diff --git a/src/codex-primer-alignment.test.ts b/src/codex-primer-alignment.test.ts
index 58a5152..59dc90e 100644
--- a/src/codex-primer-alignment.test.ts
+++ b/src/codex-primer-alignment.test.ts
@@ -1,33 +1,48 @@
-import { describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it } from 'vitest';
 
-import { shouldHoldCodexForPrimerAlignment } from './codex-primer-alignment.js';
+import {
+  ALIGNMENT_NOTICE_KEY,
+  beginPrimerAnchor,
+  endPrimerAnchor,
+  isAlignmentSlot,
+  isPrimerAnchoring,
+  shouldHoldCodexForPrimerAlignment,
+} from './codex-primer-alignment.js';
 
 const KST_OFFSET_MS = 9 * 60 * 60 * 1000;
 
-/** Build an epoch-ms value that reads as the given KST wall-clock hour/min. */
-function atKst(hour: number, minute = 0): number {
-  // shouldHold reads `new Date(ms + KST_OFFSET_MS).getUTCHours()`, so picking
-  // a UTC instant equal to the desired KST clock and subtracting the offset
-  // reproduces that KST hour exactly.
-  const kstShifted = Date.UTC(2026, 5, 10, hour, minute, 0);
+/** Build an epoch-ms value that reads as the given KST wall-clock time. */
+function atKst(hour: number, minute = 0, second = 0): number {
+  // shouldHold reads KST via `new Date(ms + KST_OFFSET_MS)`, so picking a UTC
+  // instant equal to the desired KST clock and subtracting the offset
+  // reproduces that KST time exactly.
+  const kstShifted = Date.UTC(2026, 5, 10, hour, minute, second);
   return kstShifted - KST_OFFSET_MS;
 }
 
-describe('shouldHoldCodexForPrimerAlignment', () => {
+afterEach(() => {
+  // The anchor flag is module-global; never leak it across tests.
+  endPrimerAnchor();
+});
+
+describe('shouldHoldCodexForPrimerAlignment — dawn window', () => {
   it('holds across the full 03:00–08:00 KST dawn window', () => {
     expect(shouldHoldCodexForPrimerAlignment(atKst(3, 0))).toBe(true);
     expect(shouldHoldCodexForPrimerAlignment(atKst(5, 30))).toBe(true);
-    expect(shouldHoldCodexForPrimerAlignment(atKst(7, 59))).toBe(true);
+    expect(shouldHoldCodexForPrimerAlignment(atKst(7, 59, 59))).toBe(true);
   });
 
-  it('does not hold at/after the 08:00 primer slot', () => {
-    // 08:00 is the primer slot itself — it must run, not be held.
-    expect(shouldHoldCodexForPrimerAlignment(atKst(8, 0))).toBe(false);
-    expect(shouldHoldCodexForPrimerAlignment(atKst(8, 1))).toBe(false);
+  it('keeps holding through the post-08:00 grace, then releases', () => {
+    // Grace bridges the gap between the 08:00 boundary lapsing and the primer
+    // setting its anchor flag, so a consumer poll at 08:00:00 cannot slip in.
+    expect(shouldHoldCodexForPrimerAlignment(atKst(8, 0, 0))).toBe(true);
+    expect(shouldHoldCodexForPrimerAlignment(atKst(8, 2, 59))).toBe(true);
+    expect(shouldHoldCodexForPrimerAlignment(atKst(8, 3, 1))).toBe(false);
+    expect(shouldHoldCodexForPrimerAlignment(atKst(9, 0))).toBe(false);
   });
 
   it('does not hold before the dawn window', () => {
-    expect(shouldHoldCodexForPrimerAlignment(atKst(2, 59))).toBe(false);
+    expect(shouldHoldCodexForPrimerAlignment(atKst(2, 59, 59))).toBe(false);
     expect(shouldHoldCodexForPrimerAlignment(atKst(0, 0))).toBe(false);
   });
 
