SEP-1686: Tasks (#1645)

examples/servers/simple-task-interactive/README.md

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+# Simple Interactive Task Server
+
+A minimal MCP server demonstrating interactive tasks with elicitation and sampling.
+
+## Running
+
+```bash
+cd examples/servers/simple-task-interactive
+uv run mcp-simple-task-interactive
+```
+
+The server starts on `http://localhost:8000/mcp` by default. Use `--port` to change.
+
+## What it does
+
+This server exposes two tools:
+
+### `confirm_delete` (demonstrates elicitation)
+
+Asks the user for confirmation before "deleting" a file.
+
+- Uses `task.elicit()` to request user input
+- Shows the elicitation flow: task -> input_required -> response -> complete
+
+### `write_haiku` (demonstrates sampling)
+
+Asks the LLM to write a haiku about a topic.
+
+- Uses `task.create_message()` to request LLM completion
+- Shows the sampling flow: task -> input_required -> response -> complete
+
+## Usage with the client
+
+In one terminal, start the server:
+
+```bash
+cd examples/servers/simple-task-interactive
+uv run mcp-simple-task-interactive
+```
+
+In another terminal, run the interactive client:
+
+```bash
+cd examples/clients/simple-task-interactive-client
+uv run mcp-simple-task-interactive-client
+```
+
+## Expected server output
+
+When a client connects and calls the tools, you'll see:
+
+```text
+Starting server on http://localhost:8000/mcp
+
+[Server] confirm_delete called for 'important.txt'
+[Server] Task created: <task-id>
+[Server] Sending elicitation request to client...
+[Server] Received elicitation response: action=accept, content={'confirm': True}
+[Server] Completing task with result: Deleted 'important.txt'
+
+[Server] write_haiku called for topic 'autumn leaves'
+[Server] Task created: <task-id>
+[Server] Sending sampling request to client...
+[Server] Received sampling response: Cherry blossoms fall
+Softly on the quiet pon...
+[Server] Completing task with haiku
+```
+
+## Key concepts
+
+1. **ServerTaskContext**: Provides `elicit()` and `create_message()` for user interaction
+2. **run_task()**: Spawns background work, auto-completes/fails, returns immediately
+3. **TaskResultHandler**: Delivers queued messages and routes responses
+4. **Response routing**: Responses are routed back to waiting resolvers

examples/servers/simple-task-interactive/mcp_simple_task_interactive/__main__.py

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+import sys
+
+from .server import main
+
+sys.exit(main())  # type: ignore[call-arg]

