feat: Add MCP service for server identity operations

[beonde]

Summary

Adds the MCP (Model Context Protocol) service to capiscio-core, providing gRPC operations for MCP server identity management.

Changes

New Proto (proto/capiscio/v1/mcp.proto)

• MCPService with GenerateServerKeypair RPC
• Request/response messages for keypair generation

New Package (pkg/mcp/)

File	Purpose
server_identity.go	Ed25519 keypair generation
guard.go	MCP tool authorization guard
evidence_store.go	Authorization decision audit trail
health.go	Health check utilities
types.go	Core MCP types
errors.go	Error definitions
service.go	Service orchestration

New Package (pkg/pop/)

File	Purpose
primitives.go	Proof of Possession cryptographic primitives
session_cache.go	Challenge session caching

gRPC Service (internal/rpc/mcp_service.go)

• Implements MCPService gRPC interface
• Wires keypair generation to pkg/mcp

Documentation

• Updated docs/reference/api.md with MCP service reference

Testing

All tests pass:

ok      github.com/capiscio/capiscio-core/v2/pkg/mcp    0.938s
ok      github.com/capiscio/capiscio-core/v2/pkg/pop    (cached)
ok      github.com/capiscio/capiscio-core/v2/internal/rpc       0.694s
... (all other packages pass)

RFC Alignment

• RFC-006: MCP Tool Authority
• RFC-007: MCP Server Identity

Related

• docs: Add server registration module documentation capiscio-mcp-python#2 (Python SDK using this service)
• capiscio/capiscio-sdk-python (gRPC client pending)

[Copilot]

Pull request overview

This pull request adds comprehensive MCP (Model Context Protocol) service implementation to capiscio-core, providing gRPC operations for tool authority (RFC-006) and server identity management (RFC-007).

Changes:

• New proto definition (proto/capiscio/v1/mcp.proto) with 4 RPCs for tool access evaluation, server identity verification, parsing, and health checks
• New pkg/pop/ package for Proof of Possession cryptographic primitives shared between RFC-003 and RFC-007
• New pkg/mcp/ package with complete MCP service implementation including guard, server identity verification, evidence storage, and health checks
• gRPC service implementation in internal/rpc/mcp_service.go wiring the proto to pkg/mcp
• Comprehensive test coverage for all new packages

Reviewed changes

Copilot reviewed 28 out of 30 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
proto/capiscio/v1/mcp.proto	MCP service proto with tool access and server identity RPCs
proto/buf.gen.yaml	Added Python proto generation for capiscio-mcp-python
pkg/rpc/gen/capiscio/v1/*.pb.go	Generated proto code (2 files, 1752 lines)
pkg/pop/primitives.go	Shared PoP cryptographic primitives (475 lines)
pkg/pop/session_cache.go	Session caching for verified PoP results (223 lines)
pkg/pop/*_test.go	Comprehensive tests for pop package (769 lines)
pkg/mcp/types.go	Core MCP types and enums (321 lines)
pkg/mcp/errors.go	Error definitions and mappings (205 lines)
pkg/mcp/guard.go	Tool access evaluation implementation (204 lines)
pkg/mcp/server_identity.go	Server identity verification (379 lines)
pkg/mcp/evidence_store.go	Evidence storage implementations (435 lines)
pkg/mcp/health.go	Health check utilities (133 lines)
pkg/mcp/service.go	Service orchestration (101 lines)
pkg/mcp/doc.go	Package documentation (20 lines)
pkg/mcp/*_test.go	Comprehensive tests for mcp package (1513 lines)
internal/rpc/mcp_service.go	gRPC service implementation (342 lines)
internal/rpc/server.go	Registered MCP service (3 lines added)
Makefile	Added docs generation target (7 lines)

[codecov]

Codecov Report

❌ Patch coverage is 38.32952% with 1078 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/rpc/gen/capiscio/v1/mcp.pb.go	0.00%	535 Missing ⚠️
internal/rpc/mcp_service.go	0.00%	193 Missing ⚠️
pkg/mcp/evidence_store.go	26.58%	121 Missing and 6 partials ⚠️
pkg/rpc/gen/capiscio/v1/mcp_grpc.pb.go	0.00%	92 Missing ⚠️
pkg/mcp/server_identity.go	71.33%	43 Missing ⚠️
pkg/pop/primitives.go	85.47%	17 Missing and 9 partials ⚠️
pkg/pop/session_cache.go	72.28%	20 Missing and 3 partials ⚠️
pkg/mcp/guard.go	77.01%	19 Missing and 1 partial ⚠️
pkg/mcp/types.go	85.50%	10 Missing ⚠️
pkg/mcp/errors.go	95.74%	4 Missing ⚠️
... and 2 more

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