refactor(sling): split 1560-line file into 7 focused modules

Extract sling.go into logical components following the established
<cmd>_<feature>.go pattern used elsewhere (crew_helpers.go, etc.):

- sling.go (465 lines): command definition + main runSling()
- sling_helpers.go (370): bead/tmux/agent utilities
- sling_formula.go (270): formula handling + wisp parsing
- sling_dog.go (158): dog dispatch logic
- sling_batch.go (154): batch slinging to rigs
- sling_convoy.go (125): auto-convoy creation
- sling_target.go (86): target resolution functions

No functional changes - pure code organization refactor.

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

internal/cmd/sling_target.go

@@ -0,0 +1,86 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/steveyegge/gastown/internal/session"
+	"github.com/steveyegge/gastown/internal/tmux"
+)
+
+// resolveTargetAgent converts a target spec to agent ID, pane, and hook root.
+func resolveTargetAgent(target string) (agentID string, pane string, hookRoot string, err error) {
+	// First resolve to session name
+	sessionName, err := resolveRoleToSession(target)
+	if err != nil {
+		return "", "", "", err
+	}
+
+	// Convert session name to agent ID format (this doesn't require tmux)
+	agentID = sessionToAgentID(sessionName)
+
+	// Get the pane for that session
+	pane, err = getSessionPane(sessionName)
+	if err != nil {
+		return "", "", "", fmt.Errorf("getting pane for %s: %w", sessionName, err)
+	}
+
+	// Get the target's working directory for hook storage
+	t := tmux.NewTmux()
+	hookRoot, err = t.GetPaneWorkDir(sessionName)
+	if err != nil {
+		return "", "", "", fmt.Errorf("getting working dir for %s: %w", sessionName, err)
+	}
+
+	return agentID, pane, hookRoot, nil
+}
+
+// sessionToAgentID converts a session name to agent ID format.
+// Uses session.ParseSessionName for consistent parsing across the codebase.
+func sessionToAgentID(sessionName string) string {
+	identity, err := session.ParseSessionName(sessionName)
+	if err != nil {
+		// Fallback for unparseable sessions
+		return sessionName
+	}
+	return identity.Address()
+}
+
+// resolveSelfTarget determines agent identity, pane, and hook root for slinging to self.
+func resolveSelfTarget() (agentID string, pane string, hookRoot string, err error) {
+	roleInfo, err := GetRole()
+	if err != nil {
+		return "", "", "", fmt.Errorf("detecting role: %w", err)
+	}
+
+	// Build agent identity from role
+	// Town-level agents use trailing slash to match addressToIdentity() normalization
+	switch roleInfo.Role {
+	case RoleMayor:
+		agentID = "mayor/"
+	case RoleDeacon:
+		agentID = "deacon/"
+	case RoleWitness:
+		agentID = fmt.Sprintf("%s/witness", roleInfo.Rig)
+	case RoleRefinery:
+		agentID = fmt.Sprintf("%s/refinery", roleInfo.Rig)
+	case RolePolecat:
+		agentID = fmt.Sprintf("%s/polecats/%s", roleInfo.Rig, roleInfo.Polecat)
+	case RoleCrew:
+		agentID = fmt.Sprintf("%s/crew/%s", roleInfo.Rig, roleInfo.Polecat)
+	default:
+		return "", "", "", fmt.Errorf("cannot determine agent identity (role: %s)", roleInfo.Role)
+	}
+
+	pane = os.Getenv("TMUX_PANE")
+	hookRoot = roleInfo.Home
+	if hookRoot == "" {
+		// Fallback to git root if home not determined
+		hookRoot, err = detectCloneRoot()
+		if err != nil {
+			return "", "", "", fmt.Errorf("detecting clone root: %w", err)
+		}
+	}
+
+	return agentID, pane, hookRoot, nil
+}