diff --git a/config.example.yaml b/config.example.yaml
index 653b78421..0db308f97 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -197,9 +197,9 @@ quota-exceeded:
 routing:
   strategy: "round-robin" # round-robin (default), fill-first
   # Enable universal session-sticky routing for all clients.
-  # Session IDs are extracted from: metadata.user_id (Claude Code session format),
-  # X-Session-ID, Session_id (Codex), X-Client-Request-Id (PI), conversation_id,
-  # or first few messages hash.
+  # Explicit Claude Code, Codex, OpenCode, and pi session headers are preferred,
+  # followed by prompt_cache_key, Responses conversation IDs, legacy body IDs,
+  # execution or derived session identity, and the existing first-message hash fallback.
   # Automatic failover is always enabled when bound auth becomes unavailable.
   session-affinity: false # default: false
   # How long session-to-auth bindings are retained. Default: 1h
diff --git a/internal/config/config_types.go b/internal/config/config_types.go
index 76eb6ef30..c0eaa1d6a 100644
--- a/internal/config/config_types.go
+++ b/internal/config/config_types.go
@@ -207,9 +207,9 @@ type RoutingConfig struct {
 	Strategy string `yaml:"strategy,omitempty" json:"strategy,omitempty"`
 
 	// SessionAffinity enables universal session-sticky routing for all clients.
-	// Session IDs are extracted from multiple sources:
-	// metadata.user_id (Claude Code session format), X-Session-ID, Session_id (Codex),
-	// X-Client-Request-Id (PI), metadata.user_id, conversation_id, or message hash.
+	// Explicit Claude Code, Codex, OpenCode, and pi session headers are preferred,
+	// followed by prompt_cache_key, Responses conversation IDs, legacy body IDs,
+	// execution or derived session identity, and the existing message-content hash fallback.
 	// Automatic failover is always enabled when bound auth becomes unavailable.
 	SessionAffinity bool `yaml:"session-affinity,omitempty" json:"session-affinity,omitempty"`
 
diff --git a/sdk/cliproxy/auth/conductor.go b/sdk/cliproxy/auth/conductor.go
index cf537b6df..d25524a6c 100644
--- a/sdk/cliproxy/auth/conductor.go
+++ b/sdk/cliproxy/auth/conductor.go
@@ -121,6 +121,7 @@ type Manager struct {
 	// homeSessionSelections owns retained Home selections for websocket sessions.
 	homeSessionSelections map[string]map[homeSessionSelectionKey]*HomeDispatchSelection
 	homeSessionLocks      sync.Map
+	homeSessionAliases    homeSessionAliasCache
 	// providerOffsets tracks per-model provider rotation state for multi-provider routing.
 	providerOffsets             map[string]int
 	homeDispatchBundle          atomic.Pointer[HomeDispatchBundle]
diff --git a/sdk/cliproxy/auth/conductor_cooldown.go b/sdk/cliproxy/auth/conductor_cooldown.go
index d21ab818a..6d24ce468 100644
--- a/sdk/cliproxy/auth/conductor_cooldown.go
+++ b/sdk/cliproxy/auth/conductor_cooldown.go
@@ -117,6 +117,10 @@ func (m *Manager) setConfigSnapshotLocked(cfg *internalconfig.Config) bool {
 	m.mu.RLock()
 	oldCooldownStore := m.cooldownStore
 	m.mu.RUnlock()
+	previousCfg, _ := m.runtimeConfig.Load().(*internalconfig.Config)
+	if homeSessionAliasTTL(previousCfg) != homeSessionAliasTTL(cfg) {
+		m.homeSessionAliases.clear()
+	}
 	m.runtimeConfig.Store(cfg)
 	clearedCooldowns := m.clearDisabledCooldownStates(cfg)
 	if clearedCooldowns && oldCooldownStore != nil {
diff --git a/sdk/cliproxy/auth/conductor_home.go b/sdk/cliproxy/auth/conductor_home.go
index 0c85f17a3..92ef35084 100644
--- a/sdk/cliproxy/auth/conductor_home.go
+++ b/sdk/cliproxy/auth/conductor_home.go
@@ -509,6 +509,7 @@ func (m *Manager) clearHomeRuntimeAuths() {
 	m.clearHomeRuntimeAuthsLocked()
 	selections := m.takeAllHomeSessionSelectionsLocked()
 	m.mu.Unlock()
+	m.homeSessionAliases.clear()
 	for _, selection := range selections {
 		selection.End("home_disabled")
 	}
@@ -716,7 +717,7 @@ func (m *Manager) pickHomeDispatchSelection(ctx context.Context, model string, o
 		return nil, &Error{Code: "home_unavailable", Message: "home execution registry unavailable", Retryable: true, HTTPStatus: http.StatusServiceUnavailable}
 	}
 
