[SDK-007] Add decorator-based skill authoring API

[AdeGneus]

Context

Python developers eventually need a safe @when/@action authoring API that compiles to the same SkillPackage contract as YAML.

Scope

• Create ori_sdk/decorators.py.
• Implement Agent, @when, @action, and Agent.compile().
• Compile to SkillPackage.
• Validate through the same normaliser path as YAML.

Non-Goals

• Does not execute skills locally.
• Does not bypass YAML-equivalent validation.
• Does not become required for bundled skills.

Technical Specification

@when(..., tier=...) requires explicit tier. Tier D implies bypass LLM in generated package. Tier C requires safe_default_action.

Acceptance Criteria

• Decorator output validates as SkillPackage.
• Tier C/D invariants enforced.
• pytest, mypy, and ruff pass.

Tests Required

Test	Verifies
test_agent_compile_to_skill_package	Decorators compile to typed package.
test_when_requires_tier	No implicit tier.
test_tier_c_requires_safe_default	Approval safety invariant.

Additional Test Coverage / Edge Cases

• Reject @when without explicit tier.
• Reject Tier C decorated triggers without safe_default_action.
• Ensure Tier D generated package bypasses LLM and does not generate prompts requiring LLM reasoning.
• Compile multiple triggers/actions and validate action defaults reference declared actions.
• Ensure callable/lambda condition serialization is explicit and never silently unsafe.

Invariants — Do Not Violate

• Every trigger must declare action_tier.
• Tier C requires safe default.
• Tier D bypasses LLM.

Dependencies

Blocked by:

• [SDK-001] Add typed SkillPackage models #3 — SDK-001 Add typed SkillPackage models

Unblocks:

• Nothing

Contract References

• P2-13 decorator authoring reference
• ori-specs/skill-package/v1.md

Priority

post-poc

Suggested Labels

blocked, post-poc