init pi folder

extensions/README.md

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+# Shared dependency workspace for Pi extensions
+
+This directory is the single workspace root for local custom Pi extensions.
+
+## Layout
+- Root-level `package.json` + one shared `node_modules`
+- Extensions loaded from this tree as:
+  - `*.ts` files under this root, or
+  - subfolders containing `index.ts` (current: `multiagent/`, `subagent/`)
+
+This preserves Pi auto-discovery and `/reload` behavior.
+
+## Dependency policy
+- Declare shared dependencies only in `extensions/package.json`.
+- Do not add per-extension `package.json`/`node_modules` unless you intentionally need isolation.
+
+## Note about `pi install` packages
+Extensions installed via `pi install` are isolated package roots by design and do not share this workspace `node_modules`.
+If you need dependency sharing across those, consolidate them into a single package/workspace you control and load that package instead.