Purpose
-------
Policy Engine (Layer 3) for the ``oct-mcp`` six-layer pipeline.
Maintains the tool manifest and decides whether a given tool call is
permitted under the active MCP profile.
Responsibilities
----------------
- Define :data:`TOOL_MANIFEST` mapping tool names to :class:`ToolSpec`.
- Define :class:`McpPolicy` which enforces profile-based rules.
- Return structured :class:`PolicyDecision` objects (never raises for
policy rejections - callers check the decision).
Diagnostics
-----------
Domain: MCP
Levels:
L1 - errors: unknown tool, manifest inconsistency
L2 - lifecycle: policy decision
L3 - (none): the decision is reported at L2, enforcement detail at L4
L4 - deep trace: profile enforcement details
Contracts
---------
- This module does not import ``click``, the MCP SDK, or any other
``oct.mcp.*`` module except ``config.py``.
- :meth:`McpPolicy.check` never raises for normal policy decisions.
Only ``ValueError`` is raised for programming errors (e.g. an unknown
profile string passed at construction time).
- In ``airgapped`` profile, ALL tool calls are denied regardless of
the tool manifest.
- In ``strict`` profile, only tools with ``auto_approve=True`` and
``destructive=False`` may execute, and repo-level config is ignored.
Dependencies
------------
- oct.core.diagnostics (_dbg structured logger)
1.15.0