fix(sdk-coin-flrp): update address index computation and signing logic in txn builders

[mohd-kashif]

Summary: FLRP Signature Index Bug Fix

The Bug

Problem: P-chain import/export transactions for FLRP were failing on-chain with "wrong signature" errors, while identical AVAXP transactions succeeded.

Root Cause: The FlareJS library's pvm.e.newImportTx / pvm.e.newExportTx methods use matchOwners() internally to determine sigIndices (signature positions). When all 3 wallet addresses were passed to FlareJS, matchOwners() would select different signature indices than intended, causing a mismatch between:

• Which addresses the SDK embedded signatures for
• Which signature slots the on-chain verifier expected

Example of the mismatch:

UTXO addresses (sorted by hex on-chain):
  [0] BitGo  (hex: 3094db9d...)
  [1] Backup (hex: 7f807c5e...)  
  [2] User   (hex: c20336a9...)

Expected sigIndices for User+BitGo signing: [0, 2]
FlareJS was sometimes selecting: [0, 1] or other combinations

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The Fix

Solution: Pass only the 2 intended signing addresses to FlareJS builders, not all 3 wallet addresses.

Key Changes:

1. getSigningAddresses() method - Added to atomicTransactionBuilder.ts to determine the correct 2 signers:

   • Normal flow: User (index 0) + BitGo (index 1)
   • Recovery flow: BitGo (index 1) + Backup (index 2)

2. Updated transaction builders (ImportInPTxBuilder.ts, ExportInPTxBuilder.ts, ImportInCTxBuilder.ts):

   • Pass only 2 signing addresses to FlareJS's newImportTx/newExportTx
   • FlareJS's matchOwners() now correctly selects the 2 signers from the UTXO's address list

3. Change output fix (ExportInPTxBuilder.ts):

   • FlareJS was setting change outputs with only 2 addresses (the signing addresses)
   • Fixed to explicitly set all 3 wallet addresses on change outputs for proper multisig

4. C-chain import fee (ImportInCTxBuilder.ts):

   • Ensured the 1,000,000 nFLR baseTxFee is correctly applied for EVM gas costs

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How It Works in Production

Signing Flow (User signs first, BitGo signs second):

1. Wallet Platform sends transaction request with:
   - UTXOs (each with 3 addresses: user, bitgo, backup)
   - fromAddresses: [user, bitgo, backup] (convention order)
   - recoverSigner: false (normal) or true (recovery)

2. SDK determines signing addresses:
   - Normal: [user_address, bitgo_address]
   - Recovery: [bitgo_address, backup_address]

3. FlareJS builds transaction with sigIndices pointing to the
   correct 2 positions in the sorted UTXO address list

4. User signs → embedded signature placed in correct slot
   BitGo signs → finds empty slot (embedded signature matching)

5. Transaction submitted on-chain → signatures verify correctly

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On-Chain Verified Transactions

These transactions were built with the fix and accepted on Flare Coston2 testnet:

Transaction Type	TX ID	sigIndices
Import to P-chain	bgHnEJ64td8u31aZrGDaWcDqxZ8vDV5qGd7bmSifgvUnUW8v2	[0, 2]
Export from P-chain	nSBwNcgfLbk5S425b1qaYaqTTCiMCV75KU4Fbnq8SPUUqLq2	[0, 2]
Import to C-chain	2t4gxEAdPLiiy9HsbjaQun1mVFewMoixNS64eZ56C38L4mpP1j	[0, 2]

sigIndices [0, 2] meaning:

• Position 0 = BitGo (hex 3094db9d... sorts first)
• Position 2 = User (hex c20336a9... sorts third)

This matches the expected signing pair (User + BitGo) for normal transactions.

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[Copilot]

Pull request overview

This PR fixes a critical bug in FLRP (Flare P-chain) atomic transactions where import/export transactions were failing on-chain with "wrong signature" errors. The root cause was that FlareJS's matchOwners() function was selecting different signature indices than intended when all 3 wallet addresses were passed to the transaction builders.

Changes:

• Added getSigningAddresses() method to pass only 2 signing addresses (user+BitGo or backup+BitGo) to FlareJS instead of all 3 wallet addresses
• Fixed change output creation in ExportInPTxBuilder to ensure all 3 addresses are included for proper multisig
• Updated test data with new transaction hashes reflecting the corrected sigIndices
• Added on-chain verified test cases for Import P, Import C, and Export P transactions

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
modules/sdk-coin-flrp/src/lib/atomicTransactionBuilder.ts	Added getSigningAddresses() method and simplified credential/addressMap creation logic
modules/sdk-coin-flrp/src/lib/ImportInPTxBuilder.ts	Updated to use getSigningAddresses() and pass only 2 addresses to FlareJS
modules/sdk-coin-flrp/src/lib/ImportInCTxBuilder.ts	Updated to use getSigningAddresses() and pass only 2 addresses to FlareJS
modules/sdk-coin-flrp/src/lib/ExportInPTxBuilder.ts	Updated to use getSigningAddresses() for signing but all 3 addresses for change outputs
modules/sdk-coin-flrp/test/unit/lib/signatureIndex.ts	Deleted comprehensive 1377-line test file with extensive signature index coverage
modules/sdk-coin-flrp/test/unit/lib/importInPTxBuilder.ts	Added on-chain verified test case, removed extensive address ordering tests
modules/sdk-coin-flrp/test/unit/lib/importInCTxBuilder.ts	Added on-chain verified test case, removed extensive address ordering tests
modules/sdk-coin-flrp/test/unit/lib/exportInPTxBuilder.ts	Added on-chain verified test case with change output verification, removed address ordering tests
modules/sdk-coin-flrp/test/unit/flrp.ts	Updated change amount assertions to match new transaction data
modules/sdk-coin-flrp/test/resources/transactionData/*.ts	Updated test data with new transaction hashes and hex values
modules/sdk-coin-flrp/test/resources/account.ts	Added ON_CHAIN_TEST_WALLET with verified test keys

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