feat(pczt): Add implementation of PCZT signing

[satoshiotomakan]

This pull request refactors the PSBT (Partially Signed Bitcoin Transaction) request handling across the UTXO-based chains, moving from a builder-based interface to a handler-based one. It introduces a new trait, PsbtRequestHandler, which consolidates PSBT parsing, updating, and serialization logic, and updates all relevant contexts and modules to use this new trait. The implementation for standard Bitcoin PSBT handling is moved and expanded, while redundant code is removed. These changes improve code clarity, extensibility, and unify PSBT handling logic.

Core PSBT API Refactoring

• Replaced the PsbtRequestBuilder trait with a new PsbtRequestHandler trait in rust/chains/tw_bitcoin/src/modules/psbt_request/mod.rs, consolidating PSBT parsing (parse_request), updating (update_signed), and serialization (serialize_psbt) into one interface. The default implementation for unsupported chains is provided by NoPsbtRequestBuilder.
• Updated all context implementations (tw_bitcoin, tw_bitcoincash, tw_groestlcoin, tw_decred, tw_komodo) to use PsbtRequestHandler instead of PsbtRequestBuilder, and added a Psbt associated type to the UtxoContext trait for better type safety and extensibility. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Standard PSBT Handler Implementation

• Renamed and refactored standard_psbt_request_builder.rs to standard_psbt_request_handler.rs, implementing the new PsbtRequestHandler trait with logic for parsing requests, updating signed PSBTs, and serializing them. The update logic previously found in psbt.rs is now encapsulated in the handler. [1] [2]

Codebase Cleanup

• Removed the now-unnecessary psbt.rs file and its standalone PSBT update function, as this logic is now handled by the new trait implementation. [1] [2]

Module and API Updates

• Updated all module usages and method calls throughout the codebase to use the new handler trait and method names (parse_request, update_signed, serialize_psbt) instead of the old builder and function names. This includes updates in the compiler, planner, and signer modules. [1] [2] [3] [4] [5] [6] [7] [8] [9]

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These changes collectively modernize and unify PSBT handling, making future maintenance and extension much easier.

[github-actions]

Binary size comparison

➡️ aarch64-apple-ios:

- 14.18 MB
+ 14.31 MB 	 +136 KB

➡️ aarch64-apple-ios-sim:

- 14.18 MB
+ 14.31 MB 	 +137 KB

➡️ aarch64-linux-android:

- 18.67 MB
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➡️ armv7-linux-androideabi:

- 15.62 MB
+ 15.80 MB 	 +188 KB

➡️ wasm32-unknown-emscripten:

- 13.31 MB
+ 13.46 MB 	 +150 KB

[Copilot]

Pull request overview

This pull request adds PCZT (Partially Collaborative ZCash Transaction) signing support for ZCash while refactoring the PSBT handling architecture across all UTXO-based chains from a builder-based pattern to a handler-based pattern.

Key Changes:

• Introduces a new PsbtRequestHandler trait that consolidates PSBT/PCZT parsing, updating, and serialization
• Implements PCZT format support for ZCash with deserialization, validation, transaction building, and signing
• Adds a Psbt associated type to UtxoContext for better type safety across different chain implementations

