feat(config): env-driven config with validation

internal/config/config.go

@@ -0,0 +1,79 @@
+// Package config loads and validates the MCP server configuration from env vars.
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+// Config is the validated runtime configuration. Fields are ordered
+// largest-alignment-first to satisfy the fieldalignment linter.
+type Config struct {
+	Provider    string
+	BaseURL     string
+	APIKey      string
+	Model       string
+	AudioModel  string
+	LogLevel    string
+	Temperature float64
+	Timeout     time.Duration
+	MaxTokens   int
+}
+
+var validProviders = map[string]bool{
+	"anthropic": true, "openai": true, "openai-compatible": true, "gemini": true,
+}
+
+// Load reads CAPTCHA_LLM_* env vars and returns a validated Config.
+func Load() (Config, error) {
+	c := Config{
+		Provider:   os.Getenv("CAPTCHA_LLM_PROVIDER"),
+		BaseURL:    os.Getenv("CAPTCHA_LLM_BASE_URL"),
+		APIKey:     os.Getenv("CAPTCHA_LLM_API_KEY"),
+		Model:      os.Getenv("CAPTCHA_LLM_MODEL"),
+		AudioModel: os.Getenv("CAPTCHA_LLM_AUDIO_MODEL"),
+		LogLevel:   envOr("CAPTCHA_LOG_LEVEL", "info"),
+		MaxTokens:  1024,
+		Timeout:    60 * time.Second,
+	}
+	if !validProviders[c.Provider] {
+		return Config{}, fmt.Errorf("CAPTCHA_LLM_PROVIDER must be one of anthropic|openai|openai-compatible|gemini, got %q", c.Provider)
+	}
+	if c.APIKey == "" && c.BaseURL == "" {
+		return Config{}, fmt.Errorf("CAPTCHA_LLM_API_KEY is required (or set CAPTCHA_LLM_BASE_URL for a keyless local endpoint)")
+	}
+	if c.Model == "" {
+		return Config{}, fmt.Errorf("CAPTCHA_LLM_MODEL is required")
+	}
+	if v := os.Getenv("CAPTCHA_LLM_TEMPERATURE"); v != "" {
+		f, err := strconv.ParseFloat(v, 64)
+		if err != nil {
+			return Config{}, fmt.Errorf("CAPTCHA_LLM_TEMPERATURE: %w", err)
+		}
+		c.Temperature = f
+	}
+	if v := os.Getenv("CAPTCHA_LLM_MAX_TOKENS"); v != "" {
+		n, err := strconv.Atoi(v)
+		if err != nil {
+			return Config{}, fmt.Errorf("CAPTCHA_LLM_MAX_TOKENS: %w", err)
+		}
+		c.MaxTokens = n
+	}
+	if v := os.Getenv("CAPTCHA_LLM_TIMEOUT"); v != "" {
+		d, err := time.ParseDuration(v)
+		if err != nil {
+			return Config{}, fmt.Errorf("CAPTCHA_LLM_TIMEOUT: %w", err)
+		}
+		c.Timeout = d
+	}
+	return c, nil
+}
+
+func envOr(key, def string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return def
+}