From 42d616750f4fe580a22b92dc5f52d22666bb189d Mon Sep 17 00:00:00 2001
From: Shahid Raza <razashahid532@gmail.com>
Date: Fri, 17 Jul 2026 15:44:31 +0530
Subject: [PATCH] chore(release): v0.4.0

Adds the "Cron was easy because the job was dumb" thread (Claude routines and
cron), plus reusable thread reading enhancements: hand-drawn pen annotations,
an "On this page" table of contents with scroll-spy, a styled cron diagram, and
copy-to-clipboard on code blocks.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 CHANGELOG.md                                  |  18 ++
 package-lock.json                             |   4 +-
 package.json                                  |   2 +-
 src/app/threads/[slug]/page.tsx               |   9 +
 src/components/annotate.tsx                   | 189 ++++++++++++
 src/components/code-block.tsx                 |  46 +++
 src/components/cron-diagram.tsx               |  64 ++++
 src/components/table-of-contents.tsx          |  96 ++++++
 .../threads/claude-routines-and-cron.mdx      | 274 ++++++++++++++++++
 src/mdx-components.tsx                        |  13 +
 10 files changed, 712 insertions(+), 3 deletions(-)
 create mode 100644 src/components/annotate.tsx
 create mode 100644 src/components/code-block.tsx
 create mode 100644 src/components/cron-diagram.tsx
 create mode 100644 src/components/table-of-contents.tsx
 create mode 100644 src/content/threads/claude-routines-and-cron.mdx

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ba7207..77fa4b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,24 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 Every release corresponds to a `staging` to `main` pull request and a matching
 `vX.Y.Z` tag on `main`.
 
+## [0.4.0] - 2026-07-17
+
+### Added
+
+- New thread: **"Cron was easy because the job was dumb"** — a deep, practical
+  guide to Claude routines (cron jobs whose payload is an agent). Covers routine
+  anatomy, a gallery of real routines with schedules and prompts, idempotency
+  patterns, a cron syntax refresher, routines vs. loops, and observability.
+  Includes a companion video link and a new `claude` tag.
+- Hand-drawn **pen annotations** for thread prose (`Underline`, `Circle`, `Box`,
+  `Strike`, `Highlight`) that draw themselves on scroll and are gated behind
+  `prefers-reduced-motion`. Wired into MDX, so any thread can use them.
+- **"On this page"** table of contents: a sticky right rail with scroll-spy that
+  highlights the current section and jumps to any heading.
+- **Cron diagram** component: a styled five-field breakdown replacing brittle
+  ASCII art.
+- **Copy to clipboard** buttons on thread code blocks.
+
 ## [0.3.0] - 2026-07-12
 
 ### Added
diff --git a/package-lock.json b/package-lock.json
index bead250..4913903 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "binarysemaphore",
-  "version": "0.3.0",
+  "version": "0.4.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "binarysemaphore",
-      "version": "0.3.0",
+      "version": "0.4.0",
       "dependencies": {
         "@mdx-js/loader": "^3.1.1",
         "@mdx-js/react": "^3.1.1",
diff --git a/package.json b/package.json
index a1152ce..b8a0e57 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "binarysemaphore",
-  "version": "0.3.0",
+  "version": "0.4.0",
   "private": true,
   "scripts": {
     "dev": "next dev",
diff --git a/src/app/threads/[slug]/page.tsx b/src/app/threads/[slug]/page.tsx
index d635851..8d61496 100644
--- a/src/app/threads/[slug]/page.tsx
+++ b/src/app/threads/[slug]/page.tsx
@@ -11,6 +11,7 @@ import { threadCovers } from "@/lib/thread-covers";
 import { Photo } from "@/components/photo";
 import { Header } from "@/components/header";
 import { Footer } from "@/components/footer";
+import { TableOfContents } from "@/components/table-of-contents";
 
 type Params = { slug: string };
 
@@ -67,6 +68,7 @@ export default async function ThreadPage({
       <Header />
 
       <main className="mx-auto w-full max-w-3xl flex-1 px-6 pb-20">
+       <div className="relative">
         <nav className="pt-10 pb-8 text-sm" aria-label="Breadcrumb">
           <Link
             href="/threads"
@@ -154,6 +156,13 @@ export default async function ThreadPage({
             <span aria-hidden="true">&larr;</span> All threads
           </Link>
         </div>
+
+        <aside className="absolute left-full top-0 hidden h-full pl-10 min-[1300px]:block">
+          <div className="sticky top-24 w-52">
+            <TableOfContents />
+          </div>
+        </aside>
+       </div>
       </main>
 
       <Footer />
diff --git a/src/components/annotate.tsx b/src/components/annotate.tsx
new file mode 100644
index 0000000..540a754
--- /dev/null
+++ b/src/components/annotate.tsx
@@ -0,0 +1,189 @@
+"use client";
+
+/**
+ * Hand-drawn "pen" annotations for long-form thread prose. Wrap any inline text
+ * to circle / underline / box / strike / highlight it, the way you'd mark up a
+ * printed page. Each mark draws itself when it scrolls into view (respecting
+ * `prefers-reduced-motion`, which shows it instantly).