@@ -37,3 +52,39 @@ describe('shouldHoldCodexForPrimerAlignment', () => {
     }
   });
 });
+
+describe('shouldHoldCodexForPrimerAlignment — anchor lock', () => {
+  it('holds while the primer is anchoring, even outside the dawn window', () => {
+    // Closes the 08:00 race: once the primer begins, all other Codex consumers
+    // are held until it finishes — regardless of the clock.
+    const noon = atKst(13, 0);
+    expect(shouldHoldCodexForPrimerAlignment(noon)).toBe(false);
+    beginPrimerAnchor();
+    expect(isPrimerAnchoring()).toBe(true);
+    expect(shouldHoldCodexForPrimerAlignment(noon)).toBe(true);
+    endPrimerAnchor();
+    expect(isPrimerAnchoring()).toBe(false);
+    expect(shouldHoldCodexForPrimerAlignment(noon)).toBe(false);
+  });
+});
+
+describe('isAlignmentSlot', () => {
+  it('is true only at the 08:00 KST hour', () => {
+    expect(isAlignmentSlot(atKst(8, 0))).toBe(true);
+    expect(isAlignmentSlot(atKst(8, 59))).toBe(true);
+    expect(isAlignmentSlot(atKst(7, 59))).toBe(false);
+    expect(isAlignmentSlot(atKst(13, 0))).toBe(false);
+  });
+});
+
+describe('ALIGNMENT_NOTICE_KEY', () => {
+  it('is stable within a KST day and changes across days', () => {
+    expect(ALIGNMENT_NOTICE_KEY(atKst(3, 0))).toBe(
+      ALIGNMENT_NOTICE_KEY(atKst(7, 59)),
+    );
+    const dayTwo = atKst(3, 0) + 24 * 60 * 60 * 1000;
+    expect(ALIGNMENT_NOTICE_KEY(dayTwo)).not.toBe(
+      ALIGNMENT_NOTICE_KEY(atKst(3, 0)),
+    );
+  });
+});
diff --git a/src/codex-primer-alignment.ts b/src/codex-primer-alignment.ts
index 5621166..6acc27c 100644
--- a/src/codex-primer-alignment.ts
+++ b/src/codex-primer-alignment.ts
@@ -1,42 +1,105 @@
 /**
- * Codex usage-primer alignment — narrow pre-08:00 quiet window.
+ * Codex usage-primer alignment — narrow pre-08:00 quiet window + anchor lock.
  *
  * The Codex 5h usage limit is a FIXED window: it opens on the first Codex
  * request after the previous window expires and resets exactly 5h later
- * (verified empirically — usedPercent climbs while resetsAt stays put). To pin
- * the daily reset to 13:00 KST, the 08:00 KST primer must be the *first* Codex
+ * (verified live — usedPercent climbs while resetsAt stays put). To pin the
+ * daily reset to 13:00 KST, the 08:00 KST primer must be the *first* Codex
  * request of a fresh window. Codex is otherwise used almost continuously
- * (reviewers/arbiters in every paired room, codex-owner rooms, warm-up), so
- * 08:00 normally lands mid-window and the reset drifts (e.g. observed 15:47).
+ * (reviewers/arbiters every paired room, codex-owner rooms, warm-up), so 08:00
+ * normally lands mid-window and the reset drifts (observed 15:47).
  *
- * Fix: hold all non-primer Codex execution during the 5 hours before the 08:00
- * slot (03:00–08:00 KST). One Codex window is at most 5h, so whatever opened
- * before 03:00 has expired by 08:00 — leaving the 08:00 primer to anchor a clean
- * window → 13:00 reset. This is the narrow, single-slot version chosen by the
- * user: ONLY the pre-08:00 dawn window holds; the other slots (13/18/23) and all
- * daytime hours pass through untouched.
+ * Two mechanisms, both time-based / in-process (no I/O, no reliance on the
+ * unreliable live usage figures):
  *
- * Time-based and I/O-free so every Codex path (gating, queue, warm-up) can share
- * it without import cycles or depending on the unreliable live usage figures.
+ *  1. Dawn quiet window [03:00, 08:00) KST. One Codex window is at most 5h, so
+ *     anything opened before 03:00 has expired by 08:00 — held requests can't
+ *     keep a stray window alive into the slot.
+ *
+ *  2. Anchor lock. The 08:00 primer sets an in-process flag for the duration of
+ *     its own Codex call (beginPrimerAnchor/endPrimerAnchor). Held consumers
+ *     stay held while the flag is set, so the primer wins the first-request race
+ *     even though the dawn window's clock boundary lapses at exactly 08:00. A
+ *     short post-slot grace bridges the few ms between the 08:00 boundary lapse
+ *     and the primer firing, so a consumer poll in that gap can't slip in first.
+ *
+ * Narrow by design (the broad all-slots version was previously reverted): only
+ * the 08:00 alignment slot holds; the other slots (13/18/23) and all daytime
+ * hours pass through untouched.
  */
 
