feat: gt mol attach auto-detects agent from cwd when single arg provided

When called with 1 arg from an agent working directory, gt mol attach
now auto-detects the pinned bead ID from the current agent's hook.

Uses the same role detection infrastructure as gt mail and bd. (gt-t7ekm)

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

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

internal/cmd/molecule.go

@@ -55,16 +55,20 @@ Example:
 }
 
 var moleculeAttachCmd = &cobra.Command{
-	Use:   "attach <pinned-bead-id> <molecule-id>",
+	Use:   "attach [pinned-bead-id] <molecule-id>",
 	Short: "Attach a molecule to a pinned bead",
 	Long: `Attach a molecule to a pinned/handoff bead.
 
 This records which molecule an agent is currently working on. The attachment
 is stored in the pinned bead's description and visible via 'bd show'.
 
-Example:
+When called with a single argument from an agent working directory, the
-  gt molecule attach gt-abc mol-xyz`,
+pinned bead ID is auto-detected from the current agent's hook.
-	Args: cobra.ExactArgs(2),
+
+Examples:
+  gt molecule attach gt-abc mol-xyz  # Explicit pinned bead
+  gt molecule attach mol-xyz         # Auto-detect from cwd`,
+	Args: cobra.RangeArgs(1, 2),
 	RunE: runMoleculeAttach,
 }
 

internal/cmd/molecule_attach.go

@@ -12,8 +12,24 @@ import (
 )
 
 func runMoleculeAttach(cmd *cobra.Command, args []string) error {
-	pinnedBeadID := args[0]
+	var pinnedBeadID, moleculeID string
-	moleculeID := args[1]
+
+	if len(args) == 2 {
+		// Explicit: gt mol attach <pinned-bead-id> <molecule-id>
+		pinnedBeadID = args[0]
+		moleculeID = args[1]
+	} else {
+		// Auto-detect: gt mol attach <molecule-id>
+		moleculeID = args[0]
+		var err error
+		pinnedBeadID, err = detectAgentBeadID()
+		if err != nil {
+			return fmt.Errorf("auto-detecting agent: %w", err)
+		}
+		if pinnedBeadID == "" {
+			return fmt.Errorf("could not detect agent from current directory - provide explicit pinned bead ID")
+		}
+	}
 
 	workDir, err := findLocalBeadsDir()
 	if err != nil {
@@ -37,6 +53,48 @@ func runMoleculeAttach(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+// detectAgentBeadID detects the current agent's bead ID from the working directory.
+// Returns the agent bead ID (e.g., "gt-mayor", "gt-gastown-polecat-nux") or empty string if not detectable.
+func detectAgentBeadID() (string, error) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return "", fmt.Errorf("getting current directory: %w", err)
+	}
+
+	townRoot, err := workspace.FindFromCwd()
+	if err != nil {
+		return "", fmt.Errorf("finding workspace: %w", err)
+	}
+	if townRoot == "" {
+		return "", fmt.Errorf("not in a Gas Town workspace")
+	}
+
+	roleInfo, err := GetRoleWithContext(cwd, townRoot)
+	if err != nil {
+		return "", fmt.Errorf("detecting role: %w", err)
+	}
+
+	roleCtx := RoleContext{
+		Role:     roleInfo.Role,
+		Rig:      roleInfo.Rig,
+		Polecat:  roleInfo.Polecat,
+		TownRoot: townRoot,
+		WorkDir:  cwd,
+	}
+
+	identity := buildAgentIdentity(roleCtx)
+	if identity == "" {
+		return "", fmt.Errorf("cannot determine agent identity (role: %s)", roleCtx.Role)
+	}
+
+	beadID := buildAgentBeadID(identity, roleCtx.Role)
+	if beadID == "" {
+		return "", fmt.Errorf("cannot build agent bead ID for identity: %s", identity)
+	}
+
+	return beadID, nil
+}
+
 func runMoleculeDetach(cmd *cobra.Command, args []string) error {
 	pinnedBeadID := args[0]