examples/servers/simple-task-interactive/mcp_simple_task_interactive/server.py

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+"""Simple interactive task server demonstrating elicitation and sampling.
+
+This example shows the simplified task API where:
+- server.experimental.enable_tasks() sets up all infrastructure
+- ctx.experimental.run_task() handles task lifecycle automatically
+- ServerTaskContext.elicit() and ServerTaskContext.create_message() queue requests properly
+"""
+
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+from typing import Any
+
+import click
+import mcp.types as types
+import uvicorn
+from mcp.server.experimental.task_context import ServerTaskContext
+from mcp.server.lowlevel import Server
+from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
+from starlette.applications import Starlette
+from starlette.routing import Mount
+
+server = Server("simple-task-interactive")
+
+# Enable task support - this auto-registers all handlers
+server.experimental.enable_tasks()
+
+
+@server.list_tools()
+async def list_tools() -> list[types.Tool]:
+    return [
+        types.Tool(
+            name="confirm_delete",
+            description="Asks for confirmation before deleting (demonstrates elicitation)",
+            inputSchema={
+                "type": "object",
+                "properties": {"filename": {"type": "string"}},
+            },
+            execution=types.ToolExecution(taskSupport=types.TASK_REQUIRED),
+        ),
+        types.Tool(
+            name="write_haiku",
+            description="Asks LLM to write a haiku (demonstrates sampling)",
+            inputSchema={"type": "object", "properties": {"topic": {"type": "string"}}},
+            execution=types.ToolExecution(taskSupport=types.TASK_REQUIRED),
+        ),
+    ]
+
+
+async def handle_confirm_delete(arguments: dict[str, Any]) -> types.CreateTaskResult:
+    """Handle the confirm_delete tool - demonstrates elicitation."""
+    ctx = server.request_context
+    ctx.experimental.validate_task_mode(types.TASK_REQUIRED)
+
+    filename = arguments.get("filename", "unknown.txt")
+    print(f"\n[Server] confirm_delete called for '{filename}'")
+
+    async def work(task: ServerTaskContext) -> types.CallToolResult:
+        print(f"[Server] Task {task.task_id} starting elicitation...")
+
+        result = await task.elicit(
+            message=f"Are you sure you want to delete '{filename}'?",
+            requestedSchema={
+                "type": "object",
+                "properties": {"confirm": {"type": "boolean"}},
+                "required": ["confirm"],
+            },
+        )
+
+        print(f"[Server] Received elicitation response: action={result.action}, content={result.content}")
+
+        if result.action == "accept" and result.content:
+            confirmed = result.content.get("confirm", False)
+            text = f"Deleted '{filename}'" if confirmed else "Deletion cancelled"
+        else:
+            text = "Deletion cancelled"
+
+        print(f"[Server] Completing task with result: {text}")
+        return types.CallToolResult(content=[types.TextContent(type="text", text=text)])
+
+    return await ctx.experimental.run_task(work)
+
+
+async def handle_write_haiku(arguments: dict[str, Any]) -> types.CreateTaskResult:
+    """Handle the write_haiku tool - demonstrates sampling."""
+    ctx = server.request_context
+    ctx.experimental.validate_task_mode(types.TASK_REQUIRED)
+
+    topic = arguments.get("topic", "nature")
+    print(f"\n[Server] write_haiku called for topic '{topic}'")
+
+    async def work(task: ServerTaskContext) -> types.CallToolResult:
+        print(f"[Server] Task {task.task_id} starting sampling...")
+
+        result = await task.create_message(
+            messages=[
+                types.SamplingMessage(
+                    role="user",
+                    content=types.TextContent(type="text", text=f"Write a haiku about {topic}"),
+                )
+            ],
+            max_tokens=50,
+        )
+
+        haiku = "No response"
+        if isinstance(result.content, types.TextContent):
+            haiku = result.content.text
+
+        print(f"[Server] Received sampling response: {haiku[:50]}...")
+        return types.CallToolResult(content=[types.TextContent(type="text", text=f"Haiku:\n{haiku}")])
+
+    return await ctx.experimental.run_task(work)
+
+
+@server.call_tool()
+async def handle_call_tool(name: str, arguments: dict[str, Any]) -> types.CallToolResult | types.CreateTaskResult:
+    """Dispatch tool calls to their handlers."""
+    if name == "confirm_delete":
+        return await handle_confirm_delete(arguments)
+    elif name == "write_haiku":
+        return await handle_write_haiku(arguments)
+    else:
+        return types.CallToolResult(
+            content=[types.TextContent(type="text", text=f"Unknown tool: {name}")],
+            isError=True,
+        )
+
+
+def create_app(session_manager: StreamableHTTPSessionManager) -> Starlette:
+    @asynccontextmanager
+    async def app_lifespan(app: Starlette) -> AsyncIterator[None]:
+        async with session_manager.run():
+            yield
+
+    return Starlette(
+        routes=[Mount("/mcp", app=session_manager.handle_request)],
+        lifespan=app_lifespan,
+    )
+
+
+@click.command()
+@click.option("--port", default=8000, help="Port to listen on")
+def main(port: int) -> int:
+    session_manager = StreamableHTTPSessionManager(app=server)
+    starlette_app = create_app(session_manager)
+    print(f"Starting server on http://localhost:{port}/mcp")
+    uvicorn.run(starlette_app, host="127.0.0.1", port=port)
+    return 0

examples/servers/simple-task-interactive/pyproject.toml

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+[project]
+name = "mcp-simple-task-interactive"
+version = "0.1.0"
+description = "A simple MCP server demonstrating interactive tasks (elicitation & sampling)"
+readme = "README.md"
+requires-python = ">=3.10"
+authors = [{ name = "Anthropic, PBC." }]
+keywords = ["mcp", "llm", "tasks", "elicitation", "sampling"]
+license = { text = "MIT" }
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: MIT License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+]
+dependencies = ["anyio>=4.5", "click>=8.0", "mcp", "starlette", "uvicorn"]
+
+[project.scripts]
+mcp-simple-task-interactive = "mcp_simple_task_interactive.server:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["mcp_simple_task_interactive"]
+
+[tool.pyright]
+include = ["mcp_simple_task_interactive"]
+venvPath = "."
+venv = ".venv"
+
+[tool.ruff.lint]
+select = ["E", "F", "I"]
+ignore = []
+
+[tool.ruff]
+line-length = 120
+target-version = "py310"
+
+[dependency-groups]
+dev = ["pyright>=1.1.378", "ruff>=0.6.9"]