 const KST_OFFSET_MS = 9 * 60 * 60 * 1000;
+const HOUR_MS = 60 * 60 * 1000;
 
-// Quiet window before the 08:00 KST primer slot. 5h = one full Codex window, so
-// any window opened before 03:00 is guaranteed expired by 08:00.
-export const DAWN_QUIET_START_HOUR_KST = 3;
-export const DAWN_QUIET_END_HOUR_KST = 8;
+// Dawn quiet window before the 08:00 KST primer slot. 5h = one full Codex
+// window, so any window opened before 03:00 is guaranteed expired by 08:00.
+export const DAWN_QUIET_START_MS = 3 * HOUR_MS;
+export const DAWN_QUIET_END_MS = 8 * HOUR_MS;
+
+// Grace after the 08:00 boundary during which consumers stay held even though
+// the dawn window technically lapsed — covers the gap between the boundary and
+// the primer setting its anchor flag (incl. event-loop lag at the slot).
+export const PRIMER_SLOT_GRACE_MS = 3 * 60 * 1000;
+
+/** The KST clock hour the primer aligns to (08:00). */
+export const ALIGNMENT_SLOT_HOUR_KST = 8;
+
+let primerAnchorActive = false;
+
+/** Mark the 08:00 alignment primer as in-flight so consumers stay held. */
+export function beginPrimerAnchor(): void {
+  primerAnchorActive = true;
+}
+
+/** Clear the anchor flag once the alignment primer's Codex call has finished. */
+export function endPrimerAnchor(): void {
+  primerAnchorActive = false;
+}
+
+/** Whether the 08:00 alignment primer is currently anchoring the window. */
+export function isPrimerAnchoring(): boolean {
+  return primerAnchorActive;
+}
+
+/** Milliseconds since KST midnight for the given instant. */
+function kstMsOfDay(nowMs: number): number {
+  const shifted = new Date(nowMs + KST_OFFSET_MS);
+  return (
+    ((shifted.getUTCHours() * 60 + shifted.getUTCMinutes()) * 60 +
+      shifted.getUTCSeconds()) *
+      1000 +
+    shifted.getUTCMilliseconds()
+  );
+}
+
+/** Whether the given instant is the 08:00 KST alignment slot (hour granularity). */
+export function isAlignmentSlot(nowMs: number = Date.now()): boolean {
+  return (
+    new Date(nowMs + KST_OFFSET_MS).getUTCHours() === ALIGNMENT_SLOT_HOUR_KST
+  );
+}
+
+/**
+ * A stable key identifying the current dawn hold window (its KST calendar date),
+ * used to dedupe the "please wait" notice to at most once per room per window.
+ */
+export function ALIGNMENT_NOTICE_KEY(nowMs: number = Date.now()): string {
+  return new Date(nowMs + KST_OFFSET_MS).toISOString().slice(0, 10);
+}
 
