diff --git a/backend/internal/service/openai_agent_identity_compat_test.go b/backend/internal/service/openai_agent_identity_compat_test.go
index a8f234f58c..2520eaaaeb 100644
--- a/backend/internal/service/openai_agent_identity_compat_test.go
+++ b/backend/internal/service/openai_agent_identity_compat_test.go
@@ -133,8 +133,8 @@ func TestOpenAIAgentIdentityPassthroughKeepsSessionAndPromptCacheHeaders(t *test
 	require.Equal(t, "account-agent-passthrough", req.Header.Get("chatgpt-account-id"))
 	require.NotEqual(t, "client-session", req.Header.Get("session_id"))
 	require.NotEqual(t, "client-conversation", req.Header.Get("conversation_id"))
-	require.Equal(t, isolateOpenAISessionID(0, "client-session"), req.Header.Get("session_id"))
-	require.Equal(t, isolateOpenAISessionID(0, "client-conversation"), req.Header.Get("conversation_id"))
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "client-session"), req.Header.Get("session_id"))
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "client-conversation"), req.Header.Get("conversation_id"))
 	requestBody, err := io.ReadAll(req.Body)
 	require.NoError(t, err)
 	require.Contains(t, string(requestBody), `"prompt_cache_key":"cache-agent"`)
@@ -147,7 +147,7 @@ func TestOpenAIAgentIdentityPassthroughKeepsSessionAndPromptCacheHeaders(t *test
 		Platform: PlatformOpenAI,
 		Type:     AccountTypeOAuth,
 		Credentials: map[string]any{
-			"chatgpt_account_id": "account-oauth-passthrough",
+			"chatgpt_account_id": "account-agent-passthrough",
 		},
 	}
 	oauthRecorder := httptest.NewRecorder()
diff --git a/backend/internal/service/openai_alpha_search.go b/backend/internal/service/openai_alpha_search.go
index e4fa52fe56..ac242f050c 100644
--- a/backend/internal/service/openai_alpha_search.go
+++ b/backend/internal/service/openai_alpha_search.go
@@ -30,6 +30,9 @@ func (s *OpenAIGatewayService) ForwardAlphaSearch(ctx context.Context, c *gin.Co
 	if s == nil || c == nil || account == nil {
 		return nil, fmt.Errorf("service, context, and account are required")
 	}
+	if _, err := s.prepareCodexAccountIdentitySource(ctx, c, account); err != nil {
+		return nil, err
+	}
 	modelResult := gjson.GetBytes(body, "model")
 	requestedModel := strings.TrimSpace(modelResult.String())
 	if modelResult.Type != gjson.String || requestedModel == "" {
@@ -272,10 +275,11 @@ func (s *OpenAIGatewayService) buildOpenAIAlphaSearchResponsesWebSearchRequest(c
 	}
 	apiKeyID := getAPIKeyIDFromContext(c)
 	if sessionID := strings.TrimSpace(gjson.GetBytes(alphaBody, "id").String()); sessionID != "" {
-		isolated := isolateOpenAISessionID(apiKeyID, sessionID)
+		isolated := isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), sessionID)
 		req.Header.Set("Session_ID", isolated)
 		req.Header.Set("Conversation_ID", isolated)
 	}
+	applyCodexAccountIdentityHeaders(req.Header, codexAccountIdentitySource(c, account), apiKeyID)
 	enforceCodexIdentityHeadersWithUA(req.Header, s.codexIdentityOverrideUA(account))
 	account.ApplyHeaderOverrides(req.Header)
 	return req, nil
@@ -393,6 +397,7 @@ func (s *OpenAIGatewayService) buildOpenAIAlphaSearchRequest(ctx context.Context
 		if turnMetadata := openAIAlphaSearchInboundHeader(c, "X-Codex-Turn-Metadata"); turnMetadata != "" {
 			req.Header.Set("X-Codex-Turn-Metadata", turnMetadata)
 		}
+		applyCodexAccountIdentityHeaders(req.Header, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
 		canonical := resolveCodexOutboundIdentity("")
 		if version := openAIAlphaSearchInboundHeader(c, "Version"); version != "" {
 			req.Header.Set("Version", version)
diff --git a/backend/internal/service/openai_alpha_search_test.go b/backend/internal/service/openai_alpha_search_test.go
index b5d37d1dd8..8521c2160e 100644
--- a/backend/internal/service/openai_alpha_search_test.go
+++ b/backend/internal/service/openai_alpha_search_test.go
@@ -59,6 +59,7 @@ func TestForwardAlphaSearchOAuthPreservesWire(t *testing.T) {
 	c.Request.Header.Set("User-Agent", codexCLIUserAgent)
 	c.Request.Header.Set("Originator", "codex_cli_rs")
 	c.Request.Header.Set("Version", "0.144.1")
+	c.Request.Header.Set("X-Codex-Turn-Metadata", `{"session_id":"search-session","turn_id":"search-turn"}`)
 
 	upstream := &httpUpstreamRecorder{resp: &http.Response{
 		StatusCode: http.StatusOK,
@@ -92,6 +93,14 @@ func TestForwardAlphaSearchOAuthPreservesWire(t *testing.T) {
 	require.Equal(t, "application/json", upstream.lastReq.Header.Get("Accept"))
 	require.Equal(t, codexCLIVersion, upstream.lastReq.Header.Get("Version"))
 	require.Empty(t, upstream.lastReq.Header.Get("OpenAI-Beta"))
+	require.Equal(t,
+		scopeCodexAccountIdentityValue(account, 0, "session", "search-session"),
+		gjson.Get(upstream.lastReq.Header.Get("X-Codex-Turn-Metadata"), "session_id").String(),
+	)
+	require.Equal(t,
+		scopeCodexAccountIdentityValue(account, 0, "turn", "search-turn"),
+		gjson.Get(upstream.lastReq.Header.Get("X-Codex-Turn-Metadata"), "turn_id").String(),
+	)
 	require.JSONEq(t, string(body), string(upstream.lastBody))
 }
 
