay observability', () => {
 
     expect(entries[0]).toMatchObject({
       controlClosesByCodeDelta: { 1006: 2, 4402: 1 },
+      postProofClosesByReasonDelta: { 'relay draining': 2 },
       spliceClosesByTriggerDelta: { 'host-oversize-frame': 1, 'queue-limit': 1 },
       clientAcceptsAbandonedByStageDelta: { activity: 2, credential: 1 },
       clientAcceptAbandonedMsMax: 14_250.4
     })
     expect(entries[1]).toMatchObject({
       controlClosesByCodeDelta: {},
+      postProofClosesByReasonDelta: {},
       spliceClosesByTriggerDelta: {},
       clientAcceptsAbandonedByStageDelta: {},
       clientAcceptAbandonedMsMax: 0
diff --git a/cloud/apps/relay/src/relay-observability.ts b/cloud/apps/relay/src/relay-observability.ts
index 6f43248b445..2e976a1e694 100644
--- a/cloud/apps/relay/src/relay-observability.ts
+++ b/cloud/apps/relay/src/relay-observability.ts
@@ -101,6 +101,7 @@ export interface RelayRuntimeObserver {
     fallback: boolean
   }): void
   recordControlClose?(code: number): void
+  recordPostProofClose?(reason: string): void
   recordSpliceClose?(trigger: string): void
   recordClientAcceptAbandoned?(stage: RelayClientAcceptStage, elapsedMs: number): void
   recordClientAcceptCompleted?(sample: RelayClientAcceptSample): void
@@ -200,6 +201,7 @@ type RelayMetricDeltas = {
   regionFallbacks: Record<string, number>
   unavailableRegions: Record<string, number>
   controlClosesByCode: Record<string, number>
+  postProofClosesByReason: Record<string, number>
   spliceClosesByTrigger: Record<string, number>
   clientAcceptsAbandonedByStage: Record<string, number>
   clientAcceptAbandonedMsMax: number
@@ -288,6 +290,7 @@ const emptyDeltas = (): RelayMetricDeltas => ({
   regionFallbacks: {},
   unavailableRegions: {},
   controlClosesByCode: {},
+  postProofClosesByReason: {},
   spliceClosesByTrigger: {},
   clientAcceptsAbandonedByStage: {},
   clientAcceptAbandonedMsMax: 0,
@@ -529,6 +532,10 @@ export class RelayObservability implements RelayRuntimeObserver {
     this.deltas.controlClosesByCode[key] = (this.deltas.controlClosesByCode[key] ?? 0) + 1
   }
 
+  recordPostProofClose(reason: string): void {
+    increment(this.deltas.postProofClosesByReason, reason)
+  }
+
   recordSpliceClose(trigger: string): void {
     this.deltas.spliceClosesByTrigger[trigger] =
       (this.deltas.spliceClosesByTrigger[trigger] ?? 0) + 1
@@ -670,6 +677,8 @@ export class RelayObservability implements RelayRuntimeObserver {
       regionFallbacksDelta: deltas.regionFallbacks,
       unavailableRegionsDelta: deltas.unavailableRegions,
       controlClosesByCodeDelta: deltas.controlClosesByCode,
+      // Closes after a host proof but before its control was wired; none is in the line above.
+      postProofClosesByReasonDelta: deltas.postProofClosesByReason,
       spliceClosesByTriggerDelta: deltas.spliceClosesByTrigger,
       clientAcceptsAbandonedByStageDelta: deltas.clientAcceptsAbandonedByStage,
       clientAcceptAbandonedMsMax: roundMs(deltas.clientAcceptAbandonedMsMax),