diff --git a/src/codex/auth-context.ts b/src/codex/auth-context.ts
index 812cadd22f..ac12ca7081 100644
--- a/src/codex/auth-context.ts
+++ b/src/codex/auth-context.ts
@@ -25,7 +25,9 @@ import { isNativeMainTrafficBlocked, nativeMainStartupGateSnapshot } from "./nat
 import type { NativeMainStartupBlockReason } from "./native-profile-startup";
 import {
   codexQuotaScopeForModel,
+  computeCodexUsageScore,
   getCodexQuotaHealthSnapshot,
+  isEffectiveCodexAccountPinned,
   releaseCodexQuotaProbeLease,
   releaseCodexQuotaScopeProbeLease,
   tryAcquireCodexQuotaProbeLease,
@@ -42,7 +44,7 @@ import { ACCOUNT_GATED_NATIVE_OPENAI_MODELS } from "./catalog/native-models";
 import type { CodexCooldownSource, CodexQuotaScope } from "./routing";
 import { maskAccountId } from "../lib/privacy";
 import { formatErrorResponse } from "../bridge";
-import { getAccountQuota } from "./quota";
+import { CODEX_UNKNOWN_USAGE_SCORE, getAccountQuota } from "./quota";
 import type { CodexAccountMode, OcxConfig, OcxProviderConfig } from "../types";
 import { FORWARD_HEADERS } from "../adapters/openai-responses";
 import { captureConfigGeneration } from "../lib/state-store-sweeper";
@@ -52,6 +54,21 @@ import { extractAccountId } from "../oauth/chatgpt";
 const CODEX_AFFINITY_COMPONENT_MAX_BYTES = 512;
 const CODEX_APP_AFFINITY_KEY = randomBytes(32);
 
+/**
+ * A request-owned bearer cannot inspect the physical main credential for its plan, but cached
+ * WHAM usage is still valid routing evidence for the same logical main account. Score it with
+ * the conservative unknown-plan rule: an unobserved governing window preserves the pin, while
+ * any known weekly/monthly/short value at the threshold releases it through the ordinary Pool
+ * path. This keeps the keyring boundary intact instead of reading auth.json just to classify a
+ * request that already brought its own credential (#3157).
+ */
+function requestOwnedMainPinHasQuotaHeadroom(config: OcxConfig): boolean {
+  const threshold = config.autoSwitchThreshold ?? 80;
+  if (threshold <= 0) return true;
+  const usage = computeCodexUsageScore(getAccountQuota(MAIN_CODEX_ACCOUNT_ID));
+  return usage >= CODEX_UNKNOWN_USAGE_SCORE || usage < threshold;
+}
+
 function boundedCodexAffinityComponent(value: string | null): string | undefined {
   const normalized = value?.trim();
   if (!normalized) return undefined;
@@ -372,6 +389,12 @@ export async function resolveCodexAuthContext(
   const requestScopedMainCredential = options.requestScopedMainCredential === true
     && hasCallerCodexBearer(headers);
   const fixedAccountId = options.accountId;
+  const preserveRequestOwnedMainPin = requestScopedMainCredential
+    && fixedAccountId === undefined
+    && config.activeCodexAccountPinned === MAIN_CODEX_ACCOUNT_ID
+    && isEffectiveCodexAccountPinned(config)
+    && !isCodexAccountPaused(config, MAIN_CODEX_ACCOUNT_ID)
+    && requestOwnedMainPinHasQuotaHeadroom(config);
   if (fixedAccountId !== undefined && options.excludeAccountId !== undefined) {
     throw new Error("Codex auth context cannot select and exclude an account simultaneously");
   }
@@ -425,6 +448,19 @@ export async function resolveCodexAuthContext(
       directSelectionAdmission.release();
     }
   };
+  // Pool discovery excludes request-owned main credentials by design: they must never be folded
+  // into stored-account entitlement, affinity, or persistence state. An effective manual main pin
+  // is the one exception where that exclusion is selection evidence in the opposite direction.
+  // Validate the caller's own gated-model roster before using it, and fall through to a Pool model
+  // detour when it lacks the grant. This branch performs no physical-main credential read.
