feat: add pi-coding-agent support

openspec/changes/archive/2026-01-21-add-pi-coding-agent/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-01-21

openspec/changes/archive/2026-01-21-add-pi-coding-agent/design.md

@@ -0,0 +1,51 @@
+## Context
+
+OpenSpec supports 21 AI coding assistants through a plugin-based architecture:
+- `ToolConfigurator` for root config files (e.g., CLAUDE.md)
+- `SlashCommandConfigurator` for slash command files (e.g., `.claude/commands/`)
+- `ToolRegistry` and `SlashCommandRegistry` for registration
+- `AI_TOOLS` array in `config.ts` for UI display
+
+Pi-coding-agent from badlogic/pi-mono already supports AGENTS.md files natively, so only slash command support is needed.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Enable pi users to select "Pi" during `openspec init`
+- Generate `/openspec-proposal`, `/openspec-apply`, `/openspec-archive` commands in `.pi/prompts/`
+- Follow pi's expected format: `.md` files with YAML frontmatter containing `description`
+
+**Non-Goals:**
+- Creating a separate PI.md root config file (pi reads AGENTS.md already)
+- Supporting pi's `$1`/`$@` argument syntax (not needed for OpenSpec commands)
+- Global installation support (pi prompts are project-local in `.pi/prompts/`)
+
+## Decisions
+
+### 1. Slash command file location: `.pi/prompts/openspec-*.md`
+
+**Rationale**: Pi-coding-agent loads custom commands from `.pi/prompts/*.md` where the filename becomes the command name. Using `openspec-proposal.md` creates `/openspec-proposal`.
+
+**Alternatives considered**:
+- `.pi/commands/` - Not a valid pi location
+- Global `~/.pi/agent/prompts/` - Would apply to all projects, not project-specific
+
+### 2. YAML frontmatter with `description` only
+
+**Rationale**: Pi requires minimal frontmatter - just `description`. Unlike Continue (which needs `invokable: true`) or Gemini (TOML format), pi keeps it simple.
+
+```yaml
+---
+description: Scaffold a new OpenSpec change and validate strictly.
+---
+```
+
+### 3. No ToolConfigurator needed
+
+**Rationale**: Pi-coding-agent already reads AGENTS.md files in priority order (global → parent dirs → current dir). The existing root AGENTS.md stub is sufficient. Adding a separate PI.md would be redundant.
+
+## Risks / Trade-offs
+
+**[Risk]** Pi's format may change in future versions → **Mitigation**: Implementation follows current documented format from pi-mono README. Format is stable and matches standard markdown with YAML frontmatter pattern.
+
+**[Trade-off]** No root PI.md file means pi users don't get the visual confirmation of a dedicated config file → **Acceptable**: Pi's AGENTS.md support means the existing stub works. Less file clutter is preferable.

openspec/changes/archive/2026-01-21-add-pi-coding-agent/proposal.md

@@ -0,0 +1,28 @@
+## Why
+
+Pi-coding-agent from [badlogic/pi-mono](https://github.com/badlogic/pi-mono) is a growing terminal-based coding agent with multi-model support, mid-session model switching, and RPC mode for programmatic integration. It supports the AGENTS.md standard and has its own slash command system via `.pi/prompts/*.md` files. Adding OpenSpec support enables pi users to use the proposal/apply/archive workflow natively.
+
+## What Changes
+
+- Add "Pi" as a new supported AI tool in the tool selection list
+- Create slash command configurator for pi's `.pi/prompts/*.md` format
+- Register pi in the SlashCommandRegistry
+
+Pi-coding-agent already reads AGENTS.md files, so no separate tool configurator is needed for project instructions - the existing AGENTS.md support covers that.
+
+## Capabilities
+
+### New Capabilities
+- `pi-slash-commands`: Slash command generation for pi-coding-agent using `.pi/prompts/*.md` format with YAML frontmatter
+
+### Modified Capabilities
+- `tool-registry`: Add pi to the AI_TOOLS list and SlashCommandRegistry
+
+## Impact
+
+- **Code**:
+  - `src/core/config.ts` - add pi to AI_TOOLS array
+  - `src/core/configurators/slash/pi.ts` - new slash command configurator
+  - `src/core/configurators/slash/registry.ts` - register pi configurator
+- **User-facing**: Pi users can select "Pi" during `openspec init` and get `/openspec-proposal`, `/openspec-apply`, `/openspec-archive` commands
+- **Dependencies**: None - uses existing slash command infrastructure

openspec/changes/archive/2026-01-21-add-pi-coding-agent/tasks.md

@@ -0,0 +1,21 @@
+## 1. Configuration
+
+- [x] 1.1 Add pi to AI_TOOLS array in `src/core/config.ts` with name "Pi", value "pi", available true, successLabel "Pi"
+
+## 2. Slash Command Configurator
+
+- [x] 2.1 Create `src/core/configurators/slash/pi.ts` implementing `PiSlashCommandConfigurator`
+- [x] 2.2 Define FILE_PATHS mapping for `.pi/prompts/openspec-{proposal,apply,archive}.md`
+- [x] 2.3 Define FRONTMATTER with `description` field for each command
+- [x] 2.4 Implement `getRelativePath()` and `getFrontmatter()` methods
+
+## 3. Registry
+
+- [x] 3.1 Import `PiSlashCommandConfigurator` in `src/core/configurators/slash/registry.ts`
+- [x] 3.2 Instantiate and register pi configurator in the static block
+
+## 4. Verification
+
+- [x] 4.1 Run `bun run build` to verify TypeScript compiles
+- [x] 4.2 Run `bun run test` to verify existing tests pass
+- [x] 4.3 Test `openspec init --tools pi` generates expected files in `.pi/prompts/`

openspec/specs/cli-init/spec.md

@@ -230,6 +230,13 @@ The init command SHALL generate slash command files for supported editors using
 - **AND** populate each file from shared templates so command text matches other tools
 - **AND** each template includes instructions for the relevant OpenSpec workflow stage
 
