diff --git a/sdk/cliproxy/auth/selector.go b/sdk/cliproxy/auth/selector.go
index e488878a..635b362e 100644
--- a/sdk/cliproxy/auth/selector.go
+++ b/sdk/cliproxy/auth/selector.go
@@ -759,12 +759,13 @@ func (s *SessionAffinitySelector) Pick(ctx context.Context, provider, model stri
 
 	modelKey := canonicalModelKey(model)
 	cacheKey := provider + "::" + primaryID + "::" + modelKey
+	isSubagent := isSubagentSession(primaryID, fallbackID)
 	fallbackKey := ""
 	if fallbackID != "" && fallbackID != primaryID {
 		fallbackKey = provider + "::" + fallbackID + "::" + modelKey
 	}
 	bind := func(authID string) {
-		if fallbackKey != "" {
+		if fallbackKey != "" && !isSubagent {
 			s.cache.SetAliases(authID, cacheKey, fallbackKey)
 		} else {
 			s.cache.Set(cacheKey, authID)
@@ -796,9 +797,11 @@ func (s *SessionAffinitySelector) Pick(ctx context.Context, provider, model stri
 		if cachedAuthID, ok := s.cache.Get(fallbackKey); ok {
 			for _, auth := range available {
 				if auth.ID == cachedAuthID {
-					bind(auth.ID)
-					entry.Infof("session-affinity: fallback cache hit | session=%s fallback=%s auth=%s provider=%s model=%s", truncateSessionID(primaryID), truncateSessionID(fallbackID), auth.ID, provider, model)
-					return auth, nil
+					if !isSubagent || allowsSubagentAuthInheritance(auth, model) {
+						bind(auth.ID)
+						entry.Infof("session-affinity: fallback cache hit | session=%s fallback=%s auth=%s provider=%s model=%s", truncateSessionID(primaryID), truncateSessionID(fallbackID), auth.ID, provider, model)
+						return auth, nil
+					}
 				}
 			}
 		}
@@ -1021,7 +1024,7 @@ func (s *SessionAffinitySelector) OnResult(res Result) {
 
 	cacheKey := ns + "::" + primaryID + "::" + nsModel
 	var fallbackKey string
-	if fallbackID != "" && fallbackID != primaryID {
+	if fallbackID != "" && fallbackID != primaryID && !isSubagentSession(primaryID, fallbackID) {
 		fallbackKey = ns + "::" + fallbackID + "::" + nsModel
 	}
 	if res.Success {
@@ -1045,6 +1048,39 @@ func normalizedSessionCandidate(raw string) string {
 	return cliproxysession.NormalizeExplicitID(raw)
 }
 
+func isSubagentSession(primaryID, fallbackID string) bool {
+	if strings.Contains(primaryID, ":agent:") {
+		return true
+	}
+	if fallbackID == "" || primaryID == "" || primaryID == fallbackID {
+		return false
+	}
+	return isHierarchyParent(primaryID, fallbackID)
+}
+
+func isNonInheritingProvider(provider string) bool {
+	p := strings.ToLower(strings.TrimSpace(provider))
+	return p == "antigravity" || p == "gemini" || p == "vertex" || p == "gemini-vertex" || p == "aistudio" || p == "gemini-interactions" || strings.Contains(p, "antigravity") || strings.Contains(p, "gemini")
+}
+
+func isNonInheritingModel(model string) bool {
+	baseModel := strings.ToLower(strings.TrimSpace(model))
+	if parsed := thinking.ParseSuffix(baseModel); parsed.ModelName != "" {
+		baseModel = strings.ToLower(strings.TrimSpace(parsed.ModelName))
+	}
+	return strings.HasPrefix(baseModel, "gemini-") || strings.HasPrefix(baseModel, "antigravity-")
+}
+
+func allowsSubagentAuthInheritance(auth *Auth, model string) bool {
+	if auth != nil && isNonInheritingProvider(auth.Provider) {
+		return false
+	}
+	if isNonInheritingModel(model) {
+		return false
+	}
+	return true
+}
+
 func sessionHeaderValue(headers http.Header, name string) string {
 	if headers == nil {
 		return ""
diff --git a/sdk/cliproxy/auth/selector_antigravity_subagent_test.go b/sdk/cliproxy/auth/selector_antigravity_subagent_test.go
