chore: import upstream snapshot with attribution

examples/clients/sse-polling-client/README.md

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+# MCP SSE Polling Demo Client
+
+Demonstrates client-side auto-reconnect for the SSE polling pattern (SEP-1699).
+
+## Features
+
+- Connects to SSE polling demo server
+- Automatically reconnects when server closes SSE stream
+- Resumes from Last-Event-ID to avoid missing messages
+- Respects server-provided retry interval
+
+## Usage
+
+```bash
+# First start the server:
+uv run mcp-sse-polling-demo --port 3000
+
+# Then run this client:
+uv run mcp-sse-polling-client --url http://localhost:3000/mcp
+
+# Custom options:
+uv run mcp-sse-polling-client --url http://localhost:3000/mcp --items 20 --checkpoint-every 5
+```
+
+## Options
+
+- `--url`: Server URL (default: <http://localhost:3000/mcp>)
+- `--items`: Number of items to process (default: 10)
+- `--checkpoint-every`: Checkpoint interval (default: 3)
+- `--log-level`: Logging level (default: DEBUG)

examples/clients/sse-polling-client/mcp_sse_polling_client/__init__.py

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+"""SSE Polling Demo Client - demonstrates auto-reconnect for long-running tasks."""

examples/clients/sse-polling-client/mcp_sse_polling_client/main.py

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+"""SSE Polling Demo Client
+
+Demonstrates the client-side auto-reconnect for SSE polling pattern.
+
+This client connects to the SSE Polling Demo server and calls process_batch,
+which triggers periodic server-side stream closes. The client automatically
+reconnects using Last-Event-ID and resumes receiving messages.
+
+Run with:
+    # First start the server:
+    uv run mcp-sse-polling-demo --port 3000
+
+    # Then run this client:
+    uv run mcp-sse-polling-client --url http://localhost:3000/mcp
+"""
+
+import asyncio
+import logging
+
+import click
+from mcp import ClientSession
+from mcp.client.streamable_http import streamable_http_client
+
+
+async def run_demo(url: str, items: int, checkpoint_every: int) -> None:
+    """Run the SSE polling demo."""
+    print(f"\n{'=' * 60}")
+    print("SSE Polling Demo Client")
+    print(f"{'=' * 60}")
+    print(f"Server URL: {url}")
+    print(f"Processing {items} items with checkpoints every {checkpoint_every}")
+    print(f"{'=' * 60}\n")
+
+    async with streamable_http_client(url) as (read_stream, write_stream):
+        async with ClientSession(read_stream, write_stream) as session:
+            # Initialize the connection
+            print("Initializing connection...")
+            await session.initialize()
+            print("Connected!\n")
+
+            # List available tools
+            tools = await session.list_tools()
+            print(f"Available tools: {[t.name for t in tools.tools]}\n")
+
+            # Call the process_batch tool
+            print(f"Calling process_batch(items={items}, checkpoint_every={checkpoint_every})...\n")
+            print("-" * 40)
+
+            result = await session.call_tool(
+                "process_batch",
+                {
+                    "items": items,
+                    "checkpoint_every": checkpoint_every,
+                },
+            )
+
+            print("-" * 40)
+            if result.content:
+                content = result.content[0]
+                text = getattr(content, "text", str(content))
+                print(f"\nResult: {text}")
+            else:
+                print("\nResult: No content")
+            print(f"{'=' * 60}\n")
+
+
+@click.command()
+@click.option(
+    "--url",
+    default="http://localhost:3000/mcp",
+    help="Server URL",
+)
+@click.option(
+    "--items",
+    default=10,
+    help="Number of items to process",
+)
+@click.option(
+    "--checkpoint-every",
+    default=3,
+    help="Checkpoint interval",
+)
+@click.option(
+    "--log-level",
+    default="INFO",
+    help="Logging level",
+)
+def main(url: str, items: int, checkpoint_every: int, log_level: str) -> None:
+    """Run the SSE Polling Demo client."""
+    logging.basicConfig(
+        level=getattr(logging, log_level.upper()),
+        format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    )
+    # Suppress noisy HTTP client logging
+    logging.getLogger("httpx").setLevel(logging.WARNING)
+    logging.getLogger("httpcore").setLevel(logging.WARNING)
+
+    asyncio.run(run_demo(url, items, checkpoint_every))
+
+
+if __name__ == "__main__":
+    main()

examples/clients/sse-polling-client/pyproject.toml

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+[project]
+name = "mcp-sse-polling-client"
+version = "0.1.0"
+description = "Demo client for SSE polling with auto-reconnect"
+readme = "README.md"
+requires-python = ">=3.10"
+authors = [{ name = "Model Context Protocol a Series of LF Projects, LLC." }]
+keywords = ["mcp", "sse", "polling", "client"]
+license = { text = "MIT" }
+dependencies = ["click>=8.2.0", "mcp"]
+
+[project.scripts]
+mcp-sse-polling-client = "mcp_sse_polling_client.main:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["mcp_sse_polling_client"]
+
+[tool.pyright]
+include = ["mcp_sse_polling_client"]
+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", "pytest>=8.3.3", "ruff>=0.6.9"]