+ *
+ * Wired into MDX in `src/mdx-components.tsx`, so threads can write:
+ *   Cron was <Underline>easy</Underline> because the job was <Circle>dumb</Circle>.
+ *
+ * Stroke colour comes from `currentColor`; set it with a text utility via
+ * `className` (default is the brand accent, i.e. a red-pen look).
+ */
+
+import { useEffect, useRef, useState, type ReactNode } from "react";
+
+type MarkProps = {
+  children: ReactNode;
+  /** Tailwind colour utility for the stroke, e.g. "text-accent-strong". */
+  className?: string;
+};
+
+/** Reveal once, when the element scrolls into view. Reduced-motion => instant. */
+function useDrawn<T extends Element>() {
+  const ref = useRef<T>(null);
+  const [drawn, setDrawn] = useState(false);
+
+  useEffect(() => {
+    const el = ref.current;
+    if (!el) return;
+
+    const reduce =
+      typeof window !== "undefined" &&
+      window.matchMedia?.("(prefers-reduced-motion: reduce)").matches;
+    if (reduce) {
+      const raf = requestAnimationFrame(() => setDrawn(true));
+      return () => cancelAnimationFrame(raf);
+    }
+
+    const io = new IntersectionObserver(
+      (entries) => {
+        for (const entry of entries) {
+          if (entry.isIntersecting) {
+            setDrawn(true);
+            io.disconnect();
+          }
+        }
+      },
+      { threshold: 0.85, rootMargin: "0px 0px -8% 0px" },
+    );
+    io.observe(el);
+    return () => io.disconnect();
+  }, []);
+
+  return { ref, drawn };
+}
+
+/** Common style for a self-drawing stroke path. */
+function strokeStyle(drawn: boolean, ms: number) {
+  return {
+    strokeDasharray: 1,
+    strokeDashoffset: drawn ? 0 : 1,
+    transition: `stroke-dashoffset ${ms}ms cubic-bezier(0.65, 0, 0.35, 1)`,
+  } as const;
+}
+
+/** Slightly wobbly underline that sweeps in under the text. */
+export function Underline({ children, className = "text-blue/80" }: MarkProps) {
+  const { ref, drawn } = useDrawn<HTMLSpanElement>();
+  return (
+    <span ref={ref} className="relative inline-block">
+      {children}
+      <svg
+        className={`pointer-events-none absolute -bottom-1 left-0 h-[0.5em] w-full overflow-visible ${className}`}
+        viewBox="0 0 300 12"
+        fill="none"
+        preserveAspectRatio="none"
+        aria-hidden="true"
+      >
+        <path
+          d="M3 8C58 3 118 10 178 6c40-3 80-1 119 2"
+          stroke="currentColor"
+          strokeWidth="2.5"
+          strokeLinecap="round"
+          pathLength={1}
+          style={strokeStyle(drawn, 1150)}
+        />
+      </svg>
+    </span>
+  );
+}
+
+/** Open, hand-drawn ellipse looped around the text. */
+export function Circle({ children, className = "text-violet/80" }: MarkProps) {
+  const { ref, drawn } = useDrawn<HTMLSpanElement>();
+  return (
+    <span ref={ref} className="relative inline-block px-[0.35em] py-[0.15em]">
+      {children}
+      <svg
+        className={`pointer-events-none absolute inset-0 h-full w-full overflow-visible ${className}`}
+        viewBox="0 0 300 120"
+        fill="none"
+        preserveAspectRatio="none"
+        aria-hidden="true"
+      >
+        <path
+          d="M155 9C82 6 16 28 13 60c-3 33 70 53 142 51 78-2 135-26 132-55C296 30 224 12 150 11"
+          stroke="currentColor"
+          strokeWidth="2.5"
+          strokeLinecap="round"
+          pathLength={1}
+          style={strokeStyle(drawn, 1600)}
+        />
+      </svg>
+    </span>
+  );
+}
+
+/** Rough rectangle drawn around the text. */
+export function Box({ children, className = "text-lime" }: MarkProps) {