new file mode 100644
index 00000000..1c45bcba
--- /dev/null
+++ b/sdk/cliproxy/auth/selector_antigravity_subagent_test.go
@@ -0,0 +1,496 @@
+package auth
+
+import (
+	"context"
+	"net/http"
+	"testing"
+	"time"
+
+	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+)
+
+func TestSessionAffinityAntigravitySubagentDoesNotInheritParentBinding(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	auths := []*Auth{
+		{ID: "auth-ag-1", Provider: "antigravity"},
+		{ID: "auth-ag-2", Provider: "antigravity"},
+	}
+
+	// 1. Parent request binds to auth-ag-1
+	parentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"claude-root-100"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent task"}]}`),
+		Metadata:        map[string]any{},
+	}
+	parentAuth, errParent := selector.Pick(context.Background(), "antigravity", "gemini-3.7-flash-high", parentOpts, auths)
+	if errParent != nil {
+		t.Fatalf("parent Pick() error = %v", errParent)
+	}
+	if parentAuth.ID != "auth-ag-1" {
+		t.Fatalf("parent auth = %q, want auth-ag-1", parentAuth.ID)
+	}
+
+	// 2. Subagent-1 request carries subagent ID.
+	// For Antigravity/Gemini, subagent MUST NOT inherit parent auth to prevent 429 concurrency gate.
+	subagent1Opts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-100"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-001"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent 1 task"}]}`),
+		Metadata:        map[string]any{},
+	}
+	subagent1Auth, errSub1 := selector.Pick(context.Background(), "antigravity", "gemini-3.7-flash-high", subagent1Opts, auths)
+	if errSub1 != nil {
+		t.Fatalf("subagent 1 Pick() error = %v", errSub1)
+	}
+	if subagent1Auth.ID == parentAuth.ID {
+		t.Fatalf("subagent 1 incorrectly inherited parent auth %q; should be isolated to prevent 429 rate limit", parentAuth.ID)
+	}
+	if subagent1Auth.ID != "auth-ag-2" {
+		t.Fatalf("subagent 1 auth = %q, want auth-ag-2", subagent1Auth.ID)
+	}
+
+	// 3. Subagent-1 second turn must stay sticky to auth-ag-2
+	subagent1Turn2Opts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-100"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-001"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent 1 second turn"}]}`),
+		Metadata:        map[string]any{},
+	}
+	subagent1Turn2Auth, errSub1Turn2 := selector.Pick(context.Background(), "antigravity", "gemini-3.7-flash-high", subagent1Turn2Opts, auths)
+	if errSub1Turn2 != nil {
+		t.Fatalf("subagent 1 turn 2 Pick() error = %v", errSub1Turn2)
+	}
+	if subagent1Turn2Auth.ID != "auth-ag-2" {
+		t.Fatalf("subagent 1 turn 2 did not stay sticky: got %q, want auth-ag-2", subagent1Turn2Auth.ID)
+	}
+
+	// 4. Subagent-2 request must select next available credential (auth-ag-1) and not be locked into auth-ag-2
+	subagent2Opts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-100"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-002"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent 2 task"}]}`),
+		Metadata:        map[string]any{},
+	}
+	subagent2Auth, errSub2 := selector.Pick(context.Background(), "antigravity", "gemini-3.7-flash-high", subagent2Opts, auths)
+	if errSub2 != nil {
+		t.Fatalf("subagent 2 Pick() error = %v", errSub2)
+	}
+	if subagent2Auth.ID != "auth-ag-1" {
+		t.Fatalf("subagent 2 auth = %q, want auth-ag-1", subagent2Auth.ID)
+	}
+
+	// 5. Main parent session next turn must stay sticky to auth-ag-1
