# Constraints & Limits

## 3.1 Constraints & Limits

The Modulexo system enforces explicit constraints at contract level.

These constraints are designed to:

• Prevent misuse\
• Enforce accounting integrity\
• Block invalid state transitions\
• Protect deterministic distribution

All constraints are implemented through revert conditions and bounded parameter logic.

***

## I. Asset Enablement Constraint

Recycle execution requires asset registration.

If a token is not enabled in the Registry:

```
ENGINE_ASSET_NOT_ENABLED
```

The transaction reverts.

There is no fallback path.

***

## II. Unit Availability Constraint

Recycle execution requires sufficient accounting units.

If insufficient units are available:

```
ENGINE_BAD_UNITS
LEDGER_INSUFFICIENT_ALLOWANCE
```

The transaction reverts.

Units cannot go negative.

***

## III. Cap Enforcement (Ledger)

If a registry-defined cap exists:

Ledger enforces:

```
LEDGER_CAP_EXCEEDED
```

This prevents excessive allocation per beneficiary or per token.

Cap logic is enforced before state mutation.

***

## IV. Self-Sponsor Restriction

The Ledger prevents:

```
LEDGER_SELF_SPONSOR_FORBIDDEN
```

This ensures providers cannot artificially create circular inventory relationships.

***

## V. Engine-Only Consumption

Ledger consumption is restricted:

```
LEDGER_ONLY_ENGINE
```

Only RecyclingEngine may consume units.

Users cannot directly manipulate unit balances.

***

## VI. Native Value Constraint

Recycle execution requires non-zero native payment.

If `msg.value == 0`:

```
ENGINE_NO_VALUE
```

Execution reverts.

***

## VII. Router Safety Checks

Before routing native rails:

Engine verifies:

• Router address valid\
• Rail values non-zero

If invalid:

```
ENGINE_ROUTER_MISMATCH
ENGINE_ROUTER_ZERO_RAIL
```

Execution reverts.

No partial rail allocation occurs.

***

## VIII. Division Safety

If distribution math would divide by zero:

```
ENGINE_DIV_BY_ZERO
```

Execution reverts.

This protects:

```
accNativePerWeight
```

from invalid calculation.

***

## IX. Claim Safety

During claim:

If native transfer fails:

```
ENGINE_CLAIM_TRANSFER_FAILED
```

The entire transaction reverts.

No partial debt update.

No inconsistent state.

***

## X. Parameter Bounds

RecyclingEngine parameters:

```
baseWeightPriceWei
decayPerDayPPM
linearGrowthSlopeWeiPerDay
```

May be subject to bounded validation (if implemented).

Out-of-bounds input reverts:

```
ENGINE_PARAM_OOB
```

Parameter updates emit:

```
ParamsSet(...)
```

No silent changes.

***

## XI. Ownership Safeguards

Ownership transfer requires:

```
transferOwnership()
acceptOwnership()
```

Incorrect caller reverts:

```
O2S_NOT_OWNER
O2S_NOT_PENDING_OWNER
O2S_ZERO_ADDRESS
```

Ownership cannot be hijacked.

***

## XII. Reentrancy Protection

RecyclingEngine includes:

```
ReentrancyGuardReentrantCall
```

Prevents nested execution during recycle or claim.

This protects distribution math and rail routing.

***

## XIII. Atomicity Constraint

All recycle operations execute atomically.

If any of the following fails:

• Unit consumption\
• Rail routing\
• Weight minting\
• Distribution update

The entire transaction reverts.

There is no partial execution path.

***

## XIV. No Negative Ledger States

The following invariants are enforced:

• recyclableBalance ≥ 0\
• weightOf ≥ 0\
• totalWeight ≥ 0\
• rewardDebt ≤ accrued entitlement

State cannot drift negative.

***

## XV. Separation Constraints

Recycle contracts cannot:

• Modify Fund share balances\
• Override governance\
• Access treasury directly

Fund contracts cannot:

• Modify recycle ledger\
• Alter distribution math

These boundaries prevent systemic coupling.

***

## XVI. Constraint Summary

| Constraint        | Enforced By | Failure Result |
| ----------------- | ----------- | -------------- |
| Asset enabled     | Engine      | Revert         |
| Unit availability | Ledger      | Revert         |
| Cap limit         | Ledger      | Revert         |
| Non-zero native   | Engine      | Revert         |
| Router integrity  | Engine      | Revert         |
| Division safety   | Engine      | Revert         |
| Claim transfer    | Engine      | Revert         |
| Ownership rules   | O2S         | Revert         |
| Reentrancy        | Guard       | Revert         |

No silent failure modes exist.