+  const { ref, drawn } = useDrawn<HTMLSpanElement>();
+  return (
+    <span ref={ref} className="relative inline-block px-[0.4em] py-[0.18em]">
+      {children}
+      <svg
+        className={`pointer-events-none absolute inset-0 h-full w-full overflow-visible ${className}`}
+        viewBox="0 0 300 100"
+        fill="none"
+        preserveAspectRatio="none"
+        aria-hidden="true"
+      >
+        <path
+          d="M9 13C88 8 214 7 292 13c4 26 3 49-1 74-79 6-206 7-284 1C3 62 4 39 9 13Z"
+          stroke="currentColor"
+          strokeWidth="2.5"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          pathLength={1}
+          style={strokeStyle(drawn, 1700)}
+        />
+      </svg>
+    </span>
+  );
+}
+
+/** A line struck through the text. */
+export function Strike({ children, className = "text-subtle" }: MarkProps) {
+  const { ref, drawn } = useDrawn<HTMLSpanElement>();
+  return (
+    <span ref={ref} className="relative inline-block">
+      {children}
+      <svg
+        className={`pointer-events-none absolute left-0 top-1/2 h-[0.4em] w-full -translate-y-1/2 overflow-visible ${className}`}
+        viewBox="0 0 300 10"
+        fill="none"
+        preserveAspectRatio="none"
+        aria-hidden="true"
+      >
+        <path
+          d="M4 6c60-3 130 2 190-1 40-2 70 1 102 2"
+          stroke="currentColor"
+          strokeWidth="2.5"
+          strokeLinecap="round"
+          pathLength={1}
+          style={strokeStyle(drawn, 900)}
+        />
+      </svg>
+    </span>
+  );
+}
+
+/** Marker-style highlight that wipes in behind the text. */
+export function Highlight({ children, className = "bg-sun/40" }: MarkProps) {
+  const { ref, drawn } = useDrawn<HTMLSpanElement>();
+  return (
+    <span ref={ref} className="relative inline-block">
+      <span
+        className={`absolute inset-x-[-0.15em] bottom-[0.05em] top-[0.4em] origin-left -rotate-1 rounded-[0.2em] ${className}`}
+        aria-hidden="true"
+        style={{
+          transform: `rotate(-1deg) scaleX(${drawn ? 1 : 0})`,
+          transition: "transform 900ms cubic-bezier(0.65, 0, 0.35, 1)",
+        }}
+      />
+      <span className="relative">{children}</span>
+    </span>
+  );
+}
diff --git a/src/components/code-block.tsx b/src/components/code-block.tsx
new file mode 100644
index 0000000..a02a8a2
--- /dev/null
+++ b/src/components/code-block.tsx
@@ -0,0 +1,46 @@
+"use client";
+
+/**
+ * Thread code blocks with a copy-to-clipboard button.
+ *
+ * Registered as the `pre` element in `src/mdx-components.tsx`. The incoming
+ * props (including rehype-pretty-code's `data-*` attributes and classes) are
+ * spread straight onto the real <pre>, so the highlighted output is preserved
+ * exactly; we only wrap it to position the button.
+ */
+
+import { useRef, useState, type ComponentPropsWithoutRef } from "react";
+
+export function Pre(props: ComponentPropsWithoutRef<"pre">) {
+  const ref = useRef<HTMLPreElement>(null);
+  const [copied, setCopied] = useState(false);
+  const timer = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  async function copy() {
+    const text = ref.current?.textContent ?? "";
+    if (!text) return;
+    try {
+      await navigator.clipboard.writeText(text);
+      setCopied(true);
+      if (timer.current) clearTimeout(timer.current);
+      timer.current = setTimeout(() => setCopied(false), 2000);
+    } catch {
+      // Clipboard unavailable (insecure context, denied permission): leave the
+      // button idle rather than pretending it worked.
