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# Periscope Cursor Engineering Rules

Mandatory for every Cursor agent working on Periscope. This section is copied from `docs/development/CODING_CONSTITUTION.md` and must not contradict that master.

## 1. Architecture

Three layers:

| Layer | Location | Purpose |
| --- | --- | --- |
| Core | `backend/periscopex/` (native under `periscope/src` when split) | Models, parsers, graph, validator, passives, taxonomy, derating |
| Backend | `backend/` | FastAPI, pipeline, SSE, storage |
| Frontend | `frontend/` | Next.js app: dashboard, progress, report, derating, admin |

Physical split (when present): `periscope/src` = Periscope; `periscope/dependency` = inherited PinScope in-tree. Docker copies dependency then src so native files win **only when they are real replacements**, not stamped copies.

Import switch rule: keep calling `dependency/` until pytest + deploy smoke pass for that slice, then switch imports. Fail-soft: if verification fails, leave the inherited path.

Netlist is a queryable bipartite graph (components + nets). Deterministic checks beat heuristics. Finding normalization is downgrade-only. Cross-IC excerpt budget is global plus per-neighbor.

Content-addressed datasheets live under `library/datasheets/`. DigiKey matches exact MPN only. Value-string passives stay per-project, never the shared library.

Do not add auth, billing, or extra services unless the task needs them. Do not add a second frontend component library.