 /**
  * Whether non-primer Codex execution should be held right now so the 08:00
- * fixed-slot primer is the window-anchoring first request. Holds only during the
- * 03:00–08:00 KST dawn window; every other hour returns false.
+ * fixed-slot primer is the window-anchoring first request. Holds while the
+ * alignment primer is anchoring, and during [03:00, 08:00 + grace) KST; every
+ * other hour returns false.
  */
 export function shouldHoldCodexForPrimerAlignment(
   nowMs: number = Date.now(),
 ): boolean {
-  const kstHour = new Date(nowMs + KST_OFFSET_MS).getUTCHours();
+  if (primerAnchorActive) return true;
+  const msOfDay = kstMsOfDay(nowMs);
   return (
-    kstHour >= DAWN_QUIET_START_HOUR_KST && kstHour < DAWN_QUIET_END_HOUR_KST
+    msOfDay >= DAWN_QUIET_START_MS &&
+    msOfDay < DAWN_QUIET_END_MS + PRIMER_SLOT_GRACE_MS
   );
 }
diff --git a/src/message-runtime-gating.test.ts b/src/message-runtime-gating.test.ts
index 3768541..95f71ca 100644
--- a/src/message-runtime-gating.test.ts
+++ b/src/message-runtime-gating.test.ts
@@ -1,19 +1,33 @@
-import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import type { RegisteredGroup } from './types.js';
 
-const { handleSessionCommandMock } = vi.hoisted(() => ({
-  handleSessionCommandMock: vi.fn(),
-}));
+const { handleSessionCommandMock, getEffectiveChannelLeaseMock } = vi.hoisted(
+  () => ({
+    handleSessionCommandMock: vi.fn(),
+    getEffectiveChannelLeaseMock: vi.fn(),
+  }),
+);
 
 vi.mock('./session-commands.js', () => ({
   handleSessionCommand: handleSessionCommandMock,
 }));
 
+vi.mock('./service-routing.js', () => ({
+  getEffectiveChannelLease: getEffectiveChannelLeaseMock,
+}));
+
+import {
+  beginPrimerAnchor,
+  endPrimerAnchor,
+} from './codex-primer-alignment.js';
 import { handleQueuedRunGates } from './message-runtime-gating.js';
 
-describe('message-runtime-gating', () => {
-  const baseArgs = {
-    chatJid: 'room-1',
+function makeArgs(overrides: {
+  chatJid?: string;
+  sendMessage?: () => Promise<void>;
+}) {
+  return {
+    chatJid: overrides.chatJid ?? 'room-1',
     group: {
       folder: 'room-folder',
       name: 'room',
@@ -26,11 +40,25 @@ describe('message-runtime-gating', () => {
     triggerPattern: /^코덱스/,
     timezone: 'Asia/Seoul',
     hasImplicitContinuationWindow: () => false,
-    sessionCommandDeps: {} as never,
+    sessionCommandDeps: {
+      sendMessage: overrides.sendMessage ?? (async () => {}),
+    } as never,
   };
+}
 
+describe('message-runtime-gating', () => {
   beforeEach(() => {
     handleSessionCommandMock.mockReset();
+    getEffectiveChannelLeaseMock.mockReset();
+    // Default: claude owner, no failover → no alignment hold.
+    getEffectiveChannelLeaseMock.mockReturnValue({
+      owner_agent_type: 'claude-code',
+      owner_failover_active: false,
+    });
+  });
+
+  afterEach(() => {
+    endPrimerAnchor();
   });
 
   it('returns session-command results directly when a command is handled', async () => {
@@ -39,16 +67,54 @@ describe('message-runtime-gating', () => {
       success: false,
     });
 
-    const result = await handleQueuedRunGates(baseArgs);
+    const result = await handleQueuedRunGates(makeArgs({}));
 
     expect(result).toEqual({ handled: true, success: false });
   });
 
-  it('falls through when no session command is handled', async () => {
+  it('falls through when no command and the room owner is not on Codex', async () => {
     handleSessionCommandMock.mockResolvedValue({ handled: false });
+    beginPrimerAnchor(); // force the alignment window on, isolate provider check
 