+    }
+  }
+
+  return (
+    <div className="group relative">
+      <pre ref={ref} {...props} />
+      <button
+        type="button"
+        onClick={copy}
+        aria-label={copied ? "Copied to clipboard" : "Copy code to clipboard"}
+        className="absolute right-3 top-3 rounded-md border border-border bg-card px-2 py-1 font-mono text-[11px] leading-none text-subtle opacity-0 transition-opacity duration-150 hover:text-foreground focus-visible:opacity-100 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-blue group-hover:opacity-100"
+      >
+        {copied ? "copied" : "copy"}
+      </button>
+    </div>
+  );
+}
diff --git a/src/components/cron-diagram.tsx b/src/components/cron-diagram.tsx
new file mode 100644
index 0000000..766de0e
--- /dev/null
+++ b/src/components/cron-diagram.tsx
@@ -0,0 +1,64 @@
+/**
+ * A clean cron-expression breakdown for use in threads: each field sits above
+ * the name and range it maps to, replacing fragile ASCII box-art. Pure server
+ * component (no client JS). Wildcards render in the accent colour.
+ *
+ * Usage in MDX:  <CronDiagram expr="0 8 * * *" note="every day at 08:00" />
+ */
+
+const FIELDS = [
+  { name: "minute", range: "0–59" },
+  { name: "hour", range: "0–23" },
+  { name: "day-of-month", range: "1–31" },
+  { name: "month", range: "1–12" },
+  { name: "day-of-week", range: "0–7" },
+] as const;
+
+export function CronDiagram({
+  expr = "0 8 * * *",
+  note,
+}: {
+  expr?: string;
+  note?: string;
+}) {
+  const tokens = expr.trim().split(/\s+/).slice(0, 5);
+
+  return (
+    <figure className="my-8">
+      <div className="overflow-x-auto rounded-panel border border-border bg-card shadow-soft">
+        <div className="grid min-w-[560px] grid-cols-5">
+          {FIELDS.map((field, i) => {
+            const token = tokens[i] ?? "*";
+            return (
+              <div
+                key={field.name}
+                className={`flex flex-col items-center gap-1.5 px-3 py-5 text-center ${
+                  i > 0 ? "border-l border-border" : ""
+                }`}
+              >
+                <span className="font-mono text-2xl leading-none text-foreground">
+                  {token === "*" ? (
+                    <span className="text-blue">*</span>
+                  ) : (
+                    token
+                  )}
+                </span>
+                <span className="font-mono text-[11px] leading-none text-subtle">
+                  {field.name}
+                </span>
+                <span className="font-mono text-[11px] leading-none text-subtle/60">
+                  {field.range}
+                </span>
+              </div>
+            );
+          })}
+        </div>
+      </div>
+      {note ? (
+        <figcaption className="mt-3 text-center font-mono text-xs text-subtle">
+          <span className="text-blue">→</span> {note}
+        </figcaption>
+      ) : null}
+    </figure>
+  );
+}
diff --git a/src/components/table-of-contents.tsx b/src/components/table-of-contents.tsx
new file mode 100644
index 0000000..d646531
--- /dev/null
+++ b/src/components/table-of-contents.tsx
@@ -0,0 +1,96 @@
+"use client";
+
+/**
+ * "On this page" navigator for a thread. Reads the rendered article's h2/h3
+ * headings (which already carry ids from rehype-slug), lists them, and
+ * highlights the section you're currently reading via IntersectionObserver.
+ * Clicking a heading jumps to it (native anchor + the headings' scroll-mt).
+ *
+ * Renders nothing when there are fewer than two headings, and is hidden on
+ * narrow screens by its parent (scrolling is fine there).
+ */
+
+import { useEffect, useState } from "react";
+
+type Item = { id: string; text: string; level: 2 | 3 };
+
+export function TableOfContents() {
+  const [items, setItems] = useState<Item[]>([]);
+  const [activeId, setActiveId] = useState<string>("");
+
+  useEffect(() => {
+    let io: IntersectionObserver | undefined;
+
+    // Read the rendered headings after paint so we're not calling setState
+    // synchronously in the effect body, and so ids from rehype-slug exist.
+    const raf = requestAnimationFrame(() => {
+      const headings = Array.from(
+        document.querySelectorAll<HTMLElement>(".thread h2, .thread h3"),
+      ).filter((h) => h.id);
+
+      setItems(
+        headings.map((h) => ({
+          id: h.id,
+          text: h.textContent ?? "",
+          level: h.tagName === "H3" ? 3 : 2,
+        })),
+      );
+
+      if (headings.length < 2) return;
+
+      // Track which heading is nearest the top of the viewport.
