docs(wiki): add pi agent integration guide

Document the pinb shell function that runs the Pi agent in a
notebrain-only mode: setup, flag breakdown, and usage. Link the
guide from the README documentation table.

Author: nmdra

README.md

@@ -197,6 +197,7 @@ To uninstall NoteBrain, remove the `notebrain` binary and delete the `~/.notebra
 | [Shell Completion](wiki/Shell_Completion.md)               | Tab completion setup for bash, zsh, and fish                             |
 | [AI Agent Skill Usage](wiki/Skill_Usage.md)                | Instructions for the built-in AI agent skill                             |
 | [OpenCode Agent Integration](wiki/OpenCode_Integration.md) | Configuration for NoteBrain as an OpenCode AI coding assistant           |
+| [Pi Agent Integration](wiki/Pi_Agent_Integration.md)       | Run the Pi agent in a notebrain-only mode against the vault              |
 | [DeepWiki](https://deepwiki.com/nmdra/notebrain-cli)       | AI-generated codebase documentation                                      |
 
 ## Contributing

wiki/Pi_Agent_Integration.md

@@ -0,0 +1,41 @@
+# Pi Agent Integration
+
+[Pi](https://pi.dev) is an AI coding and terminal agent. You can run Pi in a notebrain-only mode. In this mode, Pi loads one skill: the NoteBrain skill. The agent then works as a semantic retrieval assistant for your Obsidian vault.
+
+The `pinb` shell function sets up this mode. Put the function in `~/.zshrc`.
+
+---
+
+## The Setup (in `~/.zshrc`)
+
+```zsh
+# pi — notebrain-only mode: no extensions, skills, templates, or context files
+# --session-id pinb: always continues the same notebrain session (per project dir)
+pinb() {
+  pi -ne -ns -np -nc --skill "$HOME/.agents/skills/notebrain" --session-id pinb "$@"
+}
+```
+
+---
+
+## Flag Breakdown
+
+Verified against pi v0.83.0 source.
+
+| Flag                                 | Effect                                                                                                                                                                                                   |
+| ------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `-ne` / `--no-extensions`            | Disables extension discovery (vision proxy, web-access, pi-lens, usage, subagents). An explicit `-e path.ts` still loads.                                                                                |
+| `-ns` / `--no-skills`                | Disables skill **discovery**. An explicit `--skill <path>` still loads. In `resource-loader.js`: `noSkills ? mergePaths(cliEnabledSkills, additionalSkillPaths) : …`.                                    |
+| `-np` / `--no-prompt-templates`      | No `/explain`, `/brief`, `/commit`, package templates.                                                                                                                                                   |
+| `-nc` / `--no-context-files`         | No `AGENTS.md` / `CLAUDE.md` (global and project).                                                                                                                                                       |
+| `--skill ~/.agents/skills/notebrain` | Loads only the notebrain skill.                                                                                                                                                                          |
+| `--session-id pinb`                  | Reuses the same session on every run. The first run creates it. Later runs load it (`main.js`: `findLocalSessionByExactId` → load, else create). The id must match `^[A-Za-z0-9._-]+$`. `pinb` is valid. |
+| `"$@"`                               | Passes through extra arguments to pi. For example: `pinb "find notes about X"`, `pinb -p "…"` (one-shot).                                                                                                |
+
+## Usage
+
+```bash
+pinb                                # continue the persistent notebrain session
+pinb "what do I know about Redis?"  # launch with a prompt
+pinb -p "summarize my notes on K8s" # one-shot, prints result, exits
+```