Port the MCP server to mcp 2.x, and say what each tool is allowed to do

mcp 2.0.0 removed mcp.server.fastmcp; MCPServer is the same object under a
new name, so @mcp.tool() and mcp.run() are untouched and every tool keeps its
name, signature and returned shape. Verified against a clean 2.0.0 venv: all
four tools list, and the whole suite -- including test_mcp.py, which could not
even import while the dependency was broken -- passes at 100% coverage, 901
tests.

Two things the port buys, neither of which existed in 1.x:

* Tool annotations. The section banner here already said "state-only; never
  expose secrets, never mutate"; now the protocol says it too, as read-only,
  idempotent and closed-world hints, which is what lets a client run these
  without asking first. The day one of them starts writing, the annotation is
  what has to change with it.
* Structured output. 2.x derives an output schema from the return types and
  sends structured content alongside the text, so a caller no longer re-parses
  JSON we already had. No code change -- it falls out of the type hints that
  were already there.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BsXnTHyuuCUZsqetTaajcF

.pre-commit-config.yaml

@@ -101,7 +101,7 @@ repos:
           - pytest
           - gatelock @ git+https://github.com/kuhyx/utils@gatelock-v0.4.0#subdirectory=gatelock
           - crdt-sync @ git+https://github.com/kuhyx/utils@crdt-sync-v0.1.0#subdirectory=crdt-sync
-          - mcp>=1.9,<2
+          - mcp>=2,<3
           - pydantic
 
   - repo: https://github.com/PyCQA/bandit

pyproject.toml

@@ -20,7 +20,7 @@ screen-locker-status = "screen_locker.status_view:main"
 # so the systemd/CLI system-python path stays dependency-light and never has
 # to import the MCP SDK.
 [project.optional-dependencies]
-mcp = ["mcp>=1.9,<2"]
+mcp = ["mcp>=2,<3"]
 
 [tool.setuptools.packages.find]
 # This repo also holds stronglift_replacement/ (an unrelated Flutter app, not

requirements.txt

@@ -5,7 +5,7 @@ codespell>=2.2.0
 coverage>=7.4.0
 crdt-sync @ git+https://github.com/kuhyx/utils@crdt-sync-v0.1.0#subdirectory=crdt-sync
 gatelock @ git+https://github.com/kuhyx/utils@gatelock-v0.4.0#subdirectory=gatelock
-mcp>=1.9,<2
+mcp>=2,<3
 mypy>=1.8.0
 pre-commit>=3.6.0
 pylint>=3.0.0

screen_locker/_mcp.py

@@ -37,7 +37,8 @@ from pathlib import Path
 import sys
 from typing import Any
 
-from mcp.server.fastmcp import FastMCP
+from mcp.server import MCPServer
+from mcp.types import ToolAnnotations
 
 from screen_locker._compliance_state import (
     has_logged_today,
@@ -62,7 +63,18 @@ logging.basicConfig(
 )
 logger = logging.getLogger(__name__)
 
-mcp = FastMCP("screen-locker")
+mcp = MCPServer("screen-locker")
+
+# Every tool here only reads local state: the workout log, the sick history
+# and the clock. Saying so lets a client run them without asking -- and the
+# day one of them stops being read-only, this annotation is the thing that
+# has to change with it. (See the section banner below: "never mutate" was
+# already the rule; this is the machine-readable half of it.)
+_READS_ONLY = ToolAnnotations(
+    read_only_hint=True,
+    idempotent_hint=True,
+    open_world_hint=False,
+)
 
 # The workout log lives beside the package, same default as
 # ``_status_data._DEFAULT_LOG_FILE``; declared here to avoid importing a
@@ -75,7 +87,7 @@ _LOG_FILE = Path(__file__).resolve().parent / "workout_log.json"
 # ──────────────────────────────────────────────────────────────
 
 
-@mcp.tool()
+@mcp.tool(title="Workout gate status", annotations=_READS_ONLY)
 def get_status() -> dict[str, Any]:
     """Return the full read-only status snapshot.
 
@@ -87,7 +99,7 @@ def get_status() -> dict[str, Any]:
     return asdict(gather_status())
 
 
-@mcp.tool()
+@mcp.tool(title="One-line status summary", annotations=_READS_ONLY)
 def get_summary() -> dict[str, Any]:
     """Return the one-line i3blocks summary plus the compliance-state word.
 
@@ -102,7 +114,7 @@ def get_summary() -> dict[str, Any]:
     }
 
 
-@mcp.tool()
+@mcp.tool(title="Why the screen is locked", annotations=_READS_ONLY)
 def explain_lock() -> dict[str, Any]:
     """Return why the screen is or is not being locked right now.
 
@@ -114,7 +126,7 @@ def explain_lock() -> dict[str, Any]:
     return asdict(gather_status().lock_explanation)
 
 
-@mcp.tool()
+@mcp.tool(title="Lock-decision predicates", annotations=_READS_ONLY)
 def get_flags() -> dict[str, bool]:
     """Return the individual boolean lock-decision predicates for today.