* feat: add flow_structure() serializer for Flow class introspection
Adds a new flow_serializer module that introspects a Flow class and returns
a JSON-serializable dictionary describing its complete graph structure.
This enables Studio UI to render visual flow graphs (analogous to how
crew_structure() works for Crews).
The serializer extracts:
- Method metadata (type, triggers, conditions, router paths)
- Edge graph (listen and route edges between methods)
- State schema (from Pydantic model if typed)
- Human feedback and Crew reference detection
- Flow input detection
Includes 23 comprehensive tests covering linear flows, routers,
AND/OR conditions, human feedback, crew detection, state schemas,
edge cases, and JSON serialization.
* fix: lint — ruff check + format compliance for flow_serializer
* fix: address review — PydanticUndefined bug, FlowCondition tuple handling, dead code cleanup, inheritance tests
1. Fix PydanticUndefined default handling (real bug) — required fields
were serialized with sentinel value instead of null
2. Fix FlowCondition tuple type in _extract_all_methods_from_condition —
tuple conditions now properly extracted
3. Remove dead get_flow_inputs branch that did nothing
4. Document _detect_crew_reference as best-effort heuristic
5. Add 2 inheritance tests (parent→child method propagation)
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Co-authored-by: Joao Moura <joao@crewai.com>