@@ -156,7 +165,10 @@ func TestForwardAlphaSearchPATUsesResponsesWebSearchFallback(t *testing.T) {
 	require.Equal(t, "text/event-stream", upstream.lastReq.Header.Get("Accept"))
 	require.Equal(t, "responses=experimental", upstream.lastReq.Header.Get("OpenAI-Beta"))
 	require.Equal(t, codexCLIVersion, upstream.lastReq.Header.Get("Version"))
-	require.Equal(t, `{"turn_id":"turn-1"}`, upstream.lastReq.Header.Get("X-Codex-Turn-Metadata"))
+	require.Equal(t,
+		scopeCodexAccountIdentityValue(account, 0, "turn", "turn-1"),
+		gjson.Get(upstream.lastReq.Header.Get("X-Codex-Turn-Metadata"), "turn_id").String(),
+	)
 	require.Equal(t, openai.CodexDefaultOriginator, upstream.lastReq.Header.Get("Originator"))
 	require.Empty(t, upstream.lastReq.Header.Get("X-Codex-Beta-Features"))
 	require.Empty(t, upstream.lastReq.Header.Get("X-Codex-Turn-State"))
diff --git a/backend/internal/service/openai_codex_account_identity.go b/backend/internal/service/openai_codex_account_identity.go
new file mode 100644
index 0000000000..d0e336ec6c
--- /dev/null
+++ b/backend/internal/service/openai_codex_account_identity.go
@@ -0,0 +1,275 @@
+package service
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+const codexAccountIdentityNamespaceVersion = "v1"
+
+const codexAccountIdentitySourceContextKey = "openai_codex_account_identity_source"
+
+// prepareCodexAccountIdentitySource resolves credential shadows once per selected
+// attempt. The handler reuses gin.Context across failover attempts, so every entry
+// point overwrites the staged source before projecting outbound identity.
+func (s *OpenAIGatewayService) prepareCodexAccountIdentitySource(ctx context.Context, c *gin.Context, account *Account) (*Account, error) {
+	source := account
+	if account != nil && account.IsShadow() {
+		resolved, err := resolveCredentialAccount(ctx, s.accountRepo, account)
+		if err != nil {
+			return nil, err
+		}
+		source = resolved
+	}
+	if c != nil {
+		c.Set(codexAccountIdentitySourceContextKey, source)
+	}
+	return source, nil
+}
+
+func codexAccountIdentitySource(c *gin.Context, fallback *Account) *Account {
+	if c != nil {
+		if staged, ok := c.Get(codexAccountIdentitySourceContextKey); ok {
+			if source, ok := staged.(*Account); ok && source != nil {
+				return source
+			}
+		}
+	}
+	return fallback
+}
+
+// codexAccountIdentityNamespace returns a stable, credential-scoped namespace.
+// Multiple local rows that use the same ChatGPT account intentionally share the
+// same namespace. Setup tokens use an irreversible bearer fingerprint because
+// they have no refresh lifecycle or imported account metadata. Refreshable OAuth
+// otherwise falls back only to a persistent fingerprint seed: local row IDs are
+// deployment-relative and must never become upstream identity.
+func codexAccountIdentityNamespace(account *Account) string {
+	if account == nil || !account.IsOpenAIOAuthLike() {
+		return ""
+	}
+	if upstreamAccountID := strings.TrimSpace(account.GetChatGPTAccountID()); upstreamAccountID != "" {
+		if upstreamUserID := strings.TrimSpace(account.GetCredential("chatgpt_user_id")); upstreamUserID != "" {
+			return "chatgpt:" + upstreamAccountID + ":user:" + upstreamUserID
+		}
+		return "chatgpt:" + upstreamAccountID
+	}
+	if seed, ok := codexFingerprintSeed(account.Extra); ok {
+		return "seed:" + seed
+	}
+	if account.Type == AccountTypeSetupToken {
+		if token := strings.TrimSpace(account.GetOpenAIAccessToken()); token != "" {
+			sum := sha256.Sum256([]byte("openai-setup-token:" + token))
+			return fmt.Sprintf("setup-token:%x", sum[:16])
+		}
+	}
+	return ""
+}
+
+// isolateOpenAIUpstreamSessionID preserves the existing API-key isolation while
+// adding the selected OAuth credential namespace. A scheduler failover therefore
+// cannot send the same session/conversation identity through two upstream accounts.
+func isolateOpenAIUpstreamSessionID(apiKeyID int64, account *Account, raw string) string {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return ""
+	}
+	namespace := codexAccountIdentityNamespace(account)
+	if namespace == "" {
+		return isolateOpenAISessionID(apiKeyID, raw)
+	}
+	sum := sha256.Sum256([]byte(fmt.Sprintf("u%d:a%s:%s", apiKeyID, namespace, raw)))
+	return fmt.Sprintf("%x", sum[:8])
+}
+
+func scopeCodexAccountIdentityValue(account *Account, apiKeyID int64, kind, raw string) string {
+	raw = strings.TrimSpace(raw)
+	namespace := codexAccountIdentityNamespace(account)
+	if raw == "" || namespace == "" {
+		return raw
+	}
+	return deriveStableUUIDv4(fmt.Sprintf(
+		"sub2api:codex-account-identity:%s:user:%d:account:%s:kind:%s:value:%s",
+		codexAccountIdentityNamespaceVersion,
+		apiKeyID,
+		namespace,
+		kind,
+		raw,
+	))
+}
+
+var codexAccountIdentityFields = []struct {
+	name string
+	kind string
+}{
+	{name: "installation_id", kind: "installation"},
+	{name: "x-codex-installation-id", kind: "installation"},
+	{name: "session_id", kind: "session"},
+	{name: "session-id", kind: "session"},
+	{name: "thread_id", kind: "thread"},
+	{name: "thread-id", kind: "thread"},
+	{name: "turn_id", kind: "turn"},
+	{name: "turn-id", kind: "turn"},
+	{name: "window_id", kind: "window"},
+	{name: "x-codex-window-id", kind: "window"},
+	{name: "x-client-request-id", kind: "request"},
+}
+
+func applyCodexAccountIdentityFields(values map[string]any, account *Account, apiKeyID int64) bool {
+	if values == nil || codexAccountIdentityNamespace(account) == "" {
+		return false
+	}
+	changed := false
+	for _, field := range codexAccountIdentityFields {
+		raw, ok := values[field.name].(string)
+		if !ok || strings.TrimSpace(raw) == "" {
+			continue
+		}
+		next := scopeCodexAccountIdentityValue(account, apiKeyID, field.kind, raw)
+		if next != raw {
+			values[field.name] = next
+			changed = true
+		}
+	}
+	return changed
+}
+
+func applyCodexAccountIdentityEmbeddedMetadata(values map[string]any, account *Account, apiKeyID int64) bool {
+	raw, ok := values[openAIWSTurnMetadataHeader].(string)
+	if !ok || strings.TrimSpace(raw) == "" {
+		return false
+	}
+	metadata := map[string]any{}
+	if err := json.Unmarshal([]byte(raw), &metadata); err != nil || metadata == nil {
+		return false
+	}
+	if !applyCodexAccountIdentityFields(metadata, account, apiKeyID) {
+		return false
+	}
+	rebuilt, err := json.Marshal(metadata)
+	if err != nil {
+		return false
+	}
+	values[openAIWSTurnMetadataHeader] = string(rebuilt)
+	return true
+}
+
+func applyCodexAccountIdentityClientMetadataMap(requestBody map[string]any, account *Account, apiKeyID int64) bool {
+	if requestBody == nil || codexAccountIdentityNamespace(account) == "" {
+		return false
+	}
+	changed := false
+	clientMetadata, _ := requestBody["client_metadata"].(map[string]any)
+	originalBodySessionID := ""
+	if clientMetadata != nil {
+		originalBodySessionID, _ = clientMetadata["session_id"].(string)
+		if applyCodexAccountIdentityFields(clientMetadata, account, apiKeyID) {
+			changed = true
+		}
+		if applyCodexAccountIdentityEmbeddedMetadata(clientMetadata, account, apiKeyID) {
+			changed = true
+		}
+	}
+	if raw, ok := requestBody["prompt_cache_key"].(string); ok && strings.TrimSpace(raw) != "" {
+		kind := "prompt-cache"
+		if strings.TrimSpace(originalBodySessionID) != "" && raw == originalBodySessionID {
+			kind = "session"
+		}
+		next := scopeCodexAccountIdentityValue(account, apiKeyID, kind, raw)
+		if next != raw {
+			requestBody["prompt_cache_key"] = next
+			changed = true
+		}
+	}
+	return changed
+}
+
+// applyCodexAccountIdentityClientMetadataRaw scopes only the small identity
+// subobjects with gjson/sjson. The passthrough hot path never unmarshals the
+// potentially multi-megabyte request body.
+func applyCodexAccountIdentityClientMetadataRaw(body []byte, account *Account, apiKeyID int64) ([]byte, bool, error) {
+	if len(body) == 0 || codexAccountIdentityNamespace(account) == "" {
+		return body, false, nil
+	}
+	root := gjson.ParseBytes(body)
+	if !root.IsObject() {
+		return body, false, nil
+	}
+
+	next := body
+	changed := false
+	originalBodySessionID := ""
+	if cm := gjson.GetBytes(body, "client_metadata"); cm.IsObject() {
+		clientMetadata := map[string]any{}
+		if err := json.Unmarshal([]byte(cm.Raw), &clientMetadata); err != nil {
+			return body, false, fmt.Errorf("decode client_metadata for account identity: %w", err)
+		}
+		originalBodySessionID, _ = clientMetadata["session_id"].(string)
+		metadataChanged := applyCodexAccountIdentityFields(clientMetadata, account, apiKeyID)
+		if applyCodexAccountIdentityEmbeddedMetadata(clientMetadata, account, apiKeyID) {
+			metadataChanged = true
+		}
+		if metadataChanged {
+			raw, err := json.Marshal(clientMetadata)
+			if err != nil {
+				return body, false, fmt.Errorf("encode account-scoped client_metadata: %w", err)
+			}
+			var setErr error
+			next, setErr = sjson.SetRawBytes(next, "client_metadata", raw)
+			if setErr != nil {
+				return body, false, fmt.Errorf("splice account-scoped client_metadata: %w", setErr)
+			}
+			changed = true
+		}
+	}
+	if promptCacheKey := gjson.GetBytes(body, "prompt_cache_key"); promptCacheKey.Type == gjson.String && strings.TrimSpace(promptCacheKey.String()) != "" {
+		raw := promptCacheKey.String()
+		kind := "prompt-cache"
+		if strings.TrimSpace(originalBodySessionID) != "" && raw == originalBodySessionID {
+			kind = "session"
+		}
+		scoped := scopeCodexAccountIdentityValue(account, apiKeyID, kind, raw)
+		if scoped != raw {
+			rewritten, err := sjson.SetBytes(next, "prompt_cache_key", scoped)
+			if err != nil {
+				return body, false, fmt.Errorf("splice account-scoped prompt_cache_key: %w", err)
+			}
+			next = rewritten
+			changed = true
+		}
+	}
+	return next, changed, nil
+}
+
+func applyCodexAccountIdentityHeaders(headers http.Header, account *Account, apiKeyID int64) {
+	if headers == nil || codexAccountIdentityNamespace(account) == "" {
+		return
+	}
+	for _, field := range codexAccountIdentityFields {
+		// Underscore session/conversation headers are rebuilt separately from the
+		// prompt cache key by each request builder.
+		if field.name == "session_id" {
+			continue
+		}
+		raw := strings.TrimSpace(headers.Get(field.name))
+		if raw != "" {
+			headers.Set(field.name, scopeCodexAccountIdentityValue(account, apiKeyID, field.kind, raw))
+		}
+	}
+	if raw := strings.TrimSpace(headers.Get(openAIWSTurnMetadataHeader)); raw != "" {
+		metadata := map[string]any{}
+		if err := json.Unmarshal([]byte(raw), &metadata); err == nil && metadata != nil && applyCodexAccountIdentityFields(metadata, account, apiKeyID) {
+			if rebuilt, err := json.Marshal(metadata); err == nil {
+				headers.Set(openAIWSTurnMetadataHeader, string(rebuilt))
+			}
+		}
+	}
+}
diff --git a/backend/internal/service/openai_codex_account_identity_test.go b/backend/internal/service/openai_codex_account_identity_test.go
new file mode 100644
index 0000000000..ffceba2d39
--- /dev/null
+++ b/backend/internal/service/openai_codex_account_identity_test.go
@@ -0,0 +1,230 @@
+package service
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+type codexAccountIdentityRepoStub struct {
+	AccountRepository
+	account *Account
+}
+
+func (s *codexAccountIdentityRepoStub) GetByID(_ context.Context, _ int64) (*Account, error) {
+	return s.account, nil
+}
+
+func TestCodexRequestBodyIdentityNamespaceIsStablePerOAuthAccount(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.6-codex","prompt_cache_key":"client-session","client_metadata":{"x-codex-installation-id":"client-installation","session_id":"client-session","thread_id":"client-thread","x-codex-window-id":"client-window","x-codex-turn-metadata":"{\"installation_id\":\"client-installation\",\"session_id\":\"client-session\",\"thread_id\":\"client-thread\",\"turn_id\":\"client-turn\",\"window_id\":\"client-window\"}"}}`)