-	sessionID := ExtractSessionID(opts.Headers, opts.OriginalRequest, opts.Metadata)
+	sessionID := m.homeDispatchSessionID(opts)
 	dispatchHeaders := homeDispatchHeaders(ctx, opts.Headers)
 	raw, errRPop := client.RPopAuth(ctx, requestedModel, sessionID, dispatchHeaders, homeAuthCountFromMetadata(opts.Metadata))
 	if errRPop != nil {
diff --git a/sdk/cliproxy/auth/home_session_alias.go b/sdk/cliproxy/auth/home_session_alias.go
new file mode 100644
index 000000000..f422441a4
--- /dev/null
+++ b/sdk/cliproxy/auth/home_session_alias.go
@@ -0,0 +1,243 @@
+package auth
+
+import (
+	"container/list"
+	"strings"
+	"sync"
+	"time"
+
+	internalconfig "github.com/router-for-me/CLIProxyAPI/v7/internal/config"
+	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+)
+
+const (
+	defaultHomeSessionAliasTTL = time.Hour
+	homeSessionAliasCleanupOps = 256
+	homeSessionAliasSoftLimit  = 4096
+)
+
+type homeSessionAliasEntry struct {
+	canonical string
+	expiresAt time.Time
+	aliases   []string
+}
+
+// homeSessionAliasCache reconciles multiple client identifiers for one Home
+// session without changing Home's single-session-ID protocol.
+type homeSessionAliasCache struct {
+	mu               sync.Mutex
+	entries          map[string]homeSessionAliasEntry
+	groups           map[string]homeSessionAliasEntry
+	evictionOrder    *list.List
+	evictionElements map[string]*list.Element
+	ops              uint64
+}
+
+func (c *homeSessionAliasCache) canonical(primary, fallback string, ttl time.Duration, now time.Time) string {
+	primary = strings.TrimSpace(primary)
+	fallback = strings.TrimSpace(fallback)
+	if primary == "" {
+		return ""
+	}
+	if ttl <= 0 {
+		ttl = defaultHomeSessionAliasTTL
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.ensureInitializedLocked()
+	c.ops++
+	if c.ops%homeSessionAliasCleanupOps == 0 {
+		c.cleanupLocked(now)
+	}
+
+	canonical := primary
+	aliases := mergeSessionAliases(nil, primary, fallback)
+	previousGroups := make(map[string]homeSessionAliasEntry, 2)
+	remember := func(entry homeSessionAliasEntry) {
+		previousGroups[entry.canonical] = entry
+	}
+
+	primaryFound := false
+	canonicalFromLiveAlias := false
+	if existing, ok := c.entryLocked(primary, now); ok {
+		primaryFound = true
+		canonicalFromLiveAlias = true
+		canonical = existing.canonical
+		remember(existing)
+		aliases = mergeSessionAliases(aliases, existing.aliases...)
+	}
+	if fallback != "" && fallback != primary {
+		if existing, ok := c.entryLocked(fallback, now); ok {
+			canonicalFromLiveAlias = true
+			if !primaryFound {
+				canonical = existing.canonical
+			}
+			remember(existing)
+			aliases = mergeSessionAliases(aliases, existing.aliases...)
+		}
+	}
+	if canonicalFromLiveAlias {
+		if existing, ok := c.groupLocked(canonical, now); ok {
+			remember(existing)
+			aliases = mergeSessionAliases(aliases, existing.aliases...)
+		}
+	}
+	if !canonicalFromLiveAlias {
+		if _, ok := c.groupLocked(canonical, now); ok {
+			return canonical
+		}
+	}
+	aliases = compactHomeSessionAliases(mergeSessionAliases(aliases, canonical))
+	for _, previous := range previousGroups {
+		c.removeGroupLocked(previous)
+	}
+
+	c.setGroupLocked(homeSessionAliasEntry{
+		canonical: canonical,
+		expiresAt: now.Add(ttl),
+		aliases:   aliases,
+	})
+	c.enforceLimitLocked(homeSessionAliasSoftLimit)
+	return canonical
+}
+
+func (c *homeSessionAliasCache) ensureInitializedLocked() {
+	if c.entries == nil {
+		c.entries = make(map[string]homeSessionAliasEntry)
+	}
+	if c.groups == nil {
+		c.groups = make(map[string]homeSessionAliasEntry)
+	}
+	if c.evictionOrder == nil {
+		c.evictionOrder = list.New()
+	}
+	if c.evictionElements == nil {
+		c.evictionElements = make(map[string]*list.Element)
+	}
+}
+
+func (c *homeSessionAliasCache) entryLocked(alias string, now time.Time) (homeSessionAliasEntry, bool) {
+	entry, ok := c.entries[alias]
+	if !ok {
+		return homeSessionAliasEntry{}, false
+	}
+	if now.Before(entry.expiresAt) {
+		return entry, true
+	}
+	if group, exists := c.groups[entry.canonical]; exists && sameHomeSessionAliasGroup(group, entry) {
+		c.removeGroupLocked(group)
+	} else {
+		delete(c.entries, alias)
+	}
+	return homeSessionAliasEntry{}, false
+}
+
+func (c *homeSessionAliasCache) groupLocked(canonical string, now time.Time) (homeSessionAliasEntry, bool) {
+	entry, ok := c.groups[canonical]
+	if !ok {
+		return homeSessionAliasEntry{}, false
+	}
+	if now.Before(entry.expiresAt) {
+		return entry, true
+	}
+	c.removeGroupLocked(entry)
+	return homeSessionAliasEntry{}, false
+}
+
+func (c *homeSessionAliasCache) setGroupLocked(entry homeSessionAliasEntry) {
+	if existing, ok := c.groups[entry.canonical]; ok {
+		c.removeGroupLocked(existing)
+	}
+	entry.aliases = append([]string(nil), entry.aliases...)
+	c.groups[entry.canonical] = entry
+	for _, alias := range entry.aliases {
+		c.entries[alias] = entry
+	}
+	c.evictionElements[entry.canonical] = c.evictionOrder.PushBack(entry.canonical)
+}
+
+func (c *homeSessionAliasCache) removeGroupLocked(entry homeSessionAliasEntry) {
+	current, ok := c.groups[entry.canonical]
+	if !ok || !sameHomeSessionAliasGroup(current, entry) {
+		return
+	}
+	for _, alias := range current.aliases {
+		mapped, exists := c.entries[alias]
+		if exists && sameHomeSessionAliasGroup(mapped, current) {
+			delete(c.entries, alias)
+		}
+	}
+	delete(c.groups, current.canonical)
+	if element, exists := c.evictionElements[current.canonical]; exists {
+		c.evictionOrder.Remove(element)
+		delete(c.evictionElements, current.canonical)
+	}
+}
+
+func sameHomeSessionAliasGroup(left, right homeSessionAliasEntry) bool {
+	return left.canonical == right.canonical && left.expiresAt.Equal(right.expiresAt) &&
+		equalSessionAliases(left.aliases, right.aliases)
+}
+
+func (c *homeSessionAliasCache) enforceLimitLocked(limit int) {
+	if limit <= 0 {
+		return
+	}
+	for len(c.entries) > limit {
+		oldest := c.evictionOrder.Front()
+		if oldest == nil {
+			return
+		}
+		canonical, _ := oldest.Value.(string)
+		entry, ok := c.groups[canonical]
+		if !ok {
+			c.evictionOrder.Remove(oldest)
+			delete(c.evictionElements, canonical)
+			continue
+		}
+		c.removeGroupLocked(entry)
+	}
+}
+
+func (c *homeSessionAliasCache) cleanupLocked(now time.Time) {
+	for _, entry := range c.groups {
+		if !now.Before(entry.expiresAt) {
+			c.removeGroupLocked(entry)
+		}
+	}
+}
+
+func (c *homeSessionAliasCache) clear() {
+	c.mu.Lock()
+	c.entries = nil
+	c.groups = nil
+	c.evictionOrder = nil
+	c.evictionElements = nil
+	c.ops = 0
+	c.mu.Unlock()
+}
+
+func homeSessionAliasTTL(cfg *internalconfig.Config) time.Duration {
+	if cfg == nil {
+		return defaultHomeSessionAliasTTL
+	}
+	raw := strings.TrimSpace(cfg.Routing.SessionAffinityTTL)
+	if raw == "" {
+		return defaultHomeSessionAliasTTL
+	}
+	parsed, errParse := time.ParseDuration(raw)
+	if errParse != nil || parsed <= 0 {
+		return defaultHomeSessionAliasTTL
+	}
+	return parsed
+}
+
+func (m *Manager) homeDispatchSessionID(opts cliproxyexecutor.Options) string {
+	primary, fallback := extractSessionIDs(opts.Headers, opts.OriginalRequest, opts.Metadata)
+	if primary == "" || m == nil {
+		return primary
+	}
+	cfg, _ := m.runtimeConfig.Load().(*internalconfig.Config)
+	return m.homeSessionAliases.canonical(primary, fallback, homeSessionAliasTTL(cfg), time.Now())
+}
diff --git a/sdk/cliproxy/auth/home_session_alias_test.go b/sdk/cliproxy/auth/home_session_alias_test.go
new file mode 100644
index 000000000..d271aab11
--- /dev/null
+++ b/sdk/cliproxy/auth/home_session_alias_test.go
@@ -0,0 +1,329 @@
+package auth
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"sync"
+	"testing"
+	"time"
+
+	internalconfig "github.com/router-for-me/CLIProxyAPI/v7/internal/config"
+	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+)
+
+type sessionAliasCaptureDispatcher struct {
+	mu       sync.Mutex
+	sessions []string
+}
+
+func (*sessionAliasCaptureDispatcher) HeartbeatOK() bool { return true }
+
+func (d *sessionAliasCaptureDispatcher) RPopAuth(_ context.Context, _ string, sessionID string, _ http.Header, _ int) ([]byte, error) {
+	d.mu.Lock()
+	d.sessions = append(d.sessions, sessionID)
+	d.mu.Unlock()
+	return json.Marshal(homeAuthDispatchResponse{Auth: Auth{
+		ID:       "home-session-alias-auth",
+		Provider: "home-session-alias",
+		Status:   StatusActive,
+	}})
+}
+
+func (*sessionAliasCaptureDispatcher) AbortAmbiguousDispatch() {}
+
+func (d *sessionAliasCaptureDispatcher) sessionIDs() []string {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return append([]string(nil), d.sessions...)
+}
+
+func TestHomeSessionAliasCacheClearsWhenConfiguredTTLChanges(t *testing.T) {
+	manager := NewManager(nil, nil, nil)
+	manager.SetConfig(&internalconfig.Config{
+		Home:    internalconfig.HomeConfig{Enabled: true},
+		Routing: internalconfig.RoutingConfig{SessionAffinityTTL: "1h"},
+	})
+	combined := cliproxyexecutor.Options{OriginalRequest: []byte(
+		`{"conversation":{"id":"ttl-conversation"},"prompt_cache_key":"ttl-prompt"}`,
+	)}
+	conversationOnly := cliproxyexecutor.Options{OriginalRequest: []byte(
+		`{"conversation":{"id":"ttl-conversation"}}`,
+	)}
+	if got := manager.homeDispatchSessionID(combined); got != "pck:ttl-prompt" {
+		t.Fatalf("combined canonical = %q, want pck:ttl-prompt", got)
+	}
+	if got := manager.homeDispatchSessionID(conversationOnly); got != "pck:ttl-prompt" {
+		t.Fatalf("conversation canonical before reload = %q, want existing prompt canonical", got)
+	}
+
+	manager.SetConfig(&internalconfig.Config{
+		Home:    internalconfig.HomeConfig{Enabled: true},
+		Routing: internalconfig.RoutingConfig{SessionAffinityTTL: "1m"},
+	})
+	if got := manager.homeDispatchSessionID(conversationOnly); got != "conv:ttl-conversation" {
+		t.Fatalf("conversation canonical after TTL change = %q, want cleared alias cache", got)
+	}
+}
+
+func TestHomeDispatchCanonicalizesPromptCacheAndConversationAliases(t *testing.T) {
+	tests := []struct {
+		name     string
+		payloads []string
+		want     string
+	}{
+		{
+			name: "conversation then combined then prompt cache",
+			payloads: []string{
+				`{"conversation":{"id":"conversation-session"}}`,
+				`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`,
+				`{"prompt_cache_key":"shared-cache-bucket"}`,
+			},
+			want: "conv:conversation-session",
+		},
+		{
+			name: "prompt cache then combined then conversation",
+			payloads: []string{
+				`{"prompt_cache_key":"shared-cache-bucket"}`,
+				`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`,
+				`{"conversation":{"id":"conversation-session"}}`,
+			},
+			want: "pck:shared-cache-bucket",
+		},
+		{
+			name: "combined request establishes prompt cache primary",
+			payloads: []string{
+				`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`,
+				`{"conversation":{"id":"conversation-session"}}`,
+				`{"prompt_cache_key":"shared-cache-bucket"}`,
+			},
+			want: "pck:shared-cache-bucket",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dispatcher := &sessionAliasCaptureDispatcher{}
+			manager := newHomeSelectionTestManager(t, dispatcher)
+			manager.RegisterExecutor(schedulerTestExecutor{provider: "home-session-alias"})
+
+			for _, payload := range tt.payloads {
+				selection, errSelection := manager.pickHomeDispatchSelection(context.Background(), "gpt-test", cliproxyexecutor.Options{
+					OriginalRequest: []byte(payload),
+				})
+				if errSelection != nil {
+					t.Fatalf("pickHomeDispatchSelection() error = %v", errSelection)
+				}
+				selection.End("test_complete")
+			}
+
+			got := dispatcher.sessionIDs()
+			if len(got) != len(tt.payloads) {
+				t.Fatalf("Home session IDs = %#v, want %d entries", got, len(tt.payloads))
+			}
+			for index, sessionID := range got {
+				if sessionID != tt.want {
+					t.Fatalf("Home session ID[%d] = %q, want %q; all=%#v", index, sessionID, tt.want, got)
+				}
+			}
+		})
+	}
+}
+
+func TestHomeSessionAliasCachePrimaryAccessRefreshesWholeAliasGroup(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const primary = "pck:shared-cache-bucket"
+	const fallback = "conv:conversation-session"
+
+	if got := cache.canonical(primary, fallback, time.Minute, now); got != primary {
+		t.Fatalf("initial canonical = %q, want %q", got, primary)
+	}
+	cache.mu.Lock()
+	fallbackEntry := cache.entries[fallback]
+	fallbackEntry.expiresAt = now.Add(-time.Second)
+	cache.entries[fallback] = fallbackEntry
+	cache.mu.Unlock()
+
+	if got := cache.canonical(primary, "", time.Minute, now.Add(10*time.Second)); got != primary {
+		t.Fatalf("primary-only canonical = %q, want %q", got, primary)
+	}
+	if got := cache.canonical(fallback, "", time.Minute, now.Add(20*time.Second)); got != primary {
+		t.Fatalf("fallback canonical after active primary traffic = %q, want %q", got, primary)
+	}
+}
+
+func TestHomeSessionAliasCacheSharedPromptKeyPreservesConversationAliases(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const promptKey = "pck:shared-cache-bucket"
+	const conversationA = "conv:conversation-a"
+	const conversationB = "conv:conversation-b"
+
+	if got := cache.canonical(promptKey, conversationA, time.Minute, now); got != promptKey {
+		t.Fatalf("conversation A canonical = %q, want %q", got, promptKey)
+	}
+	if got := cache.canonical(promptKey, conversationB, time.Minute, now.Add(time.Second)); got != promptKey {
+		t.Fatalf("conversation B canonical = %q, want %q", got, promptKey)
+	}
+	if got := cache.canonical(conversationA, "", time.Minute, now.Add(2*time.Second)); got != promptKey {
+		t.Fatalf("conversation A alias canonical = %q, want %q", got, promptKey)
+	}
+	if got := cache.canonical(conversationB, "", time.Minute, now.Add(3*time.Second)); got != promptKey {
+		t.Fatalf("conversation B alias canonical = %q, want %q", got, promptKey)
+	}
+}
+
+func TestHomeSessionAliasCacheConversationIDContainingPromptMarkerRemainsStable(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const promptKey = "pck:shared-cache-bucket"
+	const conversation = "conv:a::pck:b"
+	if got := cache.canonical(promptKey, conversation, time.Minute, now); got != promptKey {
+		t.Fatalf("combined canonical = %q, want %q", got, promptKey)
+	}
+	if got := cache.canonical(conversation, "", time.Minute, now.Add(time.Second)); got != promptKey {
+		t.Fatalf("conversation-only canonical = %q, want %q", got, promptKey)
+	}
+}
+
+func TestHomeSessionAliasCacheSharedPromptKeyCapsStableAliasesByRecency(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const promptKey = "pck:shared-cache-bucket"
+	for index := 0; index < 128; index++ {
+		conversation := fmt.Sprintf("conv:conversation-%03d", index)
+		cache.canonical(promptKey, conversation, time.Minute, now.Add(time.Duration(index)*time.Second))
+	}
+
+	cache.mu.Lock()
+	defer cache.mu.Unlock()
+	if len(cache.entries) > 65 {
+		t.Fatalf("home alias entries = %d, want one prompt key plus at most 64 stable aliases", len(cache.entries))
+	}
+	if _, ok := cache.entries["conv:conversation-127"]; !ok {
+		t.Fatal("newest Home conversation alias was not retained")
+	}
+	if _, ok := cache.entries["conv:conversation-000"]; ok {
+		t.Fatal("oldest Home conversation alias was retained after stable-alias cap")
+	}
+}
+
+func TestHomeSessionAliasCacheRotatingPrimaryEvictsObsoleteAliases(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const fallback = "conv:conversation-session"
+	wantCanonical := "pck:cache-00"
+	for index := 0; index < 16; index++ {
+		primary := fmt.Sprintf("pck:cache-%02d", index)
+		if got := cache.canonical(primary, fallback, time.Minute, now.Add(time.Duration(index)*time.Second)); got != wantCanonical {
+			t.Fatalf("canonical at index %d = %q, want %q", index, got, wantCanonical)
+		}
+	}
+	latest := "pck:cache-15"
+
+	cache.mu.Lock()
+	defer cache.mu.Unlock()
+	if len(cache.entries) != 2 {
+		t.Fatalf("home alias entries = %d, want only latest primary and fallback", len(cache.entries))
+	}
+	if _, ok := cache.entries[latest]; !ok {
+		t.Fatalf("latest primary %q was not retained", latest)
+	}
+	if _, ok := cache.entries[fallback]; !ok {
+		t.Fatalf("fallback %q was not retained", fallback)
+	}
+	if _, ok := cache.entries[wantCanonical]; ok {
+		t.Fatalf("obsolete canonical alias %q was retained as a lookup key", wantCanonical)
+	}
+	if aliases := cache.entries[fallback].aliases; len(aliases) != 2 {
+		t.Fatalf("home fallback alias group = %#v, want exactly two active identifiers", aliases)
+	}
+}
+
+func TestHomeSessionAliasCacheDoesNotReconnectCompactedCanonicalAlias(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const obsoletePrompt = "pck:cache-a"
+	const currentPrompt = "pck:cache-b"
+	const conversation = "conv:conversation-session"
+
+	if got := cache.canonical(obsoletePrompt, conversation, time.Minute, now); got != obsoletePrompt {
+		t.Fatalf("initial canonical = %q, want %q", got, obsoletePrompt)
+	}
+	if got := cache.canonical(currentPrompt, conversation, time.Minute, now.Add(time.Second)); got != obsoletePrompt {
+		t.Fatalf("rotated canonical = %q, want stable %q", got, obsoletePrompt)
+	}
+
+	cache.mu.Lock()
+	if _, ok := cache.entries[obsoletePrompt]; ok {
+		cache.mu.Unlock()
+		t.Fatalf("obsolete prompt alias %q remained live after compaction", obsoletePrompt)
+	}
+	cache.mu.Unlock()
+
+	if got := cache.canonical(obsoletePrompt, "", time.Minute, now.Add(2*time.Second)); got != obsoletePrompt {
+		t.Fatalf("obsolete prompt canonical = %q, want standalone %q", got, obsoletePrompt)
+	}
+
+	cache.mu.Lock()
+	conversationEntry, conversationOK := cache.entries[conversation]
+	currentEntry, currentOK := cache.entries[currentPrompt]
+	_, obsoleteOK := cache.entries[obsoletePrompt]
+	cache.mu.Unlock()
+	if obsoleteOK {
+		t.Fatalf("stale canonical %q replaced the live group", obsoletePrompt)
+	}
+	if !conversationOK || !currentOK || !sameHomeSessionAliasGroup(conversationEntry, currentEntry) {
+		t.Fatalf("live aliases were disconnected: conversation=%#v current=%#v", conversationEntry, currentEntry)
+	}
+	if got := cache.canonical(conversation, "", time.Minute, now.Add(3*time.Second)); got != obsoletePrompt {
+		t.Fatalf("live conversation canonical = %q, want %q", got, obsoletePrompt)
+	}
+}
+
+func TestHomeSessionAliasCacheSoftLimitEvictsOldestTouchedGroup(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	const oldest = "session:zzzz-oldest"
+	cache.canonical(oldest, "", time.Hour, now)
+	for index := 0; index < homeSessionAliasSoftLimit; index++ {
+		cache.canonical(fmt.Sprintf("session:%05d", index), "", time.Hour, now)
+	}
+
+	cache.mu.Lock()
+	defer cache.mu.Unlock()
+	if len(cache.entries) > homeSessionAliasSoftLimit {
+		t.Fatalf("alias entries = %d, want at most %d", len(cache.entries), homeSessionAliasSoftLimit)
+	}
+	if _, ok := cache.entries[oldest]; ok {
+		t.Fatalf("oldest insertion %q remained after incremental eviction", oldest)
+	}
+	if _, ok := cache.entries["session:00000"]; !ok {
+		t.Fatal("newer insertion was evicted instead of the oldest group")
+	}
+}
+
+func TestHomeSessionAliasCacheEnforcesSoftLimit(t *testing.T) {
+	var cache homeSessionAliasCache
+	now := time.Now()
+	for i := 0; i < homeSessionAliasSoftLimit+32; i++ {
+		cache.canonical(fmt.Sprintf("session:%05d", i), "", time.Hour, now.Add(time.Duration(i)*time.Nanosecond))
+	}
+
+	cache.mu.Lock()
+	entryCount := len(cache.entries)
+	_, oldestPresent := cache.entries["session:00000"]
+	_, newestPresent := cache.entries[fmt.Sprintf("session:%05d", homeSessionAliasSoftLimit+31)]
+	cache.mu.Unlock()
+	if entryCount > homeSessionAliasSoftLimit {
+		t.Fatalf("alias entries = %d, want at most %d", entryCount, homeSessionAliasSoftLimit)
+	}
+	if oldestPresent {
+		t.Fatal("oldest alias remained after enforcing soft limit")
+	}
+	if !newestPresent {
+		t.Fatal("newest alias was evicted while enforcing soft limit")
+	}
+}
diff --git a/sdk/cliproxy/auth/selector.go b/sdk/cliproxy/auth/selector.go
index 4230bddc0..4be062570 100644
--- a/sdk/cliproxy/auth/selector.go
+++ b/sdk/cliproxy/auth/selector.go
@@ -7,7 +7,6 @@ import (
 	"hash/fnv"
 	"math"
 	"net/http"
-	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -362,10 +361,6 @@ func isAuthBlockedForModel(auth *Auth, model string, now time.Time) (bool, block
 	return false, blockReasonNone, time.Time{}
 }
 
