Dewei Zhai /writing
Field notes.
Things I figured out at work and decided were worth writing down. No tutorials, no listicles — just the parts I wish someone had told me.
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2026-08-20
Three skills that keep agentic work from turning into entropy
AI can produce code faster, but it can also produce redundancy, collisions, and false explanations faster. I use three small skills to decide what should exist, who may touch it, and what the system actually means.
#AI-agent#engineering-practice#skills#mental-model
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2026-07-27
I moved a data platform from Databricks to one VM and cut its monthly cost by 95%
A personal data platform migration retrospective: AI agents increased the cost risk of exploratory work, so I built a smaller runtime with a faster feedback loop.
#data-platform#DuckDB#DuckLake#Airflow#cloud-cost#AI-coding
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2026-06-08
Transformers are not just about language
Financial transactions are records of real events. Transaction foundation models may learn the hidden structure inside those events.
#ai#finance#llm
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2026-06-07
LLMs are relation spaces, not knowledge warehouses
A working mental model for GPT: not a database of facts, but a high-dimensional map of relationships.
#ai#llm#learning
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2026-05-21
Turning a loader that OOMed 6 times into a 52-second job
A Parquet-to-Postgres rewrite: from batch to streaming execution, from Python to Rust.
#data-engineering#rust#postgres#serverless
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2026-05-15
Secrets in the Keychain, not in your .env
A 230-line Bash wrapper around the macOS Keychain that lets me inject API keys into one command at a time — without ever exporting them to my shell or committing them to .env.
#tooling#security#shell
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2026-05-13
CLI, not MCP
Swapped a Python Outlook MCP for a 250-line Rust CLI. The email body the LLM sees dropped from 6,200 to ~500 bytes, and 700 tokens of tool schemas left the context.
#ai#agents#tooling
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2026-05-13
Cutting new-dashboard delivery from 4–6 weeks to about one working day
At a well-known fashion company, Team C analysts developed dashboard logic in notebooks, then DE rewrote it in PySpark for Airflow. After the redesign, most new dashboards took about one working day and daily data was ready before business users started work.
#data-engineering#process#platform
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2026-05-10
Hello, and what this site is for
Why I built this site, and what you can expect from it.
#meta
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2026-05-10
The cheap stack: how this site is built
Cloudflare Pages + Astro + DeepSeek. What it costs, what it doesn't, and why I chose each piece.
#infra#cloudflare#ai