+	account11 := &Account{ID: 11, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "chatgpt-account-11"}}
+	account19 := &Account{ID: 19, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "chatgpt-account-19"}}
+
+	first, changed, err := applyCodexAccountIdentityClientMetadataRaw(body, account11, 77)
+	require.NoError(t, err)
+	require.True(t, changed)
+	firstAgain, changed, err := applyCodexAccountIdentityClientMetadataRaw(body, account11, 77)
+	require.NoError(t, err)
+	require.True(t, changed)
+	second, changed, err := applyCodexAccountIdentityClientMetadataRaw(body, account19, 77)
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.JSONEq(t, string(first), string(firstAgain))
+
+	paths := []string{
+		"prompt_cache_key",
+		"client_metadata.x-codex-installation-id",
+		"client_metadata.session_id",
+		"client_metadata.thread_id",
+		"client_metadata.x-codex-window-id",
+	}
+	for _, path := range paths {
+		require.NotEqual(t, gjson.GetBytes(body, path).String(), gjson.GetBytes(first, path).String(), path)
+		require.NotEqual(t, gjson.GetBytes(first, path).String(), gjson.GetBytes(second, path).String(), path)
+	}
+	require.Equal(t, gjson.GetBytes(first, "prompt_cache_key").String(), gjson.GetBytes(first, "client_metadata.session_id").String())
+
+	var embeddedFirst map[string]any
+	var embeddedSecond map[string]any
+	require.NoError(t, json.Unmarshal([]byte(gjson.GetBytes(first, "client_metadata.x-codex-turn-metadata").String()), &embeddedFirst))
+	require.NoError(t, json.Unmarshal([]byte(gjson.GetBytes(second, "client_metadata.x-codex-turn-metadata").String()), &embeddedSecond))
+	for _, field := range []string{"installation_id", "session_id", "thread_id", "turn_id", "window_id"} {
+		require.NotEqual(t, embeddedFirst[field], embeddedSecond[field], field)
+	}
+}
+
+func TestCodexAccountIdentityNamespaceUsesStableCredentialSource(t *testing.T) {
+	firstRow := &Account{ID: 8, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "shared-upstream-account"}}
+	secondRow := &Account{ID: 19, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "shared-upstream-account"}}
+	require.Equal(t, codexAccountIdentityNamespace(firstRow), codexAccountIdentityNamespace(secondRow))
+
+	firstUser := &Account{ID: 20, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "team-account", "chatgpt_user_id": "user-1"}}
+	sameUser := &Account{ID: 21, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "team-account", "chatgpt_user_id": "user-1"}}
+	secondUser := &Account{ID: 22, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "team-account", "chatgpt_user_id": "user-2"}}
+	require.Equal(t, codexAccountIdentityNamespace(firstUser), codexAccountIdentityNamespace(sameUser))
+	require.NotEqual(t, codexAccountIdentityNamespace(firstUser), codexAccountIdentityNamespace(secondUser))
+
+	seed := "11111111-1111-4111-8111-111111111111"
+	seeded := &Account{ID: 11, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Extra: map[string]any{codexFingerprintSeedExtraKey: seed}}
+	require.Equal(t, "seed:"+seed, codexAccountIdentityNamespace(seeded))
+
+	// Local row IDs repeat across independent deployments, so they are not a
+	// safe fallback for upstream identity.
+	require.Empty(t, codexAccountIdentityNamespace(&Account{ID: 11, Platform: PlatformOpenAI, Type: AccountTypeOAuth}))
+
+	setupTokenA := &Account{ID: 30, Platform: PlatformOpenAI, Type: AccountTypeSetupToken, Credentials: map[string]any{"access_token": "setup-token-a"}}
+	setupTokenADuplicate := &Account{ID: 31, Platform: PlatformOpenAI, Type: AccountTypeSetupToken, Credentials: map[string]any{"access_token": "setup-token-a"}}
+	setupTokenB := &Account{ID: 32, Platform: PlatformOpenAI, Type: AccountTypeSetupToken, Credentials: map[string]any{"access_token": "setup-token-b"}}
+	setupNamespace := codexAccountIdentityNamespace(setupTokenA)
+	require.NotEmpty(t, setupNamespace)
+	require.NotContains(t, setupNamespace, "setup-token-a")
+	require.Equal(t, setupNamespace, codexAccountIdentityNamespace(setupTokenADuplicate))
+	require.NotEqual(t, setupNamespace, codexAccountIdentityNamespace(setupTokenB))
+}
+
+func TestCodexAccountIdentitySourceResolvesShadowAndOverwritesFailoverContext(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", nil)
+
+	parentID := int64(11)
+	parent := &Account{ID: parentID, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{
+		"chatgpt_account_id": "team-account",
+		"chatgpt_user_id":    "user-1",
+	}}
+	shadow := &Account{ID: 111, ParentAccountID: &parentID, Platform: PlatformOpenAI, Type: AccountTypeOAuth}
+	service := &OpenAIGatewayService{accountRepo: &codexAccountIdentityRepoStub{account: parent}}
+
+	resolved, err := service.prepareCodexAccountIdentitySource(context.Background(), c, shadow)
+	require.NoError(t, err)
+	require.Same(t, parent, resolved)
+	require.Same(t, parent, codexAccountIdentitySource(c, shadow))
+
+	req, err := service.buildUpstreamRequest(
+		context.Background(), c, shadow,
+		[]byte(`{"model":"gpt-5.6-codex","stream":true,"prompt_cache_key":"client-session"}`),
+		"token", true, "client-session", true,
+	)
+	require.NoError(t, err)
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, parent, "client-session"), req.Header.Get("session_id"))
+
+	next := &Account{ID: 19, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{
+		"chatgpt_account_id": "other-account",
+		"chatgpt_user_id":    "user-2",
+	}}
+	resolved, err = service.prepareCodexAccountIdentitySource(context.Background(), c, next)
+	require.NoError(t, err)
+	require.Same(t, next, resolved)
+	require.Same(t, next, codexAccountIdentitySource(c, shadow))
+}
+
+func TestBuildOpenAIWSHeadersNamespacesCodexIdentityByOAuthAccount(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodGet, "/v1/responses", nil)
+	c.Set("api_key_id", int64(77))
+	c.Request.Header.Set("x-codex-installation-id", "client-installation")
+	c.Request.Header.Set("thread-id", "client-thread")
+	c.Request.Header.Set("x-codex-window-id", "client-window")
+	c.Request.Header.Set("x-client-request-id", "client-request")
+
+	account11 := &Account{ID: 11, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "chatgpt-account-11"}}
+	account19 := &Account{ID: 19, Platform: PlatformOpenAI, Type: AccountTypeOAuth, Credentials: map[string]any{"chatgpt_account_id": "chatgpt-account-19"}}
+	service := &OpenAIGatewayService{}
+	build := func(account *Account) http.Header {
+		headers, _, err := service.buildOpenAIWSHeaders(
+			context.Background(), c, account, "token",
+			OpenAIWSProtocolDecision{Transport: OpenAIUpstreamTransportResponsesWebsocketV2},
+			true, "", "", "client-session", "", "",
+		)
+		require.NoError(t, err)
+		return headers
+	}
+
+	first := build(account11)
+	firstAgain := build(account11)
+	second := build(account19)
+	for _, header := range []string{"session_id", "x-codex-installation-id", "thread-id", "x-codex-window-id", "x-client-request-id"} {
+		require.NotEmpty(t, first.Get(header), header)
+		require.Equal(t, first.Get(header), firstAgain.Get(header), header)
+		require.NotEqual(t, first.Get(header), second.Get(header), header)
+	}
+
+	httpRequest, err := service.buildUpstreamRequest(
+		context.Background(), c, account11,
+		[]byte(`{"model":"gpt-5.6-codex","stream":true,"prompt_cache_key":"client-session"}`),
+		"token", true, "client-session", true,
+	)
+	require.NoError(t, err)
+	require.Equal(t, httpRequest.Header.Get("session_id"), first.Get("session_id"), "HTTP and WS must derive the same identity from the raw client key")
+}
+
+func TestBuildUpstreamRequestNamespacesCodexIdentityByOAuthAccount(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	svc := &OpenAIGatewayService{}
+	body := []byte(`{"model":"gpt-5.6-codex","stream":true,"prompt_cache_key":"client-session"}`)
+
+	build := func(accountID int64, chatgptAccountID string) http.Header {
+		t.Helper()
+		recorder := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(recorder)
+		c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(body))
+		c.Set("api_key", &APIKey{ID: 77})
+		c.Request.Header.Set("User-Agent", "codex_cli_rs/0.144.0")
+		c.Request.Header.Set("x-codex-installation-id", "client-installation")
+		c.Request.Header.Set("x-codex-window-id", "client-window")
+		c.Request.Header.Set("session-id", "client-session")
+		c.Request.Header.Set("thread-id", "client-thread")
+		c.Request.Header.Set("x-client-request-id", "client-request")
+		c.Request.Header.Set("x-codex-turn-metadata", `{"installation_id":"client-installation","session_id":"client-session","thread_id":"client-thread","turn_id":"client-turn","window_id":"client-window"}`)
+
+		account := &Account{
+			ID:       accountID,
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"chatgpt_account_id": chatgptAccountID,
+			},
+		}
+		req, err := svc.buildUpstreamRequest(
+			context.Background(), c, account, body, "oauth-token", true, "client-session", true,
+		)
+		require.NoError(t, err)
+		return req.Header
+	}
+
+	first := build(11, "chatgpt-account-11")
+	firstAgain := build(11, "chatgpt-account-11")
+	second := build(19, "chatgpt-account-19")
+
+	identityHeaders := []string{
+		"x-codex-installation-id",
+		"x-codex-window-id",
+		"session-id",
+		"session_id",
+		"conversation_id",
+		"thread-id",
+		"x-client-request-id",
+		"x-codex-turn-metadata",
+	}
+	checked := 0
+	for _, header := range identityHeaders {
+		if first.Get(header) == "" && second.Get(header) == "" {
+			continue
+		}
+		checked++
+		require.NotEmpty(t, first.Get(header), header)
+		require.Equal(t, first.Get(header), firstAgain.Get(header), "same account must retain stable identity: %s", header)
+		require.NotEqual(t, first.Get(header), second.Get(header), "account failover must rotate upstream identity: %s", header)
+	}
+	require.GreaterOrEqual(t, checked, 5, "test must exercise the real outbound identity surface")
+}
diff --git a/backend/internal/service/openai_compat_model_test.go b/backend/internal/service/openai_compat_model_test.go
index 7ccfbdeadd..b52a616f85 100644
--- a/backend/internal/service/openai_compat_model_test.go
+++ b/backend/internal/service/openai_compat_model_test.go
@@ -1010,7 +1010,7 @@ func TestForwardAsAnthropic_ReusesOAuthCodexTurnState(t *testing.T) {
 	require.NoError(t, err)
 	require.NotNil(t, secondResult)
 	require.Equal(t, "turn_state_first", upstream.requests[1].Header.Get("x-codex-turn-state"))
-	require.Equal(t, generateSessionUUID(isolateOpenAISessionID(0, "stable-cache-key")), upstream.requests[1].Header.Get("session_id"))
+	require.Equal(t, generateSessionUUID(isolateOpenAIUpstreamSessionID(0, account, "stable-cache-key")), upstream.requests[1].Header.Get("session_id"))
 	require.Empty(t, upstream.requests[1].Header.Get("conversation_id"))
 	requireOpenAIMessagesCodexIdentity(t, upstream.requests[1], codexCLIUserAgent, openai.CodexDefaultOriginator)
 	require.False(t, gjson.GetBytes(upstream.bodies[1], "prompt_cache_key").Exists())
diff --git a/backend/internal/service/openai_gateway_chat_completions.go b/backend/internal/service/openai_gateway_chat_completions.go
index 5699dc09e9..69c1458fdc 100644
--- a/backend/internal/service/openai_gateway_chat_completions.go
+++ b/backend/internal/service/openai_gateway_chat_completions.go
@@ -61,6 +61,9 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 ) (*OpenAIForwardResult, error) {
 	beginUpstreamResponseModelObservation(c)
 	setCodexToolNameReverse(c, nil)
+	if _, err := s.prepareCodexAccountIdentitySource(ctx, c, account); err != nil {
+		return nil, err
+	}
 
