[2.14] SEP-1686 tasks (#2378)

* Implement MCP background tasks (SEP-1686) using Docket

Adds support for background task execution via the MCP task protocol,
powered by Docket for task queue management.

- Tools, resources, and prompts can be marked with `task=True` to run async
- Progress dependency for tracking task progress
- CurrentDocket and CurrentWorker dependencies for advanced use cases
- Client API with `.call_tool(..., task=True)` returns task handles
- Task status notifications via subscriptions
- CLI worker command for distributed task processing

Configuration via environment:
- FASTMCP_ENABLE_DOCKET=true
- FASTMCP_ENABLE_TASKS=true
- FASTMCP_DOCKET_URL=redis://... (or memory:// for single-process)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* Fix tasks example import (TaskStatusResponse → GetTaskResult)

The example was using a non-existent TaskStatusResponse type.
Updated to use mcp.types.GetTaskResult which is what the
on_status_change callback actually receives.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* Fix env var name in Docket error messages

The error messages referenced FASTMCP_EXPERIMENTAL_ENABLE_DOCKET but the
actual setting is FASTMCP_ENABLE_DOCKET.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* Remove deprecated code re-added from pre-#2329 branch

- Remove ExtendedEnvSettingsSource (FASTMCP_SERVER_ prefix support)
- Remove dependencies parameter from FastMCP.__init__

* Replace fakeredis git pin with PyPI release

* Remove redundant fakeredis dev dep (pulled via pydocket)

---------

Co-authored-by: Claude <[email protected]>
Co-authored-by: Jeremiah Lowin <[email protected]>

Author: 3 people

.pre-commit-config.yaml

@@ -26,7 +26,7 @@ repos:
     hooks:
       - id: ty
         name: ty check
-        entry: uv run ty check
+        entry: uv run --isolated ty check
         language: system
         types: [python]
         files: ^src/|^tests/

docs/clients/tasks.mdx

@@ -0,0 +1,155 @@
+---
+title: Background Tasks
+sidebarTitle: Background Tasks
+description: Execute operations asynchronously and track their progress
+icon: clock
+tag: "NEW"
+---
+
+import { VersionBadge } from "/snippets/version-badge.mdx"
+
+<VersionBadge version="2.14" />
+
+The [MCP task protocol](https://modelcontextprotocol.io/specification/2025-11-25/basic/utilities/tasks) lets you request operations to run asynchronously. This returns a Task object immediately, letting you track progress, cancel operations, or await results.
+
+See [Server Background Tasks](/servers/tasks) for how to enable this on the server side.
+
+## Requesting Background Execution
+
+Pass `task=True` to run an operation as a background task:
+
+```python
+from fastmcp import Client
+
+async with Client(server) as client:
+    # Start a background task
+    task = await client.call_tool("slow_computation", {"duration": 10}, task=True)
+
+    print(f"Task started: {task.task_id}")
+
+    # Do other work while it runs...
+
+    # Get the result when ready
+    result = await task.result()
+```
+
+This works with all three operation types:
+
+```python
+# Tools
+tool_task = await client.call_tool("my_tool", args, task=True)
+
+# Resources
+resource_task = await client.read_resource("file://large.txt", task=True)
+
+# Prompts
+prompt_task = await client.get_prompt("my_prompt", args, task=True)
+```
+
+## Task Objects
+
+All task types share a common interface:
+
+### Getting Results
+
+```python
+task = await client.call_tool("analyze", {"text": "hello"}, task=True)
+
+# Wait for and get the result
+result = await task.result()
+
+# Or use await directly (shorthand for .result())
+result = await task
+```
+
+### Checking Status
+
+```python
+status = await task.status()
+
+print(f"Status: {status.status}")  # "working", "completed", "failed", "cancelled"
+print(f"Message: {status.statusMessage}")  # Progress message from server
+```
+
+### Waiting for Completion
+
+```python
+# Wait for task to complete (with timeout)
+status = await task.wait(timeout=30.0)
+
+# Wait for a specific state
+status = await task.wait(state="completed", timeout=30.0)
+```
+
+### Cancelling Tasks
+
+```python
+await task.cancel()
+```
+
+### Status Notifications
+
+Register callbacks to receive real-time status updates:
+
+```python
+def on_status_change(status):
+    print(f"Task {status.taskId}: {status.status} - {status.statusMessage}")
+
+task.on_status_change(on_status_change)
+
+# Async callbacks also supported
+async def on_status_async(status):
+    await log_status(status)
+
+task.on_status_change(on_status_async)
+```
+
+## Graceful Degradation
+
+You can always pass `task=True` regardless of whether the server supports background tasks. Per the [MCP specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/utilities/tasks), servers that don't support tasks will execute the operation immediately and return the result inline. Your code works either way:
+
+```python
+task = await client.call_tool("my_tool", args, task=True)
+
+if task.returned_immediately:
+    print("Server executed immediately (no background support)")
+else:
+    print("Running in background")
+
+# Either way, this works
+result = await task.result()
+```
+
+This means you can write task-aware client code without worrying about server capabilities—the Task API provides a consistent interface whether the operation runs in the background or completes immediately.
+
+## Complete Example
+
+```python
+import asyncio
+from fastmcp import Client
+
+async def main():
+    async with Client(server) as client:
+        # Start background task
+        task = await client.call_tool(
+            "slow_computation",
+            {"duration": 10},
+            task=True,
+        )
+
+        # Subscribe to updates
+        def on_update(status):
+            print(f"Progress: {status.statusMessage}")
+
+        task.on_status_change(on_update)
+
+        # Do other work
+        print("Doing other work while task runs...")
+        await asyncio.sleep(2)
+
+        # Wait for completion and get result
+        result = await task.result()
+        print(f"Result: {result.data}")
+
+asyncio.run(main())
+```

docs/docs.json

@@ -116,7 +116,8 @@
                   "servers/progress",
                   "servers/proxy",
                   "servers/sampling",
-                  "servers/storage-backends"
+                  "servers/storage-backends",
+                  "servers/tasks"
                 ]
               },
               {
@@ -171,6 +172,7 @@
                   "clients/logging",
                   "clients/progress",
                   "clients/sampling",
+                  "clients/tasks",
                   "clients/messages",
                   "clients/roots"
                 ]