feat(persist): HNSW vector indexes survive restart

src/barabadb/query/exec/schema.nim

@@ -17,6 +17,7 @@ const
   SchemaUserPrefix* = "_schema:users:"
   SchemaPolicyPrefix* = "_schema:policies:"
   SchemaFtsIndexPrefix* = "_schema:ftsidx:"
+  SchemaVecIndexPrefix* = "_schema:vecidx:"
   ## Legacy CREATE TABLE keys (pre-fix) used a migrations: counter suffix
   SchemaLegacyCreatePrefix* = "_schema:migrations:"
 

src/barabadb/query/executor.nim

@@ -1336,6 +1336,10 @@ proc executeQueryImpl(ctx: ExecutionContext, astNode: Node, params: seq[WireValu
                 docId = docId * 31 + uint64(ord(ch))
               vengine.insert(hnswIdx, docId, vec, meta)
       ctx.vectorIndexes[colKey] = hnswIdx
+      # Persist reconstructed DDL so restoreEngines can rebuild the index
+      # from table data after a restart (replay re-writes the same key).
+      let vecDdl = "CREATE INDEX " & idxName & " ON " & stmt.ciTarget & " (" & stmt.ciColumns.join(", ") & ") USING HNSW"
+      ctx.db.put(SchemaVecIndexPrefix & colKey, cast[seq[byte]](vecDdl))
       return okResult(msg="CREATE INDEX " & idxName & " on " & stmt.ciTarget & " USING HNSW")
 
     ctx.btrees[colKey] = newBTreeIndex[string, IndexEntry]()
@@ -1569,12 +1573,13 @@ proc executeMigrationSql(ctx: ExecutionContext, sql: string): ExecResult =
   return okResult(msg="Empty migration body")
 
 proc restoreEngines*(ctx: ExecutionContext) =
-  ## Rebuild ephemeral engines (FTS indexes) from persisted schema keys after
+  ## Rebuild ephemeral engines (FTS/HNSW indexes) from persisted schema keys
-  ## restoreSchema. Invoked via context.restoreEnginesHook at the end of
+  ## after restoreSchema. Invoked via context.restoreEnginesHook at the end of
   ## newExecutionContext. Replay re-persists the same key, so it is idempotent.
   var ddls: seq[string] = @[]
   for (key, value) in ctx.db.scanAll():
-    if not key.startsWith(SchemaFtsIndexPrefix): continue
+    if not key.startsWith(SchemaFtsIndexPrefix) and
+       not key.startsWith(SchemaVecIndexPrefix): continue
     let ddl = cast[string](value)
     if ddl.len == 0: continue
     ddls.add(ddl)

tests/test_schema_persist.nim

@@ -7,6 +7,7 @@ import barabadb/storage/lsm
 import barabadb/query/executor
 import barabadb/query/parser
 import barabadb/fts/engine
+import barabadb/vector/engine as vengine
 
 proc execSql(ctx: ExecutionContext, sql: string): ExecResult =
   let node = parse(sql)
@@ -137,6 +138,35 @@ suite "Schema persistence":
       db2.close()
     removeDir(dir)
 
+  test "HNSW vector index survives reopen":
+    let dir = "/tmp/baradb_schema_persist_vec"
+    removeDir(dir)
+    block:
+      var db = newLSMTree(dir)
+      var ctx = newExecutionContext(db)
+      check execSql(ctx, "CREATE TABLE vecs (id INTEGER PRIMARY KEY, embedding TEXT)").success
+      check execSql(ctx, "INSERT INTO vecs (id, embedding) VALUES (1, '[1.0, 0.0, 0.0]')").success
+      check execSql(ctx, "CREATE INDEX vecs_hnsw ON vecs (embedding) USING HNSW").success
+      check ctx.vectorIndexes.hasKey("vecs.embedding")
+      db.close()
+    # Reopen fresh context (simulates process restart)
+    block:
+      var db2 = newLSMTree(dir)
+      var ctx2 = newExecutionContext(db2)
+      # Index must be rebuilt from the persisted schema key — today it is
+      # silently missing, so vector searches return empty results after reopen.
+      check ctx2.vectorIndexes.hasKey("vecs.embedding")
+      if ctx2.vectorIndexes.hasKey("vecs.embedding"):
+        check vengine.search(ctx2.vectorIndexes["vecs.embedding"],
+                             @[1.0'f32, 0.0'f32, 0.0'f32], k = 5).len >= 1
+      # index keeps updating after reopen
+      check execSql(ctx2, "INSERT INTO vecs (id, embedding) VALUES (2, '[0.0, 1.0, 0.0]')").success
+      if ctx2.vectorIndexes.hasKey("vecs.embedding"):
+        check vengine.search(ctx2.vectorIndexes["vecs.embedding"],
+                             @[0.0'f32, 1.0'f32, 0.0'f32], k = 5).len >= 1
+      db2.close()
+    removeDir(dir)
+
   test "Stable schema key format":
     check tableSchemaKey("users") == "_schema:tables:users"
     check serializeTableDdl(TableDef(