 	restrictionResult := s.detectCodexClientRestriction(c, account, body)
 	logCodexCLIOnlyDetection(ctx, c, account, getAPIKeyIDFromContext(c), restrictionResult, body)
@@ -261,6 +264,7 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 		} else if promptCacheKey != "" {
 			reqBody["prompt_cache_key"] = promptCacheKey
 		}
+		applyCodexAccountIdentityClientMetadataMap(reqBody, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
 		responsesBody, err = json.Marshal(reqBody)
 		if err != nil {
 			return nil, fmt.Errorf("remarshal after codex transform: %w", err)
@@ -314,7 +318,7 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 
 	if promptCacheKey != "" {
 		apiKeyID := getAPIKeyIDFromContext(c)
-		upstreamReq.Header.Set("session_id", generateSessionUUID(isolateOpenAISessionID(apiKeyID, promptCacheKey)))
+		upstreamReq.Header.Set("session_id", generateSessionUUID(isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), promptCacheKey)))
 	}
 
 	// 7. Send request
diff --git a/backend/internal/service/openai_gateway_forward.go b/backend/internal/service/openai_gateway_forward.go
index eb2f5c55a6..ef53b6732d 100644
--- a/backend/internal/service/openai_gateway_forward.go
+++ b/backend/internal/service/openai_gateway_forward.go
@@ -24,6 +24,9 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 	clearOpenAIResponsesClientToolMapping(c)
 	clearOpenAIResponsesNamespaceNames(c)
 	setCodexToolNameReverse(c, nil)
+	if _, err := s.prepareCodexAccountIdentitySource(ctx, c, account); err != nil {
+		return nil, err
+	}
 	startTime := time.Now()
 	// 固定渠道映射后的请求级 canonical body；账号 normalize/strip 不得改写跨 failover hint。
 	canonicalImageIntentBody := body
@@ -252,6 +255,7 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 	}
 