-// sessionPattern matches Claude Code user_id format:
-// user_{hash}_account__session_{uuid}
-var sessionPattern = regexp.MustCompile(`_session_([a-f0-9-]+)$`)
-
 // SessionAffinitySelector wraps another selector with session-sticky behavior.
 // It extracts session ID from multiple sources and maintains session-to-auth
 // mappings with automatic failover when the bound auth becomes unavailable.
@@ -403,14 +398,8 @@ func NewSessionAffinitySelectorWithConfig(cfg SessionAffinityConfig) *SessionAff
 }
 
 // Pick selects an auth with session affinity when possible.
-// Priority for session ID extraction:
-//  1. metadata.user_id containing a Claude Code session
-//  2. Explicit session headers
-//  3. X-Client-Request-Id header
-//  4. Explicit request-body session and user fields
-//  5. Explicit execution session metadata
-//  6. Stable context-derived session identity
-//  7. Legacy message hash fallback
+// Explicit Claude Code, Codex, OpenCode, pi, and request-body session signals
+// precede execution metadata, stable derived identity, and the legacy hash fallback.
 //
 // Note: The cache key includes provider, session ID, and model to handle cases where
 // a session uses multiple models (e.g., gemini-2.5-pro and gemini-3-flash-preview)
@@ -430,10 +419,22 @@ func (s *SessionAffinitySelector) Pick(ctx context.Context, provider, model stri
 	}
 
 	cacheKey := provider + "::" + primaryID + "::" + model
+	fallbackKey := ""
+	if fallbackID != "" && fallbackID != primaryID {
+		fallbackKey = provider + "::" + fallbackID + "::" + model
+	}
+	bind := func(authID string) {
+		if fallbackKey != "" {
+			s.cache.SetAliases(authID, cacheKey, fallbackKey)
+			return
+		}
+		s.cache.Set(cacheKey, authID)
+	}
 
 	if cachedAuthID, ok := s.cache.GetAndRefresh(cacheKey); ok {
 		for _, auth := range available {
 			if auth.ID == cachedAuthID {
+				bind(auth.ID)
 				entry.Infof("session-affinity: cache hit | session=%s auth=%s provider=%s model=%s", truncateSessionID(primaryID), auth.ID, provider, model)
 				return auth, nil
 			}
@@ -443,17 +444,16 @@ func (s *SessionAffinitySelector) Pick(ctx context.Context, provider, model stri
 		if err != nil {
 			return nil, err
 		}
-		s.cache.Set(cacheKey, auth.ID)
+		bind(auth.ID)
 		entry.Infof("session-affinity: cache hit but auth unavailable, reselected | session=%s auth=%s provider=%s model=%s", truncateSessionID(primaryID), auth.ID, provider, model)
 		return auth, nil
 	}
 
