feat(mail): add message types and threading support

- Add MessageType enum (task, scavenge, notification, reply)
- Expand Priority from 2 to 4 levels (low, normal, high, urgent)
- Add ThreadID and ReplyTo fields to Message struct
- Add --type and --reply-to flags to 'gt mail send'
- Add 'gt mail thread <id>' command to view conversation threads
- Update inbox/read display to show type and threading info
- Auto-generate thread IDs for new messages
- Reply messages inherit thread from original

Closes: gt-hgk

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/cmd/mail.go

@@ -1,6 +1,8 @@
 package cmd
 
 import (
+	"crypto/rand"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -18,12 +20,15 @@ var (
 	mailSubject     string
 	mailBody        string
 	mailPriority    string
+	mailType        string
+	mailReplyTo     string
 	mailNotify      bool
 	mailInboxJSON   bool
 	mailReadJSON    bool
 	mailInboxUnread bool
 	mailCheckInject bool
 	mailCheckJSON   bool
+	mailThreadJSON  bool
 )
 
 var mailCmd = &cobra.Command{
@@ -46,10 +51,21 @@ Addresses:
   <rig>/<polecat>  - Send to a specific polecat
   <rig>/           - Broadcast to a rig
 
+Message types:
+  task          - Required processing
+  scavenge      - Optional first-come work
+  notification  - Informational (default)
+  reply         - Response to message
+
+Priority levels:
+  low, normal (default), high, urgent
+
 Examples:
   gt mail send gastown/Toast -s "Status check" -m "How's that bug fix going?"
   gt mail send mayor/ -s "Work complete" -m "Finished gt-abc"
-  gt mail send gastown/ -s "All hands" -m "Swarm starting" --notify`,
+  gt mail send gastown/ -s "All hands" -m "Swarm starting" --notify
+  gt mail send gastown/Toast -s "Task" -m "Fix bug" --type task --priority high
+  gt mail send mayor/ -s "Re: Status" -m "Done" --reply-to msg-abc123`,
 	Args: cobra.ExactArgs(1),
 	RunE: runMailSend,
 }
@@ -108,11 +124,26 @@ Examples:
 	RunE: runMailCheck,
 }
 
+var mailThreadCmd = &cobra.Command{
+	Use:   "thread <thread-id>",
+	Short: "View a message thread",
+	Long: `View all messages in a conversation thread.
+
+Shows messages in chronological order (oldest first).
+
+Examples:
+  gt mail thread thread-abc123`,
+	Args: cobra.ExactArgs(1),
+	RunE: runMailThread,
+}
+
 func init() {
 	// Send flags
 	mailSendCmd.Flags().StringVarP(&mailSubject, "subject", "s", "", "Message subject (required)")
 	mailSendCmd.Flags().StringVarP(&mailBody, "message", "m", "", "Message body")
-	mailSendCmd.Flags().StringVar(&mailPriority, "priority", "normal", "Message priority (normal, high)")
+	mailSendCmd.Flags().StringVar(&mailPriority, "priority", "normal", "Message priority (low, normal, high, urgent)")
+	mailSendCmd.Flags().StringVar(&mailType, "type", "notification", "Message type (task, scavenge, notification, reply)")
+	mailSendCmd.Flags().StringVar(&mailReplyTo, "reply-to", "", "Message ID this is replying to")
 	mailSendCmd.Flags().BoolVarP(&mailNotify, "notify", "n", false, "Send tmux notification to recipient")
 	mailSendCmd.MarkFlagRequired("subject")
 
@@ -127,12 +158,16 @@ func init() {
 	mailCheckCmd.Flags().BoolVar(&mailCheckInject, "inject", false, "Output format for Claude Code hooks")
 	mailCheckCmd.Flags().BoolVar(&mailCheckJSON, "json", false, "Output as JSON")
 
+	// Thread flags
+	mailThreadCmd.Flags().BoolVar(&mailThreadJSON, "json", false, "Output as JSON")
+
 	// Add subcommands
 	mailCmd.AddCommand(mailSendCmd)
 	mailCmd.AddCommand(mailInboxCmd)
 	mailCmd.AddCommand(mailReadCmd)
 	mailCmd.AddCommand(mailDeleteCmd)
 	mailCmd.AddCommand(mailCheckCmd)
+	mailCmd.AddCommand(mailThreadCmd)
 
 	rootCmd.AddCommand(mailCmd)
 }
@@ -158,10 +193,36 @@ func runMailSend(cmd *cobra.Command, args []string) error {
 	}
 
 	// Set priority
-	if mailPriority == "high" || mailNotify {
+	msg.Priority = mail.ParsePriority(mailPriority)
+	if mailNotify && msg.Priority == mail.PriorityNormal {
 		msg.Priority = mail.PriorityHigh
 	}
 
