fix: return minimal stats with counts when statistics don't exist

Previously, when no statistics file existed (e.g., first container restart
after adding entities), getStatisticsData() returned null, causing HNSW
rebuild to see entityCount=0 even though entities existed.

This fix ensures all storage adapters return minimal StatisticsData with
totalNodes/totalEdges populated from in-memory counts when statistics files
don't exist yet.

Changes:
- gcsStorage.ts: Return minimal stats instead of null on 404 errors
- memoryStorage.ts: Return minimal stats when statistics is null
- opfsStorage.ts: Return minimal stats on read errors and null checks
- s3CompatibleStorage.ts: Return minimal stats when no statistics found
- fileSystemStorage.ts: Use in-memory counts in mergeStatistics() null case

This completes the GCS persistence fix started in v3.37.3 and ensures
container restarts work correctly in all cloud environments.

Fixes: GCS container restart hang during HNSW index rebuild

src/storage/adapters/fileSystemStorage.ts

@@ -1641,13 +1641,17 @@ export class FileSystemStorage extends BaseStorage {
   ): StatisticsData {
     // Handle null cases
     if (!storageStats && !localStats) {
+      // CRITICAL FIX (v3.37.4): Statistics files don't exist yet (first init)
+      // Return minimal stats with counts instead of zeros
+      // This prevents HNSW from seeing entityCount=0 during index rebuild
       return {
         nounCount: {},
         verbCount: {},
         metadataCount: {},
         hnswIndexSize: 0,
-        totalNodes: 0,
-        totalEdges: 0,
+        totalNodes: this.totalNounCount,
+        totalEdges: this.totalVerbCount,
+        totalMetadata: 0,
         lastUpdated: new Date().toISOString()
       }
     }

src/storage/adapters/gcsStorage.ts

@@ -1543,8 +1543,20 @@ export class GcsStorage extends BaseStorage {
       }
     } catch (error: any) {
       if (error.code === 404) {
-        this.logger.trace('Statistics not found (creating new)')
-        return null
+        // CRITICAL FIX (v3.37.4): Statistics file doesn't exist yet (first restart)
+        // Return minimal stats with counts instead of null
+        // This prevents HNSW from seeing entityCount=0 during index rebuild
+        this.logger.trace('Statistics file not found - returning minimal stats with counts')
+        return {
+          nounCount: {},
+          verbCount: {},
+          metadataCount: {},
+          hnswIndexSize: 0,
+          totalNodes: this.totalNounCount,
+          totalEdges: this.totalVerbCount,
+          totalMetadata: 0,
+          lastUpdated: new Date().toISOString()
+        }
       }
 
       this.logger.error('Failed to get statistics:', error)

src/storage/adapters/memoryStorage.ts

@@ -682,7 +682,19 @@ export class MemoryStorage extends BaseStorage {
    */
   protected async getStatisticsData(): Promise<StatisticsData | null> {
     if (!this.statistics) {
-      return null
+      // CRITICAL FIX (v3.37.4): Statistics don't exist yet (first init)
+      // Return minimal stats with counts instead of null
+      // This prevents HNSW from seeing entityCount=0 during index rebuild
+      return {
+        nounCount: {},
+        verbCount: {},
+        metadataCount: {},
+        hnswIndexSize: 0,
+        totalNodes: this.totalNounCount,
+        totalEdges: this.totalVerbCount,
+        totalMetadata: 0,
+        lastUpdated: new Date().toISOString()
+      }
     }
 
     // Return a deep copy to avoid reference issues

src/storage/adapters/opfsStorage.ts

@@ -1438,14 +1438,38 @@ export class OPFSStorage extends BaseStorage {
               }
             }
           } catch (error) {
-            // If the legacy file doesn't exist either, return null
-            return null
+            // CRITICAL FIX (v3.37.4): No statistics files exist (first init)
+            // Return minimal stats with counts instead of null
+            // This prevents HNSW from seeing entityCount=0 during index rebuild
+            return {
+              nounCount: {},
+              verbCount: {},
+              metadataCount: {},
+              hnswIndexSize: 0,
+              totalNodes: this.totalNounCount,
+              totalEdges: this.totalVerbCount,
+              totalMetadata: 0,
+              lastUpdated: new Date().toISOString()
+            }
           }
         }
       }
 
-      // If we get here and statistics is null, return default statistics
-      return this.statistics ? this.statistics : null
+      // If we get here and statistics is null, return minimal stats with counts
+      if (!this.statistics) {
+        return {
+          nounCount: {},
+          verbCount: {},
+          metadataCount: {},
+          hnswIndexSize: 0,
+          totalNodes: this.totalNounCount,
+          totalEdges: this.totalVerbCount,
+          totalMetadata: 0,
+          lastUpdated: new Date().toISOString()
+        }
+      }
+
+      return this.statistics
     } catch (error) {
       console.error('Failed to get statistics data:', error)
       throw new Error(`Failed to get statistics data: ${error}`)

src/storage/adapters/s3CompatibleStorage.ts

@@ -2803,6 +2803,20 @@ export class S3CompatibleStorage extends BaseStorage {
         }
       }
 
+      // If we get here and statistics is null, return minimal stats with counts
+      if (!statistics) {
+        return {
+          nounCount: {},
+          verbCount: {},
+          metadataCount: {},
+          hnswIndexSize: 0,
+          totalNodes: this.totalNounCount,
+          totalEdges: this.totalVerbCount,
+          totalMetadata: 0,
+          lastUpdated: new Date().toISOString()
+        }
+      }
+
       // Successfully loaded statistics from storage
 
       return statistics
@@ -2817,7 +2831,19 @@ export class S3CompatibleStorage extends BaseStorage {
           totalEdges: this.totalVerbCount
         }
       }
-      return null
+      // CRITICAL FIX (v3.37.4): Statistics file doesn't exist yet (first restart)
+      // Return minimal stats with counts instead of null
+      // This prevents HNSW from seeing entityCount=0 during index rebuild
+      return {
+        nounCount: {},
+        verbCount: {},
+        metadataCount: {},
+        hnswIndexSize: 0,
+        totalNodes: this.totalNounCount,
+        totalEdges: this.totalVerbCount,
+        totalMetadata: 0,
+        lastUpdated: new Date().toISOString()
+      }
     }
   }