Reviewed changes

Copilot reviewed 30 out of 31 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
rust/chains/tw_bitcoin/src/modules/psbt_request/mod.rs	Refactored from PsbtRequestBuilder trait to PsbtRequestHandler trait with expanded methods for parsing, updating, and serializing
rust/chains/tw_bitcoin/src/modules/psbt_request/standard_psbt_request_handler.rs	Renamed from standard_psbt_request_builder.rs and implements the new handler trait with PSBT update logic moved from psbt.rs
rust/chains/tw_bitcoin/src/modules/psbt.rs	Removed - functionality moved into handler implementations
rust/chains/tw_bitcoin/src/modules/signer.rs	Updated to use new PsbtRequestHandler methods (parse_request, update_signed, serialize_psbt)
rust/chains/tw_bitcoin/src/modules/compiler.rs	Updated to use PsbtRequestHandler::parse_request instead of PsbtRequestBuilder::build
rust/chains/tw_bitcoin/src/modules/planner/psbt_planner.rs	Updated to use new handler trait methods
rust/chains/tw_bitcoin/src/context.rs	Updated BitcoinSigningContext trait to use PsbtRequestHandler and added Psbt associated type to StandardBitcoinContext
rust/chains/tw_bitcoincash/src/context.rs	Updated to use StandardPsbtRequestHandler and added Psbt associated type
rust/chains/tw_groestlcoin/src/context.rs	Updated to use StandardPsbtRequestHandler and added Psbt associated type
rust/chains/tw_decred/src/context.rs	Added Psbt = () type and updated to use NoPsbtRequestBuilder (no PSBT support)
rust/chains/tw_komodo/src/context.rs	Added Psbt = () type and updated to use NoPsbtRequestBuilder (no PSBT support)
rust/chains/tw_zcash/src/transaction/mod.rs	Refactored transaction version constants: split TRANSACTION_VERSION_4 (now 4) and OVERWINTERED_FLAG (0x80000000)
rust/chains/tw_zcash/src/modules/transaction_builder.rs	Updated to use overwintered_version() method that combines version with overwintered flag
rust/chains/tw_zcash/src/modules/signing_request.rs	Removed unused transaction_version() method, updated to use new version handling
rust/chains/tw_zcash/src/modules/pczt/mod.rs	New PCZT serialization/deserialization implementation with magic bytes and version handling
rust/chains/tw_zcash/src/modules/pczt/common.rs	PCZT global fields structure with transaction metadata and modification flags
rust/chains/tw_zcash/src/modules/pczt/transparent.rs	PCZT transparent bundle structures for inputs and outputs
rust/chains/tw_zcash/src/modules/pczt/sapling.rs	PCZT sapling bundle structure (empty spends/outputs enforced)
rust/chains/tw_zcash/src/modules/pczt/orchard.rs	PCZT orchard bundle structure (empty actions enforced)
rust/chains/tw_zcash/src/modules/pczt_request/zcash_pczt_request_handler.rs	Implements PsbtRequestHandler for ZCash with PCZT parsing, validation, and transaction building
rust/chains/tw_zcash/src/modules/pczt_request/utxo_pczt.rs	Converts PCZT inputs to internal UTXO representation with script parsing
rust/chains/tw_zcash/src/modules/pczt_request/output_pczt.rs	Converts PCZT outputs to internal transaction output representation
rust/chains/tw_zcash/src/context.rs	Updated to use PcztRequestHandler and added Psbt = pczt::Pczt type
rust/chains/tw_zcash/Cargo.toml	Added dependencies: postcard, serde, serde_with for PCZT serialization
rust/frameworks/tw_utxo/src/context.rs	Added Psbt associated type to UtxoContext trait
rust/tw_tests/tests/chains/common/bitcoin/mod.rs	Added transaction_psbt_b64() helper function for base64-encoded PSBT/PCZT
rust/tw_tests/tests/chains/zcash/zcash_sign.rs	Added tests for PCZT signing and unsupported version handling
rust/Cargo.lock	Updated with new dependencies and their transitive dependencies

Comments suppressed due to low confidence (1)

rust/chains/tw_zcash/src/transaction/mod.rs:40

• Documentation is outdated: The comment still references version 4 as 0x80000004, but the constant TRANSACTION_VERSION_4 has been changed to just 4. The overwintered flag (0x80000000) is now separate. Update the comment to reflect this change or clarify that the full version is 4 | OVERWINTERED_FLAG (which equals 0x80000004).

/// An overflow happens while converting to `i32` because 0x80000004 is greater than [`i32::MAX`].
/// However, the value will be serialized correctly.
pub const TRANSACTION_VERSION_4: u32 = 4;
pub const OVERWINTERED_FLAG: u32 = 0x80000000_u32;
pub const TRANSACTION_VERSION_GROUP_ID: u32 = 0x892F2085;
/// See https://github.com/zcash/zips/blob/main/zips/zip-0253.md#nu6-deployment CONSENSUS_BRANCH_ID section
pub const NU6_BRANCH_ID: H32 = H32::from_array([0x55, 0x10, 0xe7, 0xc8]);

const SEGWIT_NOT_SUPPORTED: bool = false;
const SAPLING_SPENDING_LEN: usize = 0;
const SAPLING_OUTPUTS_LEN: usize = 0;
const JOIN_SPLITS_LEN: usize = 0;

/// Transparent ZCash transaction (transparent).
/// https://github.com/zcash/zips/blob/998a97f2a1e5686e0d5c57f399a08b4daf100f8e/zips/zip-0243.rst
/// https://github.com/zcash/zcash/blob/a3435336b0c561799ac6805a27993eca3f9656df/src/primitives/transaction.h#L454
#[derive(Clone, Debug)]
pub struct ZcashTransaction {
    /// Transaction version.
    /// Currently, version 4 (0x80000004) is supported only.
    pub version: u32,
    // If transaction version is 4 (0x80000004), version group ID is 0x892F2085.

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