V2 P0: Claim/Evidence data foundations + Neo4j migrations

[cursor]

Background

V2 Evidence Graph and Reliability Gate need Claim/Evidence entities. DecisionEvent remains the atomic write unit today.

Problem Statement

No Claim/Evidence Pydantic models, temporal lifecycle fields, or graph schema for claims/evidence.

Proposed Solution

• Add models: Claim, Evidence, ReliabilityDecision (+ temporal fields)
• Neo4j migrations V010+: Claim/Evidence nodes; SUPPORTS / CONTRADICTS / ASSERTS
• Adapter: DecisionEvent → Claim without breaking existing writes
• Feature flag: CORTEX_EVIDENCE_GRAPH

Acceptance Criteria

• Models + migrations + migrate runner tests
• Backward-compatible Decision writes still work with flag off
• Documented in CURRENT_STATE / DECISIONS ADR

Depends on

Phase 0 audit (#67 if created)

Plan ref

todo data-foundations