fix(lint): resolve all errcheck warnings

Fix ~50 errcheck warnings across the codebase:

- Add explicit `_ =` for intentionally ignored error returns (cleanup,
  best-effort operations, etc.)
- Use `defer func() { _ = ... }()` pattern for defer statements
- Handle tmux SetEnvironment, KillSession, SendKeysRaw returns
- Handle mail router.Send returns
- Handle os.RemoveAll, os.Rename in cleanup paths
- Handle rand.Read returns for ID generation
- Handle fmt.Fprint* returns when writing to io.Writer
- Fix for-select with single case to use for-range
- Handle cobra MarkFlagRequired returns

All tests pass. Code compiles without errors.

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

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

internal/cmd/crew.go

@@ -501,8 +501,8 @@ func runCrewAt(cmd *cobra.Command, args []string) error {
 		}
 
 		// Set environment
-		t.SetEnvironment(sessionID, "GT_RIG", r.Name)
-		t.SetEnvironment(sessionID, "GT_CREW", name)
+		_ = t.SetEnvironment(sessionID, "GT_RIG", r.Name)
+		_ = t.SetEnvironment(sessionID, "GT_CREW", name)
 
 		// Start claude with skip permissions (crew workers are trusted like Mayor)
 		// Use SendKeysDelayed to allow shell initialization after NewSession
@@ -723,8 +723,8 @@ func runCrewRefresh(cmd *cobra.Command, args []string) error {
 	}
 
 	// Set environment
-	t.SetEnvironment(sessionID, "GT_RIG", r.Name)
-	t.SetEnvironment(sessionID, "GT_CREW", name)
+	_ = t.SetEnvironment(sessionID, "GT_RIG", r.Name)
+	_ = t.SetEnvironment(sessionID, "GT_CREW", name)
 
 	// Start claude
 	// Use SendKeysDelayed to allow shell initialization after NewSession

internal/cmd/handoff.go

@@ -320,7 +320,7 @@ func setRequestingState(role Role, action HandoffAction, townRoot string) error
 	// Read existing state or create new
 	state := make(map[string]interface{})
 	if data, err := os.ReadFile(stateFile); err == nil {
-		json.Unmarshal(data, &state)
+		_ = json.Unmarshal(data, &state)
 	}
 
 	// Set requesting state

internal/cmd/init.go

@@ -64,7 +64,7 @@ func runInit(cmd *cobra.Command, args []string) error {
 		// Create .gitkeep to ensure directory is tracked if needed
 		gitkeep := filepath.Join(dirPath, ".gitkeep")
 		if _, err := os.Stat(gitkeep); os.IsNotExist(err) {
-			os.WriteFile(gitkeep, []byte(""), 0644)
+			_ = os.WriteFile(gitkeep, []byte(""), 0644)
 		}
 
 		fmt.Printf("   ✓ Created %s/\n", dir)

internal/cmd/mail.go

@@ -164,7 +164,7 @@ func init() {
 	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")
+	_ = mailSendCmd.MarkFlagRequired("subject")
 
 	// Inbox flags
 	mailInboxCmd.Flags().BoolVar(&mailInboxJSON, "json", false, "Output as JSON")
@@ -363,7 +363,7 @@ func runMailRead(cmd *cobra.Command, args []string) error {
 	}
 
 	// Mark as read
-	mailbox.MarkRead(msgID)
+	_ = mailbox.MarkRead(msgID)
 
 	// JSON output
 	if mailReadJSON {
@@ -722,6 +722,6 @@ func runMailReply(cmd *cobra.Command, args []string) error {
 // generateThreadID creates a random thread ID for new message threads.
 func generateThreadID() string {
 	b := make([]byte, 6)
-	rand.Read(b)
+	_, _ = rand.Read(b)
 	return "thread-" + hex.EncodeToString(b)
 }

internal/cmd/mayor.go

@@ -120,7 +120,7 @@ func startMayorSession(t *tmux.Tmux) error {
 	}
 
 	// Set environment
-	t.SetEnvironment(MayorSessionName, "GT_ROLE", "mayor")
+	_ = t.SetEnvironment(MayorSessionName, "GT_ROLE", "mayor")
 
 	// Launch Claude in a respawn loop - session survives restarts
 	// The startup hook handles 'gt prime' automatically
@@ -148,7 +148,7 @@ func runMayorStop(cmd *cobra.Command, args []string) error {
 	fmt.Println("Stopping Mayor session...")
 
 	// Try graceful shutdown first
-	t.SendKeysRaw(MayorSessionName, "C-c")
+	_ = t.SendKeysRaw(MayorSessionName, "C-c")
 	time.Sleep(100 * time.Millisecond)
 
 	// Kill the session
@@ -246,7 +246,7 @@ func runMayorRestart(cmd *cobra.Command, args []string) error {
 	if running {
 		// Graceful restart: send Ctrl-C to exit Claude, loop will restart it
 		fmt.Println("Restarting Mayor (sending Ctrl-C to trigger respawn loop)...")
-		t.SendKeysRaw(MayorSessionName, "C-c")
+		_ = t.SendKeysRaw(MayorSessionName, "C-c")
 		fmt.Printf("%s Mayor will restart automatically. Session stays attached.\n", style.Bold.Render("✓"))
 		return nil
 	}

internal/cmd/swarm.go

@@ -119,7 +119,7 @@ func init() {
 	swarmCreateCmd.Flags().StringSliceVar(&swarmWorkers, "worker", nil, "Polecat names to assign (repeatable)")
 	swarmCreateCmd.Flags().BoolVar(&swarmStart, "start", false, "Start swarm immediately after creation")
 	swarmCreateCmd.Flags().StringVar(&swarmTarget, "target", "main", "Target branch for landing")
-	swarmCreateCmd.MarkFlagRequired("epic")
+	_ = swarmCreateCmd.MarkFlagRequired("epic")
 
 	// Status flags
 	swarmStatusCmd.Flags().BoolVar(&swarmStatusJSON, "json", false, "Output as JSON")
@@ -605,8 +605,8 @@ func runSwarmLand(cmd *cobra.Command, args []string) error {
 	// Create manager and land
 	mgr := swarm.NewManager(foundRig)
 	// Reload swarm into manager
-	mgr.Create(sw.EpicID, sw.Workers, sw.TargetBranch)
-	mgr.UpdateState(sw.ID, sw.State)
+	_, _ = mgr.Create(sw.EpicID, sw.Workers, sw.TargetBranch)
+	_ = mgr.UpdateState(sw.ID, sw.State)
 
 	fmt.Printf("Landing swarm %s to %s...\n", swarmID, sw.TargetBranch)