+  if (preserveRequestOwnedMainPin) {
+    const callerEntitled = !options.modelId
+      || !ACCOUNT_GATED_NATIVE_OPENAI_MODELS.has(options.modelId)
+      || await (
+        options.isDirectCallerEntitledToCodexModel ?? isDirectCallerEntitledToCodexModel
+      )(headers, options.modelId);
+    if (callerEntitled) return { kind: "main", accountId: null };
+  }
   // An explicit namespace binding is stronger than the provider's default mode. It must use the
   // selected stored credential even while the canonical OpenAI provider is globally Direct.
   // A request-owned bearer is deliberately not represented as `main-pool`: Pool account ids own
@@ -473,7 +509,10 @@ export async function resolveCodexAuthContext(
       // it. Retained recovery makes main wholly ineligible so pool routing continues.
       nativeMainSelectionOnly,
       isMainAccountTokenLive: requestScopedMainCredential
-        ? () => false
+        // Main stays excluded from this request's model roster below. This synthetic liveness is
+        // consulted only by shared-state preservation, so a caller-owned pin survives a model
+        // detour without reading or selecting the physical main credential.
+        ? () => preserveRequestOwnedMainPin
         : options.isMainAccountTokenLive,
       modelEligibleAccountIds,
     };
diff --git a/structure/08_openai-provider-tiers.md b/structure/08_openai-provider-tiers.md
index ab15088fb4..d563f4989f 100644
--- a/structure/08_openai-provider-tiers.md
+++ b/structure/08_openai-provider-tiers.md
@@ -108,6 +108,29 @@ pinned account and the effective active account are different questions, and the
 both (`pinned` and `pinnedAccountId`). A surface that marks only the active account loses the pin from
 view exactly when it is doing the most work — suppressing every higher tier.
 
+A keyring-backed Codex request can carry its own forwardable ChatGPT bearer while the provider remains
+in Pool mode. When the effective manual pin is `__main__`, main is not paused, and its cached quota still
+has headroom, auth resolution validates the caller bearer's own gated-model roster and uses that
+request-owned credential before stored-Pool selection. The credential never enters Pool persistence,
+affinity, entitlement cache, or health state, and this decision never reads the physical main credential.
+If the caller lacks the requested model, a stored-account model detour may serve the request without
+clearing the healthy shared main pin. A paused or quota-drained main skips this exception and follows the
+ordinary Pool promotion path.
+
+[Decision Log]
+- 목적과 의도: Keep an explicit healthy main selection from being replaced by an exhausted stored
+  account merely because the client supplied main through a request-owned keyring bearer.
+- 기존 구현 및 제약 조건: Request-owned credentials are deliberately excluded from stored-account
+  entitlement discovery, but shared-state preservation interpreted that exclusion as a dead main login.
+- 검토한 주요 대안: Persist the caller credential, read the physical main token for identity, ignore
+  the manual pin, or validate the caller independently before stored-Pool selection.
+- 선택한 방식: Use only the effective pin, pause state, cached quota, and the caller credential's own
+  gated-model check; synthesize shared-state liveness only while main stays request-ineligible.
+- 다른 대안 대신 이 방식을 선택한 이유: It preserves credential isolation and explicit operator
+  intent without admitting an unentitled model or binding an ephemeral bearer into durable Pool state.
+- 장점, 단점 및 영향: Healthy main pins survive keyring requests and model-only detours; cached quota
+  remains the only proactive drain evidence available without crossing the physical credential boundary.
