¬ just serendipity 🍀 (not just serendipity)

Previously, previously.

Problem statement: adopt caveman in pi.

Pi isn’t one of the 30+ agents caveman auto-detects. The install matrix (INSTALL.md) lists agent detection rules one by one — claude, cursor, windsurf, opencode, openclaw, etc — and pi isn’t in it. Running the one-liner installer here would just skip everything silently. Booo!

Rather than run someone else’s curl | bash against an agent it wasn’t built for, “““I””” reimplemented the terse-speak part natively, since pi already ships the two primitives needed: skills and extensions.

A skill for /skill:caveman documentation, and an extension that rewrites the system prompt on every turn via pi.on("before_agent_start", (event) => ...):

const INSTRUCTIONS = `Caveman mode: on. Respond terse. Drop articles (a/an/the), filler (just/really/basically), pleasantries, hedging. Fragments OK. Short synonyms. Technical terms exact. Pattern: [thing] [action] [reason]. [next step]. Example — not: "Sure! I'd be happy to help you with that." yes: "Bug in auth middleware. Fix:"
Boundaries, always: code blocks, commit messages, and PR descriptions stay normal full verbosity, never compressed. Drop caveman style for security warnings, irreversible/destructive actions, or when the user seems confused — resume caveman after.`;

export default function (pi: ExtensionAPI) {
  let on = true; // auto-on by default, every session

  const applyStatus = (ctx: { ui: { setStatus: (k: string, v?: string) => void } }) => {
    ctx.ui.setStatus("caveman", on ? "[caveman]" : undefined);
  };

  pi.on("session_start", async (_event, ctx) => applyStatus(ctx));

  pi.on("before_agent_start", (event) => {
    if (!on) return;
    return { systemPrompt: `${event.systemPrompt}\n\n${INSTRUCTIONS}` };
  });

  pi.registerCommand("caveman", {
    description: "Toggle caveman terse-response mode: on|off (default: on)",
    handler: async (args, ctx) => {
      const arg = args.trim().toLowerCase();
      if (arg === "off" || arg === "stop" || arg === "normal") on = false;
      else if (arg === "on" || arg === "") on = true;
      else return ctx.ui.notify(`Unknown arg "${arg}". Use: on | off`, "error");
      applyStatus(ctx);
      ctx.ui.notify(on ? "Caveman mode on." : "Caveman mode off.", "info");
    },
  });
}

before_agent_start fires on every prompt, before the agent loop starts, so the instructions are re-appended each turn instead of relying on one message that could get pruned from context. Dropped in ~/.pi/agent/extensions/caveman.ts, auto-discovered, no /reload needed after the first load.

Unlike the Claude Code plugin, I skipped lite/full/ultra/wenyan — I called that bloat back in June, and I’m not adding it to my own version either. On or off is enough.

The result, unprompted:

user: caveman on or off now?

assistant: Caveman: on.

user: how to turn it off?

assistant: /caveman off

I also skipped the parts that don’t have a pi equivalent: the statusline savings counter, /caveman-stats, the caveman-shrink MCP proxy that rewrites tool descriptions (a proxy that rewrites what an agent sees is exactly the kind of thing worth reading before installing). The 40-line extension above covers what I actually wanted.

One rule baked into both the skill and the extension: code, commits, and PRs stay full verbosity, never compressed.

This experience was an eye-opener for me to realize how bloated the upstream caveman project became.

🤖 Drafted with /bloggify.