feat: implement StateTransitionJsonConvert and fix PlatformAddress map key serialization

[Copilot]

Problem

StateTransition enum lacked StateTransitionJsonConvert implementation, forcing manual variant matching. Additionally, JSON serialization failed for address-based state transitions containing BTreeMap<PlatformAddress, V> with error "key must be a string" because PlatformAddress (enum with data) serializes as a complex object, violating JSON's string-key requirement.

Investigation revealed both serde_json::to_string_pretty() and to_json() fail identically since to_json() uses platform_value::to_value() internally, which relies on serde.

Changes

StateTransition trait implementations:

• Created json_conversion.rs - dispatches to_json() to variant implementations
• Created value_conversion.rs - dispatches conversion methods to variants
• Implemented StateTransitionFieldTypes returning empty vectors (paths are variant-specific)
• Added state-transition-json-conversion to dash-sdk-features

PlatformAddress map key serialization fix:

• Created platform_address_map_serde.rs - custom serde helpers that serialize PlatformAddress keys as Display strings ("P2PKH(hex...)") and deserialize via FromStr
• Applied to all transitions with BTreeMap<PlatformAddress, ...>:
  • AddressFundsTransferTransitionV0 (inputs, outputs)
  • AddressFundingFromAssetLockTransitionV0 (inputs, outputs)
  • AddressCreditWithdrawalTransitionV0 (inputs)
  • IdentityTopUpFromAddressesTransitionV0 (inputs)
  • IdentityCreateFromAddressesTransitionV0 (inputs)
  • IdentityCreditTransferToAddressesTransitionV0 (recipient_addresses)

WASM bindings update:

• Added state-transition-json-conversion feature to wasm-dpp2 Cargo.toml to maintain feature parity with wasm-dpp

Result

Both serialization paths now work:

// Serde (now works)
let json = serde_json::to_string_pretty(&state_transition)?;

// Custom (now works)
let json = state_transition.to_json(JsonStateTransitionSerializationOptions::default())?;

{
  "inputs": {
    "P2PKH(0101010101010101010101010101010101010101)": [1, 1000]
  }
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>feat: implement StateTransitionJsonConvert for top-level StateTransition enum</issue_title>
<issue_description>## Problem

In packages/rs-dpp/src/state_transition/mod.rs, the StateTransition enum derives Serialize (behind state-transition-serde-conversion feature), but serde_json::to_string_pretty(&state_transition) fails with "key must be a string" for any variant that contains BTreeMap<PlatformAddress, ...> (e.g. AddressFundsTransfer, AddressFundingFromAssetLock, AddressCreditWithdrawal, IdentityCreateFromAddresses, IdentityTopUpFromAddresses, IdentityCreditTransferToAddresses).

This happens because PlatformAddress is an enum that serializes as a complex structure, not a string, and JSON requires all object keys to be strings.

Every individual variant type already implements StateTransitionJsonConvert (which has a to_json() method that properly converts through platform_value::Value, stringifying identifiers and binary data). But the top-level StateTransition enum itself does NOT implement it, forcing consumers to match on all 15 variants manually.

Proposed Fix

Add an impl StateTransitionJsonConvert<'_> for StateTransition that dispatches to each variant's to_json(). This should go in a new file packages/rs-dpp/src/state_transition/json_conversion.rs (gated behind #[cfg(feature = "state-transition-json-conversion")]), similar to how value_conversion.rs or other dispatch files are structured. The implementation:

#[cfg(feature = "state-transition-json-conversion")]
impl StateTransitionJsonConvert<'_> for StateTransition {
    fn to_json(
        &self,
        options: JsonStateTransitionSerializationOptions,
    ) -> Result<serde_json::Value, ProtocolError> {
        match self {
            StateTransition::DataContractCreate(st) => st.to_json(options),
            StateTransition::DataContractUpdate(st) => st.to_json(options),
            StateTransition::Batch(st) => st.to_json(options),
            StateTransition::IdentityCreate(st) => st.to_json(options),
            StateTransition::IdentityTopUp(st) => st.to_json(options),
            StateTransition::IdentityCreditWithdrawal(st) => st.to_json(options),
            StateTransition::IdentityUpdate(st) => st.to_json(options),
            StateTransition::IdentityCreditTransfer(st) => st.to_json(options),
            StateTransition::MasternodeVote(st) => st.to_json(options),
            StateTransition::IdentityCreditTransferToAddresses(st) => st.to_json(options),
            StateTransition::IdentityCreateFromAddresses(st) => st.to_json(options),
            StateTransition::IdentityTopUpFromAddresses(st) => st.to_json(options),
            StateTransition::AddressFundsTransfer(st) => st.to_json(options),
            StateTransition::AddressFundingFromAssetLock(st) => st.to_json(options),
            StateTransition::AddressCreditWithdrawal(st) => st.to_json(options),
        }
    }
}

Note: StateTransitionJsonConvert has a blanket default to_json() that calls self.to_object() (from StateTransitionValueConvert). Since StateTransitionValueConvert is also not implemented for the top-level enum, the explicit override above is needed. It may also make sense to implement StateTransitionValueConvert for StateTransition with the same dispatch pattern.

Also consider adding state-transition-json-conversion to the dash-sdk-features list in packages/rs-dpp/Cargo.toml so SDK consumers get it by default.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes feat: implement StateTransitionJsonConvert for top-level StateTransition enum #3109

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[shumkov]

Please update wasm-dpp2 as well then

[lklimek]

@copilot Please update wasm-dpp2 to match changes in this PR.

[Copilot]

Please update wasm-dpp2 as well then

Updated in commit 314a1c6. Added state-transition-json-conversion feature to wasm-dpp2 Cargo.toml to match wasm-dpp.

@copilot Please update wasm-dpp2 to match changes in this PR.

Done in commit 314a1c6. Added state-transition-json-conversion feature to wasm-dpp2/Cargo.toml dependencies.