fix(sync): use town-level routes for prefix validation

Follow-up to 828fc11b addressing code review feedback:

1. Added LoadTownRoutes() - exported function that walks up to find
   town-level routes.jsonl (e.g., ~/gt/.beads/routes.jsonl)

2. Updated buildAllowedPrefixSet to use LoadTownRoutes instead of
   LoadRoutes, so it finds routes even when importing from a rig's
   local beads directory

3. Added unit tests for buildAllowedPrefixSet covering:
   - Primary prefix inclusion
   - allowed_prefixes config parsing
   - Routes from routes.jsonl
   - Missing routes.jsonl handling
   - Empty beadsDir handling

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/importer/importer.go

@@ -1058,15 +1058,14 @@ func buildAllowedPrefixSet(primaryPrefix string, allowedPrefixesConfig string, b
 
 	// Load prefixes from routes.jsonl for multi-rig setups (Gas Town)
 	// This allows issues from other rigs to coexist in the same JSONL
+	// Use LoadTownRoutes to find routes at town level (~/gt/.beads/routes.jsonl)
 	if beadsDir != "" {
-		routes, err := routing.LoadRoutes(beadsDir)
-		if err == nil && len(routes) > 0 {
-			for _, route := range routes {
-				// Normalize: remove trailing - if present
-				prefix := strings.TrimSuffix(route.Prefix, "-")
-				if prefix != "" {
-					allowed[prefix] = true
-				}
+		routes, _ := routing.LoadTownRoutes(beadsDir)
+		for _, route := range routes {
+			// Normalize: remove trailing - if present
+			prefix := strings.TrimSuffix(route.Prefix, "-")
+			if prefix != "" {
+				allowed[prefix] = true
 			}
 		}
 	}

internal/importer/importer_test.go

@@ -5,6 +5,8 @@ package importer
 
 import (
 	"context"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 	"time"
@@ -1708,3 +1710,92 @@ func TestMultiRepoPrefixValidation(t *testing.T) {
 		}
 	})
 }
+
+func TestBuildAllowedPrefixSet(t *testing.T) {
+	t.Run("includes primary prefix", func(t *testing.T) {
+		allowed := buildAllowedPrefixSet("gt", "", "")
+		if allowed == nil {
+			t.Fatal("Expected non-nil allowed set")
+		}
+		if !allowed["gt"] {
+			t.Error("Primary prefix 'gt' should be allowed")
+		}
+	})
+
+	t.Run("includes allowed_prefixes config", func(t *testing.T) {
+		allowed := buildAllowedPrefixSet("gt", "hq,mol-,other", "")
+		if allowed == nil {
+			t.Fatal("Expected non-nil allowed set")
+		}
+		if !allowed["gt"] {
+			t.Error("Primary prefix 'gt' should be allowed")
+		}
+		if !allowed["hq"] {
+			t.Error("Config prefix 'hq' should be allowed")
+		}
+		if !allowed["mol"] {
+			t.Error("Config prefix 'mol' (normalized from 'mol-') should be allowed")
+		}
+		if !allowed["other"] {
+			t.Error("Config prefix 'other' should be allowed")
+		}
+	})
+
+	t.Run("includes prefixes from routes.jsonl", func(t *testing.T) {
+		// Create a temp directory with routes.jsonl
+		tmpDir := t.TempDir()
+		routesPath := filepath.Join(tmpDir, "routes.jsonl")
+		routesContent := `{"prefix": "hq-", "path": "."}
+{"prefix": "gt-", "path": "gastown/mayor/rig"}
+{"prefix": "bd-", "path": "beads/mayor/rig"}
+`
+		if err := os.WriteFile(routesPath, []byte(routesContent), 0644); err != nil {
+			t.Fatalf("Failed to write routes.jsonl: %v", err)
+		}
+
+		// buildAllowedPrefixSet uses LoadTownRoutes which tries to find town root
+		// For this unit test, LoadRoutes will work since routes.jsonl is in tmpDir
+		allowed := buildAllowedPrefixSet("gt", "", tmpDir)
+		if allowed == nil {
+			t.Fatal("Expected non-nil allowed set")
+		}
+
+		// Primary prefix should always be included
+		if !allowed["gt"] {
+			t.Error("Primary prefix 'gt' should be allowed")
+		}
+
+		// Routed prefixes should be included (normalized without trailing -)
+		if !allowed["hq"] {
+			t.Error("Routed prefix 'hq' (from routes.jsonl) should be allowed")
+		}
+		if !allowed["bd"] {
+			t.Error("Routed prefix 'bd' (from routes.jsonl) should be allowed")
+		}
+	})
+
+	t.Run("handles missing routes.jsonl gracefully", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		// No routes.jsonl file in tmpDir
+		// Note: LoadTownRoutes may still find routes at town level if running in Gas Town
+
+		allowed := buildAllowedPrefixSet("gt", "", tmpDir)
+		if allowed == nil {
+			t.Fatal("Expected non-nil allowed set")
+		}
+		if !allowed["gt"] {
+			t.Error("Primary prefix 'gt' should be allowed even without local routes.jsonl")
+		}
+		// Don't check exact count - town-level routes may be found
+	})
+
+	t.Run("handles empty beadsDir", func(t *testing.T) {
+		allowed := buildAllowedPrefixSet("gt", "", "")
+		if allowed == nil {
+			t.Fatal("Expected non-nil allowed set")
+		}
+		if !allowed["gt"] {
+			t.Error("Primary prefix 'gt' should be allowed")
+		}
+	})
+}

internal/routing/routes.go

@@ -55,6 +55,16 @@ func LoadRoutes(beadsDir string) ([]Route, error) {
 	return routes, scanner.Err()
 }
 
+// LoadTownRoutes loads routes from the town-level routes.jsonl.
+// It first checks the given beadsDir, then walks up to find the town root
+// and loads routes from there. This is useful for multi-rig setups (Gas Town)
+// where routes.jsonl lives at ~/gt/.beads/ rather than in individual rig directories.
+// Returns routes and nil error on success, or nil routes if not in a town or no routes found.
+func LoadTownRoutes(beadsDir string) ([]Route, error) {
+	routes, _ := findTownRoutes(beadsDir)
+	return routes, nil
+}
+
 // ExtractPrefix extracts the prefix from an issue ID.
 // For "gt-abc123", returns "gt-".
 // For "bd-abc123", returns "bd-".