-	if fallbackID != "" && fallbackID != primaryID {
-		fallbackKey := provider + "::" + fallbackID + "::" + model
+	if fallbackKey != "" {
 		if cachedAuthID, ok := s.cache.Get(fallbackKey); ok {
 			for _, auth := range available {
 				if auth.ID == cachedAuthID {
-					s.cache.Set(cacheKey, auth.ID)
+					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
 				}
@@ -465,7 +465,7 @@ func (s *SessionAffinitySelector) Pick(ctx context.Context, provider, model stri
 	if err != nil {
 		return nil, err
 	}
-	s.cache.Set(cacheKey, auth.ID)
+	bind(auth.ID)
 	entry.Infof("session-affinity: cache miss, new binding | session=%s auth=%s provider=%s model=%s", truncateSessionID(primaryID), auth.ID, provider, model)
 	return auth, nil
 }
@@ -503,113 +503,124 @@ func (s *SessionAffinitySelector) InvalidateAuth(authID string) {
 	}
 }
 
-// ExtractSessionID extracts session identifier from multiple sources.
+// normalizedSessionCandidate validates an explicit client-provided session signal.
+// It keeps opaque printable IDs intact while rejecting values that are unsafe or
+// implausibly large for routing keys and logs.
+func normalizedSessionCandidate(raw string) string {
+	return cliproxysession.NormalizeExplicitID(raw)
+}
+
+func sessionHeaderValue(headers http.Header, name string) string {
+	if headers == nil {
+		return ""
+	}
+	if value := normalizedSessionCandidate(headers.Get(name)); value != "" {
+		return value
+	}
+	for key, values := range headers {
+		if !strings.EqualFold(key, name) {
+			continue
+		}
+		for _, raw := range values {
+			if value := normalizedSessionCandidate(raw); value != "" {
+				return value
+			}
+		}
+	}
+	return ""
+}
+
+// ExtractSessionID extracts a session identifier from explicit client signals,
+// then falls back to execution metadata, derived identity, and message history.
 // Priority order:
-//  1. metadata.user_id containing a Claude Code session
-//  2. Explicit session headers
-//  3. X-Client-Request-Id header
-//  4. Explicit request-body session and user fields
-//  5. Explicit execution session metadata
-//  6. Stable context-derived session identity
-//  7. Legacy message hash fallback
+//  1. X-Claude-Code-Session-Id
+//  2. Claude Code metadata.user_id session
+//  3. Session-Id / Session_id (Codex and compatible clients)
+//  4. X-Session-ID
+//  5. X-Session-Affinity (OpenCode)
+//  6. X-Client-Request-Id (pi Responses)
+//  7. session_id / sessionId
+//  8. prompt_cache_key, with conversation / conversation.id as an alias
+//  9. metadata.user_id and conversation_id legacy body fields
+//  10. explicit execution session metadata
+//  11. stable context-derived session identity
+//  12. stable hash from initial message content
 func ExtractSessionID(headers http.Header, payload []byte, metadata map[string]any) string {
 	primary, _ := extractSessionIDs(headers, payload, metadata)
 	return primary
 }
 
 // extractSessionIDs returns (primaryID, fallbackID) for session affinity.
-// primaryID: full hash including assistant response (stable after first turn)
-// fallbackID: short hash without assistant (used to inherit binding from first turn)
+// fallbackID preserves an earlier binding when a stronger body identifier appears
+// later, and lets callers bind both identifiers when both are present.
 func extractSessionIDs(headers http.Header, payload []byte, metadata map[string]any) (string, string) {
-	// 1. metadata.user_id with Claude Code session format (highest priority)
-	if len(payload) > 0 {
-		userID := gjson.GetBytes(payload, "metadata.user_id").String()
-		if userID != "" {
-			// Old format: user_{hash}_account__session_{uuid}
-			if matches := sessionPattern.FindStringSubmatch(userID); len(matches) >= 2 {
-				id := "claude:" + matches[1]
-				return id, ""
-			}
-			// New format: JSON object with session_id field
-			// e.g. {"device_id":"...","account_uuid":"...","session_id":"uuid"}
-			if len(userID) > 0 && userID[0] == '{' {
-				if sid := gjson.Get(userID, "session_id").String(); sid != "" {
-					return "claude:" + sid, ""
-				}
-			}
-		}
+	if sid := sessionHeaderValue(headers, "X-Claude-Code-Session-Id"); sid != "" {
+		return "claude:" + sid, ""
 	}
-
-	// 2. X-Session-ID header
-	if sessionID := sessionHeaderValue(headers, "X-Session-ID"); sessionID != "" {
-		return "header:" + sessionID, ""
+	if sid := cliproxysession.ClaudeMetadataSessionID(payload); sid != "" {
+		return "claude:" + sid, ""
 	}
-
-	// 3. Session_id header (Codex)
-	if sessionID := sessionHeaderValue(headers, "Session-Id"); sessionID != "" {
-		return "codex:" + sessionID, ""
+	if sid := sessionHeaderValue(headers, "Session-Id"); sid != "" {
+		return "codex:" + sid, ""
 	}
-	if sessionID := sessionHeaderValue(headers, "Session_id"); sessionID != "" {
-		return "codex:" + sessionID, ""
+	if sid := sessionHeaderValue(headers, "Session_id"); sid != "" {
+		return "codex:" + sid, ""
 	}
-
-	// 4. X-Client-Request-Id header (PI)
-	if requestID := sessionHeaderValue(headers, "X-Client-Request-Id"); requestID != "" {
-		return "clientreq:" + requestID, ""
+	if sid := sessionHeaderValue(headers, "X-Session-ID"); sid != "" {
+		return "header:" + sid, ""
+	}
+	if sid := sessionHeaderValue(headers, "X-Session-Affinity"); sid != "" {
+		return "affinity:" + sid, ""
+	}
+	if sid := sessionHeaderValue(headers, "X-Client-Request-Id"); sid != "" {
+		return "clientreq:" + sid, ""
 	}
 
 	if len(payload) > 0 {
-		// 5. Explicit request-body session fields.
 		for _, path := range []string{"session_id", "sessionId"} {
-			if sessionID := strings.TrimSpace(gjson.GetBytes(payload, path).String()); sessionID != "" {
-				return "session:" + sessionID, ""
+			if sid := normalizedSessionCandidate(gjson.GetBytes(payload, path).String()); sid != "" {
+				return "session:" + sid, ""
 			}
 		}
-		if userID := strings.TrimSpace(gjson.GetBytes(payload, "metadata.user_id").String()); userID != "" {
+
+		conversationID := ""
+		conversation := gjson.GetBytes(payload, "conversation")
+		if sid := normalizedSessionCandidate(conversation.Get("id").String()); sid != "" {
+			conversationID = "conv:" + sid
+		} else if conversation.Type == gjson.String {
+			if sid := normalizedSessionCandidate(conversation.String()); sid != "" {
+				conversationID = "conv:" + sid
+			}
+		}
+		if sid := normalizedSessionCandidate(gjson.GetBytes(payload, "prompt_cache_key").String()); sid != "" {
+			return "pck:" + sid, conversationID
+		}
+		if conversationID != "" {
+			return conversationID, ""
+		}
+
+		if userID := normalizedSessionCandidate(gjson.GetBytes(payload, "metadata.user_id").String()); userID != "" {
 			return "user:" + userID, ""
 		}
-		if conversationID := strings.TrimSpace(gjson.GetBytes(payload, "conversation_id").String()); conversationID != "" {
+		if conversationID := normalizedSessionCandidate(gjson.GetBytes(payload, "conversation_id").String()); conversationID != "" {
 			return "conv:" + conversationID, ""
 		}
-		if promptCacheKey := strings.TrimSpace(gjson.GetBytes(payload, "prompt_cache_key").String()); promptCacheKey != "" {
-			return "prompt:" + promptCacheKey, ""
-		}
 	}
 
-	// 6. Explicit long-lived execution session.
 	if executionID, ok := metadata[cliproxyexecutor.ExecutionSessionMetadataKey].(string); ok {
-		if executionID = strings.TrimSpace(executionID); executionID != "" {
+		if executionID = normalizedSessionCandidate(executionID); executionID != "" {
 			return "execution:" + executionID, ""
 		}
 	}
-
-	// 7. Stable context-derived session identity.
-	if derivedID := cliproxysession.DerivedID(metadata); derivedID != "" {
+	if derivedID := normalizedSessionCandidate(cliproxysession.DerivedID(metadata)); derivedID != "" {
 		return "derived:" + derivedID, ""
 	}
-
 	if len(payload) == 0 {
 		return "", ""
 	}
-
-	// 8. Legacy hash-based fallback from message content.
 	return extractMessageHashIDs(payload)
 }
 
-func sessionHeaderValue(headers http.Header, name string) string {
-	for key, values := range headers {
-		if !strings.EqualFold(key, name) {
-			continue
-		}
-		for _, value := range values {
-			if value = strings.TrimSpace(value); value != "" {
-				return value
-			}
-		}
-	}
-	return ""
-}
-
 func extractMessageHashIDs(payload []byte) (primaryID, fallbackID string) {
 	var systemPrompt, firstUserMsg, firstAssistantMsg string
 
diff --git a/sdk/cliproxy/auth/selector_test.go b/sdk/cliproxy/auth/selector_test.go
index 51e87206d..cb1bfb40f 100644
--- a/sdk/cliproxy/auth/selector_test.go
+++ b/sdk/cliproxy/auth/selector_test.go
@@ -12,6 +12,8 @@ import (
 	"time"
 
 	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
+	cliproxysession "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/session"
+	sdktranslator "github.com/router-for-me/CLIProxyAPI/v7/sdk/translator"
 )
 
 func TestFillFirstSelectorPick_Deterministic(t *testing.T) {
@@ -612,7 +614,7 @@ func TestSessionAffinitySelector_FailoverWhenAuthUnavailable(t *testing.T) {
 func TestExtractSessionID_ClaudeCodePriorityOverHeader(t *testing.T) {
 	t.Parallel()
 
