feat(smart-contract): enforce metadata and storage size validation in agent-registry

[Opulencechuks]

Closes #115

Summary

The agent-registry contract previously allowed agents to store arbitrary metadata with no size limits. This vulnerability could allow a malicious or buggy agent to write unbounded data to persistent storage, consuming the contract's rent budget and increasing ledger costs for all users. This PR addresses the issue by defining maximum size constants and adding strict size validation on agent IDs, metadata entries, metadata value bytes, and total record storage size.

Changes

• smart-contracts/contracts/agent_registry/src/lib.rs:
  • Defined maximum size constants (MAX_AGENT_ID = 64, MAX_METADATA_ENTRIES = 16, MAX_METADATA_VALUE_SIZE = 256, MAX_TOTAL_AGENT_STORAGE = 4096).
  • Updated AgentRecord to include metadata: Map<Symbol, Val> to store metadata entries.
  • Added typed contract error codes (AgentIdTooLong, TooManyMetadataEntries, MetadataValueTooLarge, StorageLimitExceeded) to the Error enum.
  • Implemented a private validate_record helper utilizing ToXdr serialization to calculate exact byte sizes.
  • Integrated validation inside register_agent().
  • Implemented update_agent(env: Env, record: AgentRecord) -> Result<(), Error> to support validated updates, including capability indexing updates if an agent changes capabilities.
  • Updated all existing unit tests to initialize the metadata map and added 7 new unit tests verifying limit validations.
• smart-contracts/contracts/agent_registry/tests/integration.rs:
  • Updated the JSON payload for mock registration records to include "metadata":{}.

Testing

• Added unit tests verifying successful registration with metadata (register_with_metadata_ok) and successful updates (update_agent_ok).
• Added boundary test cases asserting typed error codes are returned on limit violations:
  • Too many metadata entries (validation_too_many_metadata_entries)
  • Oversized metadata values (validation_metadata_value_too_large)
  • Oversized total storage size (validation_total_storage_limit_exceeded)
• Updated integration E2E mock payloads.

Related Issue

Smart-contract metadata and storage size bounds protection enhancement.

Checklist

• Tests pass
• Lint is clean
• Documentation updated if needed

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[devJaja]

Nice implementation @Opulencechuks
make the CI/smart contracts checks pass

[devJaja]

@Opulencechuks
Resolve the conflicts