as it happens - draft, needs editing

app/priv/blog/engineering/2026/04-18-coding-agent-generates-its-own-extensions.md

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+%{
+  title: "Coding agent generates its' own extensions",
+  author: "Willem van den Ende",
+  tags: ~w(ai loops),
+  description: "Handwritten note",
+  published: false
+}
+---
+
+I see a few people writing about
+sharing struggles with Llm's.
+
+for me it is easier to do at
+the moment of a small success.
+
+The challenge with writing about
+my experiments is that it gets meta pretty quickly.
+
+therefore I am going to leave out
+a bunch of things, including this commentary.
+
+the other day I tried to develop on
+extension for pi - the shitty coding agent, that would stop a model when it
+goes off the rails.
+
+I now have a local model that
+is fast, can call tools (edit Files, run test, etc) edit code etc.
+
+It does, however, perform some model assisted coding quinks frequently:
+
+- replace production code that Works With throwing an exception
+
+- write if statements in tests
+- add fallbacks for things that can't fail
+
+- Find "problems" in that works
+	(passes tests + other checks, works for
+		the user etc)
+
+Long form the Solution probably is to work
+in small Steps. But these steps come From
+experience.
+
+Catching the hovel when it happens by
+simply matching Some Lords is a starting point for that: scan for key words in
+any edits on a prompt the user for permission, or abort when the session is not interactive.
+
+Looks simple, so I let a more powerful
+but slower local model figure out how to build an extensions - pi has a system prompt for that -. After cone iteration
+we had a plan and pi generated d
+plausible looking extension.
+
+I tested it manually, in pi. Nothing happened. Back to the drawing board.
+
+I had quite a few iterations, compared with
+sample code, looked into the pi API,
+70 luck.
+
+Eventually I installed the sample extension. that worked. then I deleted most of my
+extension, added some logging - I could
+see sore thing.
+
+I learned while a bit about pi and its extension mechanism.
+
+It looks like only the last "UI notification" gets shown for any exension point (e.g. a fool call or system startup).
+
+I am not get sure if this is by design or not.
+
+I did take away the, here too, I wont to work test-first for parts that do not interface
+with the agent directly. The feedback loop
+is just too slow.
+
+this also ren vired experimentation. I did not want to set up a separate project for
+an extension that is little more than an idea. But I do want tests
+
+to asked a model again. and suggestion was
+to use Deno, because that has testing built
+in. Some more Fiddlig Adowed:
+
+- get Dena to work in the Sandbox
+- Learn that pi auto loads any thing in
+	the excusions folder. If you put a test there,
+	pi crashes
+- learn that" domain" files also don't work there.
+
+So eventually I ended up with
+
+```
+- .pi/ test
+	/ core
+	/ extensions
+```
+
+Core contains the functional cores tests ter the core, exertion, is a thin integration with
+pi that uses the core.
+
+this was clear enough that the slow, dense model could build a second extension & performance metrics in chat.) with relatively little guidance after iterations on a plan.
+
+I haven't looked at the code bet. not
+out of principle, but because it is late,
+and I want to write down my trial and error before I forget.
+
+TODO link pdf
+TODO add image from scan (in downloads)