+	parentTurn2Opts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"claude-root-100"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent follow-up"}]}`),
+		Metadata:        map[string]any{},
+	}
+	parentTurn2Auth, errParent2 := selector.Pick(context.Background(), "antigravity", "gemini-3.7-flash-high", parentTurn2Opts, auths)
+	if errParent2 != nil {
+		t.Fatalf("parent turn 2 Pick() error = %v", errParent2)
+	}
+	if parentTurn2Auth.ID != "auth-ag-1" {
+		t.Fatalf("parent turn 2 auth = %q, want auth-ag-1", parentTurn2Auth.ID)
+	}
+}
+
+func TestSessionAffinityMixedProviderAntigravitySubagentIsolation(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	auths := []*Auth{
+		{ID: "auth-ag-1", Provider: "antigravity"},
+		{ID: "auth-ag-2", Provider: "antigravity"},
+	}
+
+	// 1. Parent request in mixed pool binds to auth-ag-1
+	parentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"claude-root-200"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "gemini-3.7-flash-high",
+		},
+	}
+	parentAuth, errParent := selector.Pick(context.Background(), "mixed", "gemini-3.7-flash-high", parentOpts, auths)
+	if errParent != nil {
+		t.Fatalf("parent Pick() error = %v", errParent)
+	}
+	if parentAuth.ID != "auth-ag-1" {
+		t.Fatalf("parent auth = %q, want auth-ag-1", parentAuth.ID)
+	}
+
+	// 2. Subagent request in mixed pool with Antigravity candidates must NOT inherit parent auth
+	subOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-200"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-999"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "gemini-3.7-flash-high",
+		},
+	}
+	subAuth, errSub := selector.Pick(context.Background(), "mixed", "gemini-3.7-flash-high", subOpts, auths)
+	if errSub != nil {
+		t.Fatalf("subagent Pick() error = %v", errSub)
+	}
+	if subAuth.ID == parentAuth.ID {
+		t.Fatalf("subagent in mixed pool incorrectly inherited parent auth %q", parentAuth.ID)
+	}
+	if subAuth.ID != "auth-ag-2" {
+		t.Fatalf("subagent auth = %q, want auth-ag-2", subAuth.ID)
+	}
+}
+
+func TestSessionAffinityClaudeAndCodexStillInheritParentBinding(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	claudeAuths := []*Auth{
+		{ID: "auth-claude-1", Provider: "claude"},
+		{ID: "auth-claude-2", Provider: "claude"},
+	}
+
+	// 1. Claude parent binds to auth-claude-1
+	claudeParentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"claude-root-300"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"claude parent"}]}`),
+		Metadata:        map[string]any{},
+	}
+	claudeParentAuth, errClaudeParent := selector.Pick(context.Background(), "claude", "claude-3-7-sonnet", claudeParentOpts, claudeAuths)
+	if errClaudeParent != nil {
+		t.Fatalf("claude parent Pick() error = %v", errClaudeParent)
+	}
+	if claudeParentAuth.ID != "auth-claude-1" {
+		t.Fatalf("claude parent auth = %q, want auth-claude-1", claudeParentAuth.ID)
+	}
+
+	// 2. Claude subagent MUST inherit parent auth for KV cache reuse
+	claudeSubOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-300"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-001"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"claude subagent"}]}`),
+		Metadata:        map[string]any{},
+	}
+	claudeSubAuth, errClaudeSub := selector.Pick(context.Background(), "claude", "claude-3-7-sonnet", claudeSubOpts, claudeAuths)
+	if errClaudeSub != nil {
+		t.Fatalf("claude sub Pick() error = %v", errClaudeSub)
+	}
+	if claudeSubAuth.ID != "auth-claude-1" {
