refactor: Split large cmd/bd files to meet 800-line limit (bd-xtf5)

Split 6 files exceeding 800 lines by extracting cohesive function groups:

- show.go (1592→578): extracted show_thread.go, close.go, edit.go, update.go
- doctor.go (1295→690): extracted doctor_fix.go, doctor_health.go, doctor_pollution.go
- sync.go (1201→749): extracted sync_git.go
- compact.go (1199→775): extracted compact_tombstone.go, compact_rpc.go
- linear.go (1190→641): extracted linear_sync.go, linear_conflict.go
- main.go (1148→800): extracted main_help.go, main_errors.go, main_daemon.go

All files now under 800-line acceptance criteria.

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

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

cmd/bd/main_daemon.go

@@ -0,0 +1,119 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// DaemonStatus captures daemon connection state for the current command
+type DaemonStatus struct {
+	Mode               string `json:"mode"` // "daemon" or "direct"
+	Connected          bool   `json:"connected"`
+	Degraded           bool   `json:"degraded"`
+	SocketPath         string `json:"socket_path,omitempty"`
+	AutoStartEnabled   bool   `json:"auto_start_enabled"`
+	AutoStartAttempted bool   `json:"auto_start_attempted"`
+	AutoStartSucceeded bool   `json:"auto_start_succeeded"`
+	FallbackReason     string `json:"fallback_reason,omitempty"` // "none","flag_no_daemon","connect_failed","health_failed","auto_start_disabled","auto_start_failed"
+	Detail             string `json:"detail,omitempty"`          // short diagnostic
+	Health             string `json:"health,omitempty"`          // "healthy","degraded","unhealthy"
+}
+
+// Fallback reason constants
+const (
+	FallbackNone              = "none"
+	FallbackFlagNoDaemon      = "flag_no_daemon"
+	FallbackConnectFailed     = "connect_failed"
+	FallbackHealthFailed      = "health_failed"
+	FallbackWorktreeSafety    = "worktree_safety"
+	cmdDaemon                 = "daemon"
+	cmdImport                 = "import"
+	statusHealthy             = "healthy"
+	FallbackAutoStartDisabled = "auto_start_disabled"
+	FallbackAutoStartFailed   = "auto_start_failed"
+	FallbackDaemonUnsupported = "daemon_unsupported"
+	FallbackWispOperation     = "wisp_operation"
+)
+
+// Command group IDs for help organization
+const (
+	GroupMaintenance  = "maintenance"
+	GroupIntegrations = "integrations"
+)
+
+// signalGasTownActivity writes an activity signal for Gas Town daemon.
+// This enables exponential backoff based on bd usage detection.
+// Best-effort: silent on any failure, never affects bd operation.
+func signalGasTownActivity() {
+	// Determine town root
+	// Priority: GT_ROOT env > detect from cwd path > skip
+	townRoot := os.Getenv("GT_ROOT")
+	if townRoot == "" {
+		// Try to detect from cwd - if under ~/gt/, use that as town root
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return
+		}
+		gtRoot := filepath.Join(home, "gt")
+		cwd, err := os.Getwd()
+		if err != nil {
+			return
+		}
+		if strings.HasPrefix(cwd, gtRoot+string(os.PathSeparator)) {
+			townRoot = gtRoot
+		}
+	}
+
+	if townRoot == "" {
+		return // Not in Gas Town, skip
+	}
+
+	// Ensure daemon directory exists
+	daemonDir := filepath.Join(townRoot, "daemon")
+	if err := os.MkdirAll(daemonDir, 0755); err != nil {
+		return
+	}
+
+	// Build command line from os.Args
+	cmdLine := strings.Join(os.Args, " ")
+
+	// Determine actor (use package-level var if set, else fall back to env)
+	actorName := actor
+	if actorName == "" {
+		if bdActor := os.Getenv("BD_ACTOR"); bdActor != "" {
+			actorName = bdActor
+		} else if user := os.Getenv("USER"); user != "" {
+			actorName = user
+		} else {
+			actorName = "unknown"
+		}
+	}
+
+	// Build activity signal
+	activity := struct {
+		LastCommand string `json:"last_command"`
+		Actor       string `json:"actor"`
+		Timestamp   string `json:"timestamp"`
+	}{
+		LastCommand: cmdLine,
+		Actor:       actorName,
+		Timestamp:   time.Now().UTC().Format(time.RFC3339),
+	}
+
+	data, err := json.Marshal(activity)
+	if err != nil {
+		return
+	}
+
+	// Write atomically (write to temp, rename)
+	activityPath := filepath.Join(daemonDir, "activity.json")
+	tmpPath := activityPath + ".tmp"
+	// nolint:gosec // G306: 0644 is appropriate for a status file
+	if err := os.WriteFile(tmpPath, data, 0644); err != nil {
+		return
+	}
+	_ = os.Rename(tmpPath, activityPath)
+}