Implement mcdoc v0.1.0: public documentation server

Single-binary Go server that fetches markdown from Gitea (mc org),
renders to HTML with goldmark (GFM, chroma syntax highlighting,
heading anchors), and serves a navigable read-only documentation site.

Features:
- Boot fetch with retry, webhook refresh, 15-minute poll fallback
- In-memory cache with atomic per-repo swap
- chi router with htmx partial responses for SPA-like navigation
- HMAC-SHA256 webhook validation
- Responsive CSS, TOC generation, priority doc ordering
- $PORT env var support for MCP agent port assignment

33 tests across config, cache, render, and server packages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/config/config.go

@@ -0,0 +1,164 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"strings"
+	"time"
+
+	"github.com/pelletier/go-toml/v2"
+)
+
+type Config struct {
+	Server ServerConfig `toml:"server"`
+	Gitea  GiteaConfig  `toml:"gitea"`
+	Log    LogConfig    `toml:"log"`
+}
+
+type ServerConfig struct {
+	ListenAddr string `toml:"listen_addr"`
+}
+
+type GiteaConfig struct {
+	URL            string       `toml:"url"`
+	Org            string       `toml:"org"`
+	WebhookSecret  string       `toml:"webhook_secret"`
+	PollInterval   Duration     `toml:"poll_interval"`
+	FetchTimeout   Duration     `toml:"fetch_timeout"`
+	MaxConcurrency int          `toml:"max_concurrency"`
+	ExcludePaths   ExcludePaths `toml:"exclude_paths"`
+	ExcludeRepos   ExcludeRepos `toml:"exclude_repos"`
+}
+
+type ExcludePaths struct {
+	Patterns []string `toml:"patterns"`
+}
+
+type ExcludeRepos struct {
+	Names []string `toml:"names"`
+}
+
+type LogConfig struct {
+	Level string `toml:"level"`
+}
+
+// Duration wraps time.Duration for TOML string parsing.
+type Duration struct {
+	time.Duration
+}
+
+func (d *Duration) UnmarshalText(text []byte) error {
+	var err error
+	d.Duration, err = time.ParseDuration(string(text))
+	return err
+}
+
+func (d Duration) MarshalText() ([]byte, error) {
+	return []byte(d.String()), nil
+}
+
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path) // #nosec G304 -- config path is operator-controlled
+	if err != nil {
+		return nil, fmt.Errorf("read config: %w", err)
+	}
+
+	cfg := &Config{
+		Server: ServerConfig{
+			ListenAddr: ":8080",
+		},
+		Gitea: GiteaConfig{
+			URL:            "https://git.wntrmute.dev",
+			Org:            "mc",
+			PollInterval:   Duration{15 * time.Minute},
+			FetchTimeout:   Duration{30 * time.Second},
+			MaxConcurrency: 4,
+			ExcludePaths: ExcludePaths{
+				Patterns: []string{"vendor/", ".claude/", "node_modules/", ".junie/"},
+			},
+		},
+		Log: LogConfig{
+			Level: "info",
+		},
+	}
+
+	if err := toml.Unmarshal(data, cfg); err != nil {
+		return nil, fmt.Errorf("parse config: %w", err)
+	}
+
+	applyEnvOverrides(cfg)
+
+	if err := cfg.validate(); err != nil {
+		return nil, fmt.Errorf("validate config: %w", err)
+	}
+
+	return cfg, nil
+}
+
+func (c *Config) validate() error {
+	if c.Server.ListenAddr == "" {
+		return fmt.Errorf("server.listen_addr is required")
+	}
+	if c.Gitea.URL == "" {
+		return fmt.Errorf("gitea.url is required")
+	}
+	if c.Gitea.Org == "" {
+		return fmt.Errorf("gitea.org is required")
+	}
+	if c.Gitea.MaxConcurrency < 1 {
+		return fmt.Errorf("gitea.max_concurrency must be >= 1")
+	}
+	return nil
+}
+
+// applyEnvOverrides checks for MCDOC_* environment variables and applies
+// them to the config. Also checks $PORT for MCP agent port assignment.
+func applyEnvOverrides(cfg *Config) {
+	if port := os.Getenv("PORT"); port != "" {
+		cfg.Server.ListenAddr = ":" + port
+	}
+
+	applyEnvToStruct("MCDOC", reflect.ValueOf(cfg).Elem())
+}
+
+func applyEnvToStruct(prefix string, v reflect.Value) {
+	t := v.Type()
+	for i := range t.NumField() {
+		field := t.Field(i)
+		fv := v.Field(i)
+
+		tag := field.Tag.Get("toml")
+		if tag == "" || tag == "-" {
+			continue
+		}
+
+		envKey := prefix + "_" + strings.ToUpper(tag)
+
+		if fv.Kind() == reflect.Struct && field.Type != reflect.TypeOf(Duration{}) {
+			applyEnvToStruct(envKey, fv)
+			continue
+		}
+
+		envVal := os.Getenv(envKey)
+		if envVal == "" {
+			continue
+		}
+
+		switch fv.Kind() {
+		case reflect.String:
+			fv.SetString(envVal)
+		case reflect.Int:
+			var n int
+			if _, err := fmt.Sscanf(envVal, "%d", &n); err == nil {
+				fv.SetInt(int64(n))
+			}
+		}
+
+		if field.Type == reflect.TypeOf(Duration{}) {
+			if d, err := time.ParseDuration(envVal); err == nil {
+				fv.Set(reflect.ValueOf(Duration{d}))
+			}
+		}
+	}
+}