 	bodyModified := false
+	clientPromptCacheKey := promptCacheKey
 	var reqBody map[string]any
 	ensureReqBody := func() (map[string]any, error) {
 		if requestView.HasPatches() {
@@ -478,6 +482,15 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		if !isCompactRequest && applyCodexClientMetadata(decoded, account) {
 			markDecodedModified()
 		}
+		if currentClientPromptCacheKey, ok := decoded["prompt_cache_key"].(string); ok {
+			clientPromptCacheKey = currentClientPromptCacheKey
+		}
+		// Account namespace is orthogonal to fingerprint convergence: preserve
+		// each client's identity cardinality, but never reuse it across OAuth
+		// credentials after scheduler failover.
+		if !isCompactRequest && applyCodexAccountIdentityClientMetadataMap(decoded, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c)) {
+			markDecodedModified()
+		}
 		stageCodexFingerprintIDs(c, nil)
 		// 指纹收敛：一次性解析收敛 ID，请求体和出站头共享同一份 IDs（保证 turn_id 等随机字段一致）。
 		// fingerprintIDs 在此处解析，后续 buildUpstreamRequest 中使用同一份。
@@ -500,7 +513,13 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		if codexResult.NormalizedModel != "" {
 			upstreamModel = codexResult.NormalizedModel
 		}
-		if currentPromptCacheKey, ok := decoded["prompt_cache_key"].(string); ok && currentPromptCacheKey != "" {
+		if strings.TrimSpace(clientPromptCacheKey) != "" {
+			// The body now carries an account-scoped value. Keep the original here
+			// so the header builder derives the same namespace exactly once.
+			promptCacheKey = clientPromptCacheKey
+		} else if currentPromptCacheKey, ok := decoded["prompt_cache_key"].(string); ok && currentPromptCacheKey != "" {
+			// Fingerprint convergence may inject a default key when the client did
+			// not provide one; preserve that existing fallback.
 			promptCacheKey = currentPromptCacheKey
 		} else if codexResult.PromptCacheKey != "" {
 			promptCacheKey = codexResult.PromptCacheKey
@@ -773,6 +792,7 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 				c,
 				account,
 				wsReqBody,
+				clientPromptCacheKey,
 				token,
 				wsDecision,
 				isCodexCLI,
@@ -1321,12 +1341,12 @@ func (s *OpenAIGatewayService) buildUpstreamRequest(ctx context.Context, c *gin.
 				req.Header.Set("version", CodexCanonicalClientVersion())
 			}
 			compactSession := resolveOpenAICompactSessionID(c)
-			req.Header.Set("session_id", isolateOpenAISessionID(apiKeyID, compactSession))
+			req.Header.Set("session_id", isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), compactSession))
 		} else {
 			req.Header.Set("accept", "text/event-stream")
 		}
 		if promptCacheKey != "" {
-			isolated := isolateOpenAISessionID(apiKeyID, promptCacheKey)
+			isolated := isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), promptCacheKey)
 			req.Header.Set("session_id", isolated)
 			if !compatMessagesBridge || clientConversationID != "" {
 				req.Header.Set("conversation_id", isolated)
@@ -1350,6 +1370,10 @@ func (s *OpenAIGatewayService) buildUpstreamRequest(ctx context.Context, c *gin.
 		req.Header.Set("user-agent", CodexCanonicalUserAgent())
 	}
 
+	// 账号 namespace 不改变客户端身份基数，但确保 scheduler failover 后不会把
+	// 同一组 Codex IDs 发送给另一份 OAuth 凭据。可选指纹收敛随后仍可覆盖这些值。
+	applyCodexAccountIdentityHeaders(req.Header, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+
 	// 指纹收敛：使用 Forward() 中预计算的收敛 ID 改写出站头，与请求体使用同一份 IDs。
 	applyStagedCodexFingerprintHeaders(c, account, req.Header)
 
diff --git a/backend/internal/service/openai_gateway_messages.go b/backend/internal/service/openai_gateway_messages.go
index 734cde2cab..17c4d633d1 100644
--- a/backend/internal/service/openai_gateway_messages.go
+++ b/backend/internal/service/openai_gateway_messages.go
@@ -35,6 +35,9 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 ) (*OpenAIForwardResult, error) {
 	beginUpstreamResponseModelObservation(c)
 	setCodexToolNameReverse(c, nil)
+	if _, err := s.prepareCodexAccountIdentitySource(ctx, c, account); err != nil {
+		return nil, err
+	}
 
 	// 入口分流（国产供应商 Anthropic 协议）：上游为供应商原生 Anthropic 端点时，
 	// /v1/messages 请求零转换直通（仅模型名映射 + 少量 body 清洗），完整保留
@@ -227,6 +230,7 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 		if codexResult.PromptCacheKey != "" {
 			promptCacheKey = codexResult.PromptCacheKey
 		}
+		applyCodexAccountIdentityClientMetadataMap(reqBody, codexAccountIdentitySource(c, account), apiKeyID)
 		delete(reqBody, "prompt_cache_key")
 		if shouldAutoInjectPromptCacheKeyForCompat(upstreamModel) {
 			compatTurnState = s.getOpenAICompatSessionTurnState(ctx, c, account, promptCacheKey)
@@ -329,7 +333,7 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 	// Override session_id with a deterministic UUID derived from the isolated
 	// session key, ensuring different API keys produce different upstream sessions.
 	if account.Platform != PlatformGrok && promptCacheKey != "" {
-		isolatedSessionID := generateSessionUUID(isolateOpenAISessionID(apiKeyID, promptCacheKey))
+		isolatedSessionID := generateSessionUUID(isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), promptCacheKey))
 		upstreamReq.Header.Set("session_id", isolatedSessionID)
 		if upstreamReq.Header.Get("conversation_id") != "" {
 			upstreamReq.Header.Set("conversation_id", isolatedSessionID)
diff --git a/backend/internal/service/openai_gateway_passthrough.go b/backend/internal/service/openai_gateway_passthrough.go
index b2115357d7..d5d0c75408 100644
--- a/backend/internal/service/openai_gateway_passthrough.go
+++ b/backend/internal/service/openai_gateway_passthrough.go
@@ -180,6 +180,14 @@ func (s *OpenAIGatewayService) forwardOpenAIPassthrough(
 		}
 		reqStream = gjson.GetBytes(body, "stream").Bool()
 
