Rule modules

The single most important architectural choice in Deducible: the engine is separate from the rule-base. The compiler knows how to check a contract; what counts as compliant is supplied by a rule module — plain JSON that a scholar or standards body can author and ratify without touching Rust.

This is what closes the authority gap. Ratification becomes a module, not a fork.

Shape of a module

rules/aaoifi.rules.json

{
  "authority": "AAOIFI",
  "musharakah_mutanaqisah": {
    "required_invariants": ["risk_sharing", "no_capital_guarantee", "valuation_specified"],
    "constraints": [
      { "code": "RISK-1", "field": "loss_share", "op": "eq", "value": "by_ownership",
        "citation": "AAOIFI SS No. 12" }
    ]
  }
}

A module declares, per instrument, the invariants that must hold and the constraints ({ code, field, op, value, citation }) that encode them. The engine loads it and checks the spec against it — data-driven and regime-neutral.

Selecting a module

deducible check home.fiqh --rules aaoifi      # or: --rules dsn-mui

meta { rules: "dsn-mui"; }                 # or pin it in the spec

Modules are discovered in ./rules or $FIQHC_RULES_DIR.

Jurisdictional divergence, demonstrated

The same musharakah_mutanaqisah.fiqh is consistent under AAOIFI but refused under DSN-MUI, which additionally requires an explicit profit-sharing ratio (nisbah):

$ deducible check musharakah_mutanaqisah.fiqh --rules aaoifi
✓ consistent

$ deducible check musharakah_mutanaqisah.fiqh --rules dsn-mui
✗ INV-1  required invariant "nisbah_explicit" is missing (DSN-MUI No. 08).

A riba-disguised loan is refused under both, each with that authority’s own citations.

Why this matters

• Pluralism, honestly modelled. Fiqh differs between schools and standards bodies; the rule module makes that difference explicit and auditable instead of baking one opinion into the tool.
• A clean ratification surface. A Shari’ah-advisory firm ratifies one JSON module — a bounded, reviewable artifact — rather than auditing a compiler.
• The engine stays neutral. It enforces whatever the active, human-authored module says, and reports which authority and citation each verdict rests on.