feat(mcp): scaffold three project context tools

mcp_servers/project_context/runtime.py

@@ -0,0 +1,74 @@
+"""Fail-closed identity, policy, and provider resolution for the template server."""
+
+from __future__ import annotations
+
+import os
+import sys
+from collections.abc import Callable
+from dataclasses import dataclass
+from typing import Any
+
+from .foundation import IdentityContext, ProjectContextRuntime, ProviderError
+from .providers.change import build_provider as build_change_provider
+from .providers.issue import build_provider as build_issue_provider
+from .providers.knowledge import build_provider as build_knowledge_provider
+
+MINIMUM_PYTHON = (3, 11)
+
+
+def require_supported_python(version_info: tuple[int, ...] | None = None) -> None:
+    """Fail with an actionable message before the MCP server starts."""
+    current = version_info or tuple(sys.version_info[:3])
+    if current[:2] < MINIMUM_PYTHON:
+        raise RuntimeError(
+            "Project Context MCP requires Python 3.11 or newer; "
+            f"current runtime is {current[0]}.{current[1]}"
+        )
+
+
+@dataclass(frozen=True)
+class ProjectScopePolicy:
+    """Pilot policy: read scope and exact identity-bound project are both mandatory."""
+
+    def decide(self, identity: IdentityContext, tool_name: str, project_id: str) -> bool:
+        return "read" in identity.granted_scopes and project_id == identity.project
+
+
+PROVIDER_FACTORIES: dict[str, Callable[[IdentityContext], Any]] = {
+    "get_project_issue_context": build_issue_provider,
+    "search_project_knowledge": build_knowledge_provider,
+    "get_project_change_context": build_change_provider,
+}
+
+
+@dataclass(frozen=True)
+class ProjectProviderResolver:
+    def resolve(self, identity: IdentityContext, tool_name: str) -> Any:
+        factory = PROVIDER_FACTORIES.get(tool_name)
+        if factory is None:
+            raise ProviderError("NOT_FOUND", "The requested tool is not registered.", retryable=False)
+        return factory(identity)
+
+
+def _required_environment(name: str) -> str:
+    value = os.environ.get(name, "").strip()
+    if not value:
+        raise RuntimeError(f"Project Context MCP cannot start: required setting {name} is missing")
+    return value
+
+
+def default_runtime() -> ProjectContextRuntime:
+    """Build immutable runtime state; missing identity configuration fails at boot."""
+    require_supported_python()
+    identity = IdentityContext(
+        actor_id=_required_environment("COWORK_MCP_ACTOR_ID"),
+        org_unit=_required_environment("COWORK_MCP_ORG_UNIT"),
+        customer=_required_environment("COWORK_MCP_CUSTOMER"),
+        project=_required_environment("COWORK_MCP_PROJECT"),
+        granted_scopes=frozenset({"read"}),
+    )
+    return ProjectContextRuntime(
+        identity=identity,
+        policy=ProjectScopePolicy(),
+        credential_resolver=ProjectProviderResolver(),
+    )