-	// Claude Code metadata.user_id should have highest priority, even when X-Session-ID header is present
+	// Claude Code metadata.user_id remains higher priority than a generic X-Session-ID header.
 	headers := make(http.Header)
 	headers.Set("X-Session-ID", "header-session-id")
 
@@ -1028,6 +1030,227 @@ func TestSessionAffinitySelector_ThreeScenarios(t *testing.T) {
 	})
 }
 
+func TestSessionAffinitySelectorBodyIdentifierTransitionsPreserveBinding(t *testing.T) {
+	t.Parallel()
+
+	bothPayload := []byte(`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`)
+	primaryID, fallbackID := extractSessionIDs(nil, bothPayload, nil)
+	if primaryID != "pck:shared-cache-bucket" || fallbackID != "conv:conversation-session" {
+		t.Fatalf("extractSessionIDs() = (%q, %q), want prompt-cache primary with conversation fallback", primaryID, fallbackID)
+	}
+
+	for _, tt := range []struct {
+		name         string
+		firstPayload []byte
+	}{
+		{name: "prompt cache first", firstPayload: []byte(`{"prompt_cache_key":"shared-cache-bucket"}`)},
+		{name: "conversation first", firstPayload: []byte(`{"conversation":{"id":"conversation-session"}}`)},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+				Fallback: &RoundRobinSelector{},
+				TTL:      time.Minute,
+			})
+			defer selector.Stop()
+			auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+			provider := "responses-transition-" + tt.name
+
+			first, err := selector.Pick(context.Background(), provider, "gpt-test", cliproxyexecutor.Options{OriginalRequest: tt.firstPayload}, auths)
+			if err != nil {
+				t.Fatalf("first Pick() error = %v", err)
+			}
+			second, err := selector.Pick(context.Background(), provider, "gpt-test", cliproxyexecutor.Options{OriginalRequest: bothPayload}, auths)
+			if err != nil {
+				t.Fatalf("combined-identifier Pick() error = %v", err)
+			}
+			if second.ID != first.ID {
+				t.Fatalf("combined identifiers changed auth from %q to %q", first.ID, second.ID)
+			}
+		})
+	}
+}
+
+func TestSessionAffinitySelectorCombinedIdentifiersBindConversationFallback(t *testing.T) {
+	t.Parallel()
+
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+	auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+	provider := "responses-combined-to-conversation"
+
+	combined := []byte(`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`)
+	conversationOnly := []byte(`{"conversation":{"id":"conversation-session"}}`)
+	first, err := selector.Pick(context.Background(), provider, "gpt-test", cliproxyexecutor.Options{OriginalRequest: combined}, auths)
+	if err != nil {
+		t.Fatalf("combined-identifier Pick() error = %v", err)
+	}
+	second, err := selector.Pick(context.Background(), provider, "gpt-test", cliproxyexecutor.Options{OriginalRequest: conversationOnly}, auths)
+	if err != nil {
+		t.Fatalf("conversation-only Pick() error = %v", err)
+	}
+	if second.ID != first.ID {
+		t.Fatalf("dropping prompt_cache_key changed auth from %q to %q", first.ID, second.ID)
+	}
+}
+
+func TestSessionAffinitySelectorPrimaryTrafficKeepsConversationAliasAlive(t *testing.T) {
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+	auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+	provider := "responses-active-primary-alias"
+	model := "gpt-test"
+	combined := []byte(`{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`)
+	promptOnly := []byte(`{"prompt_cache_key":"shared-cache-bucket"}`)
+	conversationOnly := []byte(`{"conversation":{"id":"conversation-session"}}`)
+
+	first, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: combined}, auths)
+	if err != nil {
+		t.Fatalf("combined Pick() error = %v", err)
+	}
+	conversationKey := provider + "::conv:conversation-session::" + model
+	selector.cache.mu.Lock()
+	conversationEntry := selector.cache.entries[conversationKey]
+	conversationEntry.expiresAt = time.Now().Add(-time.Second)
+	selector.cache.entries[conversationKey] = conversationEntry
+	selector.cache.mu.Unlock()
+
+	primary, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: promptOnly}, auths)
+	if err != nil {
+		t.Fatalf("prompt-only Pick() error = %v", err)
+	}
+	if primary.ID != first.ID {
+		t.Fatalf("prompt-only auth = %q, want %q", primary.ID, first.ID)
+	}
+	fallback, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: conversationOnly}, auths)
+	if err != nil {
+		t.Fatalf("conversation-only Pick() error = %v", err)
+	}
+	if fallback.ID != first.ID {
+		t.Fatalf("conversation alias expired during active primary traffic: got %q, want %q", fallback.ID, first.ID)
+	}
+}
+
+func TestSessionAffinitySelectorSharedPromptKeyPreservesConversationAliases(t *testing.T) {
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+	auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+	provider := "responses-shared-prompt-key"
+	model := "gpt-test"
+
+	combinedA := []byte(`{"conversation":{"id":"conversation-a"},"prompt_cache_key":"shared-cache-bucket"}`)
+	combinedB := []byte(`{"conversation":{"id":"conversation-b"},"prompt_cache_key":"shared-cache-bucket"}`)
+	conversationA := []byte(`{"conversation":{"id":"conversation-a"}}`)
+	conversationB := []byte(`{"conversation":{"id":"conversation-b"}}`)
+
+	first, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: combinedA}, auths)
+	if err != nil {
+		t.Fatalf("conversation A combined Pick() error = %v", err)
+	}
+	second, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: combinedB}, auths)
+	if err != nil {
+		t.Fatalf("conversation B combined Pick() error = %v", err)
+	}
+	if second.ID != first.ID {
+		t.Fatalf("shared prompt key changed auth from %q to %q", first.ID, second.ID)
+	}
+	for name, payload := range map[string][]byte{"conversation A": conversationA, "conversation B": conversationB} {
+		picked, errPick := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: payload}, auths)
+		if errPick != nil {
+			t.Fatalf("%s Pick() error = %v", name, errPick)
+		}
+		if picked.ID != first.ID {
+			t.Fatalf("%s alias selected %q, want %q", name, picked.ID, first.ID)
+		}
+	}
+}
+
+func TestSessionAffinitySelectorConversationIDContainingPromptMarkerRemainsStable(t *testing.T) {
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+	auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+	provider := "responses-opaque-conversation"
+	model := "gpt-test"
+	combined := []byte(`{"conversation":{"id":"a::pck:b"},"prompt_cache_key":"shared-cache-bucket"}`)
+	conversationOnly := []byte(`{"conversation":{"id":"a::pck:b"}}`)
+
+	first, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: combined}, auths)
+	if err != nil {
+		t.Fatalf("combined Pick() error = %v", err)
+	}
+	second, err := selector.Pick(context.Background(), provider, model, cliproxyexecutor.Options{OriginalRequest: conversationOnly}, auths)
+	if err != nil {
+		t.Fatalf("conversation-only Pick() error = %v", err)
+	}
+	if second.ID != first.ID {
+		t.Fatalf("opaque conversation alias selected %q, want %q", second.ID, first.ID)
+	}
+}
+
+func TestSessionCacheSharedPromptKeyCapsStableAliasesByRecency(t *testing.T) {
+	cache := NewSessionCache(time.Minute)
+	defer cache.Stop()
+	const promptKey = "openai::pck:shared-cache-bucket::gpt-test"
+	for index := 0; index < 128; index++ {
+		conversation := fmt.Sprintf("openai::conv:conversation-%03d::gpt-test", index)
+		cache.SetAliases("auth-a", promptKey, conversation)
+	}
+
+	cache.mu.RLock()
+	defer cache.mu.RUnlock()
+	if len(cache.entries) > 65 {
+		t.Fatalf("cache entries = %d, want one prompt key plus at most 64 stable aliases", len(cache.entries))
+	}
+	if _, ok := cache.entries["openai::conv:conversation-127::gpt-test"]; !ok {
+		t.Fatal("newest conversation alias was not retained")
+	}
+	if _, ok := cache.entries["openai::conv:conversation-000::gpt-test"]; ok {
+		t.Fatal("oldest conversation alias was retained after stable-alias cap")
+	}
+}
+
+func TestSessionCacheRotatingPrimaryEvictsObsoleteAliases(t *testing.T) {
+	cache := NewSessionCache(time.Minute)
+	defer cache.Stop()
+
+	const fallback = "openai::conv:conversation-session::gpt-test"
+	for index := 0; index < 16; index++ {
+		primary := fmt.Sprintf("openai::pck:cache-%02d::gpt-test", index)
+		cache.SetAliases("auth-a", primary, fallback)
+	}
+	latest := "openai::pck:cache-15::gpt-test"
+	oldest := "openai::pck:cache-00::gpt-test"
+
+	cache.mu.RLock()
+	defer cache.mu.RUnlock()
+	if len(cache.entries) != 2 {
+		t.Fatalf("cache entries = %d, want only latest primary and fallback", len(cache.entries))
+	}
+	if _, ok := cache.entries[latest]; !ok {
+		t.Fatalf("latest primary %q was not retained", latest)
+	}
+	if _, ok := cache.entries[fallback]; !ok {
+		t.Fatalf("fallback %q was not retained", fallback)
+	}
+	if _, ok := cache.entries[oldest]; ok {
+		t.Fatalf("obsolete primary %q was retained", oldest)
+	}
+	if aliases := cache.entries[fallback].aliases; len(aliases) != 2 {
+		t.Fatalf("fallback alias group = %#v, want exactly two active identifiers", aliases)
+	}
+}
+
 func TestSessionAffinitySelector_MultiModelSession(t *testing.T) {
 	t.Parallel()
 
