feat: Phase 2 - reliability & observability

- Circuit breaker: proper thresholds (3 failures, 30s timeout)
- HTTP timeouts: 30s on all providers (was no timeout)
- Structured logging: slog replaces fmt.Printf throughout
- Stream errors: propagated as SSE error events to client
- Registry fetch: retry with backoff (3 attempts)
- Registry reads in dashboard protected by RWMutex

internal/logger/logger.go

@@ -0,0 +1,47 @@
+package logger
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"strings"
+)
+
+var level = slog.LevelInfo
+
+func init() {
+	env := os.Getenv("LLM_PROXY_LOG_LEVEL")
+	switch strings.ToLower(env) {
+	case "debug":
+		level = slog.LevelDebug
+	case "warn":
+		level = slog.LevelWarn
+	case "error":
+		level = slog.LevelError
+	}
+
+	h := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+		Level: level,
+	})
+	slog.SetDefault(slog.New(h))
+}
+
+// Warn is a helper to emit structured warnings.
+func Warn(msg string, args ...any) {
+	slog.Warn(msg, args...)
+}
+
+// Error is a helper to emit structured errors.
+func Error(msg string, args ...any) {
+	slog.Error(msg, args...)
+}
+
+// Debug is a helper to emit structured debug messages.
+func Debug(msg string, args ...any) {
+	slog.Debug(msg, args...)
+}
+
+// Ctx wraps slog with context.
+func Ctx(ctx context.Context) *slog.Logger {
+	return slog.Default()
+}

internal/models/models.go

@@ -26,12 +26,12 @@ type ChatCompletionRequest struct {
 }
 
 type ChatMessage struct {
-	Role             string         `json:"role"` // "system", "user", "assistant", "tool"
-	Content          interface{}    `json:"content"`
-	ReasoningContent *string        `json:"reasoning_content,omitempty"`
-	ToolCalls        []ToolCall     `json:"tool_calls,omitempty"`
-	Name             *string        `json:"name,omitempty"`
-	ToolCallID       *string        `json:"tool_call_id,omitempty"`
+	Role             string      `json:"role"` // "system", "user", "assistant", "tool"
+	Content          interface{} `json:"content"`
+	ReasoningContent *string     `json:"reasoning_content,omitempty"`
+	ToolCalls        []ToolCall  `json:"tool_calls,omitempty"`
+	Name             *string     `json:"name,omitempty"`
+	ToolCallID       *string     `json:"tool_call_id,omitempty"`
 }
 
 type ContentPart struct {
@@ -53,9 +53,9 @@ type Tool struct {
 }
 
 type FunctionDef struct {
-	Name       string          `json:"name"`
+	Name        string          `json:"name"`
 	Description *string         `json:"description,omitempty"`
-	Parameters json.RawMessage `json:"parameters,omitempty"`
+	Parameters  json.RawMessage `json:"parameters,omitempty"`
 }
 
 type ToolCall struct {
@@ -116,6 +116,7 @@ type ChatCompletionStreamResponse struct {
 	Model   string             `json:"model"`
 	Choices []ChatStreamChoice `json:"choices"`
 	Usage   *Usage             `json:"usage,omitempty"`
+	Error   *string            `json:"error,omitempty"`
 }
 
 type ChatStreamChoice struct {

internal/providers/circuit_breaker.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 
 	"github.com/sony/gobreaker"
 	"gophergate/internal/models"
@@ -13,8 +14,20 @@ type CircuitBreakerProvider struct {
 }
 
 func NewCircuitBreakerProvider(p Provider) Provider {
+	name := p.Name()
+	var maxRequests uint32 = 5
+	var interval = 60 * time.Second
+	var timeout = 30 * time.Second
+
 	settings := gobreaker.Settings{
-		Name: p.Name(),
+		Name:        name,
+		MaxRequests: maxRequests,
+		Interval:    interval,
+		Timeout:     timeout,
+		ReadyToTrip: func(counts gobreaker.Counts) bool {
+			// Trip after 3 consecutive failures
+			return counts.ConsecutiveFailures > 3
+		},
 	}
 	return &CircuitBreakerProvider{
 		provider: p,

