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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2026-06-08
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
Fix the contract, not the dashboards
At PVH the ticket said 'fix the dashboards.' The dashboards weren't the bug — the contract between two teams was.
#data-engineering#process#platform
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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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2026-05-10
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