native: build_graph_now() does not rebuild an existing vector graph #162

On the native build (arcadedb), VectorIndex.build_graph_now() does not rebuild a vector graph that already exists. The docstring says it triggers an immediate rebuild, and on arcadedb-jvm it does (it calls the engine's LSMVectorIndex.buildVectorGraphNow()). The native shim, _IndexShim.buildVectorGraphNow() in src/arcadedb/_native/schema_objects.py, runs one vectorNeighbors search instead. A search rebuilds synchronously only when there is no graph or the graph is under 1,000 nodes (the engine's ASYNC_REBUILD_MIN_GRAPH_SIZE), so on an index whose graph is built and at least that large the call returns at once and every vector written since stays in the delta.

Seen in a timed study (agent-memory, an agent that inserts one record per turn and searches after it): 10,000 vectors at the start, automatic rebuild off (mutations_before_rebuild very high, maxDeltaScanRatio 0), 3,000 inserts, and build_graph_now() after turn 1,000 and turn 2,000. Matched dev wheels 26.11.1.dev0 (bindings 4d012f3114, engine e353330c5c), Linux x86-64. Read from the run files of the explicit arm, every run:

On the JVM wheel each call took seconds and the graph grew by the vectors written before it; on the native wheel each call took milliseconds, the graph kept its size, and no rebuild was counted.

Fix: a build op in arcadedb_n_vindex (NativeExtras.java) that calls LSMVectorIndex.buildVectorGraphNow() on every bucket index, as the JPype wrapper does, and the shim calls it. warm_up() keeps its one search (it only has to load a persisted graph, not rebuild it). Regression test in tests/test_vector_index_introspection.py, on both builds: an index built over 1,000 vectors, 100 more written with the automatic triggers off, then build_graph_now() must leave graphNodeCount at 1,100 and raise graphRebuildCount.

Edited 2026-11-01: the size condition (graphs under 1,000 nodes are rebuilt by the search, so the old shim worked on small indexes) and the test size (first written at 200 vectors, which passed on the pre-fix native wheel) were added after the first test run.