feat(sii-gateway): Implement P1 — LangGraph State & Topology

[Copilot]

Scaffolds the LangGraph cyclic graph skeleton for the SII Recruitment Gateway, implementing P1 of the sovereign AI screening pipeline with ISO 27001:2022 control anchoring and strict modular file structure.

State Schema (src/state.py)

GraphState — 9-field dict subclass threaded through every node:

Field	Type	Notes
transcript	str	PII-redaction-ready (A.5.34)
code_payload	str	Inert data; ephemeral sandbox only (A.8.10)
security_score	float	OWASP aggregate [0.0–1.0]
logic_rubric	dict	Algo + architecture sub-scores
audit_trace	Annotated[list[dict], operator.add]	Append-only; SHA-256 chain-of-trust ready
iso_controls_applied	Annotated[list[str], operator.add]	New (P1 ISO update) — every node appends its control ID
reflection_loops	int	Bounded by MAX_REFLECTION_LOOPS = 2
consensus_score	float	Weighted: security 40%, logic 35%, arch 25%
candidate_id	str	Opaque pseudonym — never raw PII/RUT

audit_trace and iso_controls_applied use Annotated[list, operator.add] so LangGraph fan-out merges appends correctly without clobbering concurrent node writes.

Graph Topology

START → ingestor (A.8.2) → rag_router (A.8.24) → evaluators (A.8.10)
          → reflection (A.5.34) ──[consensus < 0.7 AND loops < 2]──► evaluators
                                └──[otherwise]──► report_generator (A.8.2) → END

• route_reflection() — conditional router enforcing CONSENSUS_THRESHOLD = 0.7 and MAX_REFLECTION_LOOPS = 2
• build_graph() — wires topology with placeholder stubs; docstring contains explicit IMPORTANT guard against merging node logic into this file
• Five ISO control constants (ISO_CONTROL_*) importable by P2–P5 node modules for consistent audit trail entries

Dependencies

Added sii-gateway optional extra to pyproject.toml:

langgraph>=1.1.0
structlog>=25.0.0

Testing

• 23 pytest unit tests in tests/test_state.py covering all public functions, all ISO constant values, all route_reflection routing branches (threshold boundary, loop cap, missing keys), graph node registration, conditional edge wiring, and independent instance creation.

Checklist

• CI passed

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