feat: add gt mol attach-from-mail command (gt-h6eq.7)

Allows agents to self-pin work from mail messages. The command:
1. Reads a mail message by ID
2. Extracts molecule ID from the body (attached_molecule:, molecule_id:, etc.)
3. Attaches the molecule to the agent's pinned bead (hook)
4. Marks the mail as read

Includes unit tests for the molecule ID extraction logic.

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

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

internal/cmd/molecule_attach_from_mail.go

@@ -0,0 +1,146 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/mail"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+// runMoleculeAttachFromMail handles the "gt mol attach-from-mail <mail-id>" command.
+// It reads a mail message, extracts the molecule ID from the body, and attaches
+// it to the current agent's hook (pinned bead).
+func runMoleculeAttachFromMail(cmd *cobra.Command, args []string) error {
+	mailID := args[0]
+
+	// Get current working directory and town root
+	cwd, err := os.Getwd()
+	if err != nil {
+		return fmt.Errorf("getting current directory: %w", err)
+	}
+
+	townRoot, err := workspace.FindFromCwd()
+	if err != nil || townRoot == "" {
+		return fmt.Errorf("not in a Gas Town workspace")
+	}
+
+	// Detect agent role and identity
+	roleCtx := detectRole(cwd, townRoot)
+	agentIdentity := buildAgentIdentity(roleCtx)
+	if agentIdentity == "" {
+		return fmt.Errorf("cannot determine agent identity from current directory (role: %s)", roleCtx.Role)
+	}
+
+	// Get the agent's mailbox
+	mailWorkDir, err := findMailWorkDir()
+	if err != nil {
+		return fmt.Errorf("finding mail workspace: %w", err)
+	}
+
+	router := mail.NewRouter(mailWorkDir)
+	mailbox, err := router.GetMailbox(agentIdentity)
+	if err != nil {
+		return fmt.Errorf("getting mailbox: %w", err)
+	}
+
+	// Read the mail message
+	msg, err := mailbox.Get(mailID)
+	if err != nil {
+		return fmt.Errorf("reading mail message: %w", err)
+	}
+
+	// Extract molecule ID from mail body
+	moleculeID := extractMoleculeIDFromMail(msg.Body)
+	if moleculeID == "" {
+		return fmt.Errorf("no attached_molecule field found in mail body")
+	}
+
+	// Find local beads directory
+	workDir, err := findLocalBeadsDir()
+	if err != nil {
+		return fmt.Errorf("not in a beads workspace: %w", err)
+	}
+
+	b := beads.New(workDir)
+
+	// Find the agent's pinned bead (hook)
+	pinnedBeads, err := b.List(beads.ListOptions{
+		Status:   beads.StatusPinned,
+		Assignee: agentIdentity,
+		Priority: -1,
+	})
+	if err != nil {
+		return fmt.Errorf("listing pinned beads: %w", err)
+	}
+
+	if len(pinnedBeads) == 0 {
+		return fmt.Errorf("no pinned bead found for agent %s - create one first", agentIdentity)
+	}
+
+	// Use the first pinned bead as the hook
+	hookBead := pinnedBeads[0]
+
+	// Check if molecule exists
+	_, err = b.Show(moleculeID)
+	if err != nil {
+		return fmt.Errorf("molecule %s not found: %w", moleculeID, err)
+	}
+
+	// Attach the molecule to the hook
+	issue, err := b.AttachMolecule(hookBead.ID, moleculeID)
+	if err != nil {
+		return fmt.Errorf("attaching molecule: %w", err)
+	}
+
+	// Mark mail as read
+	if err := mailbox.MarkRead(mailID); err != nil {
+		// Non-fatal: log warning but don't fail
+		fmt.Fprintf(os.Stderr, "Warning: could not mark mail as read: %v\n", err)
+	}
+
+	// Output success
+	attachment := beads.ParseAttachmentFields(issue)
+	fmt.Printf("%s Attached molecule from mail\n", style.Bold.Render("✓"))
+	fmt.Printf("  Mail: %s\n", mailID)
+	fmt.Printf("  Hook: %s\n", hookBead.ID)
+	fmt.Printf("  Molecule: %s\n", moleculeID)
+	if attachment != nil && attachment.AttachedAt != "" {
+		fmt.Printf("  Attached at: %s\n", attachment.AttachedAt)
+	}
+	fmt.Printf("\n%s Run 'gt mol status' to see progress\n", style.Dim.Render("Hint:"))
+
+	return nil
+}
+
+// extractMoleculeIDFromMail extracts a molecule ID from a mail message body.
+// It looks for patterns like:
+//   - attached_molecule: <id>
+//   - molecule_id: <id>
+//   - molecule: <id>
+//
+// The ID is expected to be on the same line after the colon.
+func extractMoleculeIDFromMail(body string) string {
+	// Try various patterns for molecule ID in mail body (case-insensitive)
+	patterns := []string{
+		`(?i)attached_molecule:\s*(\S+)`,
+		`(?i)molecule_id:\s*(\S+)`,
+		`(?i)molecule:\s*(\S+)`,
+		`(?i)mol:\s*(\S+)`,
+	}
+
+	for _, pattern := range patterns {
+		re := regexp.MustCompile(pattern)
+		matches := re.FindStringSubmatch(body)
+		if len(matches) >= 2 {
+			return strings.TrimSpace(matches[1])
+		}
+	}
+
+	return ""
+}