+      const visible = new Map<string, number>();
+      io = new IntersectionObserver(
+        (entries) => {
+          for (const entry of entries) {
+            const id = (entry.target as HTMLElement).id;
+            if (entry.isIntersecting) visible.set(id, entry.boundingClientRect.top);
+            else visible.delete(id);
+          }
+          if (visible.size > 0) {
+            const top = [...visible.entries()].sort((a, b) => a[1] - b[1])[0][0];
+            setActiveId(top);
+          }
+        },
+        { rootMargin: "-80px 0px -68% 0px", threshold: 0 },
+      );
+
+      headings.forEach((h) => io!.observe(h));
+    });
+
+    return () => {
+      cancelAnimationFrame(raf);
+      io?.disconnect();
+    };
+  }, []);
+
+  if (items.length < 2) return null;
+
+  return (
+    <nav aria-label="On this page">
+      <p className="mb-3 font-mono text-[11px] uppercase tracking-[0.2em] text-subtle">
+        On this page
+      </p>
+      <ul className="space-y-1 border-l border-border">
+        {items.map((item) => {
+          const active = activeId === item.id;
+          return (
+            <li key={item.id} className={item.level === 3 ? "pl-3" : ""}>
+              <a
+                href={`#${item.id}`}
+                aria-current={active ? "location" : undefined}
+                className={`-ml-px block border-l-2 py-1 pl-3 text-sm leading-snug transition-colors ${
+                  active
+                    ? "border-accent font-medium text-foreground"
+                    : "border-transparent text-subtle hover:border-border hover:text-foreground"
+                }`}
+              >
+                {item.text}
+              </a>
+            </li>
+          );
+        })}
+      </ul>
+    </nav>
+  );
+}
diff --git a/src/content/threads/claude-routines-and-cron.mdx b/src/content/threads/claude-routines-and-cron.mdx
new file mode 100644
index 0000000..0cf3143
--- /dev/null
+++ b/src/content/threads/claude-routines-and-cron.mdx
@@ -0,0 +1,274 @@
+---
+title: "Cron was easy because the job was dumb"
+description: "A deep, practical guide to Claude routines: cron jobs whose payload is an agent, not a script. What that breaks (determinism, idempotency, retries, overlap), a gallery of routines worth building, and how to harden one so it behaves when nobody is watching."
+date: 2026-07-17
+tags: ["ai", "agents", "claude", "cron", "distributed-systems"]
+---
+
+Cron is one of the most durable pieces of software ever written. You give it five fields and
+a command, and for forty years it has run that command on time and gotten out of the way. It
+works because it makes <Underline>almost no promises</Underline>. It fires a process; it
+<Highlight>does not care what the process does</Highlight>, whether it succeeded, or whether the
+last one is still running.
+
+Claude *routines* — scheduled agents that run on a cron expression — look like the same idea
+with a smarter payload. Point one at "every morning at 8, review yesterday's failed CI runs
+and open an issue for anything that looks like a real regression," pick a schedule, and it
+runs on its own. Underneath, the scheduling primitive really is just cron.
+
+But the payload is <Underline>no longer a script</Underline>. It's a
+<Circle>nondeterministic agent</Circle> that reads, decides, and writes to the outside world.
+That single swap invalidates most of the assumptions cron got to be simple by ignoring. This is
+a long, practical note about which assumptions break, the routines actually worth building, and
+how to design one so it behaves when nobody is watching.
+
+> **Prefer to watch?** There's a video on this same topic on YouTube:
+> [youtube.com/watch?v=eSP7PLTXNy8](https://www.youtube.com/watch?v=eSP7PLTXNy8).
+
+## The anatomy of a routine
+
+Strip away the framing and a routine has exactly <Circle className="text-blue/80">three parts</Circle>:
+
+1. **A schedule** — a cron expression (`0 8 * * *`) that decides *when* it wakes up.
+2. **A prompt** — the self-contained instruction that *is* the job.
+3. **A grant** — the tools and permissions the run is allowed to use (a repo, an MCP server,
+   a Slack channel), which decides *what it can touch*.
+
+A plain cron job has the first and third of these; the second is a shell command. The whole
+shift is that the second is now a paragraph of natural language handed to a model. Everything
+strange about routines falls out of that one substitution.
