# Simulation Bridge Prep — PREP-POLICY-ENGINE-30-002-SIMULATION-BRIDGE-C

Status: Draft (2025-11-20)
Owners: Policy Guild · Cartographer Guild
Scope: Capture the required simulation bridge inputs and outputs so POLICY-ENGINE-30-002 can start once overlay schema (30-001) lands.

## Dependencies
- Overlay projection contract (30-001) — needs metrics/log schema from 29-004.
- Cartographer graph API shape for reachability overlays.

## Proposed contract (to validate once 30-001 freezes)
- Input: overlay projection payload from 30-001 plus reachability summaries from Cartographer.
- Output (draft schema):
  - `simulation_id` (ULID), `tenant_id`, `scenario` descriptor.
  - `inputs`: overlay snapshot hash, policy profile hash, reachability baseline hash.
  - `results[]`: `{component_purl, advisory_id, status_before, status_after, reason, trace_ref}`.
  - `metrics`: duration, rule_eval_count, graph_nodes_touched.
- Determinism: stable ordering by `(tenant_id, component_purl, advisory_id)`; timestamps UTC RFC3339.

## Acceptance to flip PREP to DONE
- Overlay schema (30-001) version/Hash referenced in this file.
- Draft JSON schema for simulation bridge saved under `docs/modules/policy/schemas/simulation-bridge@draft.json`.
- Sample payload placed under `docs/modules/policy/samples/simulation-bridge@draft.json`.

## Handoff
Use this as the prep artefact for PREP-POLICY-ENGINE-30-002-SIMULATION-BRIDGE-C. Update hashes and samples once 30-001 publishes the overlay schema; then move the implementation task to DOING.