+	// Set message type
+	msg.Type = mail.ParseMessageType(mailType)
+
+	// Handle reply-to: auto-set type to reply and look up thread
+	if mailReplyTo != "" {
+		msg.ReplyTo = mailReplyTo
+		if msg.Type == mail.TypeNotification {
+			msg.Type = mail.TypeReply
+		}
+
+		// Look up original message to get thread ID
+		router := mail.NewRouter(workDir)
+		mailbox, err := router.GetMailbox(from)
+		if err == nil {
+			if original, err := mailbox.Get(mailReplyTo); err == nil {
+				msg.ThreadID = original.ThreadID
+			}
+		}
+	}
+
+	// Generate thread ID for new threads
+	if msg.ThreadID == "" {
+		msg.ThreadID = generateThreadID()
+	}
+
 	// Send via router
 	router := mail.NewRouter(workDir)
 	if err := router.Send(msg); err != nil {
@@ -170,6 +231,9 @@ func runMailSend(cmd *cobra.Command, args []string) error {
 
 	fmt.Printf("%s Message sent to %s\n", style.Bold.Render("✓"), to)
 	fmt.Printf("  Subject: %s\n", mailSubject)
+	if msg.Type != mail.TypeNotification {
+		fmt.Printf("  Type: %s\n", msg.Type)
+	}
 
 	return nil
 }
@@ -229,12 +293,16 @@ func runMailInbox(cmd *cobra.Command, args []string) error {
 		if msg.Read {
 			readMarker = "○"
 		}
+		typeMarker := ""
+		if msg.Type != "" && msg.Type != mail.TypeNotification {
+			typeMarker = fmt.Sprintf(" [%s]", msg.Type)
+		}
 		priorityMarker := ""
-		if msg.Priority == mail.PriorityHigh {
+		if msg.Priority == mail.PriorityHigh || msg.Priority == mail.PriorityUrgent {
 			priorityMarker = " " + style.Bold.Render("!")
 		}
 
-		fmt.Printf("  %s %s%s\n", readMarker, msg.Subject, priorityMarker)
+		fmt.Printf("  %s %s%s%s\n", readMarker, msg.Subject, typeMarker, priorityMarker)
 		fmt.Printf("    %s from %s\n",
 			style.Dim.Render(msg.ID),
 			msg.From)
@@ -281,16 +349,30 @@ func runMailRead(cmd *cobra.Command, args []string) error {
 
 	// Human-readable output
 	priorityStr := ""
-	if msg.Priority == mail.PriorityHigh {
+	if msg.Priority == mail.PriorityUrgent {
+		priorityStr = " " + style.Bold.Render("[URGENT]")
+	} else if msg.Priority == mail.PriorityHigh {
 		priorityStr = " " + style.Bold.Render("[HIGH PRIORITY]")
 	}
 
-	fmt.Printf("%s %s%s\n\n", style.Bold.Render("Subject:"), msg.Subject, priorityStr)
+	typeStr := ""
+	if msg.Type != "" && msg.Type != mail.TypeNotification {
+		typeStr = fmt.Sprintf(" [%s]", msg.Type)
+	}
+
+	fmt.Printf("%s %s%s%s\n\n", style.Bold.Render("Subject:"), msg.Subject, typeStr, priorityStr)
 	fmt.Printf("From: %s\n", msg.From)
 	fmt.Printf("To: %s\n", msg.To)
 	fmt.Printf("Date: %s\n", msg.Timestamp.Format("2006-01-02 15:04:05"))
 	fmt.Printf("ID: %s\n", style.Dim.Render(msg.ID))
 
+	if msg.ThreadID != "" {
+		fmt.Printf("Thread: %s\n", style.Dim.Render(msg.ThreadID))
+	}
+	if msg.ReplyTo != "" {
+		fmt.Printf("Reply-To: %s\n", style.Dim.Render(msg.ReplyTo))
+	}
+
 	if msg.Body != "" {
 		fmt.Printf("\n%s\n", msg.Body)
 	}
@@ -467,3 +549,78 @@ func runMailCheck(cmd *cobra.Command, args []string) error {
 	}
 	return nil
 }
+
+func runMailThread(cmd *cobra.Command, args []string) error {
+	threadID := args[0]
+
+	// Find workspace
+	workDir, err := findBeadsWorkDir()
+	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
+}
+
+// generateThreadID creates a random thread ID for new message threads.
+func generateThreadID() string {
+	b := make([]byte, 6)
+	rand.Read(b)
+	return "thread-" + hex.EncodeToString(b)
+}