+
 ```text
 gpt-5.6-sol                         # openai; Pool or Direct follows the provider option
 main/gpt-daybreak-blue-latest       # openai; observed account-native Daybreak, Sol capability metadata
diff --git a/tests/codex-auth-context.test.ts b/tests/codex-auth-context.test.ts
index 93653a3002..9a424f1b32 100644
--- a/tests/codex-auth-context.test.ts
+++ b/tests/codex-auth-context.test.ts
@@ -47,6 +47,7 @@ import {
   handleCodexAuthAPI,
   isAccountNeedsReauth,
   markAccountNeedsReauth,
+  setAccountQuotaFromParsed,
 } from "../src/codex/auth-api";
 import { __resetGuardianState, guardianSweep } from "../src/oauth/token-guardian";
 import {
@@ -1088,6 +1089,91 @@ describe("Codex auth context", () => {
       clearAccountNeedsReauth(MAIN_CODEX_ACCOUNT_ID);
     }
   });
+
+  async function resolveRequestOwnedMainPinCase(options: {
+    mainWeeklyPercent: number;
+    poolWeeklyPercent: number;
+    callerEntitled: boolean;
+  }): Promise<{
+    cfg: OcxConfig;
+    context: Awaited<ReturnType<typeof resolveCodexAuthContext>>;
+    directEntitlementChecks: number;
+  }> {
+    const cfg = config();
+    cfg.accountPoolStrategy = "quota";
+    cfg.autoSwitchThreshold = 90;
+    cfg.activeCodexAccountId = MAIN_CODEX_ACCOUNT_ID;
+    cfg.activeCodexAccountPinned = MAIN_CODEX_ACCOUNT_ID;
+    cfg.codexAccountPriorities = {
+      [MAIN_CODEX_ACCOUNT_ID]: 0,
+      "pool-a": 0,
+    };
+    resetCodexRoutingForManualSelection(MAIN_CODEX_ACCOUNT_ID);
+    saveCodexAccountCredential("pool-a", {
+      accessToken: "pool-token",
+      refreshToken: "pool-refresh",
+      expiresAt: Date.now() + 5 * 60_000,
+      chatgptAccountId: "pool-account",
+    });
+    setAccountQuotaFromParsed(MAIN_CODEX_ACCOUNT_ID, { weeklyPercent: options.mainWeeklyPercent });
+    setAccountQuotaFromParsed("pool-a", { weeklyPercent: options.poolWeeklyPercent });
+    let directEntitlementChecks = 0;
+    const context = await resolveCodexAuthContext(new Headers({
+      authorization: "Bearer caller-keyring-token",
+      "chatgpt-account-id": "caller-keyring-account",
+    }), cfg, "pool", {
+      requestScopedMainCredential: true,
+      modelId: "gpt-5.6-sol",
+      isDirectCallerEntitledToCodexModel: async () => {
+        directEntitlementChecks += 1;
+        return options.callerEntitled;
+      },
+      resolveCodexModelEntitlements: async () => ({
+        modelsByAccount: new Map([["pool-a", new Set(["gpt-5.6-sol"])]]),
+        clientVersionByAccount: new Map([["pool-a", "0.150.1"]]),
+        confirmedAccountIds: new Set(["pool-a"]),
+        credentialIdentities: new Map([["pool-a", "pool:1:pool-account"]]),
+      }),
+    });
+    return { cfg, context, directEntitlementChecks };
+  }
+
+  test("a healthy manual main pin keeps the validated caller bearer ahead of an exhausted pool account (#3157)", async () => {
+    const { cfg, context, directEntitlementChecks } = await resolveRequestOwnedMainPinCase({
+      mainWeeklyPercent: 16,
+      poolWeeklyPercent: 100,
+      callerEntitled: true,
+    });
+    expect(context).toMatchObject({ kind: "main", accountId: null });
+    expect(directEntitlementChecks).toBe(1);
+    expect(cfg.activeCodexAccountId).toBe(MAIN_CODEX_ACCOUNT_ID);
+    expect(cfg.activeCodexAccountPinned).toBe(MAIN_CODEX_ACCOUNT_ID);
+  });
+
+  test("an exhausted request-owned main pin still yields to the healthy Pool account (#3157)", async () => {
+    const { cfg, context, directEntitlementChecks } = await resolveRequestOwnedMainPinCase({
+      mainWeeklyPercent: 100,
+      poolWeeklyPercent: 16,
+      callerEntitled: true,
+    });
+    expect(context).toMatchObject({ kind: "pool", accountId: "pool-a" });
+    expect(directEntitlementChecks).toBe(0);
+    expect(cfg.activeCodexAccountId).toBe("pool-a");
+    expect(cfg.activeCodexAccountPinned).toBeUndefined();
+  });
+
+  test("a caller entitlement miss uses a Pool model detour without clearing the healthy main pin (#3157)", async () => {
+    const { cfg, context, directEntitlementChecks } = await resolveRequestOwnedMainPinCase({
+      mainWeeklyPercent: 16,
+      poolWeeklyPercent: 20,
+      callerEntitled: false,
+    });
+    expect(context).toMatchObject({ kind: "pool", accountId: "pool-a" });
+    expect(directEntitlementChecks).toBe(1);
+    expect(cfg.activeCodexAccountId).toBe(MAIN_CODEX_ACCOUNT_ID);
+    expect(cfg.activeCodexAccountPinned).toBe(MAIN_CODEX_ACCOUNT_ID);
+  });
+
   test("selects pool auth independently of the routed provider", async () => {
     saveCodexAccountCredential("pool-a", {
       accessToken: "pool_token",