Feat/issue 12 manifest metadata

[Leoyzen]

Summary

Resolves #12 - Enables support for YAML anchors and metadata fields in AgentsManifest configuration files.

Changes

New Features

• Metadata Fields: Allows top-level fields with prefixes ., _, and x- for YAML anchors and custom metadata
• Warning System: Unknown fields now trigger warnings instead of raising validation errors, improving user experience
• YAML Anchors: Users can now define anchors (e.g., &default_settings) and reference them (e.g., *default_settings) to reduce configuration duplication

Implementation

• Modified src/agentpool/models/manifest.py:
  • Changed extra="allow" in model_config to accept extra top-level fields
  • Added @model_validator(mode="after") to validate and warn about unknown fields
  • Preserved strict validation for nested models (agents, teams, etc.)
• Added comprehensive test suite in tests/manifest/test_metadata_fields.py:
  • Tests for allowed metadata fields (.anchor, _meta, x-custom)
  • Tests for warning generation on unknown fields
  • Tests for mixed scenarios

Test Coverage

All tests passing (27/27):

• ✅ New metadata field tests (3 tests)
• ✅ Existing manifest tests (24 tests)
• ✅ Regression test fixed for missing response references

Example Usage

# Define anchors for reuse
.shared_config: &default_settings
  type: native
  model: "openai:gpt-4o"
  system_prompt: "You are a helpful assistant"
# Custom metadata
x-version: "1.0.0"
_internal: "for internal use only"
responses:
  MyResponse:
    type: object
    fields:
      message: str
agents:
  coder: *default_settings
    name: coder
    tools:
      - read
      - write

Technical Details

• Validation Logic: validate_extra_fields() method checks all extra top-level keys
• Allowed Prefixes:
  • . (dot) - for YAML anchors and hidden fields
  • _ (underscore) - for internal/metadata fields
  • x- - for custom extensions (following OpenAPI convention)
• Warning Behavior: Unknown fields log a WARNING with message: "Unknown field '{key}' in manifest. This field will be IGNORED."

Related Issue

Fixes #12