+		t.Fatalf("claude subagent auth = %q, want inherited parent auth-claude-1", claudeSubAuth.ID)
+	}
+
+	// 3. Codex parent and subagent inheritance
+	codexAuths := []*Auth{
+		{ID: "auth-codex-1", Provider: "codex"},
+		{ID: "auth-codex-2", Provider: "codex"},
+	}
+	codexParentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"Session-Id": []string{"codex-parent-400"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"codex parent"}]}`),
+		Metadata:        map[string]any{},
+	}
+	codexParentAuth, errCodexParent := selector.Pick(context.Background(), "codex", "gpt-5.4", codexParentOpts, codexAuths)
+	if errCodexParent != nil {
+		t.Fatalf("codex parent Pick() error = %v", errCodexParent)
+	}
+	if codexParentAuth.ID != "auth-codex-1" {
+		t.Fatalf("codex parent auth = %q, want auth-codex-1", codexParentAuth.ID)
+	}
+
+	codexSubOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"Session-Id":               []string{"codex-child-400"},
+			"x-codex-parent-thread-id": []string{"codex-parent-400"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"codex subagent"}]}`),
+		Metadata:        map[string]any{},
+	}
+	codexSubAuth, errCodexSub := selector.Pick(context.Background(), "codex", "gpt-5.4", codexSubOpts, codexAuths)
+	if errCodexSub != nil {
+		t.Fatalf("codex sub Pick() error = %v", errCodexSub)
+	}
+	if codexSubAuth.ID != "auth-codex-1" {
+		t.Fatalf("codex subagent auth = %q, want inherited parent auth-codex-1", codexSubAuth.ID)
+	}
+}
+
+func TestSessionAffinityMixedPoolClaudeInheritsWhileAntigravityIsolates(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	// 1. Parent session selects Claude credential in mixed pool
+	claudeCandidate := []*Auth{
+		{ID: "auth-claude-primary", Provider: "claude"},
+	}
+	parentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"mixed-sess-claude"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	parentAuth, errParent := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", parentOpts, claudeCandidate)
+	if errParent != nil {
+		t.Fatalf("parent Pick() error = %v", errParent)
+	}
+	if parentAuth.ID != "auth-claude-primary" {
+		t.Fatalf("parent auth = %q, want auth-claude-primary", parentAuth.ID)
+	}
+
+	// 2. Subagent of Claude parent in mixed pool (where both Claude and Antigravity are available)
+	// MUST inherit auth-claude-primary for prompt cache reuse
+	mixedAuths := []*Auth{
+		{ID: "auth-ag-other", Provider: "antigravity"},
+		{ID: "auth-claude-primary", Provider: "claude"},
+	}
+	subClaudeOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"mixed-sess-claude"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-claude-1"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	subClaudeAuth, errSubClaude := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", subClaudeOpts, mixedAuths)
+	if errSubClaude != nil {
+		t.Fatalf("subagent Claude Pick() error = %v", errSubClaude)
+	}
+	if subClaudeAuth.ID != "auth-claude-primary" {
+		t.Fatalf("subagent in mixed pool with Claude parent did not inherit Claude auth: got %q, want auth-claude-primary", subClaudeAuth.ID)
+	}
+
+	// 3. Parent session that selected Antigravity credential in mixed pool
+	agCandidate := []*Auth{
+		{ID: "auth-ag-primary", Provider: "antigravity"},
+	}
+	parentAgOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"mixed-sess-ag"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	parentAgAuth, errParentAg := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", parentAgOpts, agCandidate)
+	if errParentAg != nil {
