post: stop writing agent prompts for deterministic work (EN+ZH) + og/banner images

scripts/banner-gen/generate.mjs

@@ -1070,6 +1070,27 @@ BANNERS['loop-engineering-without-a-coding-agent'] = {
   ],
 };
 
+BANNERS['stop-writing-agent-prompts-for-deterministic-work'] = {
+  titlebar: 'root@hermes — deterministic check, no model',
+  lines: [
+    { t: 'prompt', text: '$' }, { t: 'cmd', text: 'registry.npmjs.org/<pkg>/latest  vs  local version' },
+    { t: 'prompt', text: 'WARN' }, { t: 'err', text: 'agent mode: [drift_skip] × 29 — died before it could speak' },
+    { t: 'prompt', text: '' }, { t: 'dim', text: 'silent-because-healthy  ==  silent-because-crashed' },
+    { t: 'prompt', text: '$' }, { t: 'cmd', text: 'rewrite: exit 0 = measured · exit 1 = CANNOT MEASURE' },
+    { t: 'prompt', text: 'INFO' }, { t: 'cmd', text: 'script stdout delivered as the notice · no LLM in the path' },
+    { t: 'prompt', text: 'INFO' }, { t: 'cmd', text: 'the test: write down what success AND failure print' },
+    { t: 'prompt', text: 'INFO' }, { t: 'cmd', text: 'number or string → script · "it depends" → model + verifier' },
+    { t: 'prompt', text: '' }, { t: 'ok', text: '→ 8 of 11 loops now carry no model ✓' },
+  ],
+  flow: [
+    { n: '1', label: 'compare' },
+    { n: '2', label: 'agent ✗', err: true },
+    { n: '3', label: 'script' },
+    { n: '4', label: 'exit 1 ≠ silent' },
+    { n: '5', label: 'green ✓' },
+  ],
+};
+
 // ---------- read frontmatter ----------
 const postPath = join(ROOT, 'src', 'content', 'posts', `${slug}.md`);
 let category = 'devops';

scripts/og-gen/generate.mjs

@@ -326,6 +326,11 @@ TERMINALS['loop-engineering-without-a-coding-agent'] = `
     <div class="line"><span class="prompt">&nbsp;</span><span class="err">agent-mode job: [drift_skip] × 29 runs — silent broken and silent healthy</span></div>
     <div class="line"><span class="prompt">$</span><span class="cmd">rewrite as a script · exit 1 = CANNOT MEASURE</span><span class="fix">→ 1,618 ticks ✓</span></div>`;
 
+TERMINALS['stop-writing-agent-prompts-for-deterministic-work'] = `
+    <div class="line"><span class="prompt">$</span><span class="cmd">hermes cron: CLI version check · agent mode</span></div>
+    <div class="line"><span class="prompt">&nbsp;</span><span class="err">[drift_skip] × 29 runs — silent, and silence reads as "nothing to report"</span></div>
+    <div class="line"><span class="prompt">$</span><span class="cmd">rewrite as a script · stdout IS the notification</span><span class="fix">→ green since ✓</span></div>`;
+
 // ---------- read frontmatter ----------
 const postPath = join(ROOT, 'src', 'content', 'posts', `${slug}.md`);
 if (!existsSync(postPath)) {

