slabbed-compat-safety-contract

name	slabbed-compat-safety-contract
description	Define Slabbed’s compatibility guardrails to avoid breaking vanilla behavior or modded blocks while adding slab-top support.

Slabbed — Compatibility Safety Contract

Goal

Keep Slabbed safe and predictable in modpacks:

• Do not break vanilla placement/survival rules outside slab-top support
• Do not assume all partial blocks behave like slabs
• Avoid global hooks that change unrelated behavior

Non-goals

• Full “compat with every mod” promise
• Special handling for stairs/fences/walls/trapdoors unless explicitly planned

Scope of support

Slabbed extends “top support” only for:

• Vanilla SlabBlock bottom/top/double variants
• Explicitly whitelisted slab-like blocks (only if added later with clear criteria)

Slabbed does NOT automatically treat as support:

• stairs
• fences
• walls
• trapdoors
• panes
• carpet-like custom shapes unless explicitly added later.

Hook strategy rules

1. Prefer the narrowest hook that fixes the category.
2. Prefer per-block/category hooks over global redirects if the global change impacts unrelated blocks.
3. If using a shared helper predicate, it must be limited to slab semantics only.
4. All slab semantics must route through SlabSupport (single source of truth).

Modded block safety

• Never assume a modded slab extends vanilla SlabBlock.
• If handling modded slabs later, gate by:
  • interface/marker (preferred), or
  • explicit registry whitelist, or
  • shape predicate proven equivalent to slab top face
• Do not attempt heuristic “any half height block counts” logic.

Vanilla behavior preservation (mandatory checks)

After any new hook:

• Baseline full-block lane must behave exactly like vanilla
• Existing categories must not regress
• No new placement allowed on air/liquids that vanilla forbids
• No changes to collision behavior for slabs themselves

Failure protocol

If a hook causes unintended changes:

1. Revert to last known good tag
2. Reduce scope (targeted mixin)
3. Add regression test notes to the test matrix
4. Re-apply in smaller pieces

Output report format

When invoking this contract during review, report:

• Hook type: shared vs targeted
• Potential blast radius (1–2 lines)
• Vanilla behavior checks performed
• Modded block assumptions made (must be “none” unless explicitly justified)

Stop conditions

• If you cannot explain why a hook is safe in 2 sentences, it’s too broad
• If a shared hook alters behavior outside slab contexts, revert and target