[Smart Contracts] Add Storage Size Limits Per-Agent to Prevent Unbounded Growth

[devJaja]

Problem

The agent-registry contract allows agents to store arbitrary metadata with no size limits. A malicious or buggy agent could write unbounded data to storage, consuming the contract's rent budget and increasing costs for all users.

Current State

Agent data stored in agent_registry includes metadata blobs with no size validation:

pub struct AgentData {
    pub agent_type: Symbol,
    pub metadata: Map<Symbol, Val>,  // unbounded!
    pub status: Symbol,
}

Proposed Solution

1. Define maximum sizes:
   • MAX_AGENT_ID: usize = 64
   • MAX_METADATA_ENTRIES: usize = 16
   • MAX_METADATA_VALUE_SIZE: usize = 256 (bytes)
   • MAX_TOTAL_AGENT_STORAGE: usize = 4096 (bytes)
2. Add validation in register_agent() and update_agent():
   • Check symbol lengths
   • Check metadata map size
   • Check total serialized size
3. Return typed errors for size violations
4. Add tests for boundary conditions

Acceptance Criteria

• Size constants defined
• Validation rejects oversized agent IDs
• Validation rejects too many metadata entries
• Validation rejects oversized metadata values
• Total agent storage bounded
• Tests verify rejection at each boundary
• Error messages indicate which limit was exceeded

Difficulty

Medium — validation logic only, no storage layout changes

Labels

smart-contract stellar enhancement

[aweledavid3]

Hello maintainer I'll like to work on this issue please can you assign me

[OpensrcLord]

Hello @maintainer, I’ve gone through the requirements and I’m confident I can implement a proper solution that matches the acceptance criteria. Kindly assign this issue to me. And I will deliver at the shortest possible time.

[Opulencechuks]

I am confident that I can implement this issue having worked on similar issues in the past

[grantfox-oss]

🦊 GrantFox — @Opulencechuks has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #115)
2. Your PR will be reviewed by the Epta-Node maintainers

Good luck! Track your progress on GrantFox.