Function create_pczt_from_proposal 

pub fn create_pczt_from_proposal<DbT, ParamsT, InputsErrT, FeeRuleT, ChangeErrT, N>(
    wallet_db: &mut DbT,
    params: &ParamsT,
    clock: &impl Clock,
    rng: &mut impl CryptoRng,
    account_id: <DbT as WalletRead>::AccountId,
    ovk_policy: OvkPolicy,
    proposal: &Proposal<FeeRuleT, N>,
    expiry_height: Option<BlockHeight>,
    orchard_pool_padding: BundlePadding,
) -> Result<Pczt, CreateErrT<DbT, InputsErrT, FeeRuleT, ChangeErrT, N>>
where
    DbT: WalletWrite + WalletCommitmentTrees,
    ParamsT: Parameters + Clone,
    FeeRuleT: FeeRule,
    <DbT as WalletRead>::AccountId: Serialize,

Available on crate feature pczt only.

Constructs a transaction using the inputs supplied by the given proposal.

Only single-step proposals are currently supported.

Returns a partially-created Zcash transaction (PCZT) that is ready to be authorized. You can use the following roles for this:

• pczt::roles::prover::Prover
• pczt::roles::signer::Signer (if you have local access to the spend authorizing keys)
• pczt::roles::combiner::Combiner (if you create proofs and apply signatures in parallel)

Before sending the PCZT to an external Signer, create a signer view with redact_pczt_for_signer and retain the original for combination. A Signer that independently obtains the relevant full viewing keys and returns only Orchard-protocol signature contributions can instead use redact_pczt_for_batch_signer.

Once the PCZT fully authorized, call extract_and_store_transaction_from_pczt to finish transaction creation.

expiry_height, when set, replaces the builder-derived expiry before the PCZT is finalized. Applying this override after finalization can invalidate dummy spend signatures.

A nonzero expiry_height below the proposal’s min_target_height is rejected with Error::ExpiryHeightBelowTargetHeight. An expiry_height of zero, which disables expiry, is exempt from this check.

orchard_pool_padding selects the transactional bundle padding for the Orchard bundle; pass BundlePadding::DEFAULT. The Ironwood bundle’s padding is not a caller’s to choose: it is derived from the proposal by Step::ironwood_bundle_padding, so that it matches the action count the fee was computed from.

rng supplies the randomness used to construct the PCZT and to sign its dummy spends.