@@ -1314,3 +1537,248 @@ func TestSessionAffinitySelector_Concurrent(t *testing.T) {
 	default:
 	}
 }
+
+func TestExtractSessionIDNativeSignals(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name    string
+		headers http.Header
+		payload string
+		want    string
+	}{
+		{
+			name:    "claude code header",
+			headers: http.Header{"X-Claude-Code-Session-Id": []string{"claude-session"}},
+			want:    "claude:claude-session",
+		},
+		{
+			name:    "lowercase claude code header",
+			headers: http.Header{"x-claude-code-session-id": []string{"lowercase-session"}},
+			want:    "claude:lowercase-session",
+		},
+		{
+			name:    "codex hyphen header",
+			headers: http.Header{"Session-Id": []string{"codex-session"}},
+			want:    "codex:codex-session",
+		},
+		{
+			name:    "codex underscore header",
+			headers: http.Header{"Session_id": []string{"legacy-codex-session"}},
+			want:    "codex:legacy-codex-session",
+		},
+		{
+			name:    "open code session affinity",
+			headers: http.Header{"X-Session-Affinity": []string{"ses_opencode"}},
+			want:    "affinity:ses_opencode",
+		},
+		{
+			name:    "prompt cache key",
+			payload: `{"prompt_cache_key":"prompt-session"}`,
+			want:    "pck:prompt-session",
+		},
+		{
+			name:    "responses conversation object",
+			payload: `{"conversation":{"id":"conv-object"}}`,
+			want:    "conv:conv-object",
+		},
+		{
+			name:    "responses conversation string",
+			payload: `{"conversation":"conv-string"}`,
+			want:    "conv:conv-string",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if got := ExtractSessionID(tt.headers, []byte(tt.payload), nil); got != tt.want {
+				t.Fatalf("ExtractSessionID() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestExtractSessionIDNativeSignalPriority(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name    string
+		headers http.Header
+		payload string
+		want    string
+	}{
+		{
+			name: "claude header beats metadata",
+			headers: http.Header{
+				"X-Claude-Code-Session-Id": []string{"header-session"},
+			},
+			payload: `{"metadata":{"user_id":"user_hash_account__session_22222222-2222-4222-8222-222222222222"}}`,
+			want:    "claude:header-session",
+		},
+		{
+			name: "claude metadata beats codex header",
+			headers: http.Header{
+				"Session-Id": []string{"codex-session"},
+			},
+			payload: `{"metadata":{"user_id":"user_hash_account__session_22222222-2222-4222-8222-222222222222"}}`,
+			want:    "claude:22222222-2222-4222-8222-222222222222",
+		},
+		{
+			name: "codex header beats x session id and prompt key",
+			headers: http.Header{
+				"Session-Id":   []string{"codex-session"},
+				"X-Session-Id": []string{"generic-session"},
+			},
+			payload: `{"prompt_cache_key":"prompt-session"}`,
+			want:    "codex:codex-session",
+		},
+		{
+			name: "x session id beats affinity",
+			headers: http.Header{
+				"X-Session-Id":       []string{"generic-session"},
+				"X-Session-Affinity": []string{"affinity-session"},
+			},
+			want: "header:generic-session",
+		},
+		{
+			name:    "prompt cache key beats conversation id",
+			payload: `{"conversation":{"id":"conversation-session"},"prompt_cache_key":"shared-cache-bucket"}`,
+			want:    "pck:shared-cache-bucket",
+		},
+		{
+			name: "client request id beats body fallbacks",
+			headers: http.Header{
+				"X-Client-Request-Id": []string{"client-session"},
+			},
+			payload: `{"prompt_cache_key":"prompt-session","conversation":{"id":"conversation-session"}}`,
+			want:    "clientreq:client-session",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if got := ExtractSessionID(tt.headers, []byte(tt.payload), nil); got != tt.want {
+				t.Fatalf("ExtractSessionID() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestExtractSessionIDRejectsInvalidExplicitSignals(t *testing.T) {
+	t.Parallel()
+	tooLong := strings.Repeat("a", 257)
+	tests := []struct {
+		name    string
+		headers http.Header
+		payload string
+		want    string
+	}{
+		{
+			name:    "whitespace",
+			headers: http.Header{"X-Claude-Code-Session-Id": []string{"   "}},
+			want:    "",
+		},
+		{
+			name:    "newline",
+			headers: http.Header{"X-Session-Id": []string{"bad\nsession"}},
+			want:    "",
+		},
+		{
+			name:    "control character",
+			headers: http.Header{"Session-Id": []string{"bad\x00session"}},
+			want:    "",
+		},
+		{
+			name:    "too long",
+			headers: http.Header{"X-Client-Request-Id": []string{tooLong}},
+			want:    "",
+		},
+		{
+			name: "invalid stronger signal falls through",
+			headers: http.Header{
+				"X-Claude-Code-Session-Id": []string{"bad\nsession"},
+				"Session-Id":               []string{"valid-codex"},
+			},
+			want: "codex:valid-codex",
+		},
+		{
+			name:    "invalid prompt key falls through to conversation",
+			payload: `{"prompt_cache_key":"   ","conversation":{"id":"valid-conversation"}}`,
+			want:    "conv:valid-conversation",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if got := ExtractSessionID(tt.headers, []byte(tt.payload), nil); got != tt.want {
+				t.Fatalf("ExtractSessionID() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestExtractSessionIDClaudeMetadataParsesBeforeBoundingSessionID(t *testing.T) {
+	t.Parallel()
+	const sessionID = "11111111-1111-4111-8111-111111111111"
+	metadata := map[string]string{
+		"device_id":         strings.Repeat("d", 64),
+		"account_uuid":      "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa",
+		"session_id":        sessionID,
+		"organization_uuid": "bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb",
+		"email":             "user@example.com",
+	}
+
+	for _, tt := range []struct {
+		name   string
+		encode func(any) ([]byte, error)
+	}{
+		{name: "rich compact json", encode: json.Marshal},
+		{name: "pretty printed json", encode: func(v any) ([]byte, error) { return json.MarshalIndent(v, "", "  ") }},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			userID, errMarshal := tt.encode(metadata)
+			if errMarshal != nil {
+				t.Fatalf("marshal metadata: %v", errMarshal)
+			}
+			payload, errPayload := json.Marshal(map[string]any{
+				"metadata": map[string]string{"user_id": string(userID)},
+			})
+			if errPayload != nil {
+				t.Fatalf("marshal payload: %v", errPayload)
+			}
+			if got := ExtractSessionID(nil, payload, nil); got != "claude:"+sessionID {
+				t.Fatalf("ExtractSessionID() = %q, want %q", got, "claude:"+sessionID)
+			}
+		})
+	}
+}
+
+func TestSessionAffinitySelectorUsesRequestPayloadWhenOriginalRequestMissing(t *testing.T) {
+	selector := NewSessionAffinitySelectorWithConfig(SessionAffinityConfig{
+		Fallback: &RoundRobinSelector{},
+		TTL:      time.Minute,
+	})
+	defer selector.Stop()
+
+	request := cliproxyexecutor.Request{
+		Model:   "gpt-test",
+		Payload: []byte(`{"conversation":{"id":"request-only-conversation"},"input":"hello"}`),
+	}
+	_, opts := cliproxysession.Enrich(request, cliproxyexecutor.Options{
+		SourceFormat: sdktranslator.FormatOpenAIResponse,
+	})
+	auths := []*Auth{{ID: "auth-a"}, {ID: "auth-b"}}
+
+	first, errFirst := selector.Pick(context.Background(), "openai", request.Model, opts, auths)
+	if errFirst != nil {
+		t.Fatalf("first Pick() error = %v", errFirst)
+	}
+	second, errSecond := selector.Pick(context.Background(), "openai", request.Model, opts, auths)
+	if errSecond != nil {
+		t.Fatalf("second Pick() error = %v", errSecond)
+	}
+	if second.ID != first.ID {
+		t.Fatalf("request-only conversation changed auth from %q to %q", first.ID, second.ID)
+	}
+}
diff --git a/sdk/cliproxy/auth/session_cache.go b/sdk/cliproxy/auth/session_cache.go
index a812e581b..54bf3867b 100644
--- a/sdk/cliproxy/auth/session_cache.go
+++ b/sdk/cliproxy/auth/session_cache.go
@@ -1,14 +1,18 @@
 package auth
 
 import (
+	"strings"
 	"sync"
 	"time"
 )
 
-// sessionEntry stores auth binding with expiration.
+const maxStableSessionAliases = 64
+
+// sessionEntry stores an auth binding, its identifier aliases, and expiration.
 type sessionEntry struct {
 	authID    string
 	expiresAt time.Time
+	aliases   []string
 }
 
 // SessionCache provides TTL-based session to auth mapping with automatic cleanup.
@@ -40,66 +44,212 @@ func (c *SessionCache) Get(sessionID string) (string, bool) {
 	if sessionID == "" {
 		return "", false
 	}
+	now := time.Now()
 	c.mu.RLock()
 	entry, ok := c.entries[sessionID]
+	if ok && now.Before(entry.expiresAt) {
+		c.mu.RUnlock()
+		return entry.authID, true
+	}
 	c.mu.RUnlock()
 	if !ok {
 		return "", false
 	}
-	if time.Now().After(entry.expiresAt) {
-		c.mu.Lock()
-		delete(c.entries, sessionID)
-		c.mu.Unlock()
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	entry, ok = c.entries[sessionID]
+	if !ok {
 		return "", false
 	}
-	return entry.authID, true
+	if time.Now().Before(entry.expiresAt) {
+		return entry.authID, true
+	}
+	c.removeAliasGroupLocked(entry)
+	return "", false
 }
 
-// GetAndRefresh retrieves the auth ID bound to a session and refreshes TTL on hit.
-// This extends the binding lifetime for active sessions.
+// GetAndRefresh retrieves the auth ID bound to a session and refreshes the TTL
+// for every identifier known to represent the same logical session.
 func (c *SessionCache) GetAndRefresh(sessionID string) (string, bool) {
 	if sessionID == "" {
 		return "", false
 	}
 	now := time.Now()
 	c.mu.Lock()
+	defer c.mu.Unlock()
 	entry, ok := c.entries[sessionID]
 	if !ok {
-		c.mu.Unlock()
 		return "", false
 	}
-	if now.After(entry.expiresAt) {
-		delete(c.entries, sessionID)
-		c.mu.Unlock()
+	if !now.Before(entry.expiresAt) {
+		c.removeAliasGroupLocked(entry)
 		return "", false
 	}
-	// Refresh TTL on successful access
-	entry.expiresAt = now.Add(c.ttl)
-	c.entries[sessionID] = entry
-	c.mu.Unlock()
+
+	aliases := compactSessionAliases(mergeSessionAliases([]string{sessionID}, entry.aliases...))
+	c.replaceAliasGroupsLocked(entry.authID, now.Add(c.ttl), aliases, entry)
 	return entry.authID, true
 }
 
