# Preservation Rules

## Immutable Assets

- Code blocks and fence language.
- Image URLs, alt text, and ordering.
- Regulated wording or fixed numeric thresholds.

## Controlled Rewriting

Allowed:
- Filler removal.
- Sentence smoothing.
- Structural reorganization for lesson clarity.

Not allowed:
- Silent factual changes.
- Unmarked omission of required source evidence.
- Variable references before collection.

## Deterministic Block Policy

Use deterministic blocks only for truly fixed content. Do not lock entire lessons in fixed syntax.