+
+### A routine is a cold start every time
+
+The first thing to internalize: a scheduled run does **not** inherit the conversation you were
+in when you created it. It starts <Box>cold</Box>. No memory of "the above," no working
+directory you had open, no half-finished reasoning. The prompt you save is
+<Highlight>the entire context the next run gets</Highlight>.
+
+This is the right design — a job that only works because of state trapped in one person's
+terminal session is not a job, it's a demo — but it flips how you write the instruction. You're
+not talking to an assistant that already knows what you meant. You're writing a spec for
+<Underline>a stranger who will execute it once</Underline>, alone, months from now:
+
+```text
+Bad:  "do that check we talked about and let me know"
+Good: "Fetch the last 24h of runs from the `deploy-production` workflow in
+       BiSemaphore/binarysemaphore. For each failure, read the logs. If the
+       failure is a real regression (not a flaky timeout or a cancelled run),
+       open a GitHub issue titled `CI regression: <job>` with the failing step
+       and a link. If everything passed, do nothing and post no message."
+```
+
+Everything the run needs — repo, tool, definition of "real regression," what to do on the happy
+path — is in the text, because there is nothing else. The discipline this forces is the same
+discipline behind a good `README` or a good on-call runbook:
+<Underline className="text-violet/80">assume the reader has none of your context</Underline>,
+because they don't.
+
+## A gallery of routines worth building
+
+The abstract argument lands better against concrete jobs. Here are routines that earn their
+keep, each with a schedule and the shape of its prompt. Notice how every one ends with an
+explicit <Circle>otherwise, do nothing</Circle> — that clause is load-bearing, and we'll come
+back to why.
+
+**Nightly CI regression triage** — turn a wall of red into a short list of real bugs.
+
+```text
+schedule: 0 7 * * 1-5          # 07:00 on weekdays
+prompt:   Read failed runs from the last 24h in <repo>. Cluster them.
+          Open one issue per distinct real regression (skip flaky timeouts and
+          cancelled runs), each with the failing step and a permalink. If an
+          open issue with that title already exists, comment instead. Otherwise
+          do nothing.
+```
+
+**Morning dependency & advisory digest** — the security email you'd never read, summarized.
+
+```text
+schedule: 30 8 * * 1           # 08:30 every Monday
+prompt:   List dependencies with a new release or CVE since last Monday. For
+          each, one line: package, old -> new, why it matters, breaking? Post a
+          single message to #eng. If nothing changed, say "no updates" once.
+```
+
+**Stale issue & PR sweep** — the janitorial pass nobody volunteers for.
+
+```text
+schedule: 0 16 * * 5           # 16:00 every Friday
+prompt:   Find issues with no activity in 30 days and PRs green but unmerged for
+          7. Add a "stale" comment with a specific next step, not a generic ping.
+          Never close anything. Summarize what you touched in one message.
+```
+
+**On-call handoff** — a written summary at the shift boundary.
+
+```text
+schedule: 0 9,21 * * *         # 09:00 and 21:00 daily
+prompt:   Summarize alerts, deploys, and incident-channel activity since the
+          last handoff. What's still open, what to watch. Post to #on-call.
+```
+
+**Docs freshness check** — catch the doc that now lies.
+
+```text
+schedule: 0 3 * * 2            # 03:00 every Tuesday
+prompt:   Find docs referencing code paths, flags, or env vars that no longer
+          exist in the repo. Open one issue listing them with file:line. If the
+          list is empty, do nothing.
+```
+
+Two patterns run through the whole gallery. First, **narrow verbs**: "cluster," "comment,"
+"summarize," never <Strike>"manage"</Strike>. Second, **a defined empty case**: the boring
+night, where the right output is nothing at all. A routine that can't stay quiet becomes noise
+you learn to ignore, and <Underline>an ignored routine is worse than no routine</Underline>.
+
+## Cron's promises, and which ones the agent revokes
+
+Cron's simplicity came from a short list of things it refused to guarantee. Each one was fine
+when the payload was `backup.sh`. Each one is now yours to think about.
+
+| Cron quietly assumes | Fine for a script because | Now that the payload is an agent |
+| --- | --- | --- |
+| The job is deterministic | Same input, same output | Same prompt can produce different actions each run |
+| Retrying is safe | Re-running `rsync` is idempotent | A retry might file the issue *again* |
+| Overlap is your problem | Two `backup.sh` rarely race | Two runs can both act on the same event |
+| Exit code 0 means success | The script knows if it failed | "Success" is a judgement the model is making |
+| Missed runs just… don't happen | You'll notice a stale backup | A skipped morning review is silent |
+
+None of these are reasons not to use routines. They're the checklist you'd apply to any
+unattended distributed job, surfaced by the fact that the payload can now think. The good news
+is the fixes are old and well understood.
