Engineer building AI agents — the planning, memory, and tool-use that make models genuinely useful. Projects, writing, and notes on calm software.https://ethanyan.me/https://ethanyan.me/writing/inside-kimi-code-agent-engine/https://ethanyan.me/writing/inside-kimi-code-agent-engine/I cloned a shipping coding agent and read it the way I read a paper — to see which design decisions survive contact with production. Here are the ones worth stealing.Mon, 22 Jun 2026 00:00:00 GMThttps://ethanyan.me/writing/dont-put-symptoms-in-the-prompt/https://ethanyan.me/writing/dont-put-symptoms-in-the-prompt/When an agent misses a case, the reflex is to teach it that case in the system prompt. That's whack-a-mole. The fix is structural.Sat, 20 Jun 2026 00:00:00 GMThttps://ethanyan.me/writing/the-verifier-is-the-hard-part/https://ethanyan.me/writing/the-verifier-is-the-hard-part/Loop engineering took off in coding because coding ships with a free oracle. Everywhere else, you have to build one.Tue, 16 Jun 2026 00:00:00 GMThttps://ethanyan.me/writing/the-day-my-agent-lied/https://ethanyan.me/writing/the-day-my-agent-lied/A daily digest agent reported "all sources fetched" — while quietly dropping one. The bug wasn't the fetch. It was the missing guardrail.Fri, 12 Jun 2026 00:00:00 GMThttps://ethanyan.me/writing/from-context-to-loop-engineering/https://ethanyan.me/writing/from-context-to-loop-engineering/The thing worth getting right keeps moving up a level — prompt, context, harness, loop. The hard part was never the while-loop.Mon, 08 Jun 2026 00:00:00 GMThttps://ethanyan.me/writing/the-agentic-composition-stack/https://ethanyan.me/writing/the-agentic-composition-stack/Stop adding a tool for every request. Autonomy is a stack of composition types with two layers of glue, not a single trick.Sun, 24 May 2026 00:00:00 GMThttps://ethanyan.me/writing/why-my-runtime-stays-in-process/https://ethanyan.me/writing/why-my-runtime-stays-in-process/I migrated a production agent onto a server runtime, ran the whole playbook, then rolled it all back. Sometimes the senior move is not adopting the thing.Sat, 16 May 2026 00:00:00 GMThttps://ethanyan.me/writing/code-action-not-more-tools/https://ethanyan.me/writing/code-action-not-more-tools/Standard tool-calling can't express composition. So stop picking tools — let the model write the code that calls them.Sun, 10 May 2026 00:00:00 GMThttps://ethanyan.me/writing/designing-for-mistakes/https://ethanyan.me/writing/designing-for-mistakes/Reliable agent UX isn't about preventing errors — it's about making the wrong answer cheap to notice and undo.Tue, 28 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/four-layers-of-agent-memory/https://ethanyan.me/writing/four-layers-of-agent-memory/Everyone treats agent memory as one framework, and compares the options as if they're rivals. They answer different questions — here's the map.Fri, 24 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/four-ways-to-give-a-model-knowledge/https://ethanyan.me/writing/four-ways-to-give-a-model-knowledge/Vector RAG, RAGFlow, GraphRAG, PageIndex, an LLM wiki, Obsidian — they get lumped together as rivals. They aren't even at the same layer. A field guide to which one fits which job.Sat, 18 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/no-best-agent-framework/https://ethanyan.me/writing/no-best-agent-framework/I scored two agent frameworks across eleven dimensions. Strip the weights and they tie. The gap was never about quality — it was about who I am.Thu, 16 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/knowledge-base-notebook/https://ethanyan.me/writing/knowledge-base-notebook/Everyone is racing to build a smarter index. The labs that build the models quietly went the other way — toward plain text the agent reads and tidies itself.Sun, 12 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/agents-need-memory/https://ethanyan.me/writing/agents-need-memory/A bigger context window buys you a better goldfish. Persistence is a different problem — and most of the work happens between the prompts.Mon, 06 Apr 2026 00:00:00 GMThttps://ethanyan.me/writing/tool-use-loops/https://ethanyan.me/writing/tool-use-loops/Every retry feels free in isolation. Stacked across a session, they are where latency, cost, and confusion quietly accumulate.Sun, 15 Mar 2026 00:00:00 GMT