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/daemon/daemon.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -20,6 +21,7 @@ import (
 	"github.com/steveyegge/gastown/internal/config"
 	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/deacon"
+	"github.com/steveyegge/gastown/internal/events"
 	"github.com/steveyegge/gastown/internal/feed"
 	"github.com/steveyegge/gastown/internal/polecat"
 	"github.com/steveyegge/gastown/internal/refinery"
@@ -41,8 +43,24 @@ type Daemon struct {
 	ctx     context.Context
 	cancel  context.CancelFunc
 	curator *feed.Curator
+
+	// Mass death detection: track recent session deaths
+	deathsMu     sync.Mutex
+	recentDeaths []sessionDeath
 }
 
+// sessionDeath records a detected session death for mass death analysis.
+type sessionDeath struct {
+	sessionName string
+	timestamp   time.Time
+}
+
+// Mass death detection parameters
+const (
+	massDeathWindow    = 30 * time.Second // Time window to detect mass death
+	massDeathThreshold = 3                // Number of deaths to trigger alert
+)
+
 // New creates a new daemon instance.
 func New(config *Config) (*Daemon, error) {
 	// Ensure daemon directory exists
@@ -735,6 +753,9 @@ func (d *Daemon) checkPolecatHealth(rigName, polecatName string) {
 	d.logger.Printf("CRASH DETECTED: polecat %s/%s has hook_bead=%s but session %s is dead",
 		rigName, polecatName, info.HookBead, sessionName)
 
+	// Track this death for mass death detection
+	d.recordSessionDeath(sessionName)
+
 	// Auto-restart the polecat
 	if err := d.restartPolecatSession(rigName, polecatName, sessionName); err != nil {
 		d.logger.Printf("Error restarting polecat %s/%s: %v", rigName, polecatName, err)
@@ -745,6 +766,56 @@ func (d *Daemon) checkPolecatHealth(rigName, polecatName string) {
 	}
 }
 
+// recordSessionDeath records a session death and checks for mass death pattern.
+func (d *Daemon) recordSessionDeath(sessionName string) {
+	d.deathsMu.Lock()
+	defer d.deathsMu.Unlock()
+
+	now := time.Now()
+
+	// Add this death
+	d.recentDeaths = append(d.recentDeaths, sessionDeath{
+		sessionName: sessionName,
+		timestamp:   now,
+	})
+
+	// Prune deaths outside the window
+	cutoff := now.Add(-massDeathWindow)
+	var recent []sessionDeath
+	for _, death := range d.recentDeaths {
+		if death.timestamp.After(cutoff) {
+			recent = append(recent, death)
+		}
+	}
+	d.recentDeaths = recent
+
+	// Check for mass death
+	if len(d.recentDeaths) >= massDeathThreshold {
+		d.emitMassDeathEvent()
+	}
+}
+
+// emitMassDeathEvent logs a mass death event when multiple sessions die in a short window.
+func (d *Daemon) emitMassDeathEvent() {
+	// Collect session names
+	var sessions []string
+	for _, death := range d.recentDeaths {
+		sessions = append(sessions, death.sessionName)
+	}
+
+	count := len(sessions)
+	window := massDeathWindow.String()
+
+	d.logger.Printf("MASS DEATH DETECTED: %d sessions died in %s: %v", count, window, sessions)
+
+	// Emit feed event
+	_ = events.LogFeed(events.TypeMassDeath, "daemon",
+		events.MassDeathPayload(count, window, sessions, ""))
+
+	// Clear the deaths to avoid repeated alerts
+	d.recentDeaths = nil
+}
+
 // restartPolecatSession restarts a crashed polecat session.
 func (d *Daemon) restartPolecatSession(rigName, polecatName, sessionName string) error {
 	// Check rig operational state before auto-restarting