perf(mcp): cache MCP tool argument names

[morluto]

Fixes #737.

Change

Derive each tool’s accepted argument names once from the extension’s existing tools() bindings during initialization. Request interception now uses that immutable map instead of rebuilding bindings and inspecting handlers for every call.

The public tool definitions remain the single source of truth, including the reasoning-enabled math.run signature. Unknown unregistered tool names now take the adapter’s invalid-input error path if they reach the interceptor directly; normal MCP dispatch rejects them before that point.

Coverage

The tool-surface tests cover the stable OFF mode plus the reasoning identifiers required by the enabled math.run handler. The MCP SDK conformance test exercises unknown-argument rejection through a live client/server call.

Validation

• make test-unit TESTS=tests/unit/tooling/test_mcp_tool_surface.py — 6 passed
• make test-mcp TESTS=tests/boundary/mcp/test_mcp_sdk_2_conformance.py — 2 passed
• make check-static — passed
• make npm-test — 45 passed

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