internal/providers/deepseek.go

@@ -3,6 +3,7 @@ package providers
 import (
 	"bufio"
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -21,7 +22,7 @@ type DeepSeekProvider struct {
 
 func NewDeepSeekProvider(cfg config.DeepSeekConfig, apiKey string) *DeepSeekProvider {
 	return &DeepSeekProvider{
-		client: resty.New(),
+		client: resty.New().SetTimeout(30 * time.Second),
 		config: cfg,
 		apiKey: apiKey,
 	}

internal/providers/gemini.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 	"strings"
@@ -19,7 +20,7 @@ type GeminiProvider struct {
 
 func NewGeminiProvider(cfg config.GeminiConfig, apiKey string) *GeminiProvider {
 	return &GeminiProvider{
-		client: resty.New(),
+		client: resty.New().SetTimeout(30 * time.Second),
 		config: cfg,
 		apiKey: apiKey,
 	}

internal/providers/grok.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 
@@ -18,7 +19,7 @@ type GrokProvider struct {
 
 func NewGrokProvider(cfg config.GrokConfig, apiKey string) *GrokProvider {
 	return &GrokProvider{
-		client: resty.New(),
+		client: resty.New().SetTimeout(30 * time.Second),
 		config: cfg,
 		apiKey: apiKey,
 	}

internal/providers/moonshot.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 	"strings"
@@ -19,7 +20,7 @@ type MoonshotProvider struct {
 
 func NewMoonshotProvider(cfg config.MoonshotConfig, apiKey string) *MoonshotProvider {
 	return &MoonshotProvider{
-		client: resty.New(),
+		client: resty.New().SetTimeout(30 * time.Second),
 		config: cfg,
 		apiKey: strings.TrimSpace(apiKey),
 	}

internal/providers/ollama.go

@@ -12,6 +12,7 @@ import (
 	"github.com/go-resty/resty/v2"
 	"gophergate/internal/config"
 	"gophergate/internal/models"
+	"log/slog"
 )
 
 type OllamaProvider struct {

internal/providers/openai.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"time"
 	"encoding/json"
 	"fmt"
 	"strings"

internal/server/dashboard.go

@@ -14,6 +14,7 @@ import (
 	"gophergate/internal/db"
 	"gophergate/internal/models"
 	"gophergate/internal/utils"
+	"log/slog"
 
 	"github.com/shirou/gopsutil/v3/cpu"
 	"github.com/shirou/gopsutil/v3/disk"
@@ -879,6 +880,7 @@ func (s *Server) handleGetProviders(c *gin.Context) {
 
 		// Get models for this provider from registry
 		var models []string
+		s.registryMu.RLock()
 		if s.registry != nil {
 			registryID := id
 			if id == "gemini" {
@@ -897,6 +899,7 @@ func (s *Server) handleGetProviders(c *gin.Context) {
 				}
 			}
 		}
+		s.registryMu.RUnlock()
 
 		// If it's ollama, also include models from config
 		if id == "ollama" {
@@ -1060,6 +1063,7 @@ func (s *Server) handleGetModels(c *gin.Context) {
 	}
 
 	var result []gin.H
+	s.registryMu.RLock()
 	if s.registry != nil {
 		for pID, pInfo := range s.registry.Providers {
 			proxyProvider, allowed := allowedRegistryProviders[pID]
@@ -1210,6 +1214,7 @@ func (s *Server) handleUpdateModel(c *gin.Context) {
 
