feat(groups): Add structured JSON output for enable_tools/disable_tools

Replace text-formatted responses with Pydantic models (EnableToolsResult,
DisableToolsResult) that FastMCP automatically serializes via ToolResult's
structured_content parameter.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: chughtapan

docs/middleware/groups.md

@@ -0,0 +1,139 @@
+# Groups
+
+When MCP servers expose many tools, agents can become overwhelmed with options, leading to poor tool selection and increased token usage. The `GroupsMiddleware` in <span class="wags-brand">wags</span> enables progressive tool disclosure by organizing tools into hierarchical groups that agents can enable or disable as needed.
+
+## How It Works
+
+Tools are assigned to groups using the `@in_group` decorator. The middleware:
+
+1. Hides all grouped tools initially (or starts with configured `initial_groups`)
+2. Exposes `enable_tools` and `disable_tools` meta-tools
+3. Progressively reveals child groups as parents are enabled
+4. Enforces optional `max_tools` limits
+
+## Example
+
+```python linenums="1" title="handlers.py"
+from wags.middleware import GroupsMiddleware, GroupDefinition, in_group
+
+class GithubHandlers:
+    @in_group("issues")
+    async def create_issue(self, owner: str, repo: str, title: str):
+        pass
+
+    @in_group("issues")
+    async def list_issues(self, owner: str, repo: str):
+        pass
+
+    @in_group("repos")
+    async def create_repository(self, name: str):
+        pass
+```
+
+Configure the middleware with group definitions:
+
+```python title="main.py"
+from wags.middleware import GroupsMiddleware, GroupDefinition
+
+handlers = GithubHandlers()
+mcp.add_middleware(
+    GroupsMiddleware(
+        groups={
+            "issues": GroupDefinition(description="Issue tracking"),
+            "repos": GroupDefinition(description="Repository management"),
+        },
+        handlers=handlers,
+        initial_groups=["issues"],  # Start with issues enabled
+        max_tools=10,  # Optional limit
+    )
+)
+```
+
+## Hierarchical Groups
+
+Groups can be nested using the `parent` parameter for progressive disclosure:
+
+```python
+groups = {
+    "code": GroupDefinition(description="Code management"),
+    "repos": GroupDefinition(description="Repositories", parent="code"),
+    "branches": GroupDefinition(description="Branches", parent="repos"),
+}
+```
+
+With this hierarchy:
+
+- Only `code` is visible initially (root group)
+- Enabling `code` reveals `repos` as an option
+- Enabling `repos` reveals `branches` as an option
+- Disabling `code` cascades to disable `repos` and `branches`
+
+## Agent Interaction
+
+When an agent calls `enable_tools(groups=["issues"])`, it receives a structured JSON response:
+
+```json
+{
+  "enabled": ["issues"],
+  "enabled_groups": ["issues"],
+  "available_tools": ["create_issue", "list_issues"],
+  "available_groups": [],
+  "errors": []
+}
+```
+
+The response includes:
+
+- `enabled`: Groups that were newly enabled by this call
+- `enabled_groups`: All currently enabled groups
+- `available_tools`: Tools now available to the agent
+- `available_groups`: Child groups that can now be enabled
+- `errors`: Any validation errors (unknown groups, already enabled, etc.)
+
+Similarly, `disable_tools` returns:
+
+```json
+{
+  "disabled": ["issues"],
+  "enabled_groups": [],
+  "available_tools": [],
+  "errors": []
+}
+```
+
+A `tools/list_changed` notification is sent whenever groups are enabled or disabled, prompting the client to refresh its tool list.
+
+When a tool from a disabled group is called, the agent receives an error message with a hint about which group to enable.
+
+## API Documentation
+
+::: wags.middleware.groups.in_group
+    options:
+      show_source: false
+      members: []
+      show_signature: false
+
+::: wags.middleware.groups.GroupDefinition
+    options:
+      show_source: false
+      members: []
+      show_signature: false
+
+::: wags.middleware.groups.GroupsMiddleware
+    options:
+      show_source: false
+      show_bases: false
+      members: []
+      show_signature: false
+
+::: wags.middleware.groups.EnableToolsResult
+    options:
+      show_source: false
+      members: []
+      show_signature: false
+
+::: wags.middleware.groups.DisableToolsResult
+    options:
+      show_source: false
+      members: []
+      show_signature: false

docs/middleware/overview.md

@@ -17,6 +17,7 @@ The <span class="wags-brand">wags</span> middleware toolkit further provides *fi
 
 Understand what features different middlewares provide and how to configure them:
 
+- [Groups](groups.md) for progressive tool disclosure via hierarchical groups.
 - [TodoList](todo.md) to ensure agents perform complex tasks correctly.
 - [Roots](roots.md) to enable client-configured fine-grained access control for MCP servers.
 - [Elicitation](elicitation.md) add human-in-the-loop features to improve UX.

mkdocs.yml

@@ -41,6 +41,7 @@ nav:
   - Onboarding Servers: onboarding.md
   - Middleware:
     - Overview: middleware/overview.md
+    - Groups: middleware/groups.md
     - TodoList: middleware/todo.md
     - Roots: middleware/roots.md
     - Elicitation: middleware/elicitation.md

src/wags/middleware/__init__.py

@@ -1,11 +1,23 @@
 """WAGS middleware components."""
 
 from .elicitation import ElicitationMiddleware, RequiresElicitation
+from .groups import (
+    DisableToolsResult,
+    EnableToolsResult,
+    GroupDefinition,
+    GroupsMiddleware,
+    in_group,
+)
 from .roots import RootsMiddleware, requires_root
 
 __all__ = [
+    "DisableToolsResult",
     "ElicitationMiddleware",
+    "EnableToolsResult",
+    "GroupDefinition",
+    "GroupsMiddleware",
     "RequiresElicitation",
     "RootsMiddleware",
+    "in_group",
     "requires_root",
 ]