+#### Scenario: Generating slash commands for Pi
+- **WHEN** the user selects Pi during initialization
+- **THEN** create `.pi/prompts/openspec-proposal.md`, `.pi/prompts/openspec-apply.md`, and `.pi/prompts/openspec-archive.md`
+- **AND** populate each file with YAML frontmatter containing only a `description` field that summarizes the workflow stage
+- **AND** wrap the shared template body with OpenSpec markers so `openspec update` can refresh the content
+- **AND** each template includes instructions for the relevant OpenSpec workflow stage
+
 #### Scenario: Generating slash commands for Windsurf
 - **WHEN** the user selects Windsurf during initialization
 - **THEN** create `.windsurf/workflows/openspec-proposal.md`, `.windsurf/workflows/openspec-apply.md`, and `.windsurf/workflows/openspec-archive.md`

src/core/config.ts

@@ -34,6 +34,7 @@ export const AI_TOOLS: AIToolOption[] = [
   { name: 'iFlow', value: 'iflow', available: true, successLabel: 'iFlow' },
   { name: 'Kilo Code', value: 'kilocode', available: true, successLabel: 'Kilo Code' },
   { name: 'OpenCode', value: 'opencode', available: true, successLabel: 'OpenCode' },
+  { name: 'Pi', value: 'pi', available: true, successLabel: 'Pi' },
   { name: 'Qoder (CLI)', value: 'qoder', available: true, successLabel: 'Qoder' },
   { name: 'Qwen Code', value: 'qwen', available: true, successLabel: 'Qwen Code' },
   { name: 'RooCode', value: 'roocode', available: true, successLabel: 'RooCode' },

src/core/configurators/slash/pi.ts

@@ -0,0 +1,42 @@
+import { SlashCommandConfigurator } from './base.js';
+import { SlashCommandId } from '../../templates/index.js';
+
+const FILE_PATHS: Record<SlashCommandId, string> = {
+  proposal: '.pi/prompts/openspec-proposal.md',
+  apply: '.pi/prompts/openspec-apply.md',
+  archive: '.pi/prompts/openspec-archive.md'
+};
+
+/*
+ * Pi-coding-agent .pi/prompts format uses YAML frontmatter with description:
+ * ---
+ * description: description text
+ * ---
+ * Body...
+ *
+ * The filename becomes the command name, so openspec-proposal.md becomes /openspec-proposal.
+ */
+const FRONTMATTER: Record<SlashCommandId, string> = {
+  proposal: `---
+description: Scaffold a new OpenSpec change and validate strictly.
+---`,
+  apply: `---
+description: Implement an approved OpenSpec change and keep tasks in sync.
+---`,
+  archive: `---
+description: Archive a deployed OpenSpec change and update specs.
+---`
+};
+
+export class PiSlashCommandConfigurator extends SlashCommandConfigurator {
+  readonly toolId = 'pi';
+  readonly isAvailable = true;
+
+  protected getRelativePath(id: SlashCommandId): string {
+    return FILE_PATHS[id];
+  }
+
+  protected getFrontmatter(id: SlashCommandId): string {
+    return FRONTMATTER[id];
+  }
+}

src/core/configurators/slash/registry.ts

@@ -20,6 +20,7 @@ import { RooCodeSlashCommandConfigurator } from './roocode.js';
 import { AntigravitySlashCommandConfigurator } from './antigravity.js';
 import { IflowSlashCommandConfigurator } from './iflow.js';
 import { ContinueSlashCommandConfigurator } from './continue.js';
+import { PiSlashCommandConfigurator } from './pi.js';
 
 export class SlashCommandRegistry {
   private static configurators: Map<string, SlashCommandConfigurator> = new Map();
@@ -46,6 +47,7 @@ export class SlashCommandRegistry {
     const antigravity = new AntigravitySlashCommandConfigurator();
     const iflow = new IflowSlashCommandConfigurator();
     const continueTool = new ContinueSlashCommandConfigurator();
+    const pi = new PiSlashCommandConfigurator();
 
     this.configurators.set(claude.toolId, claude);
     this.configurators.set(codeBuddy.toolId, codeBuddy);
@@ -68,6 +70,7 @@ export class SlashCommandRegistry {
     this.configurators.set(antigravity.toolId, antigravity);
     this.configurators.set(iflow.toolId, iflow);
     this.configurators.set(continueTool.toolId, continueTool);
+    this.configurators.set(pi.toolId, pi);
   }
 
   static register(configurator: SlashCommandConfigurator): void {