fix: migrate legacy tables by adding missing scope/timestamp/metadata columns (#326)

Previously doInitialize() only logged a warning when detecting missing columns
but never actually added them, causing stats/list/search/update/delete to fail
with "No field named scope" on databases upgraded from legacy memory-lancedb.

Now uses table.schema() to detect missing columns and table.addColumns() to
add them with sensible defaults (scope='global', timestamp=0.0, metadata='{}').
Handles concurrent initialization race via "already exists" error detection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: AliceLJY

src/store.ts

@@ -258,16 +258,39 @@ export class MemoryStore {
     try {
       table = await db.openTable(TABLE_NAME);
 
-      // Check if we need to add scope column for backward compatibility
+      // Migrate legacy tables: add missing columns for backward compatibility
       try {
-        const sample = await table.query().limit(1).toArray();
-        if (sample.length > 0 && !("scope" in sample[0])) {
+        const schema = await table.schema();
+        const fieldNames = new Set(schema.fields.map((f: { name: string }) => f.name));
+
+        const missingColumns: Array<{ name: string; valueSql: string }> = [];
+        if (!fieldNames.has("scope")) {
+          missingColumns.push({ name: "scope", valueSql: "'global'" });
+        }
+        if (!fieldNames.has("timestamp")) {
+          missingColumns.push({ name: "timestamp", valueSql: "CAST(0 AS DOUBLE)" });
+        }
+        if (!fieldNames.has("metadata")) {
+          missingColumns.push({ name: "metadata", valueSql: "'{}'" });
+        }
+
+        if (missingColumns.length > 0) {
           console.warn(
-            "Adding scope column for backward compatibility with existing data",
+            `memory-lancedb-pro: migrating legacy table — adding columns: ${missingColumns.map((c) => c.name).join(", ")}`,
+          );
+          await table.addColumns(missingColumns);
+          console.log(
+            `memory-lancedb-pro: migration complete — ${missingColumns.length} column(s) added`,
           );
         }
       } catch (err) {
-        console.warn("Could not check table schema:", err);
+        const msg = String(err);
+        if (msg.includes("already exists")) {
+          // Concurrent initialization race — another process already added the columns
+          console.log("memory-lancedb-pro: migration columns already exist (concurrent init)");
+        } else {
+          console.warn("memory-lancedb-pro: could not check/migrate table schema:", err);
+        }
       }
     } catch (_openErr) {
       // Table doesn't exist yet — create it