feat(milvus): add Milvus/Zilliz Cloud vector store backend

[supmo668]

Summary

Milvus/Zilliz Cloud implementation for the pluggable VectorStoreClient interface introduced in #1264. Provides hybrid vector + BM25 search as an acceleration layer alongside any graph database (Neo4j or FalkorDB).

Depends on: #1264 (Part 1 — provider-agnostic plugin interface)
RFC: #1263

Type of Change

• New feature

Objective

Enable Graphiti users to leverage Milvus/Zilliz Cloud for high-performance hybrid retrieval (dense vector + BM25 sparse) while keeping their existing graph database for entity resolution, episode storage, and graph traversal. This is an overlay, not a replacement — the graph DB remains the source of truth.

Architecture

flowchart LR
    subgraph "Write Path"
        A[Graphiti Core] -->|primary| B[Graph DB<br/>Neo4j / FalkorDB]
        A -->|dual-write| C[Milvus / Zilliz]
    end
    subgraph "Read Path"
        D[Search Query] --> E{SearchInterface}
        E -->|hybrid search| C
        E -->|graph traversal| B
    end

Loading

Key Features

• 4 collections: entity_nodes, entity_edges, episodic_nodes, community_nodes
• Hybrid search: HNSW dense vectors (COSINE) + BM25 sparse vectors
• Multi-tenancy: group_id as partition key
• Auto-attach: MilvusSearchInterface auto-wired when MilvusVectorStoreClient is passed
• Backfill utility: Sync existing graph DB data to Milvus for brownfield deployments
• MCP server: Full Docker Compose stacks for Neo4j+Milvus and FalkorDB+Milvus
• MILVUS_URI auto-detect: Set the env var and the MCP server auto-configures

New Files

File	Purpose
vector_store/milvus_client.py	MilvusVectorStoreClient — 10 domain-aware methods
vector_store/milvus_utils.py	Collection schemas, serialization, constants
vector_store/milvus_search_interface.py	SearchInterface impl for hybrid retrieval
vector_store/milvus_graph_operations.py	GraphOperationsInterface impl for CRUD
utils/vector_store_sync.py	Backfill utility for graph DB → Milvus sync

Testing

• Unit tests added/updated (153 pass)
• Integration tests added/updated (10 pass against Zilliz Cloud)
• All existing tests pass

Test File	Count	Description
test_milvus_vector_store_client.py	46	Client save/delete/ensure_ready/errors
test_milvus_utils.py	~30	Schema and serialization helpers
test_milvus_search_interface.py	~30	SearchInterface contract
test_milvus_graph_operations.py	~30	GraphOperationsInterface contract
test_milvus_search_int.py	10	Integration tests (Zilliz Cloud)
test_vector_store_sync.py	~20	Backfill utility
test_graphiti_vector_store.py	+3	Milvus auto-attach tests

Breaking Changes

• This PR contains breaking changes

No breaking changes. Milvus is an optional extra (pip install "graphiti-core[milvus]"). All existing behavior is unchanged.

Checklist

• Code follows project style guidelines (make lint passes — 0 errors)
• Self-review completed
• No secrets or sensitive information committed
• pyright passes (0 errors, 0 warnings)

Related Issues

Part 2 of RFC #1263
Depends on #1264 (Part 1)

[supmo668]

All CI checks pass (ruff, pyright, unit-tests, database-integration-tests, CodeQL). Rebased on latest main.

This is Part 2 of the vector store integration (RFC #1263), building on the plugin interface in #1264. The Milvus implementation is fully self-contained — 153 unit tests + 10 integration tests against Zilliz Cloud all pass.

Happy to walk through any of the implementation choices or address feedback. @danielchalef @prasmussen15