feat: add Pi as first-class Mosaic runtime (#339)

packages/mosaic/src/runtime/detector.ts

@@ -33,6 +33,12 @@ const RUNTIME_DEFS: Record<
     versionFlag: 'version',
     installHint: 'See https://opencode.ai for install instructions',
   },
+  pi: {
+    label: 'Pi',
+    command: 'pi',
+    versionFlag: '--version',
+    installHint: 'npm install -g @mariozechner/pi-coding-agent',
+  },
 };
 
 export function detectRuntime(name: RuntimeName): RuntimeInfo {

packages/mosaic/src/runtime/installer.ts

@@ -7,6 +7,7 @@ export function formatInstallInstructions(name: RuntimeName): string {
     claude: 'Claude Code',
     codex: 'Codex',
     opencode: 'OpenCode',
+    pi: 'Pi',
   };
   return `To install ${labels[name]}:\n  ${hint}`;
 }

packages/mosaic/src/runtime/mcp-config.ts

@@ -16,6 +16,8 @@ export function configureMcpForRuntime(runtime: RuntimeName): void {
       return configureCodexMcp();
     case 'opencode':
       return configureOpenCodeMcp();
+    case 'pi':
+      return configurePiMcp();
   }
 }
 
@@ -69,6 +71,31 @@ function configureCodexMcp(): void {
   writeFileSync(configPath, content, 'utf-8');
 }
 
+function configurePiMcp(): void {
+  const settingsPath = join(homedir(), '.pi', 'agent', 'settings.json');
+  ensureDir(settingsPath);
+
+  let data: Record<string, unknown> = {};
+  if (existsSync(settingsPath)) {
+    try {
+      data = JSON.parse(readFileSync(settingsPath, 'utf-8')) as Record<string, unknown>;
+    } catch {
+      // Start fresh if corrupt
+    }
+  }
+
+  if (
+    !data['mcpServers'] ||
+    typeof data['mcpServers'] !== 'object' ||
+    Array.isArray(data['mcpServers'])
+  ) {
+    data['mcpServers'] = {};
+  }
+  (data['mcpServers'] as Record<string, unknown>)['sequential-thinking'] = MCP_ENTRY;
+
+  writeFileSync(settingsPath, JSON.stringify(data, null, 2) + '\n', 'utf-8');
+}
+
 function configureOpenCodeMcp(): void {
   const configPath = join(homedir(), '.config', 'opencode', 'config.json');
   ensureDir(configPath);