-    const result = await handleQueuedRunGates(baseArgs);
+    const result = await handleQueuedRunGates(makeArgs({}));
 
     expect(result).toEqual({ handled: false });
   });
+
+  it('holds a codex-owner turn during the alignment window and notifies once', async () => {
+    handleSessionCommandMock.mockResolvedValue({ handled: false });
+    getEffectiveChannelLeaseMock.mockReturnValue({
+      owner_agent_type: 'codex',
+      owner_failover_active: false,
+    });
+    beginPrimerAnchor();
+    const sendMessage = vi.fn(async () => {});
+
+    const first = await handleQueuedRunGates(
+      makeArgs({ chatJid: 'room-codex', sendMessage }),
+    );
+    const second = await handleQueuedRunGates(
+      makeArgs({ chatJid: 'room-codex', sendMessage }),
+    );
+
+    expect(first).toEqual({ handled: true, success: true });
+    expect(second).toEqual({ handled: true, success: true });
+    // Notice deduped: sent once across repeated holds in the same window.
+    expect(sendMessage).toHaveBeenCalledTimes(1);
+  });
+
+  it('holds a claude-owner room when global failover routes the owner to Codex', async () => {
+    handleSessionCommandMock.mockResolvedValue({ handled: false });
+    getEffectiveChannelLeaseMock.mockReturnValue({
+      owner_agent_type: 'claude-code',
+      owner_failover_active: true,
+    });
+    beginPrimerAnchor();
+
+    const result = await handleQueuedRunGates(
+      makeArgs({ chatJid: 'room-failover' }),
+    );
+
+    expect(result).toEqual({ handled: true, success: true });
+  });
 });
diff --git a/src/message-runtime-gating.ts b/src/message-runtime-gating.ts
index 29555fd..5a2f56f 100644
--- a/src/message-runtime-gating.ts
+++ b/src/message-runtime-gating.ts
@@ -1,14 +1,29 @@
-import { shouldHoldCodexForPrimerAlignment } from './codex-primer-alignment.js';
+import {
+  ALIGNMENT_NOTICE_KEY,
+  shouldHoldCodexForPrimerAlignment,
+} from './codex-primer-alignment.js';
 import { logger } from './logger.js';
+import { getEffectiveChannelLease } from './service-routing.js';
 import {
   handleSessionCommand,
   type SessionCommandDeps,
 } from './session-commands.js';
-import type { AgentType, NewMessage, RegisteredGroup } from './types.js';
+import type { NewMessage, RegisteredGroup } from './types.js';
 
 const CODEX_ALIGNMENT_AUTO_REPLY =
   '코덱스 5시간 한도 리셋을 매일 오후 1시에 고정하기 위해, 새벽 03~08시 구간은 정렬용으로 잠시 대기합니다. 08시 이후 다시 보내주세요.';
 
+// Per-room dedupe so a held owner room gets the wait notice at most once per
+// dawn hold window, instead of on every re-poll while it stays held.
+const lastAlignmentNoticeKeyByChat = new Map<string, string>();
+
+function shouldSendAlignmentNotice(chatJid: string): boolean {
+  const key = ALIGNMENT_NOTICE_KEY();
+  if (lastAlignmentNoticeKeyByChat.get(chatJid) === key) return false;
+  lastAlignmentNoticeKeyByChat.set(chatJid, key);
+  return true;
+}
+
 export async function handleQueuedRunGates(args: {
   chatJid: string;
   group: RegisteredGroup;
@@ -37,12 +52,17 @@ export async function handleQueuedRunGates(args: {
 