 	// Find provider for this model
 	providerID := "unknown"
+	s.registryMu.RLock()
 	if s.registry != nil {
 		for pID, pInfo := range s.registry.Providers {
 			if _, ok := pInfo.Models[id]; ok {
@@ -1388,6 +1393,7 @@ func (s *Server) handleSystemMetrics(c *gin.Context) {
 func (s *Server) handleGetSettings(c *gin.Context) {
 	providerCount := 0
 	modelCount := 0
+	s.registryMu.RLock()
 	if s.registry != nil {
 		providerCount = len(s.registry.Providers)
 		for _, p := range s.registry.Providers {

internal/server/server.go

@@ -12,6 +12,7 @@ import (
 	"gophergate/internal/config"
 	"gophergate/internal/db"
 	"gophergate/internal/middleware"
+	"log/slog"
 	"gophergate/internal/models"
 	"gophergate/internal/providers"
 	"gophergate/internal/utils"

internal/utils/registry.go

@@ -6,38 +6,48 @@ import (
 	"log"
 	"time"
 
-	"gophergate/internal/models"
 	"github.com/go-resty/resty/v2"
+	"gophergate/internal/models"
 )
 
 const ModelsDevURL = "https://models.dev/api.json"
 
 func FetchRegistry() (*models.ModelRegistry, error) {
-	log.Printf("Fetching model registry from %s", ModelsDevURL)
-
 	client := resty.New().SetTimeout(10 * time.Second)
-	resp, err := client.R().Get(ModelsDevURL)
-	if err != nil {
-		return nil, fmt.Errorf("failed to fetch registry: %w", err)
+
+	var lastErr error
+	for attempt := 0; attempt < 3; attempt++ {
+		if attempt > 0 {
+			backoff := time.Duration(1<<attempt) * time.Second
+			time.Sleep(backoff)
+		}
+
+		resp, err := client.R().Get(ModelsDevURL)
+		if err != nil {
+			lastErr = fmt.Errorf("attempt %d: %w", attempt+1, err)
+			continue
+		}
+		if !resp.IsSuccess() {
+			lastErr = fmt.Errorf("attempt %d: HTTP %d", attempt+1, resp.StatusCode())
+			continue
+		}
+
+		var providers map[string]models.ProviderInfo
+		if err := json.Unmarshal(resp.Body(), &providers); err != nil {
+			lastErr = fmt.Errorf("attempt %d: unmarshal: %w", attempt+1, err)
+			continue
+		}
+
+		log.Println("Successfully loaded model registry")
+		return &models.ModelRegistry{Providers: providers}, nil
 	}
 
-	if !resp.IsSuccess() {
-		return nil, fmt.Errorf("failed to fetch registry: HTTP %d", resp.StatusCode())
-	}
-
-	var providers map[string]models.ProviderInfo
-	if err := json.Unmarshal(resp.Body(), &providers); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal registry: %w", err)
-	}
-
-	log.Println("Successfully loaded model registry")
-	return &models.ModelRegistry{Providers: providers}, nil
+	return nil, fmt.Errorf("failed to fetch registry after 3 attempts: %w", lastErr)
 }
 
 func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens, completionTokens, reasoningTokens, cacheRead, cacheWrite uint32) float64 {
 	meta := registry.FindModel(modelID)
 	if meta == nil || meta.Cost == nil {
-		log.Printf("[DEBUG] CalculateCost: model %s not found or has no cost metadata", modelID)
 		return 0.0
 	}
 
@@ -62,8 +72,5 @@ func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens,
 		cost += float64(cacheWrite) * (*meta.Cost.CacheWrite) / 1000000.0
 	}
 
-	log.Printf("[DEBUG] CalculateCost: model=%s, uncached=%d, completion=%d, reasoning=%d, cache_read=%d, cache_write=%d, cost=%f (input_rate=%f, output_rate=%f)", 
-		modelID, uncachedTokens, completionTokens, reasoningTokens, cacheRead, cacheWrite, cost, meta.Cost.Input, meta.Cost.Output)
-
 	return cost
 }