refactor(beads,mail): split large files into focused modules

Break down monolithic beads.go and mail.go into smaller, single-purpose files:

beads package:
- beads_agent.go: Agent-related bead operations
- beads_delegation.go: Delegation bead handling
- beads_dog.go: Dog pool operations
- beads_merge_slot.go: Merge slot management
- beads_mr.go: Merge request operations
- beads_redirect.go: Redirect bead handling
- beads_rig.go: Rig bead operations
- beads_role.go: Role bead management

cmd package:
- mail_announce.go: Announcement subcommand
- mail_check.go: Mail check subcommand
- mail_identity.go: Identity management
- mail_inbox.go: Inbox operations
- mail_queue.go: Queue subcommand
- mail_search.go: Search functionality
- mail_send.go: Send subcommand
- mail_thread.go: Thread operations

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

internal/cmd/mail_thread.go

@@ -0,0 +1,145 @@
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/mail"
+	"github.com/steveyegge/gastown/internal/style"
+)
+
+func runMailThread(cmd *cobra.Command, args []string) error {
+	threadID := args[0]
+
+	// All mail uses town beads (two-level architecture)
+	workDir, err := findMailWorkDir()
+	if err != nil {
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	// Determine which inbox
+	address := detectSender()
+
+	// Get mailbox and thread messages
+	router := mail.NewRouter(workDir)
+	mailbox, err := router.GetMailbox(address)
+	if err != nil {
+		return fmt.Errorf("getting mailbox: %w", err)
+	}
+
+	messages, err := mailbox.ListByThread(threadID)
+	if err != nil {
+		return fmt.Errorf("getting thread: %w", err)
+	}
+
+	// JSON output
+	if mailThreadJSON {
+		enc := json.NewEncoder(os.Stdout)
+		enc.SetIndent("", "  ")
+		return enc.Encode(messages)
+	}
+
+	// Human-readable output
+	fmt.Printf("%s Thread: %s (%d messages)\n\n",
+		style.Bold.Render("🧵"), threadID, len(messages))
+
+	if len(messages) == 0 {
+		fmt.Printf("  %s\n", style.Dim.Render("(no messages in thread)"))
+		return nil
+	}
+
+	for i, msg := range messages {
+		typeMarker := ""
+		if msg.Type != "" && msg.Type != mail.TypeNotification {
+			typeMarker = fmt.Sprintf(" [%s]", msg.Type)
+		}
+		priorityMarker := ""
+		if msg.Priority == mail.PriorityHigh || msg.Priority == mail.PriorityUrgent {
+			priorityMarker = " " + style.Bold.Render("!")
+		}
+
+		if i > 0 {
+			fmt.Printf("  %s\n", style.Dim.Render("│"))
+		}
+		fmt.Printf("  %s %s%s%s\n", style.Bold.Render("●"), msg.Subject, typeMarker, priorityMarker)
+		fmt.Printf("    %s from %s to %s\n",
+			style.Dim.Render(msg.ID),
+			msg.From, msg.To)
+		fmt.Printf("    %s\n",
+			style.Dim.Render(msg.Timestamp.Format("2006-01-02 15:04")))
+
+		if msg.Body != "" {
+			fmt.Printf("    %s\n", msg.Body)
+		}
+	}
+
+	return nil
+}
+
+func runMailReply(cmd *cobra.Command, args []string) error {
+	msgID := args[0]
+
+	// All mail uses town beads (two-level architecture)
+	workDir, err := findMailWorkDir()
+	if err != nil {
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	// Determine current address
+	from := detectSender()
+
+	// Get the original message
+	router := mail.NewRouter(workDir)
+	mailbox, err := router.GetMailbox(from)
+	if err != nil {
+		return fmt.Errorf("getting mailbox: %w", err)
+	}
+
+	original, err := mailbox.Get(msgID)
+	if err != nil {
+		return fmt.Errorf("getting message: %w", err)
+	}
+
+	// Build reply subject
+	subject := mailReplySubject
+	if subject == "" {
+		if strings.HasPrefix(original.Subject, "Re: ") {
+			subject = original.Subject
+		} else {
+			subject = "Re: " + original.Subject
+		}
+	}
+
+	// Create reply message
+	reply := &mail.Message{
+		From:     from,
+		To:       original.From, // Reply to sender
+		Subject:  subject,
+		Body:     mailReplyMessage,
+		Type:     mail.TypeReply,
+		Priority: mail.PriorityNormal,
+		ReplyTo:  msgID,
+		ThreadID: original.ThreadID,
+	}
+
+	// If original has no thread ID, create one
+	if reply.ThreadID == "" {
+		reply.ThreadID = generateThreadID()
+	}
+
+	// Send the reply
+	if err := router.Send(reply); err != nil {
+		return fmt.Errorf("sending reply: %w", err)
+	}
+
+	fmt.Printf("%s Reply sent to %s\n", style.Bold.Render("✓"), original.From)
+	fmt.Printf("  Subject: %s\n", subject)
+	if original.ThreadID != "" {
+		fmt.Printf("  Thread: %s\n", style.Dim.Render(original.ThreadID))
+	}
+
+	return nil
+}