feat: restructure as pnpm monorepo workspace

- Move limit-turns.ts into packages/pi-turn-limit/src/index.ts
- Add root package.json (private workspace manifest)
- Add pnpm-workspace.yaml
- Add shared tsconfig.json
- Add pi package manifest to extension (pi.extensions, pi-package keyword)
- Update AGENTS.md with monorepo workflow

.gitignore

@@ -0,0 +1,3 @@
+node_modules/
+.pnpm-store/
+pnpm-lock.yaml

AGENTS.md

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+This is a monorepo for pi extensions using pnpm workspaces.
+
+## Structure
+
+```
+packages/
+  pi-turn-limit/   # First extension: limits the number of turns
+```
+
+## Development
+
+```bash
+pnpm install          # Install all workspace dependencies
+```
+
+Each extension lives in `packages/<name>/` with its own `package.json`.
+The root `package.json` is the workspace manifest.
+
+## Adding a new extension
+
+1. Create `packages/<name>/` directory
+2. Add `package.json` with `"pi-package"` keyword and `pi.extensions` manifest
+3. Put source in `packages/<name>/src/index.ts`
+4. Run `pnpm install`
+
+## Extension packaging
+
+Extensions are loaded by pi as TypeScript files via jiti (no compilation needed).
+The `pi` key in `package.json` tells pi which files to load.
+
+See `~/.local/share/mise/installs/node/24.0.1/lib/node_modules/@mariozechner/pi-coding-agent/docs/extensions.md`
+and `packages.md` for full details.

package.json

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+{
+  "name": "pi-extensions",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Pi coding agent extensions monorepo",
+  "type": "module",
+  "license": "MIT",
+  "engines": {
+    "node": ">=24"
+  }
+}

packages/pi-turn-limit/package.json

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+{
+  "name": "pi-turn-limit",
+  "version": "0.1.0",
+  "description": "Pi coding agent extension to limit number of turns taken by a model",
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "keywords": ["pi-package"],
+  "pi": {
+    "extensions": ["src/index.ts"]
+  },
+  "peerDependencies": {
+    "@mariozechner/pi-coding-agent": "*"
+  },
+  "license": "MIT"
+}

packages/pi-turn-limit/src/index.ts

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+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+
+// ============================================================================
+// Configuration
+// ============================================================================
+
+const DEFAULT_MAX_TURNS = 25;
+
+function getMaxTurns(): number {
+  const env = process.env.PI_MAX_TURNS;
+  if (!env) return DEFAULT_MAX_TURNS;
+  const parsed = parseInt(env, 10);
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : DEFAULT_MAX_TURNS;
+}
+
+// ============================================================================
+// Pure detection logic (testable)
+// ============================================================================
+
+export function checkTurnLimit(
+  turnIndex: number,
+  maxTurns: number,
+): { exceeded: boolean; turnIndex: number; maxTurns: number } {
+  return {
+    exceeded: turnIndex > maxTurns,
+    turnIndex,
+    maxTurns,
+  };
+}
+
+// ============================================================================
+// Extension handler
+// ============================================================================
+
+export default function (pi: ExtensionAPI) {
+  let turnCount = 0;
+  const maxTurns = getMaxTurns();
+
+  pi.on("agent_start", async (_event, ctx) => {
+    // Reset counter for each new user prompt
+    turnCount = 0;
+  });
+
+  pi.on("turn_start", async (event, ctx) => {
+    turnCount++;
+
+    const { exceeded } = checkTurnLimit(event.turnIndex, maxTurns);
+    if (exceeded && ctx.hasUI) {
+      ctx.ui.notify(
+        `Turn limit exceeded: ${maxTurns} turns reached. Agent aborted.`,
+        "error",
+      );
+      ctx.abort();
+    }
+  });
+}

pnpm-workspace.yaml

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+packages:
+  - "packages/*"

tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true
+  },
+  "include": ["packages/**/*"],
+  "exclude": ["node_modules"]
+}