Integrating IBTs and wrappers

Core v2 expects its IBT to implement a FungibleVault-style surface. A compatible vault can be used directly; incompatible yield sources require a wrapper.

Expected behavior

The PT relies on the IBT for:

• Underlying and share token identity and decimals.
• Deposit, redeem, and exact-output withdrawal operations.
• Preview functions and maximum serviceable amounts.
• A consistent share-to-underlying conversion rate.
• Transferable SEP-41 shares and allowances.

The IBT must already have positive total assets before a PT market can initialize.

Wrapper framework

The abstract Spectra wrapper provides shared vault logic, conversion previews, slippage-aware variants, pause and upgrade controls, and optional reward-proxy hooks. It is a Rust library and does not produce a deployable contract by itself.

A concrete wrapper supplies the yield-source operations and rate model while preserving the wrapper solvency invariant:

backing position >= outstanding wrapper shares

Blend adapter

Blend bTokens are lending-pool positions rather than transferable token contracts. The Blend wrapper holds the position and issues transferable shares representing bTokens one-for-one.

The adapter uses Blend's 12-decimal b_rate and limits exits to available pool liquidity. Core refreshes the rate before withdrawal-sensitive calculations to handle rate decreases caused by bad-debt socialization.

Review checklist

• Confirm the vault surface and SEP-41 authorization behavior.
• The IBT should closely follow the FungibleVault/ERC-4626 model.
• Check whether the IBT charges fees; preview_redeem should account for them.
• Round deposits and redemptions conservatively and enforce minimum outputs.
• Make max_* views reflect serviceable liquidity, not only accounting value.
• Define pause, upgrade, reward, and emergency-withdrawal authorities.
• Wrapper conversion and preview functions should reproduce the exact rate behavior used by the IBT's deposit and redemption flows.
• Test rate decreases, loss recovery, reward claims, and same-ledger state changes.