feat(registry): introduce ModelRegistryHook for monitoring model registrations and unregistrations

Added support for external hooks to observe model registry events using the `ModelRegistryHook` interface. Implemented thread-safe, non-blocking execution of hooks with panic recovery. Comprehensive tests added to verify hook behavior during registration, unregistration, blocking, and panic scenarios.

internal/registry/model_registry.go

@@ -4,6 +4,7 @@
 package registry
 
 import (
+	"context"
 	"fmt"
 	"sort"
 	"strings"
@@ -84,6 +85,13 @@ type ModelRegistration struct {
 	SuspendedClients map[string]string
 }
 
+// ModelRegistryHook provides optional callbacks for external integrations to track model list changes.
+// Hook implementations must be non-blocking and resilient; calls are executed asynchronously and panics are recovered.
+type ModelRegistryHook interface {
+	OnModelsRegistered(ctx context.Context, provider, clientID string, models []*ModelInfo)
+	OnModelsUnregistered(ctx context.Context, provider, clientID string)
+}
+
 // ModelRegistry manages the global registry of available models
 type ModelRegistry struct {
 	// models maps model ID to registration information
@@ -97,6 +105,8 @@ type ModelRegistry struct {
 	clientProviders map[string]string
 	// mutex ensures thread-safe access to the registry
 	mutex *sync.RWMutex
+	// hook is an optional callback sink for model registration changes
+	hook ModelRegistryHook
 }
 
 // Global model registry instance
@@ -117,6 +127,53 @@ func GetGlobalRegistry() *ModelRegistry {
 	return globalRegistry
 }
 
+// SetHook sets an optional hook for observing model registration changes.
+func (r *ModelRegistry) SetHook(hook ModelRegistryHook) {
+	if r == nil {
+		return
+	}
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+	r.hook = hook
+}
+
+const defaultModelRegistryHookTimeout = 5 * time.Second
+
+func (r *ModelRegistry) triggerModelsRegistered(provider, clientID string, models []*ModelInfo) {
+	hook := r.hook
+	if hook == nil {
+		return
+	}
+	modelsCopy := cloneModelInfosUnique(models)
+	go func() {
+		defer func() {
+			if recovered := recover(); recovered != nil {
+				log.Errorf("model registry hook OnModelsRegistered panic: %v", recovered)
+			}
+		}()
+		ctx, cancel := context.WithTimeout(context.Background(), defaultModelRegistryHookTimeout)
+		defer cancel()
+		hook.OnModelsRegistered(ctx, provider, clientID, modelsCopy)
+	}()
+}
+
+func (r *ModelRegistry) triggerModelsUnregistered(provider, clientID string) {
+	hook := r.hook
+	if hook == nil {
+		return
+	}
+	go func() {
+		defer func() {
+			if recovered := recover(); recovered != nil {
+				log.Errorf("model registry hook OnModelsUnregistered panic: %v", recovered)
+			}
+		}()
+		ctx, cancel := context.WithTimeout(context.Background(), defaultModelRegistryHookTimeout)
+		defer cancel()
+		hook.OnModelsUnregistered(ctx, provider, clientID)
+	}()
+}
+
 // RegisterClient registers a client and its supported models
 // Parameters:
 //   - clientID: Unique identifier for the client
@@ -177,6 +234,7 @@ func (r *ModelRegistry) RegisterClient(clientID, clientProvider string, models [
 		} else {
 			delete(r.clientProviders, clientID)
 		}
+		r.triggerModelsRegistered(provider, clientID, models)
 		log.Debugf("Registered client %s from provider %s with %d models", clientID, clientProvider, len(rawModelIDs))
 		misc.LogCredentialSeparator()
 		return
@@ -310,6 +368,7 @@ func (r *ModelRegistry) RegisterClient(clientID, clientProvider string, models [
 		delete(r.clientProviders, clientID)
 	}
 
