Mehran Dashti — Writing https://mehrandashti.ir/writing/ Notes on agent systems, retrieval and distributed backends. en Tue, 11 Aug 2026 09:00:00 GMT Hybrid retrieval with Milvus: BGE-M3, RRF and relevance gating https://mehrandashti.ir/writing/hybrid-retrieval-with-milvus-and-rrf/ https://mehrandashti.ir/writing/hybrid-retrieval-with-milvus-and-rrf/ Why pure vector search returns confident nonsense, and how reciprocal-rank fusion plus a relevance gate fixed it — measured with MRR and precision@k. Tue, 11 Aug 2026 09:00:00 GMT Mehran Dashti Milvus RAG retrieval BGE-M3 Python Reversible PII masking with Presidio in agent pipelines https://mehrandashti.ir/writing/reversible-pii-masking-with-presidio/ https://mehrandashti.ir/writing/reversible-pii-masking-with-presidio/ Pseudonymisation that survives a multi-turn conversation: recognizer design, a reversible mapping, and the failure modes that leak data. Tue, 28 Jul 2026 09:00:00 GMT Mehran Dashti Presidio PII GDPR AI security Python Prompt injection defense in a LangGraph agent system https://mehrandashti.ir/writing/prompt-injection-defense-in-langgraph/ https://mehrandashti.ir/writing/prompt-injection-defense-in-langgraph/ Fencing, closed-schema extraction and hard-block chokepoints — where to put each one in a supervisor/worker graph, and why fail-closed matters. Tue, 14 Jul 2026 09:00:00 GMT Mehran Dashti LangGraph AI security prompt injection Python