internal/mail/mailbox.go

@@ -379,3 +379,71 @@ func (m *Mailbox) rewriteLegacy(messages []*Message) error {
 	// Atomic rename
 	return os.Rename(tmpPath, m.path)
 }
+
+// ListByThread returns all messages in a given thread.
+func (m *Mailbox) ListByThread(threadID string) ([]*Message, error) {
+	if m.legacy {
+		return m.listByThreadLegacy(threadID)
+	}
+	return m.listByThreadBeads(threadID)
+}
+
+func (m *Mailbox) listByThreadBeads(threadID string) ([]*Message, error) {
+	// bd message thread <thread-id> --json
+	cmd := exec.Command("bd", "message", "thread", threadID, "--json")
+	cmd.Dir = m.workDir
+	cmd.Env = append(cmd.Environ(), "BD_IDENTITY="+m.identity)
+
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	if err := cmd.Run(); err != nil {
+		errMsg := strings.TrimSpace(stderr.String())
+		if errMsg != "" {
+			return nil, errors.New(errMsg)
+		}
+		return nil, err
+	}
+
+	var beadsMsgs []BeadsMessage
+	if err := json.Unmarshal(stdout.Bytes(), &beadsMsgs); err != nil {
+		if len(stdout.Bytes()) == 0 || string(stdout.Bytes()) == "null" {
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	var messages []*Message
+	for _, bm := range beadsMsgs {
+		messages = append(messages, bm.ToMessage())
+	}
+
+	// Sort by timestamp (oldest first for thread view)
+	sort.Slice(messages, func(i, j int) bool {
+		return messages[i].Timestamp.Before(messages[j].Timestamp)
+	})
+
+	return messages, nil
+}
+
+func (m *Mailbox) listByThreadLegacy(threadID string) ([]*Message, error) {
+	messages, err := m.List()
+	if err != nil {
+		return nil, err
+	}
+
+	var thread []*Message
+	for _, msg := range messages {
+		if msg.ThreadID == threadID {
+			thread = append(thread, msg)
+		}
+	}
+
+	// Sort by timestamp (oldest first for thread view)
+	sort.Slice(thread, func(i, j int) bool {
+		return thread[i].Timestamp.Before(thread[j].Timestamp)
+	})
+
+	return thread, nil
+}

internal/mail/router.go

@@ -36,9 +36,23 @@ func (r *Router) Send(msg *Message) error {
 		"-s", msg.Subject,
 	}
 
-	// Add importance flag for high priority
-	if msg.Priority == PriorityHigh {
-		args = append(args, "--importance", "high")
+	// Add priority flag
+	beadsPriority := PriorityToBeads(msg.Priority)
+	args = append(args, "--priority", fmt.Sprintf("%d", beadsPriority))
+
+	// Add message type if set
+	if msg.Type != "" && msg.Type != TypeNotification {
+		args = append(args, "--type", string(msg.Type))
+	}
+
+	// Add thread ID if set
+	if msg.ThreadID != "" {
+		args = append(args, "--thread-id", msg.ThreadID)
+	}
+
+	// Add reply-to if set
+	if msg.ReplyTo != "" {
+		args = append(args, "--reply-to", msg.ReplyTo)
 	}
 
 	cmd := exec.Command("bd", args...)
@@ -57,7 +71,7 @@ func (r *Router) Send(msg *Message) error {
 	}
 
 	// Optionally notify if recipient is a polecat with active session
-	if isPolecat(msg.To) && msg.Priority == PriorityHigh {
+	if isPolecat(msg.To) && (msg.Priority == PriorityHigh || msg.Priority == PriorityUrgent) {
 		r.notifyPolecat(msg)
 	}
 

internal/mail/types.go

@@ -11,11 +11,34 @@ import (
 type Priority string
 
 const (
+	// PriorityLow is for non-urgent messages.
+	PriorityLow Priority = "low"
+
 	// PriorityNormal is the default priority.
 	PriorityNormal Priority = "normal"
 
-	// PriorityHigh indicates an urgent message.
+	// PriorityHigh indicates an important message.
 	PriorityHigh Priority = "high"
+
+	// PriorityUrgent indicates an urgent message requiring immediate attention.
+	PriorityUrgent Priority = "urgent"
+)
+
+// MessageType indicates the purpose of a message.
+type MessageType string
+
+const (
+	// TypeTask indicates a message requiring action from the recipient.
+	TypeTask MessageType = "task"
+
+	// TypeScavenge indicates optional first-come-first-served work.
+	TypeScavenge MessageType = "scavenge"
+
+	// TypeNotification is an informational message (default).
+	TypeNotification MessageType = "notification"
+
+	// TypeReply is a response to another message.
+	TypeReply MessageType = "reply"
 )
 
 // Message represents a mail message between agents.
@@ -44,9 +67,18 @@ type Message struct {
 
