fix(sling): resolve rig path for cross-rig bead hooking

gt sling failed when hooking rig-level beads from town root because
bd update doesn't support cross-database routing like bd show does.

The fix adds a ResolveHookDir helper that:
1. Extracts the prefix from bead ID (e.g., "ap-xxx" → "ap-")
2. Looks up the rig path from routes.jsonl
3. Falls back to townRoot if prefix not found

Also removes the BEADS_DIR environment override which was preventing
routing from working correctly.

Fixes #148

internal/cmd/beads_routing_integration_test.go

@@ -443,6 +443,73 @@ func TestBeadsRemoveRoute(t *testing.T) {
 	}
 }
 
+// TestSlingCrossRigRoutingResolution verifies that sling can resolve rig paths
+// for cross-rig bead hooking using ExtractPrefix and GetRigPathForPrefix.
+// This is the fix for https://github.com/steveyegge/gastown/issues/148
+func TestSlingCrossRigRoutingResolution(t *testing.T) {
+	townRoot := setupRoutingTestTown(t)
+
+	tests := []struct {
+		beadID       string
+		expectedPath string // Relative to townRoot, or "." for town-level
+	}{
+		{"gt-mol-abc", "gastown/mayor/rig"},
+		{"tr-task-xyz", "testrig/mayor/rig"},
+		{"hq-cv-123", "."}, // Town-level beads
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.beadID, func(t *testing.T) {
+			// Step 1: Extract prefix from bead ID
+			prefix := beads.ExtractPrefix(tc.beadID)
+			if prefix == "" {
+				t.Fatalf("ExtractPrefix(%q) returned empty", tc.beadID)
+			}
+
+			// Step 2: Resolve rig path from prefix
+			rigPath := beads.GetRigPathForPrefix(townRoot, prefix)
+			if rigPath == "" {
+				t.Fatalf("GetRigPathForPrefix(%q, %q) returned empty", townRoot, prefix)
+			}
+
+			// Step 3: Verify the path is correct
+			var expectedFull string
+			if tc.expectedPath == "." {
+				expectedFull = townRoot
+			} else {
+				expectedFull = filepath.Join(townRoot, tc.expectedPath)
+			}
+
+			if rigPath != expectedFull {
+				t.Errorf("GetRigPathForPrefix resolved to %q, want %q", rigPath, expectedFull)
+			}
+
+			// Step 4: Verify the .beads directory exists at that path
+			beadsDir := filepath.Join(rigPath, ".beads")
+			if _, err := os.Stat(beadsDir); os.IsNotExist(err) {
+				t.Errorf(".beads directory doesn't exist at resolved path: %s", beadsDir)
+			}
+		})
+	}
+}
+
+// TestSlingCrossRigUnknownPrefix verifies behavior for unknown prefixes.
+func TestSlingCrossRigUnknownPrefix(t *testing.T) {
+	townRoot := setupRoutingTestTown(t)
+
+	// An unknown prefix should return empty string
+	unknownBeadID := "xx-unknown-123"
+	prefix := beads.ExtractPrefix(unknownBeadID)
+	if prefix != "xx-" {
+		t.Fatalf("ExtractPrefix(%q) = %q, want %q", unknownBeadID, prefix, "xx-")
+	}
+
+	rigPath := beads.GetRigPathForPrefix(townRoot, prefix)
+	if rigPath != "" {
+		t.Errorf("GetRigPathForPrefix for unknown prefix returned %q, want empty", rigPath)
+	}
+}
+
 // TestBeadsGetPrefixForRig verifies prefix lookup by rig name.
 func TestBeadsGetPrefixForRig(t *testing.T) {
 	tmpDir := t.TempDir()

internal/cmd/sling.go

@@ -406,20 +406,10 @@ func runSling(cmd *cobra.Command, args []string) error {
 		beadID = wispRootID
 	}
 
-	// Hook the bead using bd update
-	// For town-level beads (hq-*), set BEADS_DIR to town beads
-	// For rig-level beads (gt-*, bd-*, etc.), use redirect-based routing from hookWorkDir
+	// Hook the bead using bd update.
+	// See: https://github.com/steveyegge/gastown/issues/148
 	hookCmd := exec.Command("bd", "--no-daemon", "update", beadID, "--status=hooked", "--assignee="+targetAgent)
-	if strings.HasPrefix(beadID, "hq-") {
-		// Town-level bead: set BEADS_DIR explicitly
-		hookCmd.Env = append(os.Environ(), "BEADS_DIR="+townBeadsDir)
-		hookCmd.Dir = townRoot
-	} else if hookWorkDir != "" {
-		// Rig-level bead: use redirect from polecat's worktree
-		hookCmd.Dir = hookWorkDir
-	} else {
-		hookCmd.Dir = townRoot
-	}
+	hookCmd.Dir = beads.ResolveHookDir(townRoot, beadID, hookWorkDir)
 	hookCmd.Stderr = os.Stderr
 	if err := hookCmd.Run(); err != nil {
 		return fmt.Errorf("hooking bead: %w", err)
@@ -939,11 +929,10 @@ func runSlingFormula(args []string) error {
 
 	fmt.Printf("%s Wisp created: %s\n", style.Bold.Render("✓"), wispResult.RootID)
 
-	// Step 3: Hook the wisp bead using bd update (discovery-based approach)
-	// Set BEADS_DIR to town-level beads so hq-* beads are accessible
+	// Step 3: Hook the wisp bead using bd update.
+	// See: https://github.com/steveyegge/gastown/issues/148
 	hookCmd := exec.Command("bd", "--no-daemon", "update", wispResult.RootID, "--status=hooked", "--assignee="+targetAgent)
-	hookCmd.Env = append(os.Environ(), "BEADS_DIR="+townBeadsDir)
-	hookCmd.Dir = townRoot
+	hookCmd.Dir = beads.ResolveHookDir(townRoot, wispResult.RootID, "")
 	hookCmd.Stderr = os.Stderr
 	if err := hookCmd.Run(); err != nil {
 		return fmt.Errorf("hooking wisp bead: %w", err)
@@ -1432,17 +1421,10 @@ func runBatchSling(beadIDs []string, rigName string, townBeadsDir string) error
 			}
 		}
 
-		// Hook the bead
-		// For town-level beads (hq-*), set BEADS_DIR; for rig-level beads use redirect
+		// Hook the bead. See: https://github.com/steveyegge/gastown/issues/148
+		townRoot := filepath.Dir(townBeadsDir)
 		hookCmd := exec.Command("bd", "--no-daemon", "update", beadID, "--status=hooked", "--assignee="+targetAgent)
-		if strings.HasPrefix(beadID, "hq-") {
-			// Town-level bead: set BEADS_DIR and run from town root (parent of townBeadsDir)
-			hookCmd.Env = append(os.Environ(), "BEADS_DIR="+townBeadsDir)
-			hookCmd.Dir = filepath.Dir(townBeadsDir)
-		} else if hookWorkDir != "" {
-			// Rig-level bead: use redirect from polecat's worktree
-			hookCmd.Dir = hookWorkDir
-		}
+		hookCmd.Dir = beads.ResolveHookDir(townRoot, beadID, hookWorkDir)
 		hookCmd.Stderr = os.Stderr
 		if err := hookCmd.Run(); err != nil {
 			results = append(results, slingResult{beadID: beadID, polecat: spawnInfo.PolecatName, success: false, errMsg: "hook failed"})