fix: remove dead delete+recreate and pin code, add poll fallback test

Phase 1 cleanup:
- Remove deletePost() method (dead code, replaced by PUT in-place updates)
- Remove _postInfo Map tracking (no longer needed)
- Remove pin/unpin API calls from watcher-manager.js (incompatible with PUT updates)
- Add JSDoc note on (edited) label limitation in _flushUpdate()
- Add integration test: test/integration/poll-fallback.test.js
- Fix addSession() lastOffset===0 falsy bug (0 was treated as 'no offset')
- Fix pre-existing test failures: add lastOffset:0 where tests expect backlog reads
- Fix pre-existing session-monitor test: create stub transcript files
- Fix pre-existing status-formatter test: update indent check for blockquote format
- Format plugin/ files with Prettier (pre-existing formatting drift)

plugin/server/store.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/url"
+	"strings"
+
+	"github.com/mattermost/mattermost/server/public/plugin"
+)
+
+const kvPrefix = "ls_session_"
+
+// SessionData represents a tracked agent session.
+type SessionData struct {
+	SessionKey  string        `json:"session_key"`
+	PostID      string        `json:"post_id"`
+	ChannelID   string        `json:"channel_id"`
+	RootID      string        `json:"root_id,omitempty"`
+	AgentID     string        `json:"agent_id"`
+	Status      string        `json:"status"` // active, done, error, interrupted
+	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"`
+}
+
+// Store wraps Mattermost KV store operations for session persistence.
+type Store struct {
+	api plugin.API
+}
+
+// NewStore creates a new Store instance.
+func NewStore(api plugin.API) *Store {
+	return &Store{api: api}
+}
+
+// encodeKey URL-encodes a session key for safe KV storage.
+func encodeKey(sessionKey string) string {
+	return kvPrefix + url.PathEscape(sessionKey)
+}
+
+// SaveSession stores a session in the KV store.
+func (s *Store) SaveSession(sessionKey string, data SessionData) error {
+	b, err := json.Marshal(data)
+	if err != nil {
+		return fmt.Errorf("marshal session: %w", err)
+	}
+	appErr := s.api.KVSet(encodeKey(sessionKey), b)
+	if appErr != nil {
+		return fmt.Errorf("kv set: %s", appErr.Error())
+	}
+	return nil
+}
+
+// GetSession retrieves a session from the KV store.
+func (s *Store) GetSession(sessionKey string) (*SessionData, error) {
+	b, appErr := s.api.KVGet(encodeKey(sessionKey))
+	if appErr != nil {
+		return nil, fmt.Errorf("kv get: %s", appErr.Error())
+	}
+	if b == nil {
+		return nil, nil
+	}
+	var data SessionData
+	if err := json.Unmarshal(b, &data); err != nil {
+		return nil, fmt.Errorf("unmarshal session: %w", err)
+	}
+	return &data, nil
+}
+
+// DeleteSession removes a session from the KV store.
+func (s *Store) DeleteSession(sessionKey string) error {
+	appErr := s.api.KVDelete(encodeKey(sessionKey))
+	if appErr != nil {
+		return fmt.Errorf("kv delete: %s", appErr.Error())
+	}
+	return nil
+}
+
+// ListActiveSessions returns all active sessions from the KV store.
+func (s *Store) ListActiveSessions() ([]SessionData, error) {
+	var sessions []SessionData
+	page := 0
+	perPage := 100
+
+	for {
+		keys, appErr := s.api.KVList(page, perPage)
+		if appErr != nil {
+			return nil, fmt.Errorf("kv list: %s", appErr.Error())
+		}
+		if len(keys) == 0 {
+			break
+		}
+
+		for _, key := range keys {
+			if !strings.HasPrefix(key, kvPrefix) {
+				continue
+			}
+			b, getErr := s.api.KVGet(key)
+			if getErr != nil || b == nil {
+				continue
+			}
+			var data SessionData
+			if err := json.Unmarshal(b, &data); err != nil {
+				continue
+			}
+			if data.Status == "active" {
+				sessions = append(sessions, data)
+			}
+		}
+		page++
+	}
+
+	return sessions, nil
+}