Deterministic tool-call receipt schema for invocation steps #4502
Description
Problem
Tool-call evidence is not fully standardized as a deterministic, machine-readable receipt contract across invocation steps.
Expected behavior
- Invocation tool steps should emit a stable receipt shape suitable for replay/audit automation.
Acceptance criteria
- Define/implement receipt schema for tool call step metadata.
- Add tests validating required fields and deterministic serialization behavior.
Validation
- Unit tests asserting schema presence and stable field expectations.
- Existing invocation/tool flow tests continue to pass.