examples/servers/simple-task/README.md

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+# Simple Task Server
+
+A minimal MCP server demonstrating the experimental tasks feature over streamable HTTP.
+
+## Running
+
+```bash
+cd examples/servers/simple-task
+uv run mcp-simple-task
+```
+
+The server starts on `http://localhost:8000/mcp` by default. Use `--port` to change.
+
+## What it does
+
+This server exposes a single tool `long_running_task` that:
+
+1. Must be called as a task (with `task` metadata in the request)
+2. Takes ~3 seconds to complete
+3. Sends status updates during execution
+4. Returns a result when complete
+
+## Usage with the client
+
+In one terminal, start the server:
+
+```bash
+cd examples/servers/simple-task
+uv run mcp-simple-task
+```
+
+In another terminal, run the client:
+
+```bash
+cd examples/clients/simple-task-client
+uv run mcp-simple-task-client
+```

examples/servers/simple-task/mcp_simple_task/__main__.py

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+import sys
+
+from .server import main
+
+sys.exit(main())  # type: ignore[call-arg]

examples/servers/simple-task/mcp_simple_task/server.py

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+"""Simple task server demonstrating MCP tasks over streamable HTTP."""
+
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+from typing import Any
+
+import anyio
+import click
+import mcp.types as types
+import uvicorn
+from mcp.server.experimental.task_context import ServerTaskContext
+from mcp.server.lowlevel import Server
+from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
+from starlette.applications import Starlette
+from starlette.routing import Mount
+
+server = Server("simple-task-server")
+
+# One-line setup: auto-registers get_task, get_task_result, list_tasks, cancel_task
+server.experimental.enable_tasks()
+
+
+@server.list_tools()
+async def list_tools() -> list[types.Tool]:
+    return [
+        types.Tool(
+            name="long_running_task",
+            description="A task that takes a few seconds to complete with status updates",
+            inputSchema={"type": "object", "properties": {}},
+            execution=types.ToolExecution(taskSupport=types.TASK_REQUIRED),
+        )
+    ]
+
+
+async def handle_long_running_task(arguments: dict[str, Any]) -> types.CreateTaskResult:
+    """Handle the long_running_task tool - demonstrates status updates."""
+    ctx = server.request_context
+    ctx.experimental.validate_task_mode(types.TASK_REQUIRED)
+
+    async def work(task: ServerTaskContext) -> types.CallToolResult:
+        await task.update_status("Starting work...")
+        await anyio.sleep(1)
+
+        await task.update_status("Processing step 1...")
+        await anyio.sleep(1)
+
+        await task.update_status("Processing step 2...")
+        await anyio.sleep(1)
+
+        return types.CallToolResult(content=[types.TextContent(type="text", text="Task completed!")])
+
+    return await ctx.experimental.run_task(work)
+
+
+@server.call_tool()
+async def handle_call_tool(name: str, arguments: dict[str, Any]) -> types.CallToolResult | types.CreateTaskResult:
+    """Dispatch tool calls to their handlers."""
+    if name == "long_running_task":
+        return await handle_long_running_task(arguments)
+    else:
+        return types.CallToolResult(
+            content=[types.TextContent(type="text", text=f"Unknown tool: {name}")],
+            isError=True,
+        )
+
+
+@click.command()
+@click.option("--port", default=8000, help="Port to listen on")
+def main(port: int) -> int:
+    session_manager = StreamableHTTPSessionManager(app=server)
+
+    @asynccontextmanager
+    async def app_lifespan(app: Starlette) -> AsyncIterator[None]:
+        async with session_manager.run():
+            yield
+
+    starlette_app = Starlette(
+        routes=[Mount("/mcp", app=session_manager.handle_request)],
+        lifespan=app_lifespan,
+    )
+
+    print(f"Starting server on http://localhost:{port}/mcp")
+    uvicorn.run(starlette_app, host="127.0.0.1", port=port)
+    return 0

examples/servers/simple-task/pyproject.toml

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+[project]
+name = "mcp-simple-task"
+version = "0.1.0"
+description = "A simple MCP server demonstrating tasks"
+readme = "README.md"
+requires-python = ">=3.10"
+authors = [{ name = "Anthropic, PBC." }]
+keywords = ["mcp", "llm", "tasks"]
+license = { text = "MIT" }
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: MIT License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+]
+dependencies = ["anyio>=4.5", "click>=8.0", "mcp", "starlette", "uvicorn"]
+
+[project.scripts]
+mcp-simple-task = "mcp_simple_task.server:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["mcp_simple_task"]
+
+[tool.pyright]
+include = ["mcp_simple_task"]
+venvPath = "."
+venv = ".venv"
+
+[tool.ruff.lint]
+select = ["E", "F", "I"]
+ignore = []
+
+[tool.ruff]
+line-length = 120
+target-version = "py310"
+
+[dependency-groups]
+dev = ["pyright>=1.1.378", "ruff>=0.6.9"]