+		accountScopedBody, accountScoped, scopeErr := applyCodexAccountIdentityClientMetadataRaw(body, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+		if scopeErr != nil {
+			return nil, scopeErr
+		}
+		if accountScoped {
+			body = accountScopedBody
+		}
+
 		stageCodexFingerprintIDs(c, nil)
 		// 指纹收敛：与非透传路径同门控（仅 OAuth、legacy compact 形态跳过）。
 		// 一次性解析收敛 ID：请求体 client_metadata 在此改写（raw 字节外科
@@ -670,10 +678,10 @@ func (s *OpenAIGatewayService) buildUpstreamRequestOpenAIPassthrough(
 			clientConversationID = promptCacheKey
 		}
 		if clientSessionID != "" {
-			req.Header.Set("session_id", isolateOpenAISessionID(apiKeyID, clientSessionID))
+			req.Header.Set("session_id", isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), clientSessionID))
 		}
 		if clientConversationID != "" {
-			req.Header.Set("conversation_id", isolateOpenAISessionID(apiKeyID, clientConversationID))
+			req.Header.Set("conversation_id", isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), clientConversationID))
 		}
 	} else if isOpenAIResponsesCompactPath(c) {
 		// 透传白名单会放行客户端的 Accept: text/event-stream；compact 上游是
@@ -690,6 +698,8 @@ func (s *OpenAIGatewayService) buildUpstreamRequestOpenAIPassthrough(
 	if s.cfg != nil && s.cfg.Gateway.ForceCodexCLI {
 		req.Header.Set("user-agent", CodexCanonicalUserAgent())
 	}
+	applyCodexAccountIdentityHeaders(req.Header, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+
 	// 指纹收敛：使用 forwardOpenAIPassthrough 中预计算的收敛 ID 改写出站头，
 	// 与请求体 client_metadata 共享同一份 IDs（与非透传路径相同的相对位置：
 	// 会话隔离之后、终态身份收口之前）。
diff --git a/backend/internal/service/openai_setup_token_compat_test.go b/backend/internal/service/openai_setup_token_compat_test.go
index 7405deb419..8f2f2bfcee 100644
--- a/backend/internal/service/openai_setup_token_compat_test.go
+++ b/backend/internal/service/openai_setup_token_compat_test.go
@@ -227,7 +227,7 @@ func TestOpenAISetupTokenMessagesUsesCodexBridgeAndTurnState(t *testing.T) {
 	require.NotNil(t, secondResult)
 	require.True(t, isOpenAICompatMessagesBridgeContext(secondCtx))
 	require.Equal(t, "turn_state_setup", upstream.requests[1].Header.Get("x-codex-turn-state"))
-	require.Equal(t, generateSessionUUID(isolateOpenAISessionID(0, "stable-cache-key")), upstream.requests[1].Header.Get("session_id"))
+	require.Equal(t, generateSessionUUID(isolateOpenAIUpstreamSessionID(0, account, "stable-cache-key")), upstream.requests[1].Header.Get("session_id"))
 	require.Empty(t, upstream.requests[1].Header.Get("conversation_id"))
 	requireOpenAIMessagesCodexIdentity(t, upstream.requests[1], codexCLIUserAgent, "codex-tui")
 }
diff --git a/backend/internal/service/openai_ws_forwarder_ingress.go b/backend/internal/service/openai_ws_forwarder_ingress.go
index 0265ad6903..5eff93fc2e 100644
--- a/backend/internal/service/openai_ws_forwarder_ingress.go
+++ b/backend/internal/service/openai_ws_forwarder_ingress.go
@@ -86,6 +86,9 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 	// A handler may reuse the same gin context across account failover attempts.
 	// Never let an OAuth attempt's response aliases leak into the next account.
 	setCodexToolNameReverse(c, nil)
+	if _, err := s.prepareCodexAccountIdentitySource(ctx, c, account); err != nil {
+		return err
+	}
 	if err := validateOpenAIWSBearerToken(account, token); err != nil {
 		return err
 	}
@@ -181,15 +184,16 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 	isCodexCLI := openai.IsCodexOfficialClientByHeaders(c.GetHeader("User-Agent"), c.GetHeader("originator")) || (s.cfg != nil && s.cfg.Gateway.ForceCodexCLI)
 
 	type openAIWSClientPayload struct {
-		payloadRaw         []byte
-		rawForHash         []byte
-		promptCacheKey     string
-		previousResponseID string
-		originalModel      string
-		imageBillingModel  string
-		imageSizeTier      string
-		imageInputSize     string
-		payloadBytes       int
+		payloadRaw               []byte
+		accountIdentitySourceRaw []byte
+		rawForHash               []byte
+		promptCacheKey           string
+		previousResponseID       string
+		originalModel            string
+		imageBillingModel        string
+		imageSizeTier            string
+		imageInputSize           string
+		payloadBytes             int
 	}
 	ingressSessionOriginalModel := ""
 
@@ -308,6 +312,14 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 			}
 			normalized = next
 		}
+		accountIdentitySourceRaw := append([]byte(nil), normalized...)
+		accountScopedPayload, accountScoped, scopeErr := applyCodexAccountIdentityClientMetadataRaw(normalized, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+		if scopeErr != nil {
+			return openAIWSClientPayload{}, NewOpenAIWSClientCloseError(coderws.StatusPolicyViolation, "invalid websocket identity metadata", scopeErr)
+		}
+		if accountScoped {
+			normalized = accountScopedPayload
+		}
 		if account.IsOpenAIOAuthLike() && isOpenAIResponsesLiteWebSocketPayload(normalized) {
 			litePayload, _, liteErr := normalizeOpenAIResponsesLiteToolsPayload(normalized)
 			if liteErr != nil {
@@ -450,15 +462,16 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 		ingressSessionOriginalModel = originalModel
 
 		return openAIWSClientPayload{
-			payloadRaw:         normalized,
-			rawForHash:         trimmed,
-			promptCacheKey:     promptCacheKey,
-			previousResponseID: previousResponseID,
-			originalModel:      originalModel,
-			imageBillingModel:  imageBillingModel,
-			imageSizeTier:      imageSizeTier,
-			imageInputSize:     imageInputSize,
-			payloadBytes:       len(normalized),
+			payloadRaw:               normalized,
+			accountIdentitySourceRaw: accountIdentitySourceRaw,
+			rawForHash:               trimmed,
+			promptCacheKey:           promptCacheKey,
+			previousResponseID:       previousResponseID,
+			originalModel:            originalModel,
+			imageBillingModel:        imageBillingModel,
+			imageSizeTier:            imageSizeTier,
+			imageInputSize:           imageInputSize,
+			payloadBytes:             len(normalized),
 		}, nil
 	}
 
@@ -645,7 +658,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 				var failoverErr *UpstreamFailoverError
 				if turn > 1 && errors.As(bridgeErr, &failoverErr) && failoverErr != nil {
 					retryPayload, retrySafe, retryPayloadErr := buildOpenAIWSCurrentTurnRetryPayload(
-						bridgePayloadRaw,
+						currentBridgePayload.accountIdentitySourceRaw,
 						turnAccountFailoverInput,
 						turnAccountFailoverInputExists,
 						currentBridgePayload.originalModel,
diff --git a/backend/internal/service/openai_ws_forwarder_ingress_session_test.go b/backend/internal/service/openai_ws_forwarder_ingress_session_test.go
index 7633c9061e..097d845037 100644
--- a/backend/internal/service/openai_ws_forwarder_ingress_session_test.go
+++ b/backend/internal/service/openai_ws_forwarder_ingress_session_test.go
@@ -1242,7 +1242,7 @@ func TestOpenAIGatewayService_ProxyResponsesWebSocketFromClient_PassthroughHeade
 		t.Fatal("等待 passthrough websocket 结束超时")
 	}
 