+		t.Fatalf("parent Ag Pick() error = %v", errParentAg)
+	}
+	if parentAgAuth.ID != "auth-ag-primary" {
+		t.Fatalf("parent Ag auth = %q, want auth-ag-primary", parentAgAuth.ID)
+	}
+
+	// 4. Subagent of Antigravity parent in mixed pool where Claude is also available
+	// MUST NOT inherit Antigravity auth, and independently picking Claude must NOT overwrite parent binding
+	mixedCandidates := []*Auth{
+		{ID: "auth-ag-primary", Provider: "antigravity"},
+		{ID: "auth-claude-primary", Provider: "claude"},
+	}
+	subAgOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"mixed-sess-ag"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-ag-1"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	subAgAuth, errSubAg := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", subAgOpts, mixedCandidates)
+	if errSubAg != nil {
+		t.Fatalf("subagent Ag Pick() error = %v", errSubAg)
+	}
+	if subAgAuth.ID == parentAgAuth.ID {
+		t.Fatalf("subagent with Antigravity parent incorrectly inherited parent auth %q", parentAgAuth.ID)
+	}
+	if subAgAuth.ID != "auth-claude-primary" {
+		t.Fatalf("subagent Ag auth = %q, want auth-claude-primary", subAgAuth.ID)
+	}
+
+	// 5. Verify parent binding in cache was NOT overwritten by subagent picking Claude
+	if bound, ok := selector.cache.Get("mixed::claude:mixed-sess-ag::claude-3-7-sonnet"); !ok || bound != "auth-ag-primary" {
+		t.Fatalf("parent cache binding was overwritten by subagent: got (%q, %v), want (auth-ag-primary, true)", bound, ok)
+	}
+
+	// 6. Subagent turn 2 must stay sticky to auth-claude-primary
+	subAgTurn2Auth, errSubAg2 := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", subAgOpts, mixedCandidates)
+	if errSubAg2 != nil {
+		t.Fatalf("subagent turn 2 Pick() error = %v", errSubAg2)
+	}
+	if subAgTurn2Auth.ID != "auth-claude-primary" {
+		t.Fatalf("subagent turn 2 auth = %q, want auth-claude-primary", subAgTurn2Auth.ID)
+	}
+
+	// 7. Parent turn 2 must stay sticky to auth-ag-primary
+	parentAgTurn2Auth, errParentAg2 := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", parentAgOpts, mixedCandidates)
+	if errParentAg2 != nil {
+		t.Fatalf("parent turn 2 Pick() error = %v", errParentAg2)
+	}
+	if parentAgTurn2Auth.ID != "auth-ag-primary" {
+		t.Fatalf("parent turn 2 auth = %q, want auth-ag-primary", parentAgTurn2Auth.ID)
+	}
+}
+
+func TestSessionAffinityAntigravitySubagentOnResultFailureDoesNotUnbindParent(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	auths := []*Auth{
+		{ID: "auth-ag-1", Provider: "antigravity"},
+		{ID: "auth-ag-2", Provider: "antigravity"},
+	}
+
+	// 1. Parent request in mixed pool binds to auth-ag-1 with model claude-3-7-sonnet
+	parentOpts := cliproxyexecutor.Options{
+		Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"claude-root-500"}},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	parentAuth, errParent := selector.Pick(context.Background(), "mixed", "claude-3-7-sonnet", parentOpts, auths)
+	if errParent != nil {
+		t.Fatalf("parent Pick() error = %v", errParent)
+	}
+	if parentAuth.ID != "auth-ag-1" {
+		t.Fatalf("parent auth = %q, want auth-ag-1", parentAuth.ID)
+	}
+
+	// Verify parent key is bound in cache
+	if bound, ok := selector.cache.Get("mixed::claude:claude-root-500::claude-3-7-sonnet"); !ok || bound != "auth-ag-1" {
+		t.Fatalf("parent cache binding = (%q, %v), want (auth-ag-1, true)", bound, ok)
+	}
+
+	// 2. Subagent in mixed pool with exact same namespace and model
+	subOpts := cliproxyexecutor.Options{
