Add custom agents and Flutter accessibility agent documentation

sites/docs/src/content/ai/get-started.md

@@ -20,16 +20,19 @@ An **agent plugin** bundles the tools and knowledge that an AI assistant needs
 to understand and modify your Flutter codebase.
 
 When you install an official Flutter agent plugin, it connects your assistant
-to two core capabilities:
+to three core capabilities:
 
-* **[Agent skills](/ai/tools#agent-skills)**: On-demand procedural guides from
+* **[Agent skills](/ai/tools#agent-skills)**: on-demand procedural guides from
   the official Flutter and Dart repositories that teach the assistant how to
   perform specific tasks, such as creating responsive layouts, managing state,
   or writing widget tests.
 * **[Dart and Flutter MCP server](/ai/tools#dart-and-flutter-mcp-server)**:
-  A Model Context Protocol (MCP) server that connects the assistant to the
+  a Model Context Protocol (MCP) server that connects the assistant to the
   Dart SDK, giving it real-time access to analyzer diagnostics, symbol
   resolution, test runners, and runtime inspection.
+* **[Specialized agents](/ai/tools#specialized-agents)**: focused assistant
+  personas tailored for dedicated workflows, such as the Flutter Accessibility
+  (`a11y`) agent for automated accessibility audits and code fixes.
 
 These tools work together automatically: the assistant uses MCP tools to query
 live project state and static analysis, while using agent skills to guide its

sites/docs/src/content/ai/tools.md

@@ -12,18 +12,21 @@ development tasks accurately.
 
 ## Tooling ecosystem overview
 
-The Flutter AI tooling ecosystem consists of four complementary components:
+The Flutter AI tooling ecosystem consists of five complementary components:
 
-1. **Agent skills**: Task-oriented blueprints that teach assistants how to
+1. **Agent skills**: task-oriented blueprints that teach assistants how to
    perform specific workflows (such as creating responsive layouts or writing
    tests).
-2. **Dart and Flutter MCP server**: A Model Context Protocol (MCP) server
+2. **Dart and Flutter MCP server**: a Model Context Protocol (MCP) server
    exposing real-time SDK diagnostics, symbol resolution, and runtime
    introspection to assistants.
-3. **Developer Knowledge MCP server**: A cloud-hosted documentation search
+3. **Developer Knowledge MCP server**: a cloud-hosted documentation search
    server giving assistants direct access to official Flutter and Dart docs.
-4. **Package skills**: Skills published directly inside third-party `pub.dev`
+4. **Package skills**: skills published directly inside third-party `pub.dev`
    packages, giving assistants instant expertise on specific libraries.
+5. **Specialized agents**: dedicated agent personas equipped with focused tools
+   and system instructions for isolated workflows, such as accessibility
+   auditing.
 
 ---
 
@@ -108,6 +111,50 @@ To learn how to install or publish package skills, check out
 
 ---
 
+## Specialized agents
+
+**Specialized agents** (referred to as custom agents in platforms like
+Antigravity) are AI assistants configured with dedicated system prompts,
+curated tool sets, and focused skill subsets.
+
+While agent skills guide general-purpose assistants during active coding,
+specialized agents run in isolated contexts to perform deep, single-purpose
+workflows without cluttering your primary conversation history.
+
+### Flutter Accessibility agent
+
+The **Flutter Accessibility (`a11y`) agent** is an official specialized agent
+designed to audit Flutter widget trees and recommend accessibility
+improvements. The accessibility agent is currently available in
+[Google Antigravity](https://antigravity.google).
+
+Key capabilities of the accessibility agent include:
+
+* **Semantic label inspection**: identifies interactive widgets (such as
+  `IconButton` or `InkWell`) that lack descriptive semantic labels.
+* **Touch target validation**: flags interactive elements with hit test
+  areas smaller than the recommended 48x48 logical pixels.
+* **Contrast and visual checks**: highlights potential contrast ratio issues
+  and missing focus indicators.
+* **Automated code fixes**: generates idiomatic Flutter fixes (such as
+  wrapping widgets in `Semantics` or adjusting tap bounds) that you can review
+  and accept.
+
+### Using the accessibility agent in Antigravity
+
+After installing the official [Dart and Flutter plugin](
+https://antigravity.google/docs/build-with-google/#dart-and-flutter)
+in Antigravity, you can invoke the accessibility agent directly when chatting
+with Antigravity by selecting the **Flutter Accessibility Agent** from the
+agent picker, mentioning `@flutter_a11y_agent`, or asking your assistant to
+review your code for accessibility:
+
+```text
+@flutter_a11y_agent Audit this screen for accessibility issues.
+```
+
+---
+
 ## When to use what
 
 Use the following mental model to understand how different AI mechanisms
@@ -119,6 +166,7 @@ interact:
 | **Dart MCP server** | Local SDK tools | Diagnostics, tests, runtime |
 | **Developer Knowledge MCP** | Online search | Live docs, API references |
 | **Package skill** | From dependencies | Library APIs, code generation |
+| **Specialized agent** | Isolated subagent | Accessibility audits |
 
 {:.table .table-striped}