-	require.Equal(t, isolateOpenAISessionID(0, "pcache_passthrough"), captureDialer.lastHeaders.Get("session_id"))
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "pcache_passthrough"), captureDialer.lastHeaders.Get("session_id"))
 	require.Equal(t, "turn-state-1", captureDialer.lastHeaders.Get(openAIWSTurnStateHeader))
 	require.Equal(t, "turn-meta-1", captureDialer.lastHeaders.Get(openAIWSTurnMetadataHeader))
 	require.Len(t, upstreamConn.writes, 1)
diff --git a/backend/internal/service/openai_ws_forwarder_payload.go b/backend/internal/service/openai_ws_forwarder_payload.go
index 89d0dfc18c..94738221a2 100644
--- a/backend/internal/service/openai_ws_forwarder_payload.go
+++ b/backend/internal/service/openai_ws_forwarder_payload.go
@@ -121,10 +121,10 @@ func (s *OpenAIGatewayService) buildOpenAIWSHeaders(
 	if account != nil && account.UsesOpenAICodexProtocol() {
 		apiKeyID := getAPIKeyIDFromContext(c)
 		if sessionResolution.SessionID != "" {
-			headers.Set("session_id", isolateOpenAISessionID(apiKeyID, sessionResolution.SessionID))
+			headers.Set("session_id", isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), sessionResolution.SessionID))
 		}
 		if sessionResolution.ConversationID != "" {
-			headers.Set("conversation_id", isolateOpenAISessionID(apiKeyID, sessionResolution.ConversationID))
+			headers.Set("conversation_id", isolateOpenAIUpstreamSessionID(apiKeyID, codexAccountIdentitySource(c, account), sessionResolution.ConversationID))
 		}
 	} else {
 		if sessionResolution.SessionID != "" {
@@ -140,6 +140,7 @@ func (s *OpenAIGatewayService) buildOpenAIWSHeaders(
 	if metadata := strings.TrimSpace(turnMetadata); metadata != "" {
 		headers.Set(openAIWSTurnMetadataHeader, metadata)
 	}
+	applyCodexAccountIdentityHeaders(headers, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
 	applyStagedCodexFingerprintHeaders(c, account, headers)
 
 	if account != nil && account.UsesOpenAICodexProtocol() {
diff --git a/backend/internal/service/openai_ws_forwarder_success_test.go b/backend/internal/service/openai_ws_forwarder_success_test.go
index 24f23f0d2b..e775104fa2 100644
--- a/backend/internal/service/openai_ws_forwarder_success_test.go
+++ b/backend/internal/service/openai_ws_forwarder_success_test.go
@@ -430,7 +430,7 @@ func TestOpenAIGatewayService_BuildOpenAIWSHeadersPreservesCodexIdentity(t *test
 	require.Empty(t, headers.Get("X-Test"))
 }
 
-func TestOpenAIGatewayService_BuildOpenAIWSHeadersDeviceModePreservesClientSessionIdentity(t *testing.T) {
+func TestOpenAIGatewayService_BuildOpenAIWSHeadersDeviceModePreservesNamespacedClientSessionIdentity(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	rec := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(rec)
@@ -465,10 +465,10 @@ func TestOpenAIGatewayService_BuildOpenAIWSHeadersDeviceModePreservesClientSessi
 	require.NoError(t, err)
 	require.Equal(t, ids.installationID, headers.Get("x-codex-installation-id"))
 	require.NotEqual(t, "client-installation", headers.Get("x-codex-installation-id"))
-	require.Equal(t, "client-window", headers.Get("x-codex-window-id"))
-	require.Equal(t, "client-session", headers.Get("session-id"))
-	require.Equal(t, "client-thread", headers.Get("thread-id"))
-	require.Equal(t, "client-request", headers.Get("x-client-request-id"))
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "window", "client-window"), headers.Get("x-codex-window-id"))
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "session", "client-session"), headers.Get("session-id"))
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "thread", "client-thread"), headers.Get("thread-id"))
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "request", "client-request"), headers.Get("x-client-request-id"))
 }
 
 func TestLogOpenAIWSBindResponseAccountWarn(t *testing.T) {
@@ -798,10 +798,10 @@ func TestOpenAIGatewayService_Forward_WSv2_OAuthStoreFalseByDefault(t *testing.T
 	require.Equal(t, "native-wsv2", gjson.Get(requestJSON, "input.0.namespace").String(), "OAuth WSv2 应保留原生 namespace")
 	require.Equal(t, openAIWSBetaV2Value, captureDialer.lastHeaders.Get("OpenAI-Beta"))
 	require.Equal(t, "remote_compaction_v2", captureDialer.lastHeaders.Get("x-codex-beta-features"))
-	// OAuth 账号的 session_id/conversation_id 应被 isolateOpenAISessionID 隔离，
+	// OAuth 账号的 session_id/conversation_id 应同时按 API key 和上游账号隔离，
 	// 测试中未设置 api_key 到 context，apiKeyID=0。
-	require.Equal(t, isolateOpenAISessionID(0, "sess-oauth-1"), captureDialer.lastHeaders.Get("session_id"))
-	require.Equal(t, isolateOpenAISessionID(0, "conv-oauth-1"), captureDialer.lastHeaders.Get("conversation_id"))
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "sess-oauth-1"), captureDialer.lastHeaders.Get("session_id"))
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "conv-oauth-1"), captureDialer.lastHeaders.Get("conversation_id"))
 }
 
 func TestOpenAIGatewayService_Forward_WSv2_OAuthOriginatorCompatibility(t *testing.T) {
@@ -1023,8 +1023,8 @@ func TestOpenAIGatewayService_Forward_WSv2_HeaderSessionFallbackFromPromptCacheK
 	require.NotNil(t, result)
 	require.Equal(t, "resp_prompt_cache_key", result.RequestID)
 
-	// OAuth 账号的 session_id 应被 isolateOpenAISessionID 隔离（apiKeyID=0，未在 context 设置）。
-	require.Equal(t, isolateOpenAISessionID(0, "pcache_123"), captureDialer.lastHeaders.Get("session_id"))
+	// OAuth 账号的 session_id 应同时按 API key 和上游账号隔离（apiKeyID=0）。
+	require.Equal(t, isolateOpenAIUpstreamSessionID(0, account, "pcache_123"), captureDialer.lastHeaders.Get("session_id"))
 	require.Empty(t, captureDialer.lastHeaders.Get("conversation_id"))
 	require.NotNil(t, captureConn.lastWrite)
 	require.True(t, gjson.Get(requestToJSONString(captureConn.lastWrite), "stream").Exists())
diff --git a/backend/internal/service/openai_ws_forwarder_v2.go b/backend/internal/service/openai_ws_forwarder_v2.go
index 06af82c7fb..7702ebe797 100644
--- a/backend/internal/service/openai_ws_forwarder_v2.go
+++ b/backend/internal/service/openai_ws_forwarder_v2.go
@@ -22,6 +22,7 @@ func (s *OpenAIGatewayService) forwardOpenAIWSV2(
 	c *gin.Context,
 	account *Account,
 	reqBody map[string]any,
+	clientPromptCacheKey string,
 	token string,
 	decision OpenAIWSProtocolDecision,
 	isCodexCLI bool,
@@ -72,7 +73,12 @@ func (s *OpenAIGatewayService) forwardOpenAIWSV2(
 	applyStagedCodexFingerprintClientMetadata(c, account, payload)
 	previousResponseID := openAIWSPayloadString(payload, "previous_response_id")
 	previousResponseIDKind := ClassifyOpenAIPreviousResponseIDKind(previousResponseID)
-	promptCacheKey := openAIWSPayloadString(payload, "prompt_cache_key")
+	promptCacheKey := strings.TrimSpace(clientPromptCacheKey)
+	if promptCacheKey == "" {
+		// Fingerprint convergence may inject a default key when the client did
+		// not send one; retain that fallback without replacing an explicit raw key.
+		promptCacheKey = openAIWSPayloadString(payload, "prompt_cache_key")
+	}
 	_, hasTools := payload["tools"]
 	debugEnabled := isOpenAIWSModeDebugEnabled()
 	payloadBytes := -1
diff --git a/backend/internal/service/openai_ws_http_bridge_resume_test.go b/backend/internal/service/openai_ws_http_bridge_resume_test.go
index 074c08f8ce..1468892bbe 100644
--- a/backend/internal/service/openai_ws_http_bridge_resume_test.go
+++ b/backend/internal/service/openai_ws_http_bridge_resume_test.go
@@ -150,11 +150,13 @@ func TestOpenAIWSHTTPBridgeLaterTurn429RetriesCurrentTurnOnReplacementAccount(t
 	account := &Account{
 		ID: 129, Name: "limited", Platform: PlatformOpenAI, Type: AccountTypeOAuth,
 		Status: StatusActive, Schedulable: true, Concurrency: 1,
-		Extra: map[string]any{"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeHTTPBridge},
+		Extra:       map[string]any{"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeHTTPBridge},
+		Credentials: map[string]any{"chatgpt_account_id": "account-a", "chatgpt_user_id": "user-a"},
 	}
 	nextAccount := *account
 	nextAccount.ID = 130
 	nextAccount.Name = "replacement"
+	nextAccount.Credentials = map[string]any{"chatgpt_account_id": "account-b", "chatgpt_user_id": "user-b"}
 
