feat(agentcore): Add AWS Agent Registry discovery tools

[pymia]

Add four registry MCP tools to the amazon-bedrock-agentcore-mcp-server
package for discovering and inspecting AWS Agent Registry resources:

Tool	Description
search_registry	Semantic search across approved registry records
list_records	List all records in a specific registry
get_record	Get full details of a specific registry record
list_registries	List all registries in the AWS account

Implementation details:

• New tools/registry.py module with lazy boto3 client initialization
• Two clients: control plane (CRUD) and data plane (semantic search)
• Inline JSON parsing for MCP/A2A/custom descriptors
• Service-enable guard via _is_service_enabled("registry")
• 21 unit tests covering all tools, error handling, and client init
• README updated with tool docs and environment variable reference

Fixes N/A

Summary

Changes

Add four AWS Agent Registry MCP tools (search_registry, list_records, get_record, list_registries) to the existing amazon-bedrock-agentcore-mcp-server package. The Registry is a fully managed discovery service within Amazon Bedrock AgentCore that provides a centralized catalog for organizing, curating, and discovering MCP servers, A2A agents, agent skills, and custom resources.

New files:

• tools/registry.py — Registry tool module with lazy boto3 client initialization (control plane + data plane), inline JSON parsing for MCP/A2A/custom descriptors, and error handling as JSON return values
• tests/test_registry.py — 21 unit tests covering all four tools, error paths, MCP descriptor parsing, client initialization, and region configuration

Modified files:

• server.py — Register registry tools behind _is_service_enabled('registry') guard
• README.md — Added tool documentation, feature listing, and environment variable reference

User experience

Before: Users had no way to discover or inspect AWS Agent Registry resources through the MCP server.

After: Users can:

• Search registries using natural language queries to find relevant MCP servers, A2A agents, and other resources
• List all records in a specific registry to see available resources
• Get full details of a specific registry record including parsed descriptor content
• List all registries in their AWS account
• Enable/disable registry tools via AGENTCORE_ENABLE_TOOLS / AGENTCORE_DISABLE_TOOLS environment variables

Checklist

If your change doesn't seem to apply, please leave them unchecked.

• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Is this a breaking change? N

RFC issue number: N/A

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.