https://aibussin.com/categories/typescript/ Recent content in TypeScript on AIBussin — AI applications, systems and books Hugo en-US Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/15-chapter/ Fri, 02 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/15-chapter/ <p>The review guard can instruct the model to run <code>scripts/run-checks.sh</code>, but a skill cannot itself register a new model-callable operation, intercept tool execution, or register a status display. Those integrations need an extension; the script a skill asks the model to run is still executable code, but it is not an extension hook.</p> <p>This chapter builds the smallest extension that does something a skill cannot.</p> <h2 id="what-an-extension-is">What an extension is</h2> <p><code>extensions.md</code>: extensions are TypeScript modules loaded into the Pi process, and their factory functions register tools, commands, shortcuts, providers, event handlers, renderers, and terminal UI.</p> https://aibussin.com/books/pi/16-chapter/ Fri, 02 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/16-chapter/ <p>The review guard can suggest running the checks. It cannot stop a <code>git push --force</code> that the model decides to run while fixing a conflict.</p> <p>A <code>tool_call</code> handler can block a matching invocation of a tool before its body runs. That makes it a useful extension-level guard, not an unconditional prohibition: commands can reach the same effect through other tools or paths the handler does not inspect. Getting this right requires knowing the lifecycle, because handlers run in registration order and a return value only matters for events declared to accept one.</p> https://aibussin.com/books/pi/17-chapter/ Fri, 02 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/17-chapter/ <p><a href="https://aibussin.com/books/pi/15-chapter/">Chapter 15&rsquo;s</a> <code>review-scope</code> tool told the model which command to run. That is a tool shaped like a suggestion. This chapter turns it into a tool shaped like a tool: It can execute work, return structured data, publish risk hints, and control how it is exposed to the model.</p> <h2 id="five-exposures">Five exposures</h2> <p><code>exposure</code> controls how the model reaches a tool. &ldquo;Callable&rdquo; means callable from other tools through <code>ctx.executeTool()</code> — which is what <code>codemode</code> scripts do.</p> https://aibussin.com/books/pi/36-chapter/ Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/36-chapter/ <p>Everything so far has run inside a coding agent. You have been using a tool that reads files, runs commands and keeps a session, and you have been attaching to it. That is the right place to start, because Pi&rsquo;s host is where most people meet Pi.</p> <p>It is the wrong place to stop, because most of what an application needs from a model is not an agent. It is one question and one answer: <em>is this claim supported by this evidence?</em> One input, one typed result, nothing to run, nothing to remember.</p> https://aibussin.com/books/pi/37-chapter/ Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/37-chapter/ <p>The claim checker from <a href="https://aibussin.com/books/pi/36-chapter/">chapter 36</a> has a limit. Given the evidence you handed it, it can produce a schema-valid assessment, including <code>insufficient</code> when the evidence is inadequate. It cannot independently fetch more evidence in that single call, and the model may still judge the evidence incorrectly.</p> <p>Looking for more is a loop: the model asks for something, you run it, you give the result back, and the model decides again. You have seen that loop for thirty-six chapters, from the outside. This chapter runs it from the inside, in about forty lines, using the same class the coding agent is built on.</p> https://aibussin.com/books/pi/38-chapter/ Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/38-chapter/ <p>An unconstrained agent may finish with prose, and prose is a fragile interface between software components.</p> <p>You can pass a paragraph to another function, but branching on its meaning requires interpretation or parsing whose behavior you must define and test. An ordinary agent can stop after deciding it is finished, without producing the structure a downstream function expects. This chapter puts a validated value at that boundary instead.</p> <p><a href="https://aibussin.com/books/pi/36-chapter/">Chapter 36</a> fixed this for a single call. This chapter fixes it for a loop. The result is the most reusable idea in the book, and it fits in one function.</p> https://aibussin.com/books/pi/39-chapter/ Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/39-chapter/ <p><a href="https://aibussin.com/books/pi/01-chapter/">Chapter 1</a> ended on a sentence that has been quietly organising the book since:</p> <blockquote> <p>An extension point is a real architectural seam only for decisions it can intercept before those decisions become irreversible.</p> </blockquote> <p>It was stated there as a finding about forks of the coding agent, and it was argued from three cases. This chapter tests it on something you can run. The agent core has nine function-shaped options that run around a request or a tool call, and for each one the useful question is not <em>what does it give me</em> but <em>what can I still decide by the time it fires</em>.</p> https://aibussin.com/books/pi/40-chapter/ Sun, 04 Oct 2026 09:00:00 +0100 https://aibussin.com/books/pi/40-chapter/ <p>The tempting next move is to make every part of the pipeline an agent. One agent retrieves, another assesses, another summarises, and they talk. That may be useful when the tasks genuinely require independent decisions or work, but it introduces more model calls, coordination and failure paths than this claim checker needs.</p> <p>This chapter is the argument against doing that by default, made with a pipeline you can run. The rule it demonstrates:</p>