 	serverErrCh := make(chan error, 1)
 	failoverCh := make(chan []byte, 1)
@@ -212,7 +214,7 @@ func TestOpenAIWSHTTPBridgeLaterTurn429RetriesCurrentTurnOnReplacementAccount(t
 	require.Equal(t, "response.completed", gjson.GetBytes(completed, "type").String())
 
 	writeCtx, cancel = context.WithTimeout(context.Background(), 3*time.Second)
-	err = clientConn.Write(writeCtx, websocket.MessageText, []byte(`{"type":"response.create","model":"gpt-5.6-sol","previous_response_id":"resp_first","input":[{"type":"function_call_output","call_id":"call_1","output":"second"}]}`))
+	err = clientConn.Write(writeCtx, websocket.MessageText, []byte(`{"type":"response.create","model":"gpt-5.6-sol","previous_response_id":"resp_first","prompt_cache_key":"client-session","client_metadata":{"session_id":"client-session","thread_id":"client-thread"},"input":[{"type":"function_call_output","call_id":"call_1","output":"second"}]}`))
 	cancel()
 	require.NoError(t, err)
 
@@ -237,6 +239,8 @@ func TestOpenAIWSHTTPBridgeLaterTurn429RetriesCurrentTurnOnReplacementAccount(t
 		require.Contains(t, input.Raw, "second")
 		require.Equal(t, 1, strings.Count(input.Raw, `"id":"fc_1"`))
 		require.Equal(t, 2, strings.Count(input.Raw, `"call_id":"call_1"`))
+		require.Equal(t, "client-session", gjson.GetBytes(retryPayload, "client_metadata.session_id").String())
+		require.Equal(t, "client-thread", gjson.GetBytes(retryPayload, "client_metadata.thread_id").String())
 	case <-time.After(5 * time.Second):
 		t.Fatal("timed out waiting for current-turn failover")
 	}
@@ -249,7 +253,11 @@ func TestOpenAIWSHTTPBridgeLaterTurn429RetriesCurrentTurnOnReplacementAccount(t
 	}
 	require.Len(t, upstream.bodies, 3)
 	require.Contains(t, string(upstream.bodies[0]), "first")
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "session", "client-session"), gjson.GetBytes(upstream.bodies[1], "client_metadata.session_id").String())
+	require.Equal(t, scopeCodexAccountIdentityValue(account, 0, "thread", "client-thread"), gjson.GetBytes(upstream.bodies[1], "client_metadata.thread_id").String())
 	require.NotContains(t, string(upstream.bodies[2]), "previous_response_id")
 	require.Contains(t, string(upstream.bodies[2]), "second")
+	require.Equal(t, scopeCodexAccountIdentityValue(&nextAccount, 0, "session", "client-session"), gjson.GetBytes(upstream.bodies[2], "client_metadata.session_id").String())
+	require.Equal(t, scopeCodexAccountIdentityValue(&nextAccount, 0, "thread", "client-thread"), gjson.GetBytes(upstream.bodies[2], "client_metadata.thread_id").String())
 	require.Empty(t, upstream.requests[2].Header.Get(openAIWSTurnStateHeader))
 }
diff --git a/backend/internal/service/openai_ws_v2_passthrough_adapter.go b/backend/internal/service/openai_ws_v2_passthrough_adapter.go
index c8fcd87525..96e1c859bb 100644
--- a/backend/internal/service/openai_ws_v2_passthrough_adapter.go
+++ b/backend/internal/service/openai_ws_v2_passthrough_adapter.go
@@ -693,6 +693,7 @@ func (s *OpenAIGatewayService) proxyResponsesWebSocketV2Passthrough(
 	}
 	requestModel := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "model").String())
 	requestPreviousResponseID := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "previous_response_id").String())
+	promptCacheKey := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "prompt_cache_key").String())
 	logOpenAIWSV2Passthrough(
 		"relay_start account_id=%d model=%s previous_response_id=%s first_message_type=%s first_message_bytes=%d",
 		account.ID,
@@ -749,6 +750,13 @@ func (s *OpenAIGatewayService) proxyResponsesWebSocketV2Passthrough(
 			firstClientMessage = aliasedBody
 		}
 	}
+	accountScopedFirst, accountScoped, scopeErr := applyCodexAccountIdentityClientMetadataRaw(firstClientMessage, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+	if scopeErr != nil {
+		return NewOpenAIWSClientCloseError(coderws.StatusPolicyViolation, "invalid websocket identity metadata", scopeErr)
+	}
+	if accountScoped {
+		firstClientMessage = accountScopedFirst
+	}
 	usageMeta := newOpenAIWSPassthroughUsageMeta(initialRequestModel, firstClientMessage)
 	updatedFirst, blocked, policyErr := s.applyOpenAIFastPolicyToWSResponseCreate(ctx, account, capturedSessionModel, firstClientMessage)
 	if policyErr != nil {
@@ -789,8 +797,6 @@ func (s *OpenAIGatewayService) proxyResponsesWebSocketV2Passthrough(
 	usageMeta.initFromFirstFrame(firstClientMessage, capturedSessionModel)
 	_, initialUpstreamModel := usageMeta.turnModels(initialRequestModel)
 	SetOpsUpstreamModel(c, initialUpstreamModel)
-	promptCacheKey := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "prompt_cache_key").String())
-
 	wsURL, err := s.buildOpenAIResponsesWSURL(account)
 	if err != nil {
 		return fmt.Errorf("build ws url: %w", err)
@@ -995,6 +1001,15 @@ func (s *OpenAIGatewayService) proxyResponsesWebSocketV2Passthrough(
 					payload = aliasedBody
 				}
 			}
+			if isResponseCreate || eventType == "session.update" {
+				accountScopedPayload, accountScoped, scopeErr := applyCodexAccountIdentityClientMetadataRaw(payload, codexAccountIdentitySource(c, account), getAPIKeyIDFromContext(c))
+				if scopeErr != nil {
+					return payload, nil, NewOpenAIWSClientCloseError(coderws.StatusPolicyViolation, "invalid websocket identity metadata", scopeErr)
+				}
+				if accountScoped {
+					payload = accountScopedPayload
+				}
+			}
 			if isResponseCreate {
 				if account.IsOpenAIOAuthLike() && isOpenAIResponsesLiteWebSocketPayload(payload) {
 					litePayload, _, liteErr := normalizeOpenAIResponsesLiteToolsPayload(payload)