-// Set binds a session to an auth ID with TTL refresh.
+// Set binds a session to an auth ID with TTL refresh. Existing aliases for the
+// same logical session remain attached when the binding is refreshed or moved.
 func (c *SessionCache) Set(sessionID, authID string) {
-	if sessionID == "" || authID == "" {
-		return
-	}
-	c.mu.Lock()
-	c.entries[sessionID] = sessionEntry{
-		authID:    authID,
-		expiresAt: time.Now().Add(c.ttl),
-	}
-	c.mu.Unlock()
+	c.SetAliases(authID, sessionID)
 }
 
-// Invalidate removes a specific session binding.
+// SetAliases binds multiple identifiers for one logical session to an auth ID.
+func (c *SessionCache) SetAliases(authID string, sessionIDs ...string) {
+	if authID == "" {
+		return
+	}
+	now := time.Now()
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	aliases := mergeSessionAliases(nil, sessionIDs...)
+	previousGroups := make([]sessionEntry, 0, len(sessionIDs))
+	for _, sessionID := range sessionIDs {
+		entry, ok := c.entries[sessionID]
+		if !ok {
+			continue
+		}
+		if !now.Before(entry.expiresAt) {
+			c.removeAliasGroupLocked(entry)
+			continue
+		}
+		previousGroups = append(previousGroups, entry)
+		aliases = mergeSessionAliases(aliases, entry.aliases...)
+	}
+	aliases = compactSessionAliases(aliases)
+	if len(aliases) == 0 {
+		return
+	}
+	c.replaceAliasGroupsLocked(authID, now.Add(c.ttl), aliases, previousGroups...)
+}
+
+func (c *SessionCache) replaceAliasGroupsLocked(authID string, expiresAt time.Time, aliases []string, previousGroups ...sessionEntry) {
+	for _, previous := range previousGroups {
+		c.removeAliasGroupLocked(previous)
+	}
+	entry := sessionEntry{authID: authID, expiresAt: expiresAt, aliases: aliases}
+	for _, alias := range aliases {
+		c.entries[alias] = entry
+	}
+}
+
+func (c *SessionCache) removeAliasGroupLocked(entry sessionEntry) {
+	for _, alias := range entry.aliases {
+		current, ok := c.entries[alias]
+		if !ok || current.authID != entry.authID || !current.expiresAt.Equal(entry.expiresAt) ||
+			!equalSessionAliases(current.aliases, entry.aliases) {
+			continue
+		}
+		delete(c.entries, alias)
+	}
+}
+
+func compactSessionAliases(aliases []string) []string {
+	return compactSessionAliasesWith(aliases, isLocalPromptCacheSessionAlias)
+}
+
+func compactHomeSessionAliases(aliases []string) []string {
+	return compactSessionAliasesWith(aliases, func(alias string) bool {
+		return strings.HasPrefix(alias, "pck:")
+	})
+}
+
+func compactSessionAliasesWith(aliases []string, isPromptCacheAlias func(string) bool) []string {
+	compacted := make([]string, 0, len(aliases))
+	hasPromptCacheKey := false
+	stableAliases := 0
+	for _, alias := range aliases {
+		if isPromptCacheAlias(alias) {
+			if hasPromptCacheKey {
+				continue
+			}
+			hasPromptCacheKey = true
+		} else {
+			if stableAliases >= maxStableSessionAliases {
+				continue
+			}
+			stableAliases++
+		}
+		compacted = append(compacted, alias)
+	}
+	return compacted
+}
+
+func isLocalPromptCacheSessionAlias(alias string) bool {
+	if strings.HasPrefix(alias, "pck:") {
+		return true
+	}
+	_, sessionAndModel, ok := strings.Cut(alias, "::")
+	return ok && strings.HasPrefix(sessionAndModel, "pck:")
+}
+
+func equalSessionAliases(left, right []string) bool {
+	if len(left) != len(right) {
+		return false
+	}
+	for index := range left {
+		if left[index] != right[index] {
+			return false
+		}
+	}
+	return true
+}
+
+func mergeSessionAliases(existing []string, candidates ...string) []string {
+	aliases := make([]string, 0, len(existing)+len(candidates))
+	seen := make(map[string]struct{}, cap(aliases))
+	add := func(alias string) {
+		if alias == "" {
+			return
+		}
+		if _, ok := seen[alias]; ok {
+			return
+		}
+		seen[alias] = struct{}{}
+		aliases = append(aliases, alias)
+	}
+	for _, alias := range existing {
+		add(alias)
+	}
+	for _, alias := range candidates {
+		add(alias)
+	}
+	return aliases
+}
+
+// Invalidate removes a specific session binding without allowing another alias
+// in the same group to recreate it on its next refresh.
 func (c *SessionCache) Invalidate(sessionID string) {
 	if sessionID == "" {
 		return
 	}
 	c.mu.Lock()
+	entry, ok := c.entries[sessionID]
 	delete(c.entries, sessionID)
+	if ok {
+		for _, alias := range entry.aliases {
+			if alias == sessionID {
+				continue
+			}
+			current, exists := c.entries[alias]
+			if !exists || current.authID != entry.authID {
+				continue
+			}
+			filtered := make([]string, 0, len(current.aliases))
+			for _, candidate := range current.aliases {
+				if candidate != sessionID {
+					filtered = append(filtered, candidate)
+				}
+			}
+			current.aliases = filtered
+			c.entries[alias] = current
+		}
+	}
 	c.mu.Unlock()
 }
 
@@ -144,7 +294,7 @@ func (c *SessionCache) cleanup() {
 	now := time.Now()
 	c.mu.Lock()
 	for sid, entry := range c.entries {
-		if now.After(entry.expiresAt) {
+		if !now.Before(entry.expiresAt) {
 			delete(c.entries, sid)
 		}
 	}
diff --git a/sdk/cliproxy/session/identity.go b/sdk/cliproxy/session/identity.go
index 3d6c9fffe..696e0372a 100644
--- a/sdk/cliproxy/session/identity.go
+++ b/sdk/cliproxy/session/identity.go
@@ -2,11 +2,14 @@
 package session
 
 import (
+	"bytes"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"regexp"
 	"strings"
+	"unicode"
 
 	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v7/sdk/cliproxy/executor"
 	sdktranslator "github.com/router-for-me/CLIProxyAPI/v7/sdk/translator"
@@ -19,6 +22,8 @@ const (
 	instructionRuneLimit = 50
 )
 
+var legacyClaudeSessionPattern = regexp.MustCompile(`_session_([a-f0-9-]+)$`)
+
 type canonicalRoot struct {
 	Version      string          `json:"version"`
 	Format       string          `json:"format"`
@@ -34,6 +39,41 @@ type canonicalPart struct {
 	Value string `json:"value"`
 }
 
+// NormalizeExplicitID validates an explicit client-provided session identifier.
+// It preserves opaque printable values while rejecting oversized or control-bearing IDs.
+func NormalizeExplicitID(raw string) string {
+	for _, r := range raw {
+		if unicode.IsControl(r) {
+			return ""
+		}
+	}
+	raw = strings.TrimSpace(raw)
+	if raw == "" || len(raw) > 256 {
+		return ""
+	}
+	return raw
+}
+
+// ClaudeMetadataSessionID extracts the explicit Claude Code session from
+// current JSON metadata or the legacy user_id suffix before bounding the
+// surrounding metadata container.
+func ClaudeMetadataSessionID(payload []byte) string {
+	if len(payload) == 0 {
+		return ""
+	}
+	userID := strings.TrimSpace(gjson.GetBytes(payload, "metadata.user_id").String())
+	if userID == "" {
+		return ""
+	}
+	if strings.HasPrefix(userID, "{") {
+		return NormalizeExplicitID(gjson.Get(userID, "session_id").String())
+	}
+	if matches := legacyClaudeSessionPattern.FindStringSubmatch(userID); len(matches) >= 2 {
+		return NormalizeExplicitID(matches[1])
+	}
+	return ""
+}
+
 // CallerScope returns an irreversible namespace for a downstream caller credential.
 func CallerScope(value string) string {
 	value = strings.TrimSpace(value)
@@ -56,24 +96,26 @@ func DerivedID(metadata map[string]any) string {
 // Enrich derives a session identity once and places it in both request and option metadata.
 func Enrich(req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (cliproxyexecutor.Request, cliproxyexecutor.Options) {
 	payload := opts.OriginalRequest
-	if len(payload) == 0 {
-		payload = req.Payload
+	if len(payload) == 0 && len(req.Payload) > 0 {
+		opts.OriginalRequest = bytes.Clone(req.Payload)
+		payload = opts.OriginalRequest
 	}
-	if executionID := firstMetadataString(cliproxyexecutor.ExecutionSessionMetadataKey, opts.Metadata, req.Metadata); executionID != "" {
+	if executionID := firstNormalizedMetadataID(cliproxyexecutor.ExecutionSessionMetadataKey, opts.Metadata, req.Metadata); executionID != "" {
 		req.Metadata = metadataWithValue(metadataWithoutKey(req.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey), cliproxyexecutor.ExecutionSessionMetadataKey, executionID)
 		opts.Metadata = metadataWithValue(metadataWithoutKey(opts.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey), cliproxyexecutor.ExecutionSessionMetadataKey, executionID)
 		return req, opts
 	}
+	req.Metadata = metadataWithoutKey(req.Metadata, cliproxyexecutor.ExecutionSessionMetadataKey)
+	opts.Metadata = metadataWithoutKey(opts.Metadata, cliproxyexecutor.ExecutionSessionMetadataKey)
 	if hasExplicitSession(opts.Headers, payload) {
 		req.Metadata = metadataWithoutKey(req.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey)
 		opts.Metadata = metadataWithoutKey(opts.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey)
 		return req, opts
 	}
 
