feat: Add DNS-AID tools for agent discovery via DNS

[IngmarVG-IB]

Feature Request

Add DNS-AID (DNS-based Agent Identification and Discovery) tools to Google ADK, enabling agents to discover, publish, and unpublish other agents via DNS SVCB records.

Motivation

AI agent ecosystems need a decentralized, standards-based discovery mechanism. DNS-AID (IETF draft-mozleywilliams-dnsop-dnsaid-01) uses DNS SVCB records to publish agent metadata — capabilities, endpoints, protocols, and versions — making agents discoverable without centralized registries.

Google ADK already supports A2A (Agent-to-Agent) protocol. DNS-AID complements A2A by providing the discovery layer: agents publish their A2A endpoints to DNS, and other agents find them via standard DNS queries. This enables:

• Decentralized discovery: No central registry needed
• DNS-native: Leverages existing DNS infrastructure, caching, and security (DNSSEC)
• A2A bridge: DNS-discovered agents with protocol=a2a can be converted to ADK RemoteAgent references

Proposed Implementation

1. FunctionTool wrappers: discover_agents, publish_agent, unpublish_agent async functions wrapped as FunctionTool objects
2. Tool factory: get_dns_aid_tools(backend_name=...) for convenient tool creation with DNS backend binding
3. A2A bridge: a2a_agent_from_record() to convert DNS-AID discovered agents into ADK-compatible RemoteAgent references

Related PR

PR #4856 implements this feature.

[klateefa]

@IngmarVG-IB Thank you for submitting this feature request. It’s currently under review by our team, and I’ll keep you posted on any updates. We appreciate your input!