Pi Extensions — LLM Master Reference

Start Here (Read Order)

Priority	Document	Read When
1	`ARCHITECTURE.md`	Before writing ANY extension code
2	`PATTERNS.md`	When you need copy-paste code for a specific task
3	`ANTI-PATTERNS.md`	When reviewing or debugging extension code

The guides/ and references/ directories contain deeper narratives and examples. Use them after scanning the three master docs above.

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One-Line Directives

• Writing a new extension? → Read `ARCHITECTURE.md` §1–§5, then copy the matching pattern from `PATTERNS.md`.
• Extension is broken? → Check `ANTI-PATTERNS.md` first.
• Need TUI component? → `PATTERNS.md` §P12–§P14, then `guides/02-paradigms.md` for narrative.
• Need beautiful TUI rendering? → `references/tui-beautiful-rendering.md` — box drawing, overlays, badges, SVG widgets.
• Need multi-agent patterns? → `references/extension-patterns-from-source.md` — agent coordination, tasks, feeds.
• Need custom provider/OAuth? → `PATTERNS.md` §P19–§P20, then `guides/07-advanced-patterns.md`.
• Need RPC safety? → `ANTI-PATTERNS.md` §A2, then `guides/05-rpc-mode.md`.

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Master Decision Trees

Which document do I need?

I need to understand how extensions work
  └─► ARCHITECTURE.md

I need working code to copy
  └─► PATTERNS.md

I need to know what NOT to do
  └─► ANTI-PATTERNS.md

I need a step-by-step first tutorial
  └─► guides/01-quickstart.md

I need deep narrative on tools/events/UI
  └─► guides/02-paradigms.md

I need state persistence strategies
  └─► guides/03-state.md

I need production architecture (workflows, memory)
  └─► guides/04-production.md

I need RPC mode specifics
  └─► guides/05-rpc-mode.md

I need pi internals (loader, runner, binding)
  └─► guides/06-internals.md

I need provider plugins, OAuth, overrides
  └─► guides/07-advanced-patterns.md

Which paradigm should I use?

Need LLM to perform action? ───────────────► Tool (PATTERNS P2–P5)
Need user to type /command? ───────────────► Command (PATTERNS P6–P7)
Need keyboard shortcut? ───────────────────► Shortcut (guides/02-paradigms.md)
Need to react to system events? ───────────► Event handler (PATTERNS P8–P11)
Need interactive TUI? ─────────────────────► Custom UI (PATTERNS P12–P14)
Need to inject a model provider? ──────────► registerProvider (PATTERNS P19–P20)
Need to override a built-in tool? ─────────► Tool override (PATTERNS P4)

Which state persistence mechanism?

State should go to LLM context? ───────────► sendMessage({ customType, ... })
State is extension-private? ───────────────► appendEntry("customType", data)
State is user preference (cross-project)? ─► File in ~/.pi/agent/
State is project-local? ───────────────────► File in .pi/
State is temporary cache? ─────────────────► Local variable (reconstructed on reload)

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Document Map

Master References (Read First)

File	Purpose	Length
`ARCHITECTURE.md`	Mental model, execution flow, exact event semantics	~9KB
`PATTERNS.md`	38 copy-paste patterns with exact imports	~17KB
`ANTI-PATTERNS.md`	15 common mistakes with corrections	~9KB

Progressive Guides (Read as Needed)

File	Level	Topic
`guides/01-quickstart.md`	🌱 Beginner	First extension in 5 minutes
`guides/02-paradigms.md`	🌿 Intermediate	Tools, commands, events, UI deep dive
`guides/03-state.md`	🌳 Advanced	Persistent and branch-resilient state
`guides/04-production.md`	🏔️ Expert	Multi-mode, workflows, memory systems
`guides/05-rpc-mode.md`	🔌 RPC	RPC mode compatibility and degradation
`guides/06-internals.md`	⚙️ Internals	Loader, runner, event dispatch, binding
`guides/07-advanced-patterns.md`	🚀 Advanced	Provider plugins, OAuth, tool overrides, file mutation queues

Reference Docs

File	Purpose
`references/api.md`	Complete API documentation
`references/api-quickref.md`	Quick reference card
`references/events.md`	Full event reference
`references/examples.md`	Additional code examples
`references/ui-components.md`	TUI component catalog
`references/extension-patterns-from-source.md`	Multi-agent, diff rendering, config patterns from 10+ extensions
`references/tui-beautiful-rendering.md`	Beautiful TUI: box drawing, transcript, overlays, badges, SVG/HTML widgets

Tutorials

File	Topic
`tutorials/tool-browser.md`	Build a searchable tool list with fuzzy filtering

Examples

File	Purpose
`examples/gallery.md`	Annotated real-world extensions

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5-Minute Quick Test

Prerequisite: This skill is installed (cloned to skills/pi-extensions).
Below creates a sample Extension, placed in ~/.pi/agent/extensions/ — separate from the skill directory.

# 1. Create the sample extension file
mkdir -p ~/.pi/agent/extensions
cat > ~/.pi/agent/extensions/hello.ts << 'EOF'
import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";

export default function (pi: ExtensionAPI) {
  pi.registerCommand("hello", {
    description: "Say hello",
    handler: async (_args, ctx) => {
      ctx.ui.notify("Hello from Pi Extensions!", "success");
    },
  });
}
EOF

# 2. Test with -e flag (temporary load)
pi -e ~/.pi/agent/extensions/hello.ts
# Then type: /hello
#
# Tip: Extensions in ~/.pi/agent/extensions/ are auto-discovered.
#      The -e flag is only needed for temporary testing.

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Quick Import Cheat Sheet

// Core types
import type { ExtensionAPI, ExtensionContext } from "@earendil-works/pi-coding-agent";

// Schema
import { Type } from "@sinclair/typebox";
import { StringEnum } from "@earendil-works/pi-ai";

// TUI
import { Container, Text, SelectList } from "@earendil-works/pi-tui";

// Utilities
import { withFileMutationQueue } from "@earendil-works/pi-coding-agent";
import { isToolCallEventType, isBashToolResult } from "@earendil-works/pi-coding-agent";

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Hot Topics

Dynamic Model Injection

Use pi.registerProvider() for proxies, custom endpoints, or team-wide model configs. See `PATTERNS.md` §P19–P20 and `guides/07-advanced-patterns.md`.

Tool Override

Register a tool with the same name as a built-in (read, bash, edit, write) to wrap or replace it. See `PATTERNS.md` §P4.

Parallel Execution Safety

Custom tools that mutate files must use withFileMutationQueue() to avoid race conditions with built-in edit/write. See `PATTERNS.md` §P5 and `ANTI-PATTERNS.md` §A4.

RPC Safety

ctx.hasUI is true in RPC, but custom() returns undefined. Use select/confirm/input/editor for blocking dialogs that work in both modes. See `ANTI-PATTERNS.md` §A2 and `guides/05-rpc-mode.md`.

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Master references: ARCHITECTURE · PATTERNS · ANTI-PATTERNS