# Todo 45.2 Event Fallback Semantics Plan

**Status:** done

## Result

Fallback now represents missing information rather than arbitrary invalid input. Complete-invalid and provider-resolved arguments skip fallback; strict JSON type/raw consistency and definition-error separation are covered.

## Goal

Make fallback and validation semantics suitable for latency/cost experiments: invoke LLM fallback only for incomplete deterministic resolution, compare raw and parsed JSON with type sensitivity, and distinguish plugin-definition failures from user argument errors.

## Scope

- Fall back only when required information is missing or a structured resolver explicitly marks its result incomplete.
- Complete but invalid arguments return `INVALID_ARGUMENTS` without an LLM call.
- Compare fallback raw JSON and parsed arguments canonically with JSON type sensitivity and reject non-standard JSON values.
- Add `DEFINITION_ERROR` for validator/schema infrastructure failures.
- Deep-copy/freeze registered schemas so post-registration mutation cannot bypass validation.
- Add focused regression tests for each quality-review finding.

## Files

- Modify: `src/agent_lab/application/events/models.py`
- Modify: `src/agent_lab/application/events/registry.py`
- Modify: `src/agent_lab/application/events/kernel.py`
- Modify: `src/agent_lab/application/tools.py` only for status compatibility mapping
- Modify: `tests/test_event_kernel.py`
- Modify: `tests/test_event_agent.py` only if fallback contracts change

## Plan

### Plan

1. Add RED tests for complete-invalid no-fallback, JSON type-sensitive mismatch, broken `$ref`, and schema mutation.
2. Verify each fails for the reviewed reason.
3. Implement explicit resolution completeness, canonical strict JSON consistency, definition-error status, and registry schema copying.
4. Run focused and full regressions.

### Act

- Test resolver output with all required fields present but wrong type/enum/additional property; fallback call count must remain zero.
- Test missing required fields; fallback remains exactly one call.
- Test raw `true` vs parsed `1`, raw `1` vs parsed `1.0`, nested mismatches, NaN, and Infinity; reject inconsistent/non-standard data.
- Test an unresolved or failing `$ref`; return `DEFINITION_ERROR`, not `INVALID_ARGUMENTS`.
- Register a definition, mutate the caller-owned schema afterward, and prove registry validation behavior is unchanged.
- If structured deterministic resolution is introduced, preserve plain-dict resolver compatibility and require an explicit incomplete flag only for optional-schema cases.
- Run RED, minimum implementation, focused/full verification.

### Observe

Confirm fallback counts now reflect missing information rather than arbitrary validation failures, raw/parsed values remain auditable, and plugin configuration failures are distinguishable from user mistakes.

### Update

- Mark 45, 45.1, and 45.2 `done` only after renewed reviews.
- Commit separately with latency/cost and definition-error risks in the body.

## Verification

- `uv run pytest tests/test_event_kernel.py tests/test_event_agent.py -q`
- `uv run pytest`
- `git diff --check`