+	r.triggerModelsRegistered(provider, clientID, models)
 	if len(added) == 0 && len(removed) == 0 && !providerChanged {
 		// Only metadata (e.g., display name) changed; skip separator when no log output.
 		return
@@ -400,6 +459,25 @@ func cloneModelInfo(model *ModelInfo) *ModelInfo {
 	return &copyModel
 }
 
+func cloneModelInfosUnique(models []*ModelInfo) []*ModelInfo {
+	if len(models) == 0 {
+		return nil
+	}
+	cloned := make([]*ModelInfo, 0, len(models))
+	seen := make(map[string]struct{}, len(models))
+	for _, model := range models {
+		if model == nil || model.ID == "" {
+			continue
+		}
+		if _, exists := seen[model.ID]; exists {
+			continue
+		}
+		seen[model.ID] = struct{}{}
+		cloned = append(cloned, cloneModelInfo(model))
+	}
+	return cloned
+}
+
 // UnregisterClient removes a client and decrements counts for its models
 // Parameters:
 //   - clientID: Unique identifier for the client to remove
@@ -460,6 +538,7 @@ func (r *ModelRegistry) unregisterClientInternal(clientID string) {
 	log.Debugf("Unregistered client %s", clientID)
 	// Separator line after completing client unregistration (after the summary line)
 	misc.LogCredentialSeparator()
+	r.triggerModelsUnregistered(provider, clientID)
 }
 