+		Headers: http.Header{
+			"X-Claude-Code-Session-Id": []string{"claude-root-500"},
+			"X-Claude-Code-Agent-Id":   []string{"subagent-err-1"},
+		},
+		OriginalRequest: []byte(`{"messages":[{"role":"user","content":"subagent task"}]}`),
+		Metadata: map[string]any{
+			cliproxyexecutor.SessionAffinityProviderMetadataKey: "mixed",
+			cliproxyexecutor.SessionAffinityModelMetadataKey:    "claude-3-7-sonnet",
+		},
+	}
+	// Simulate subagent executing on auth-ag-1 (same auth ID as parent) and hitting 429
+	selector.OnResult(Result{
+		AuthID:   "auth-ag-1",
+		Provider: "antigravity",
+		Model:    "claude-3-7-sonnet",
+		Success:  false,
+		Error:    &Error{HTTPStatus: http.StatusTooManyRequests, Message: "429 rate limited"},
+		Options:  subOpts,
+	})
+
+	// 3. Parent binding in cache must remain untouched
+	if bound, ok := selector.cache.Get("mixed::claude:claude-root-500::claude-3-7-sonnet"); !ok || bound != "auth-ag-1" {
+		t.Fatalf("parent cache binding was destroyed by subagent OnResult failure: got (%q, %v)", bound, ok)
+	}
+
+	// 4. Simulate subagent success on auth-ag-2: must not touch or overwrite parent key
+	selector.OnResult(Result{
+		AuthID:   "auth-ag-2",
+		Provider: "antigravity",
+		Model:    "claude-3-7-sonnet",
+		Success:  true,
+		Options:  subOpts,
+	})
+	if bound, ok := selector.cache.Get("mixed::claude:claude-root-500::claude-3-7-sonnet"); !ok || bound != "auth-ag-1" {
+		t.Fatalf("parent cache binding was altered by subagent OnResult success: got (%q, %v)", bound, ok)
+	}
+}
+
+func TestSessionAffinityOtherGoogleProvidersSubagentIsolation(t *testing.T) {
+	t.Parallel()
+
+	for _, provider := range []string{"gemini", "vertex", "aistudio", "gemini-interactions"} {
+		t.Run(provider, func(t *testing.T) {
+			selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+				Fallback: &RoundRobinSelector{},
+				TTL:      time.Minute,
+			})
+			defer selector.Stop()
+
+			auths := []*Auth{
+				{ID: "auth-1", Provider: provider},
+				{ID: "auth-2", Provider: provider},
+			}
+
+			parentOpts := cliproxyexecutor.Options{
+				Headers:         http.Header{"X-Claude-Code-Session-Id": []string{"root-google-sess"}},
+				OriginalRequest: []byte(`{"messages":[{"role":"user","content":"parent"}]}`),
+				Metadata:        map[string]any{},
+			}
+			parentAuth, errParent := selector.Pick(context.Background(), provider, "custom-model", parentOpts, auths)
+			if errParent != nil {
+				t.Fatalf("provider %s parent Pick() error = %v", provider, errParent)
+			}
+			if parentAuth.ID != "auth-1" {
+				t.Fatalf("provider %s parent auth = %q, want auth-1", provider, parentAuth.ID)
+			}
+
+			subOpts := cliproxyexecutor.Options{
+				Headers: http.Header{
+					"X-Claude-Code-Session-Id": []string{"root-google-sess"},
+					"X-Claude-Code-Agent-Id":   []string{"subagent-001"},
+				},
+				OriginalRequest: []byte(`{"messages":[{"role":"user","content":"sub"}]}`),
+				Metadata:        map[string]any{},
+			}
+			subAuth, errSub := selector.Pick(context.Background(), provider, "custom-model", subOpts, auths)
+			if errSub != nil {
+				t.Fatalf("provider %s subagent Pick() error = %v", provider, errSub)
+			}
+			if subAuth.ID == parentAuth.ID {
+				t.Fatalf("provider %s subagent incorrectly inherited parent auth %q", provider, parentAuth.ID)
+			}
+			if subAuth.ID != "auth-2" {
+				t.Fatalf("provider %s subagent auth = %q, want auth-2", provider, subAuth.ID)
+			}
+		})
+	}
+}