-	derivedID := DerivedID(opts.Metadata)
-	if derivedID == "" {
-		derivedID = DerivedID(req.Metadata)
-	}
+	derivedID := firstNormalizedMetadataID(cliproxyexecutor.DerivedSessionIDMetadataKey, opts.Metadata, req.Metadata)
+	req.Metadata = metadataWithoutKey(req.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey)
+	opts.Metadata = metadataWithoutKey(opts.Metadata, cliproxyexecutor.DerivedSessionIDMetadataKey)
 	if derivedID == "" {
 		callerScope := metadataString(opts.Metadata, cliproxyexecutor.CallerScopeMetadataKey)
 		if callerScope == "" {
@@ -90,8 +132,8 @@ func Enrich(req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (clipro
 }
 
 func hasExplicitSession(headers map[string][]string, payload []byte) bool {
-	for _, header := range []string{"X-Session-ID", "Session-Id", "Session_id", "X-Client-Request-Id"} {
-		if strings.TrimSpace(headerValue(headers, header)) != "" {
+	for _, header := range []string{"X-Claude-Code-Session-Id", "X-Session-ID", "Session-Id", "Session_id", "X-Session-Affinity", "X-Client-Request-Id"} {
+		if NormalizeExplicitID(headerValue(headers, header)) != "" {
 			return true
 		}
 	}
@@ -99,20 +141,35 @@ func hasExplicitSession(headers map[string][]string, payload []byte) bool {
 		return false
 	}
 	root := gjson.ParseBytes(payload)
-	for _, path := range []string{"metadata.user_id", "session_id", "sessionId", "conversation_id", "prompt_cache_key"} {
-		if strings.TrimSpace(root.Get(path).String()) != "" {
+	for _, path := range []string{"session_id", "sessionId", "conversation_id", "prompt_cache_key"} {
+		if NormalizeExplicitID(root.Get(path).String()) != "" {
 			return true
 		}
 	}
-	return false
+	if ClaudeMetadataSessionID(payload) != "" {
+		return true
+	}
+	userID := strings.TrimSpace(root.Get("metadata.user_id").String())
+	if NormalizeExplicitID(userID) != "" {
+		return true
+	}
+	conversation := root.Get("conversation")
+	if NormalizeExplicitID(conversation.Get("id").String()) != "" {
+		return true
+	}
+	return conversation.Type == gjson.String && NormalizeExplicitID(conversation.String()) != ""
 }
 
 func headerValue(headers map[string][]string, name string) string {
 	for key, values := range headers {
-		if !strings.EqualFold(key, name) || len(values) == 0 {
+		if !strings.EqualFold(key, name) {
 			continue
 		}
-		return values[0]
+		for _, value := range values {
+			if normalized := NormalizeExplicitID(value); normalized != "" {
+				return normalized
+			}
+		}
 	}
 	return ""
 }
@@ -468,6 +525,22 @@ func metadataWithoutKey(metadata map[string]any, key string) map[string]any {
 	return cloned
 }
 
+func firstNormalizedMetadataID(key string, metadataSets ...map[string]any) string {
+	for _, metadata := range metadataSets {
+		if metadata == nil {
+			continue
+		}
+		raw, ok := metadata[key].(string)
+		if !ok {
+			continue
+		}
+		if normalized := NormalizeExplicitID(raw); normalized != "" {
+			return normalized
+		}
+	}
+	return ""
+}
+
 func firstMetadataString(key string, metadataSets ...map[string]any) string {
 	for _, metadata := range metadataSets {
 		if value := metadataString(metadata, key); value != "" {
diff --git a/sdk/cliproxy/session/identity_test.go b/sdk/cliproxy/session/identity_test.go
index 1fbc498cb..7211d3798 100644
--- a/sdk/cliproxy/session/identity_test.go
+++ b/sdk/cliproxy/session/identity_test.go
@@ -1,6 +1,7 @@
 package session
 
 import (
+	"bytes"
 	"net/http"
 	"strings"
 	"testing"
@@ -134,10 +135,42 @@ func TestEnrichSkipsDerivationForExplicitSessions(t *testing.T) {
 			payload: []byte(`not-json`),
 			headers: http.Header{"X-Session-ID": []string{"header-session"}},
 		},
+		{
+			name:    "Claude Code session header",
+			payload: []byte(`{"messages":[{"role":"user","content":"hello"}]}`),
+			headers: http.Header{"X-Claude-Code-Session-Id": []string{"claude-session"}},
+		},
+		{
+			name:    "later valid multi-value session header",
+			payload: []byte(`{"messages":[{"role":"user","content":"hello"}]}`),
+			headers: http.Header{"X-Session-Affinity": []string{"", "later-valid-session"}},
+		},
+		{
+			name:    "OpenCode affinity header",
+			payload: []byte(`{"messages":[{"role":"user","content":"hello"}]}`),
+			headers: http.Header{"X-Session-Affinity": []string{"opencode-session"}},
+		},
+		{
+			name:    "Responses conversation object",
+			payload: []byte(`{"conversation":{"id":"conversation-session"},"messages":[{"role":"user","content":"hello"}]}`),
+		},
+		{
+			name:    "Responses conversation string",
+			payload: []byte(`{"conversation":"conversation-session","messages":[{"role":"user","content":"hello"}]}`),
+		},
 		{
 			name:    "metadata user id",
 			payload: []byte(`{"metadata":{"user_id":"explicit-user"},"messages":[{"role":"user","content":"hello"}]}`),
 		},
+		{
+			name: "long legacy Claude metadata session",
+			payload: []byte(`{"metadata":{"user_id":"` + strings.Repeat("x", 300) +
+				`_session_ac980658-63bd-4fb3-97ba-8da64cb1e344"},"messages":[{"role":"user","content":"hello"}]}`),
+		},
+		{
+			name:    "JSON metadata user id without nested session",
+			payload: []byte(`{"metadata":{"user_id":"{\"device_id\":\"abc123\"}"},"messages":[{"role":"user","content":"hello"}]}`),
+		},
 		{
 			name:    "body session id",
 			payload: []byte(`{"session_id":"body-session","messages":[{"role":"user","content":"hello"}]}`),
@@ -196,6 +229,83 @@ func TestEnrichSkipsDerivationForExplicitSessions(t *testing.T) {
 	}
 }
 
+func TestEnrichDerivesAfterInvalidSessionIdentity(t *testing.T) {
+	t.Parallel()
+
+	baseMessages := `"input":"hello"`
+	tests := []struct {
+		name            string
+		payload         []byte
+		headers         http.Header
+		requestMetadata map[string]any
+		optionMetadata  map[string]any
+	}{
+		{
+			name:    "oversized prompt cache key",
+			payload: []byte(`{"prompt_cache_key":"` + strings.Repeat("x", 257) + `",` + baseMessages + `}`),
+		},
+		{
+			name:    "trailing control character prompt cache key",
+			payload: []byte(`{"prompt_cache_key":"tenant\n",` + baseMessages + `}`),
+		},
+		{
+			name:    "leading control character prompt cache key",
+			payload: []byte(`{"prompt_cache_key":"\ttenant",` + baseMessages + `}`),
+		},
+		{
+			name:    "control character session header",
+			payload: []byte(`{` + baseMessages + `}`),
+			headers: http.Header{"X-Session-Affinity": []string{"bad\nsession"}},
+		},
+		{
+			name:           "oversized execution session option metadata",
+			payload:        []byte(`{"input":"hello"}`),
+			optionMetadata: map[string]any{cliproxyexecutor.ExecutionSessionMetadataKey: strings.Repeat("x", 257)},
+		},
+		{
+			name:            "control character execution session request metadata",
+			payload:         []byte(`{"input":"hello"}`),
+			requestMetadata: map[string]any{cliproxyexecutor.ExecutionSessionMetadataKey: "bad\nsession"},
+		},
+		{
+			name:           "oversized retained derived session option metadata",
+			payload:        []byte(`{"input":"hello"}`),
+			optionMetadata: map[string]any{cliproxyexecutor.DerivedSessionIDMetadataKey: strings.Repeat("x", 257)},
+		},
+		{
+			name:            "control character retained derived session request metadata",
+			payload:         []byte(`{"input":"hello"}`),
+			requestMetadata: map[string]any{cliproxyexecutor.DerivedSessionIDMetadataKey: "bad\nsession"},
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			req := cliproxyexecutor.Request{Payload: test.payload, Metadata: test.requestMetadata}
+			opts := cliproxyexecutor.Options{
+				OriginalRequest: test.payload,
+				SourceFormat:    sdktranslator.FormatOpenAIResponse,
+				Headers:         test.headers,
+				Metadata:        test.optionMetadata,
+			}
+			enrichedReq, enrichedOpts := Enrich(req, opts)
+			requestID := DerivedID(enrichedReq.Metadata)
+			optionsID := DerivedID(enrichedOpts.Metadata)
+			wantID := DeriveID(sdktranslator.FormatOpenAIResponse, test.payload, "")
+			if requestID != wantID || optionsID != wantID {
+				t.Fatalf("derived identities = request:%q options:%q, want %q", requestID, optionsID, wantID)
+			}
+			if got := metadataString(enrichedReq.Metadata, cliproxyexecutor.ExecutionSessionMetadataKey); got != "" {
+				t.Fatalf("request execution session = %q, want invalid value removed", got)
+			}
+			if got := metadataString(enrichedOpts.Metadata, cliproxyexecutor.ExecutionSessionMetadataKey); got != "" {
+				t.Fatalf("options execution session = %q, want invalid value removed", got)
+			}
+		})
+	}
+}
+
 func TestEnrichCopiesDerivedIdentityToRequestAndOptions(t *testing.T) {
 	t.Parallel()
 
@@ -216,3 +326,23 @@ func TestEnrichCopiesDerivedIdentityToRequestAndOptions(t *testing.T) {
 		t.Fatal("Enrich() mutated original request metadata")
 	}
 }
+
+func TestEnrichCarriesRequestPayloadIntoSelectionOptions(t *testing.T) {
+	t.Parallel()
+
+	payload := []byte(`{"conversation":{"id":"request-only-conversation"},"input":"hello"}`)
+	_, enrichedOpts := Enrich(
+		cliproxyexecutor.Request{Payload: payload},
+		cliproxyexecutor.Options{SourceFormat: sdktranslator.FormatOpenAIResponse},
+	)
+
+	if !bytes.Equal(enrichedOpts.OriginalRequest, payload) {
+		t.Fatalf("OriginalRequest = %q, want request payload %q", enrichedOpts.OriginalRequest, payload)
+	}
+	if len(enrichedOpts.OriginalRequest) > 0 && &enrichedOpts.OriginalRequest[0] == &payload[0] {
+		t.Fatal("OriginalRequest aliases Request.Payload instead of preserving a snapshot")
+	}
+	if got := DerivedID(enrichedOpts.Metadata); got != "" {
+		t.Fatalf("DerivedSessionID = %q, want explicit conversation to remain authoritative", got)
+	}
+}