   // ── Codex primer-alignment hold (codex-owner rooms) ──
   // Reviewer/arbiter Codex turns are held at their own dispatch site; here we
-  // cover rooms whose *owner* runs on Codex, so a fresh human turn doesn't
-  // anchor the shared window before the 08:00 fixed-slot primer. Keyed on the
-  // room's configured owner agent type. Only fires inside the 03:00–08:00 KST
-  // dawn window, so daytime turns are never delayed.
-  const ownerAgentType: AgentType = args.group.agentType ?? 'claude-code';
-  if (ownerAgentType === 'codex' && shouldHoldCodexForPrimerAlignment()) {
+  // cover rooms whose *owner* effectively runs on Codex, so a fresh human turn
+  // doesn't anchor the shared window before the 08:00 fixed-slot primer. Keyed
+  // on the EFFECTIVE owner backend — configured codex owner OR a global-failover
+  // override to Codex — not just the static group agent type. Only fires inside
+  // the dawn hold window, so daytime turns are never delayed. Returning handled
+  // without advancing the message cursor lets the turn resume on the next poll
+  // exactly once after the window clears.
+  const lease = getEffectiveChannelLease(args.chatJid);
+  const ownerRunsCodex =
+    lease.owner_agent_type === 'codex' || lease.owner_failover_active === true;
+  if (ownerRunsCodex && shouldHoldCodexForPrimerAlignment()) {
     logger.info(
       {
         chatJid: args.chatJid,
@@ -51,10 +71,12 @@ export async function handleQueuedRunGates(args: {
       },
       'Holding fresh Codex owner turn — keeping 08:00 primer slot as first request',
     );
-    try {
-      await args.sessionCommandDeps.sendMessage(CODEX_ALIGNMENT_AUTO_REPLY);
-    } catch (err) {
-      logger.warn({ err }, 'Failed to send Codex alignment notice');
+    if (shouldSendAlignmentNotice(args.chatJid)) {
+      try {
+        await args.sessionCommandDeps.sendMessage(CODEX_ALIGNMENT_AUTO_REPLY);
+      } catch (err) {
+        logger.warn({ err }, 'Failed to send Codex alignment notice');
+      }
     }
     return { handled: true, success: true };
   }
diff --git a/src/usage-primer.ts b/src/usage-primer.ts
index cee20c0..aa34431 100644
--- a/src/usage-primer.ts
+++ b/src/usage-primer.ts
@@ -2,6 +2,11 @@ import { spawn } from 'child_process';
 import fs from 'fs';
 import path from 'path';
 
+import {
+  beginPrimerAnchor,
+  endPrimerAnchor,
+  isAlignmentSlot,
+} from './codex-primer-alignment.js';
 import { CODEX_WARMUP_CONFIG } from './config.js';
 import { refreshActiveCodexUsage } from './codex-usage-collector.js';
 import { runCodexWarmupCycle } from './codex-warmup.js';
@@ -149,6 +154,12 @@ async function runClaudePrimerCycle(): Promise<void> {
 }
 
 export async function runCodexPrimerCycle(): Promise<void> {
+  // At the 08:00 alignment slot, hold all other Codex consumers (via the shared
+  // shouldHoldCodexForPrimerAlignment flag) for the duration of this primer's
+  // Codex call, so the primer wins the first-request race that opens the fresh
+  // 5h window. Other slots run without the anchor lock.
+  const anchoring = isAlignmentSlot();
+  if (anchoring) beginPrimerAnchor();
   try {
     // Fire immediately at the slot. There is NO pre-call usage refresh on
     // purpose: forceAttempt fires regardless of usage, so reading usage first
@@ -170,13 +181,12 @@ export async function runCodexPrimerCycle(): Promise<void> {
     );
     logger.info({ result }, 'Codex primer cycle finished');
     // Observability only — runs AFTER the call so it never delays it: refresh
-    // so the newly-anchored reset window shows up in usage data/logs. A slot
-    // may still land while the trailing 5h window is exhausted (records
-    // `failed`); we do not chase the reported reset time, since a trailing
-    // window keeps sliding with later usage.
+    // so the newly-anchored reset window shows up in usage data/logs.
     await refreshActiveCodexUsage();
   } catch (err) {
     logger.warn({ err }, 'Codex primer cycle threw');
+  } finally {
+    if (anchoring) endPrimerAnchor();
   }
 }