+
+### Make the action idempotent, not the agent
+
+You cannot make the model deterministic, and you shouldn't try. What you *can* do is
+<Highlight>make the side effect safe to repeat</Highlight>. This is the same move you make with
+any <Circle>at-least-once system</Circle>: push idempotency into
+<Underline>the write, not the caller</Underline>. A few patterns cover almost everything:
+
+- **Check before write.** "Open an issue *if one with this title doesn't already exist*." The
+  title becomes a natural idempotency key.
+- **Scope by period.** "Post the digest *for this ISO week*, and check the channel for one
+  already posted this week first." The time window is the key.
+- **Prefer upsert over insert.** Update-or-create against a stable identifier instead of
+  blindly appending, so the second run converges instead of duplicating.
+- **Make "nothing to do" a first-class outcome.** The happy path for most runs is a no-op, and
+  the prompt should say so explicitly, or the model will invent activity to look useful.
+
+Here's the same routine written the naive way and the safe way. The diff is small and it is the
+whole ballgame:
+
+```diff
+- Open a GitHub issue for the regression.
+- Post a summary to #eng.
++ If an open issue titled "CI regression: <job>" exists, add a comment; else open it.
++ Post the summary tagged with today's date; if today's is already in #eng, skip.
+```
+
+The routine is allowed to run twice — because eventually it will — and the second run is a
+no-op. A cron job for a dumb script gets this for free. A routine gets it because you designed
+the *target* of the action to tolerate a duplicate.
+
+### Decide what overlap means before it happens
+
+If your review job takes eleven minutes and you schedule it every five, cron will happily start
+a second one while the first is still going. For `backup.sh` that's an annoyance. For an agent
+with write access it's <Underline className="text-violet/80">two runs reasoning about the same
+world</Underline> and possibly both acting on it — the classic double-file, now with extra
+steps.
+
+Pick a schedule with generous headroom over the worst-case runtime, and lean on the idempotent
+writes above as the real backstop, since headroom is a guess and
+<Highlight>idempotency is a guarantee</Highlight>.
+
+## A cron refresher, because the boring part still bites
+
+The agent is the interesting part, but the cron expression itself is still where a lot of
+routines quietly go wrong. Worth having the five fields cold:
+
+<CronDiagram expr="0 8 * * *" note="every day at 08:00" />
+
+Each field takes more than a single number:
+
+- `*` — every value. `*/15` — every 15th (a **step**): `*/15 * * * *` is every quarter hour.
+- `1-5` — a **range** (Monday to Friday in the weekday field).
+- `1,15` — a **list** (the 1st and the 15th).
+- `@daily`, `@hourly`, `@weekly`, `@reboot` — shorthands some schedulers accept for the common
+  cases.
+
+Three failure modes survive intact into the AI era:
+
+- **Time zones.** `0 8 * * *` is 8am in *some* zone. If you don't know which, you don't know
+  when your routine runs. <Underline>State the zone explicitly</Underline>; don't let a server's
+  `UTC` default decide your "every morning" is happening at midnight local.
+- **Daylight saving.** Twice a year a wall-clock time either doesn't exist or happens twice. A
+  job at `2:30` on the spring-forward night can be skipped entirely; on the fall-back night it
+  can fire twice. If the run matters, keep it out of the 1am–3am window, and — again — make it
+  idempotent so a double-fire is harmless.
+- **The day-of-month / day-of-week trap.** When you set *both* of those fields, cron treats
+  them as <Circle>OR, not AND</Circle>. `0 9 13 * 5` is not "the 13th if it's a Friday." It's
+  "the 13th, *and also* every Friday." This has been surprising people since the 1970s and it
+  will surprise you too. Want "the 13th only when it's Friday"? You can't say it in one
+  expression; schedule the 13th and let the job check the weekday itself.
+
+The routine wrapper doesn't rescue you from any of this. Cron semantics are cron semantics; the
+agent just does something more expensive than usual when the expression is wrong.