 	// Priority is the message priority.
 	Priority Priority `json:"priority"`
+
+	// Type indicates the message type (task, scavenge, notification, reply).
+	Type MessageType `json:"type"`
+
+	// ThreadID groups related messages into a conversation thread.
+	ThreadID string `json:"thread_id,omitempty"`
+
+	// ReplyTo is the ID of the message this is replying to.
+	ReplyTo string `json:"reply_to,omitempty"`
 }
 
-// NewMessage creates a new message with a generated ID (for legacy JSONL mode).
+// NewMessage creates a new message with a generated ID and thread ID.
 func NewMessage(from, to, subject, body string) *Message {
 	return &Message{
 		ID:        generateID(),
@@ -57,6 +89,25 @@ func NewMessage(from, to, subject, body string) *Message {
 		Timestamp: time.Now(),
 		Read:      false,
 		Priority:  PriorityNormal,
+		Type:      TypeNotification,
+		ThreadID:  generateThreadID(),
+	}
+}
+
+// NewReplyMessage creates a reply message that inherits the thread from the original.
+func NewReplyMessage(from, to, subject, body string, original *Message) *Message {
+	return &Message{
+		ID:        generateID(),
+		From:      from,
+		To:        to,
+		Subject:   subject,
+		Body:      body,
+		Timestamp: time.Now(),
+		Read:      false,
+		Priority:  PriorityNormal,
+		Type:      TypeReply,
+		ThreadID:  original.ThreadID,
+		ReplyTo:   original.ID,
 	}
 }
 
@@ -67,6 +118,13 @@ func generateID() string {
 	return "msg-" + hex.EncodeToString(b)
 }
 
+// generateThreadID creates a random thread ID.
+func generateThreadID() string {
+	b := make([]byte, 6)
+	rand.Read(b)
+	return "thread-" + hex.EncodeToString(b)
+}
+
 // BeadsMessage represents a message as returned by bd mail commands.
 type BeadsMessage struct {
 	ID          string    `json:"id"`
@@ -74,16 +132,34 @@ type BeadsMessage struct {
 	Description string    `json:"description"` // Body
 	Sender      string    `json:"sender"`      // From identity
 	Assignee    string    `json:"assignee"`    // To identity
-	Priority    int       `json:"priority"`    // 0=urgent, 2=normal
+	Priority    int       `json:"priority"`    // 0=urgent, 1=high, 2=normal, 3=low
 	Status      string    `json:"status"`      // open=unread, closed=read
 	CreatedAt   time.Time `json:"created_at"`
+	Type        string    `json:"type,omitempty"`      // Message type
+	ThreadID    string    `json:"thread_id,omitempty"` // Thread identifier
+	ReplyTo     string    `json:"reply_to,omitempty"`  // Original message ID
 }
 
 // ToMessage converts a BeadsMessage to a GGT Message.
 func (bm *BeadsMessage) ToMessage() *Message {
-	priority := PriorityNormal
-	if bm.Priority == 0 {
+	// Convert beads priority (0=urgent, 1=high, 2=normal, 3=low) to GGT Priority
+	var priority Priority
+	switch bm.Priority {
+	case 0:
+		priority = PriorityUrgent
+	case 1:
 		priority = PriorityHigh
+	case 3:
+		priority = PriorityLow
+	default:
+		priority = PriorityNormal
+	}
+
+	// Convert message type, default to notification
+	msgType := TypeNotification
+	switch MessageType(bm.Type) {
+	case TypeTask, TypeScavenge, TypeReply:
+		msgType = MessageType(bm.Type)
 	}
 
 	return &Message{
@@ -95,6 +171,44 @@ func (bm *BeadsMessage) ToMessage() *Message {
 		Timestamp: bm.CreatedAt,
 		Read:      bm.Status == "closed",
 		Priority:  priority,
+		Type:      msgType,
+		ThreadID:  bm.ThreadID,
+		ReplyTo:   bm.ReplyTo,
+	}
+}
+
+// PriorityToBeads converts a GGT Priority to beads priority integer.
+// Returns: 0=urgent, 1=high, 2=normal, 3=low
+func PriorityToBeads(p Priority) int {
+	switch p {
+	case PriorityUrgent:
+		return 0
+	case PriorityHigh:
+		return 1
+	case PriorityLow:
+		return 3
+	default:
+		return 2 // normal
+	}
+}
+
+// ParsePriority parses a priority string, returning PriorityNormal for invalid values.
+func ParsePriority(s string) Priority {
+	switch Priority(s) {
+	case PriorityLow, PriorityNormal, PriorityHigh, PriorityUrgent:
+		return Priority(s)
+	default:
+		return PriorityNormal
+	}
+}
+
+// ParseMessageType parses a message type string, returning TypeNotification for invalid values.
+func ParseMessageType(s string) MessageType {
+	switch MessageType(s) {
+	case TypeTask, TypeScavenge, TypeNotification, TypeReply:
+		return MessageType(s)
+	default:
+		return TypeNotification
 	}
 }