sandbox phase 2: SIS → PDP transform + validation

[William-Hill]

Parent: #116 · Spec: docs/superpowers/specs/2026-05-02-sis-pdp-ar-sandbox-design.md

Scope

• sandbox/sis_to_pdp.py reads sandbox_sis, applies PDP transformations (field maps, derived columns, cohort assignment), writes to sandbox_pdp schema.
• Two-pass validation: preflight (report-only) and submit (writes + emits upload_event).
• Rules expressed in sandbox/pdp_rules.yaml for non-engineer auditability.
• Validation output is structured (row-level errors, coercions, anomalies) and consumable by phase 5 UI.

Acceptance

• Preflight produces a structured report without writing
• Submit writes to sandbox_pdp + emits upload_event
• Rules file is human-readable and covers all PDP-required transformations
• Validation output schema documented for phase 5 UI consumption

Estimate: 3–5 days. Depends on phase 1 (#).