Feat v0.9.0 multi-surface packages (#73)

Packages can declare a `surfaces` array with per-path access controls,
titles, and layouts. A single package can serve a public form, an
authenticated dashboard, and an admin page — each with independent
access enforcement.

Kernel:
- Manifest validation for surfaces array (path, access, duplicates)
- Auto-synthesis from legacy auth/layout for existing packages
- Unified /s/:slug route tree (RegisterExtensionRoutes) dispatches
  between surface rendering and ext API calls
- matchSurface() with Gin-style :param support and specificity ordering
- evaluateAccess() for per-surface access checks
- Nav filters out pending_review packages (pre-existing bug fix)

Frontend:
- __SURFACE_PATH__ and __SURFACE_PARAMS__ template injection
- sw.navigate(path, params) for SPA-style intra-package routing
- surface.navigate event + popstate handling
- SDK version bumped to 0.9.0

Docs:
- MULTI-SURFACE-GUIDE.md — full developer guide
- PACKAGE-FORMAT.md — surfaces field reference
- CHANGELOG.md, ROADMAP.md updated

22 new tests (11 manifest validation, 11 route matching/nav).

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

server/handlers/package_validate.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"regexp"
+	"strings"
 )
 
 // validManifestID matches lowercase alphanumeric slugs with optional hyphens.
@@ -21,6 +22,7 @@ type ManifestInfo struct {
 	Tier          string
 	SchemaVersion int
 	HasRoute      bool
+	HasSurfaces   bool
 	HasTools      bool
 	HasPipes      bool
 	HasHooks      bool
@@ -81,7 +83,64 @@ func ValidateManifest(manifest map[string]any) (*ManifestInfo, error) {
 	}
 	info.Signature, _ = manifest["signature"].(string)
 
-	info.HasRoute = manifest["route"] != nil || manifest["routes"] != nil
+	// ── Surfaces validation ─────────────────────────────────────
+	if rawSurfaces, ok := manifest["surfaces"].([]any); ok {
+		if len(rawSurfaces) == 0 {
+			return nil, fmt.Errorf("surfaces array cannot be empty")
+		}
+		seen := map[string]bool{}
+		for i, raw := range rawSurfaces {
+			s, ok := raw.(map[string]any)
+			if !ok {
+				return nil, fmt.Errorf("surfaces[%d] must be an object", i)
+			}
+			path, _ := s["path"].(string)
+			if path == "" {
+				return nil, fmt.Errorf("surfaces[%d] requires a path", i)
+			}
+			if !strings.HasPrefix(path, "/") {
+				return nil, fmt.Errorf("surfaces[%d] path must start with /", i)
+			}
+			if seen[path] {
+				return nil, fmt.Errorf("duplicate surface path: %s", path)
+			}
+			seen[path] = true
+			if access, ok := s["access"].(string); ok {
+				if !validAccessLevels(access) {
+					return nil, fmt.Errorf("surfaces[%d] invalid access: %s", i, access)
+				}
+			}
+		}
+		info.HasSurfaces = true
+		info.HasRoute = true
+	} else if manifest["surfaces"] != nil {
+		// surfaces key present but not an array
+		return nil, fmt.Errorf("surfaces must be an array")
+	} else {
+		// No surfaces declared — synthesize from legacy fields.
+		// This ensures every routable package always has a surfaces array.
+		if info.Type == "surface" || info.Type == "full" {
+			auth, _ := manifest["auth"].(string)
+			if auth == "" {
+				auth = "authenticated"
+			}
+			layout, _ := manifest["layout"].(string)
+			if layout == "" {
+				layout = "single"
+			}
+			manifest["surfaces"] = []any{
+				map[string]any{
+					"path":   "/",
+					"access": auth,
+					"layout": layout,
+					"title":  info.Title,
+				},
+			}
+			info.HasSurfaces = true
+		}
+		info.HasRoute = manifest["route"] != nil || manifest["routes"] != nil || info.HasSurfaces
+	}
+
 	info.HasTools = manifest["tools"] != nil
 	info.HasPipes = manifest["pipes"] != nil
 	info.HasHooks = manifest["hooks"] != nil
@@ -156,6 +215,18 @@ func ValidateManifest(manifest map[string]any) (*ManifestInfo, error) {
 	return info, nil
 }
 
+// validAccessLevels checks whether an access string is a recognized value.
+func validAccessLevels(access string) bool {
+	switch {
+	case access == "public", access == "authenticated", access == "admin":
+		return true
+	case strings.HasPrefix(access, "group:"):
+		return strings.TrimPrefix(access, "group:") != ""
+	default:
+		return false
+	}
+}
+
 // ValidateManifestJSON parses raw JSON bytes into a manifest map and validates.
 func ValidateManifestJSON(data []byte) (map[string]any, *ManifestInfo, error) {
 	var manifest map[string]any