src/content/posts/stop-writing-agent-prompts-for-deterministic-work.md

@@ -0,0 +1,91 @@
+---
+title: "Stop Writing Agent Prompts for Deterministic Work"
+description: "One of my scheduled jobs failed 29 times in a row because I put a model in a loop that only needed a string comparison. Here is the rule I use now."
+pubDate: 2026-10-01
+category: notes
+tags: ["loop-engineering", "cron", "ai-agents", "automation"]
+ogImage: "/og/stop-writing-agent-prompts-for-deterministic-work.png"
+banner: "/banners/stop-writing-agent-prompts-for-deterministic-work.png"
+draft: false
+---
+
+One of my scheduled jobs failed 29 times in a row. Nobody told me, because
+it was designed to speak only when it had something to report — and a run
+that dies before it can speak looks exactly like a run that found nothing
+wrong.
+
+The job was a version check: ask npm for the latest published version of a
+CLI I use, compare it with the one installed here, and tell me if there is a
+newer one. That is the entire task. It is two strings and an inequality.
+
+I had built it as an agent job, because that was the pattern I had in my
+head at the time. Every tick, the model would read the injected script
+output and decide whether to write a notification. It worked for a while.
+Then my global default model changed, and the job — which records the model
+it was created with — stopped running entirely. It printed `[drift_skip]`
+and exited. Twenty-nine times.
+
+The fix was not a better prompt. It was deleting the model from the loop.
+
+## The rule
+
+**If the stop condition is a comparison — a string, a number, a status code — a model in that loop can only add failure modes.**
+
+There is no judgment to make in "is `3.8.50` newer than `3.8.50`". The model
+was not deciding anything the code could not; it was adding a dependency (a
+model route, a provider, a config snapshot, a token bill) and a new way to
+fail. So I rewrote the checker as 125 lines of Python with an explicit exit
+path for every branch, and flipped the job to script mode: the script's
+stdout is delivered as the notification, with no LLM anywhere in the path.
+
+It has run clean ever since. Anthropic's own guidance says the same thing in
+one line — *use scripts for deterministic work; running a script is cheaper
+than reasoning through the steps* — but the cost was never the interesting
+part for me. The reliability was.
+
+## Where the model does earn its place
+
+Of the eleven loops I run, eight now have no model in the path. The three
+that do all handle something I genuinely cannot express as code:
+
+- **Is this email important?** A mailbox produces promos, DMARC reports, container alerts and a customer asking for a quote. Fetching mail is deterministic. Ranking it is not.
+- **Is this shop voucher about to overspend?** The arithmetic is trivial; deciding what a finding means for money I have already committed is not.
+- **Is this project stalled?** Reading two markdown files is a script's job. Noticing that the plan has not moved in three weeks is not.
+
+The test I apply to a new loop: **write down what the check would print on
+success and on failure.** If both answers are a number or a string, it is a
+script. If the answer is "it depends what it says", it needs a model — and
+then it needs a verifier I trust more than the agent, because I am no longer
+able to predict the output.
+
+## The part that actually bit me
+
+The failure mode was not the drift. It was the **silence**.
+
+A loop that speaks only when something is wrong is the only kind of loop I
+can tolerate — I do not want a daily status report from eleven jobs. But
+"silent because healthy" and "silent because it crashed before it could
+speak" are the same observation from my side of the phone. Twenty-nine runs
+of evidence were sitting in the job's execution log the whole time; I was
+trusting the absence of a notification instead of reading the history.
+
+So every script in the fleet now has a second exit path: exit 0 means
+*measured, here is what I found*, and exit 1 means *I could not measure* —
+and exit 1 is never silent. Missing config, unparseable state, an unexpected
+exception: all of them print a line and exit 1. That one change would have
+surfaced this bug on the first run instead of the twenty-ninth.
+
+If you have a loop that has been "quiet for a while", go and read its last
+ten runs before you conclude it is working. That advice cost me three weeks.
+
+## The short version
+
+- Deterministic check → script. Judgment → model. Do not mix them for convenience.
+- Give the silent-on-success convention one exception: "I could not measure" must always be loud.
+- Read the runner's own execution history, not just your notifications.
+
+Want a version of this for your own site or shop — uptime, certificates,
+backups, mail that only pings you when it matters?
+**[WhatsApp +60 12-797 2969](https://wa.me/60127972969)** ·
+**[[email protected]](mailto:[email protected]?subject=Self-hosted%20monitoring)** ·
+**[hoelee.com](https://hoelee.com)**

