feat: RHS panel initial fetch, floating widget, session cleanup (#5)

Phase 1: Fix RHS panel to fetch existing sessions on mount
- Add initial API fetch in useAllStatusUpdates() hook
- Allow GET /sessions endpoint without shared secret auth
- RHS panel now shows sessions after page refresh

Phase 2: Floating widget component (registerRootComponent)
- New floating_widget.tsx with auto-show/hide behavior
- Draggable, collapsible to pulsing dot with session count
- Shows last 5 lines of most recent active session
- Position persisted to localStorage
- CSS styles using Mattermost theme variables

Phase 3: Session cleanup and KV optimization
- Add LastUpdateMs field to SessionData for staleness tracking
- Set LastUpdateMs on session create and update
- Add periodic cleanup goroutine (every 5 min)
- Stale active sessions (>30 min no update) marked interrupted
- Expired non-active sessions (>1 hr) deleted from KV
- Add ListAllSessions and keep ListActiveSessions as helper
- Add debug logging to daemon file polling

Closes #5

plugin/server/store.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/url"
 	"strings"
+	"time"
 
 	"github.com/mattermost/mattermost/server/public/plugin"
 )
@@ -22,8 +23,9 @@ type SessionData struct {
 	Lines       []string      `json:"lines"`
 	ElapsedMs   int64         `json:"elapsed_ms"`
 	TokenCount  int           `json:"token_count"`
-	Children    []SessionData `json:"children,omitempty"`
-	StartTimeMs int64         `json:"start_time_ms"`
+	Children     []SessionData `json:"children,omitempty"`
+	StartTimeMs  int64         `json:"start_time_ms"`
+	LastUpdateMs int64         `json:"last_update_ms"`
 }
 
 // Store wraps Mattermost KV store operations for session persistence.
@@ -79,8 +81,8 @@ func (s *Store) DeleteSession(sessionKey string) error {
 	return nil
 }
 
-// ListActiveSessions returns all active sessions from the KV store.
-func (s *Store) ListActiveSessions() ([]SessionData, error) {
+// ListAllSessions returns all sessions from the KV store (active and non-active).
+func (s *Store) ListAllSessions() ([]SessionData, error) {
 	var sessions []SessionData
 	page := 0
 	perPage := 100
@@ -106,12 +108,59 @@ func (s *Store) ListActiveSessions() ([]SessionData, error) {
 			if err := json.Unmarshal(b, &data); err != nil {
 				continue
 			}
-			if data.Status == "active" {
-				sessions = append(sessions, data)
-			}
+			sessions = append(sessions, data)
 		}
 		page++
 	}
 
 	return sessions, nil
 }
+
+// ListActiveSessions returns only active sessions from the KV store.
+func (s *Store) ListActiveSessions() ([]SessionData, error) {
+	all, err := s.ListAllSessions()
+	if err != nil {
+		return nil, err
+	}
+	var active []SessionData
+	for _, sess := range all {
+		if sess.Status == "active" {
+			active = append(active, sess)
+		}
+	}
+	return active, nil
+}
+
+// CleanStaleSessions marks stale active sessions as interrupted and deletes expired completed sessions.
+// staleThresholdMs: active sessions with no update for this long are marked interrupted.
+// expireThresholdMs: non-active sessions older than this are deleted from KV.
+func (s *Store) CleanStaleSessions(staleThresholdMs, expireThresholdMs int64) (cleaned int, expired int, err error) {
+	now := time.Now().UnixMilli()
+	all, err := s.ListAllSessions()
+	if err != nil {
+		return 0, 0, err
+	}
+	for _, session := range all {
+		lastUpdate := session.LastUpdateMs
+		if lastUpdate == 0 {
+			lastUpdate = session.StartTimeMs
+		}
+		if lastUpdate == 0 {
+			continue
+		}
+		age := now - lastUpdate
+
+		if session.Status == "active" && age > staleThresholdMs {
+			// Mark stale sessions as interrupted
+			session.Status = "interrupted"
+			session.LastUpdateMs = now
+			_ = s.SaveSession(session.SessionKey, session)
+			cleaned++
+		} else if session.Status != "active" && age > expireThresholdMs {
+			// Delete expired completed/interrupted sessions
+			_ = s.DeleteSession(session.SessionKey)
+			expired++
+		}
+	}
+	return cleaned, expired, nil
+}