feat: add built-in browser tool

Add a first-class browser tool backed by agent-browser and enable it by default in coding sessions.

Include CLI and system-prompt wiring plus focused coverage for the new tool.

Co-authored-by: Codex <noreply@openai.com>

packages/coding-agent/src/cli/args.ts

@@ -5,7 +5,11 @@
 import type { ThinkingLevel } from "@mariozechner/pi-agent-core";
 import chalk from "chalk";
 import { APP_NAME, CONFIG_DIR_NAME, ENV_AGENT_DIR } from "../config.js";
-import { allTools, type ToolName } from "../core/tools/index.js";
+import {
+  allTools,
+  defaultCodingToolNames,
+  type ToolName,
+} from "../core/tools/index.js";
 
 export type Mode = "text" | "json" | "rpc";
 
@@ -193,7 +197,11 @@ export function parseArgs(
 }
 
 export function printHelp(): void {
-  console.log(`${chalk.bold(APP_NAME)} - AI coding assistant with read, bash, edit, write tools
+  const defaultToolsText = defaultCodingToolNames.join(",");
+  const availableToolsText = Object.keys(allTools).join(", ");
+  const defaultToolsLabel = defaultCodingToolNames.join(", ");
+
+  console.log(`${chalk.bold(APP_NAME)} - AI coding assistant with read, bash, browser, edit, write tools
 
 ${chalk.bold("Usage:")}
   ${APP_NAME} [options] [@files...] [messages...]
@@ -224,8 +232,8 @@ ${chalk.bold("Options:")}
   --models <patterns>            Comma-separated model patterns for Ctrl+P cycling
                                  Supports globs (anthropic/*, *sonnet*) and fuzzy matching
   --no-tools                     Disable all built-in tools
-  --tools <tools>                Comma-separated list of tools to enable (default: read,bash,edit,write)
-                                 Available: read, bash, edit, write, grep, find, ls
+  --tools <tools>                Comma-separated list of tools to enable (default: ${defaultToolsText})
+                                 Available: ${availableToolsText}
   --thinking <level>             Set thinking level: off, minimal, low, medium, high, xhigh
   --extension, -e <path>         Load an extension file (can be used multiple times)
   --no-extensions, -ne           Disable extension discovery (explicit -e paths still work)
@@ -322,9 +330,10 @@ ${chalk.bold("Environment Variables:")}
   PI_SHARE_VIEWER_URL              - Base URL for /share command (default: https://pi.dev/session/)
   PI_AI_ANTIGRAVITY_VERSION        - Override Antigravity User-Agent version (e.g., 1.23.0)
 
-${chalk.bold("Available Tools (default: read, bash, edit, write):")}
+${chalk.bold(`Available Tools (default: ${defaultToolsLabel}):`)}
   read   - Read file contents
   bash   - Execute bash commands
+  browser - Browser automation with persistent state
   edit   - Edit files with find/replace
   write  - Write files (creates/overwrites)
   grep   - Search file contents (read-only, off by default)