+
+## Routines vs. loops: schedule vs. session
+
+There's a neighbouring feature worth drawing a line against, because they solve different
+problems. A **loop** re-runs a prompt on an interval *inside the current session* — it keeps
+your context and is meant for "watch this thing until it's done": babysit a deploy, poll a build,
+iterate on a task while you're around. A **routine** is a scheduled *cloud* run with no session
+and no you: it wakes up cold, does one self-contained job, and exits.
+
+The rule of thumb: if the work needs the conversation you're in right now,
+<Underline>it's a loop</Underline>. If the work should happen whether or not you're at your
+machine, <Underline className="text-violet/80">it's a routine</Underline>. Reaching for a
+routine to babysit something you're actively watching gives you a cold agent fumbling for
+context it would have had for free in-session. Reaching for a loop to run a nightly job means it
+only runs on the nights you happened to leave the session open.
+
+## Knowing it ran: observability for something you never see
+
+A cron job mailed you its stdout. A routine, left alone, is a black box that may or may not be
+doing its work at 3am. Before you trust one, wire up three things:
+
+- **A heartbeat.** Have it leave a trace even on the empty case — a one-line "checked CI, all
+  green" — at least until you trust it.
+  <Highlight>A silent routine is indistinguishable from a broken one</Highlight>, and "it hasn't
+  posted in a week" should read as *alarming*, not *calm*.
+- **A dry run.** For anything with a write, run it once in a mode where it reports what it
+  *would* do instead of doing it. You are
+  <Underline>reviewing the model's judgement before you let it act unattended</Underline>; do
+  that while you're watching.
+- **A bounded blast radius.** Same instinct as [starting an MCP server
+  read-only](/threads/an-mcp-server-for-your-notes): give the routine exactly the reach its job
+  needs and nothing more. An unattended agent with broad write access is a
+  <Circle>standing risk that fires on a timer</Circle>.
+
+## Design a routine like an unattended job, because it is one
+
+Strip away the novelty and a routine is a cron-scheduled batch job whose worker happens to be a
+language model. The engineering that makes it trustworthy is the same engineering that makes any
+unattended job trustworthy, and none of it is new:
+
+1. **Keep the scope narrow.** <Underline>One routine, one job</Underline>. "Review CI failures"
+   is a routine. "Manage the repo" is a wish. A tight objective is easier to write, cheaper to
+   run, and far easier to trust when nobody's watching.
+2. **Make success and failure observable.** Leave a trace even on the "nothing to do" path.
+   Cron mailed you the job's stdout for exactly this reason.
+3. **Make the writes idempotent.** The <Highlight>single highest-leverage habit</Highlight>.
+   Assume at-least-once, design for it, stop worrying about double-fires.
+4. **Bound the blast radius.** Give the routine exactly the reach its job needs and nothing
+   more.
+5. **Define the empty case.** Say what "nothing happened" looks like, or the model will fill the
+   silence.
+
+Cron got to be simple because it never had to understand its payload. Routines hand the payload
+a mind, which is genuinely useful — a nightly job that can *read logs and judge* is worth a
+lot — but the price is that all the guarantees cron waved off are now yours to provide. Provide
+them, and a routine is a <Underline className="text-lime">tireless teammate that shows up on
+schedule</Underline>. Skip them, and it's a very articulate way to do the wrong thing at 8am
+every day.
diff --git a/src/mdx-components.tsx b/src/mdx-components.tsx
index 0662326..7eb3950 100644
--- a/src/mdx-components.tsx
+++ b/src/mdx-components.tsx
@@ -1,6 +1,9 @@
 import type { MDXComponents } from "mdx/types";
 import Link from "next/link";
 import type { AnchorHTMLAttributes } from "react";
+import { Underline, Circle, Box, Strike, Highlight } from "@/components/annotate";
+import { CronDiagram } from "@/components/cron-diagram";
+import { Pre } from "@/components/code-block";
 
 /**
  * Global MDX element styling for thread content. Required by @next/mdx in the
@@ -84,6 +87,16 @@ const components: MDXComponents = {
   td: (props) => (
     <td className="border-b border-border px-3 py-2 text-muted" {...props} />
   ),
+  // Hand-drawn pen annotations, usable inline in any thread.
+  Underline,
+  Circle,
+  Box,
+  Strike,
+  Highlight,
+  // Cron expression breakdown.
+  CronDiagram,
+  // Code blocks, with a copy-to-clipboard button.
+  pre: Pre,
 };
 
 export function useMDXComponents(): MDXComponents {