feat(crash): improve crash logging and mass death detection

Add comprehensive crash logging improvements to help diagnose mass session death events:

- Add TypeSessionDeath and TypeMassDeath event types for feed visibility
- Log pre-death events before killing sessions (who killed, why)
- Add mass death detection in daemon (3+ deaths in 30s triggers alert)
- Add macOS crash report check in gt doctor
- Support session death events in townlog and feed curator

Closes hq-kt1o6

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

internal/doctor/crash_report_check.go

@@ -0,0 +1,185 @@
+package doctor
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sort"
+	"strings"
+	"time"
+)
+
+// CrashReportCheck looks for recent macOS crash reports related to tmux or Claude.
+// This helps diagnose mass session death events.
+type CrashReportCheck struct {
+	BaseCheck
+	crashReports []crashReport // Cached during Run for display
+}
+
+// crashReport represents a found crash report file.
+type crashReport struct {
+	path     string
+	name     string
+	modTime  time.Time
+	process  string // "tmux", "claude", "node", etc.
+}
+
+// NewCrashReportCheck creates a new crash report check.
+func NewCrashReportCheck() *CrashReportCheck {
+	return &CrashReportCheck{
+		BaseCheck: BaseCheck{
+			CheckName:        "crash-reports",
+			CheckDescription: "Check for recent macOS crash reports (tmux, Claude)",
+		},
+	}
+}
+
+// Run checks for recent crash reports in macOS diagnostic directories.
+func (c *CrashReportCheck) Run(ctx *CheckContext) *CheckResult {
+	// Only run on macOS
+	if runtime.GOOS != "darwin" {
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusOK,
+			Message: "Crash report check not applicable (non-macOS)",
+		}
+	}
+
+	// Look for crash reports in the last 24 hours
+	lookbackWindow := 24 * time.Hour
+	cutoff := time.Now().Add(-lookbackWindow)
+
+	// macOS crash report locations
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusWarning,
+			Message: "Could not determine home directory",
+			Details: []string{err.Error()},
+		}
+	}
+
+	crashDirs := []string{
+		filepath.Join(homeDir, "Library", "Logs", "DiagnosticReports"),
+		"/Library/Logs/DiagnosticReports",
+	}
+
+	// Processes we care about
+	relevantProcesses := []string{
+		"tmux",
+		"claude",
+		"claude-code",
+		"node",
+	}
+
+	var reports []crashReport
+
+	for _, dir := range crashDirs {
+		entries, err := os.ReadDir(dir)
+		if err != nil {
+			continue // Directory may not exist
+		}
+
+		for _, entry := range entries {
+			if entry.IsDir() {
+				continue
+			}
+
+			name := entry.Name()
+
+			// Check if this is a crash report for a relevant process
+			var matchedProcess string
+			nameLower := strings.ToLower(name)
+			for _, proc := range relevantProcesses {
+				if strings.Contains(nameLower, proc) {
+					matchedProcess = proc
+					break
+				}
+			}
+
+			if matchedProcess == "" {
+				continue
+			}
+
+			// Check modification time
+			info, err := entry.Info()
+			if err != nil {
+				continue
+			}
+
+			if info.ModTime().Before(cutoff) {
+				continue // Too old
+			}
+
+			reports = append(reports, crashReport{
+				path:    filepath.Join(dir, name),
+				name:    name,
+				modTime: info.ModTime(),
+				process: matchedProcess,
+			})
+		}
+	}
+
+	// Sort by time (most recent first)
+	sort.Slice(reports, func(i, j int) bool {
+		return reports[i].modTime.After(reports[j].modTime)
+	})
+
+	// Cache for display
+	c.crashReports = reports
+
+	if len(reports) == 0 {
+		return &CheckResult{
+			Name:    c.Name(),
+			Status:  StatusOK,
+			Message: "No recent crash reports found",
+		}
+	}
+
+	// Group by process
+	processCounts := make(map[string]int)
+	for _, r := range reports {
+		processCounts[r.process]++
+	}
+
+	// Build details
+	var details []string
+	for _, r := range reports {
+		age := time.Since(r.modTime).Round(time.Minute)
+		details = append(details, fmt.Sprintf("%s (%s ago): %s", r.process, age, r.name))
+	}
+
+	// Build summary
+	var summary []string
+	for proc, count := range processCounts {
+		summary = append(summary, fmt.Sprintf("%d %s", count, proc))
+	}
+
+	message := fmt.Sprintf("Found %d crash report(s): %s", len(reports), strings.Join(summary, ", "))
+
+	// tmux crashes are particularly concerning
+	status := StatusWarning
+	if processCounts["tmux"] > 0 {
+		message += " - TMUX CRASHED (may explain session deaths)"
+	}
+
+	return &CheckResult{
+		Name:    c.Name(),
+		Status:  status,
+		Message: message,
+		Details: details,
+		FixHint: "Review crash reports in Console.app → User Reports or check ~/Library/Logs/DiagnosticReports/",
+	}
+}
+
+// Fix does nothing - crash reports are informational.
+func (c *CrashReportCheck) Fix(ctx *CheckContext) error {
+	return nil
+}
+
+// CanFix returns false - crash reports cannot be auto-fixed.
+func (c *CrashReportCheck) CanFix() bool {
+	return false
+}