Re-vendor the shared files from sneak/prompts at dd4027b (closes #52)

Takes .golangci.yml, .dockerignore, .gitignore, .editorconfig, the
workflow and REPO_POLICIES.md from sneak/prompts dd4027b, keeping this
repository's own entries after the shared content. Lint (golangci-lint
v2.14.0) and test become Dockerfile phases that script/lint and
script/test build alone and uncached; the image build depends on both,
and script/cibuild bootstraps, runs script/check, then builds the image.
The agent guidance file moves to AGENTS.md. The Go code is fixed for
what the new configuration finds; reads that iterate rows now also
report an iteration error.

Model: opus-5-5

internal/config/config.go

@@ -2,6 +2,7 @@
 package config
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -27,6 +28,12 @@ const (
 	maxPort = 65535
 )
 
+var (
+	errRelativeXDGDataHome = errors.New("XDG_DATA_HOME must be an absolute path")
+	errUnsupportedOS       = errors.New("unsupported operating system")
+	errInvalidPort         = errors.New("PORT must be a whole number")
+)
+
 // Config holds configuration for the entire application
 type Config struct {
 	// StateDir is the directory for all application state (database, snapshots)
@@ -38,11 +45,14 @@ type Config struct {
 	// MaxRuntime is the maximum runtime (0 = run forever)
 	MaxRuntime time.Duration
 
-	// EnableBatchedDatabaseWrites enables batched database operations for better performance
+	// EnableBatchedDatabaseWrites enables batched database operations for
+	// better performance
 	EnableBatchedDatabaseWrites bool
 
-	// RouteExpirationTimeout is how long a route can go without being refreshed before expiring
-	// Default is 2 hours which is conservative for BGP (typical BGP hold time is 90-180 seconds)
+	// RouteExpirationTimeout is how long a route can go without being
+	// refreshed before expiring
+	// Default is 2 hours which is conservative for BGP (typical BGP hold
+	// time is 90-180 seconds)
 	RouteExpirationTimeout time.Duration
 }
 
@@ -59,11 +69,14 @@ func New() (*Config, error) {
 	}
 
 	return &Config{
-		StateDir:                    stateDir,
-		Port:                        port,
-		MaxRuntime:                  0,                                           // Run forever by default
-		EnableBatchedDatabaseWrites: true,                                        // Enable batching by default
-		RouteExpirationTimeout:      defaultRouteExpirationMinutes * time.Minute, // For active route monitoring
+		StateDir: stateDir,
+		Port:     port,
+		// Run forever by default
+		MaxRuntime: 0,
+		// Enable batching by default
+		EnableBatchedDatabaseWrites: true,
+		// For active route monitoring
+		RouteExpirationTimeout: defaultRouteExpirationMinutes * time.Minute,
 	}, nil
 }
 
@@ -89,7 +102,7 @@ func getStateDirectory() (string, error) {
 		// the database somewhere unexpected.
 		xdgData := os.Getenv("XDG_DATA_HOME")
 		if xdgData != "" && !filepath.IsAbs(xdgData) {
-			return "", fmt.Errorf("XDG_DATA_HOME must be an absolute path, got %q", xdgData)
+			return "", fmt.Errorf("%w, got %q", errRelativeXDGDataHome, xdgData)
 		}
 
 		// Unix-like: /var/lib/berlin.sneak.app.routewatch if root, else XDG_DATA_HOME
@@ -111,7 +124,7 @@ func getStateDirectory() (string, error) {
 		return filepath.Join(home, ".local", "share", AppIdentifier), nil
 
 	default:
-		return "", fmt.Errorf("unsupported operating system: %s", runtime.GOOS)
+		return "", fmt.Errorf("%w: %s", errUnsupportedOS, runtime.GOOS)
 	}
 }
 
@@ -125,7 +138,8 @@ func getPort() (int, error) {
 	// ParseUint, unlike Atoi, refuses a sign: the health check URL cannot use "+9090"
 	port, err := strconv.ParseUint(value, 10, 0)
 	if err != nil || port < 1 || port > maxPort {
-		return 0, fmt.Errorf("PORT must be a whole number from 1 to %d, got %q", maxPort, value)
+		return 0, fmt.Errorf("%w from 1 to %d, got %q",
+			errInvalidPort, maxPort, value)
 	}
 
 	return int(port), nil
@@ -134,7 +148,8 @@ func getPort() (int, error) {
 // EnsureDirectories creates all necessary directories if they don't exist
 func (c *Config) EnsureDirectories() error {
 	// Ensure state directory exists
-	if err := os.MkdirAll(c.StateDir, dirPermissions); err != nil {
+	err := os.MkdirAll(c.StateDir, dirPermissions)
+	if err != nil {
 		return fmt.Errorf("failed to create state directory: %w", err)
 	}
 

internal/config/config_internal_test.go

@@ -36,7 +36,8 @@ func TestNewRefusesInvalidPort(t *testing.T) {
 			t.Setenv("PORT", value)
 			t.Setenv("XDG_DATA_HOME", "")
 
-			if _, err := New(); err == nil {
+			_, err := New()
+			if err == nil {
 				t.Errorf("New() with PORT=%q returned no error", value)
 			}
 		})
@@ -51,12 +52,16 @@ func TestNewRefusesRelativeXDGDataHome(t *testing.T) {
 	t.Setenv("PORT", "")
 
 	t.Setenv("XDG_DATA_HOME", "relative/path")
-	if _, err := New(); err == nil {
+
+	_, err := New()
+	if err == nil {
 		t.Error("New() with a relative XDG_DATA_HOME returned no error")
 	}
 
 	t.Setenv("XDG_DATA_HOME", "/var/lib")
-	if _, err := New(); err != nil {
+
+	_, err = New()
+	if err != nil {
 		t.Errorf("New() with XDG_DATA_HOME=/var/lib: %v", err)
 	}
 }