 // SetModelQuotaExceeded marks a model as quota exceeded for a specific client

internal/registry/model_registry_hook_test.go

@@ -0,0 +1,204 @@
+package registry
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+)
+
+func newTestModelRegistry() *ModelRegistry {
+	return &ModelRegistry{
+		models:           make(map[string]*ModelRegistration),
+		clientModels:     make(map[string][]string),
+		clientModelInfos: make(map[string]map[string]*ModelInfo),
+		clientProviders:  make(map[string]string),
+		mutex:            &sync.RWMutex{},
+	}
+}
+
+type registeredCall struct {
+	provider string
+	clientID string
+	models   []*ModelInfo
+}
+
+type unregisteredCall struct {
+	provider string
+	clientID string
+}
+
+type capturingHook struct {
+	registeredCh   chan registeredCall
+	unregisteredCh chan unregisteredCall
+}
+
+func (h *capturingHook) OnModelsRegistered(ctx context.Context, provider, clientID string, models []*ModelInfo) {
+	h.registeredCh <- registeredCall{provider: provider, clientID: clientID, models: models}
+}
+
+func (h *capturingHook) OnModelsUnregistered(ctx context.Context, provider, clientID string) {
+	h.unregisteredCh <- unregisteredCall{provider: provider, clientID: clientID}
+}
+
+func TestModelRegistryHook_OnModelsRegisteredCalled(t *testing.T) {
+	r := newTestModelRegistry()
+	hook := &capturingHook{
+		registeredCh:   make(chan registeredCall, 1),
+		unregisteredCh: make(chan unregisteredCall, 1),
+	}
+	r.SetHook(hook)
+
+	inputModels := []*ModelInfo{
+		{ID: "m1", DisplayName: "Model One"},
+		{ID: "m2", DisplayName: "Model Two"},
+	}
+	r.RegisterClient("client-1", "OpenAI", inputModels)
+
+	select {
+	case call := <-hook.registeredCh:
+		if call.provider != "openai" {
+			t.Fatalf("provider mismatch: got %q, want %q", call.provider, "openai")
+		}
+		if call.clientID != "client-1" {
+			t.Fatalf("clientID mismatch: got %q, want %q", call.clientID, "client-1")
+		}
+		if len(call.models) != 2 {
+			t.Fatalf("models length mismatch: got %d, want %d", len(call.models), 2)
+		}
+		if call.models[0] == nil || call.models[0].ID != "m1" {
+			t.Fatalf("models[0] mismatch: got %#v, want ID=%q", call.models[0], "m1")
+		}
+		if call.models[1] == nil || call.models[1].ID != "m2" {
+			t.Fatalf("models[1] mismatch: got %#v, want ID=%q", call.models[1], "m2")
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for OnModelsRegistered hook call")
+	}
+}
+
+func TestModelRegistryHook_OnModelsUnregisteredCalled(t *testing.T) {
+	r := newTestModelRegistry()
+	hook := &capturingHook{
+		registeredCh:   make(chan registeredCall, 1),
+		unregisteredCh: make(chan unregisteredCall, 1),
+	}
+	r.SetHook(hook)
+
+	r.RegisterClient("client-1", "OpenAI", []*ModelInfo{{ID: "m1"}})
+	select {
+	case <-hook.registeredCh:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for OnModelsRegistered hook call")
+	}
+
+	r.UnregisterClient("client-1")
+
+	select {
+	case call := <-hook.unregisteredCh:
+		if call.provider != "openai" {
+			t.Fatalf("provider mismatch: got %q, want %q", call.provider, "openai")
+		}
+		if call.clientID != "client-1" {
+			t.Fatalf("clientID mismatch: got %q, want %q", call.clientID, "client-1")
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for OnModelsUnregistered hook call")
+	}
+}
+
+type blockingHook struct {
+	started chan struct{}
+	unblock chan struct{}
+}
+
+func (h *blockingHook) OnModelsRegistered(ctx context.Context, provider, clientID string, models []*ModelInfo) {
+	select {
+	case <-h.started:
+	default:
+		close(h.started)
+	}
+	<-h.unblock
+}
+
+func (h *blockingHook) OnModelsUnregistered(ctx context.Context, provider, clientID string) {}
+
+func TestModelRegistryHook_DoesNotBlockRegisterClient(t *testing.T) {
+	r := newTestModelRegistry()
+	hook := &blockingHook{
+		started: make(chan struct{}),
+		unblock: make(chan struct{}),
+	}
+	r.SetHook(hook)
+	defer close(hook.unblock)
+
+	done := make(chan struct{})
+	go func() {
+		r.RegisterClient("client-1", "OpenAI", []*ModelInfo{{ID: "m1"}})
+		close(done)
+	}()
+
+	select {
+	case <-hook.started:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for hook to start")
+	}
+
+	select {
+	case <-done:
+	case <-time.After(200 * time.Millisecond):
+		t.Fatal("RegisterClient appears to be blocked by hook")
+	}
+
+	if !r.ClientSupportsModel("client-1", "m1") {
+		t.Fatal("model registration failed; expected client to support model")
+	}
+}
+
+type panicHook struct {
+	registeredCalled   chan struct{}
+	unregisteredCalled chan struct{}
+}
+
+func (h *panicHook) OnModelsRegistered(ctx context.Context, provider, clientID string, models []*ModelInfo) {
+	if h.registeredCalled != nil {
+		h.registeredCalled <- struct{}{}
+	}
+	panic("boom")
+}
+
+func (h *panicHook) OnModelsUnregistered(ctx context.Context, provider, clientID string) {
+	if h.unregisteredCalled != nil {
+		h.unregisteredCalled <- struct{}{}
+	}
+	panic("boom")
+}
+
+func TestModelRegistryHook_PanicDoesNotAffectRegistry(t *testing.T) {
+	r := newTestModelRegistry()
+	hook := &panicHook{
+		registeredCalled:   make(chan struct{}, 1),
+		unregisteredCalled: make(chan struct{}, 1),
+	}
+	r.SetHook(hook)
+
+	r.RegisterClient("client-1", "OpenAI", []*ModelInfo{{ID: "m1"}})
+
+	select {
+	case <-hook.registeredCalled:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for OnModelsRegistered hook call")
+	}
+
+	if !r.ClientSupportsModel("client-1", "m1") {
+		t.Fatal("model registration failed; expected client to support model")
+	}
+
+	r.UnregisterClient("client-1")
+
+	select {
+	case <-hook.unregisteredCalled:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for OnModelsUnregistered hook call")
+	}
+}