src/content/posts/zh/stop-writing-agent-prompts-for-deterministic-work.md

@@ -0,0 +1,54 @@
+---
+title: "确定性的活，别再用 Agent Prompt 去跑"
+description: "我有一个定时任务连续失败 29 次，原因是我在一个只需要字符串比较的循环里塞了个模型。这是我现在用的规则。"
+pubDate: 2026-10-01
+category: notes
+tags: ["loop-engineering", "cron", "ai-agents", "automation"]
+ogImage: "/og/stop-writing-agent-prompts-for-deterministic-work.png"
+banner: "/banners/stop-writing-agent-prompts-for-deterministic-work.png"
+draft: false
+---
+
+我有一个定时任务连续失败了 29 次。没人告诉我，因为它被设计成只在有东西可报的时候才开口——而一个还没来得及开口就崩掉的运行，看起来和一个「什么都没发现」的运行一模一样。
+
+那个任务是个版本检查：问 npm 某个我常用的 CLI 最新发布版本是多少，和本机装的版本比一下，有更新就告诉我。整个任务就这些。它就是两个字符串加一次比较。
+
+我当初把它做成了 agent 任务，因为那阵子我脑子里的默认模式就是这个。每次 tick，模型读一遍注入的脚本输出，然后判断要不要写一条通知。它正常跑了一阵子。后来我改了全局默认模型，而这个任务会记录自己创建时的模型，于是它干脆整个不跑了，打印一行 `[drift_skip]` 就退出。连续 29 次。
+
+修法不是写一个更好的 prompt，而是把模型从循环里删掉。
+
+## 规则
+
+**如果停止条件是一次比较——一个字符串、一个数字、一个状态码——那么循环里的模型只能带来新的失败模式。**
+
+「`3.8.50` 是不是比 `3.8.50` 新」这件事里没有任何判断可做。模型并没有在决定代码决定不了的事；它带来的是一条依赖（一条模型路由、一个提供商、一份配置快照、一张 token 账单）和一种全新的出错方式。所以我把它重写成 125 行 Python，每条分支都有明确出口，再把任务切成脚本模式：脚本的 stdout 直接作为通知内容，整条路径上没有任何 LLM。
+
+从此一路干净。Anthropic 自己的建议也是一句话——*确定性的活用脚本，跑脚本比让模型去推理步骤便宜*——但对我来说成本从来不是重点，可靠性才是。
+
+## 模型该用在哪
+
+我跑的 11 个循环里，现在有 8 个整条路径上没有模型。用模型的那 3 个，处理的都是我确实写不成代码的东西：
+
+- **这封邮件重不重要？** 一个邮箱里同时有促销、DMARC 报告、容器告警，和一位来问报价的客户。抓邮件是确定性的，给它排优先级不是。
+- **这张店铺优惠券是不是快超支了？** 算术很简单；判断一个发现对我已经承诺出去的钱意味着什么，不简单。
+- **这个项目是不是卡住了？** 读两个 markdown 文件是脚本的活。发现「计划已经三周没动过」不是。
+
+我给新循环做的测试是：**写下这个检查在成功和失败时分别会打印什么。** 如果两个答案都是一个数字或一个字符串，那它就是脚本。如果答案是「要看它说了什么」，那它需要模型——而这时候它就需要一个我比 agent 更信任的验证器，因为我已经无法预测输出了。
+
+## 真正咬到我的是哪一部分
+
+失败模式不是 drift，是**沉默**。
+
+一个只在出事时才开口的循环，是我唯一能忍受的那种——我不想让 11 个任务每天给我发状态报告。但「健康所以安静」和「崩了所以来不及开口」，从我手机这端看是同一个现象。29 次运行的证据一直躺在那个任务的执行日志里；我却一直在相信「没有通知」这件事本身，而没去读历史。
+
+所以现在这套脚本都多了一条出口：退出码 0 表示*量过了，这是结果*，退出码 1 表示*我量不了*——而退出码 1 永远不静默。配置缺失、状态文件解析失败、没预料到的异常：全都打印一行并退出 1。就这一处改动，本该让这个 bug 在第 1 次就暴露，而不是第 29 次。
+
+如果你有一个循环「已经安静一阵子」了，先去翻它最近十次运行，再下结论说它正常。这条建议花了我三个星期才换到。
+
+## 简短版
+
+- 确定性的检查 → 脚本。判断 → 模型。别为了方便把两者混在一起。
+- 给「成功则静默」这条约定开一个例外：「我量不了」必须永远大声。
+- 去读 runner 自己的执行历史，而不是只看你收到的通知。
+
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