fix: avoid lazy RegTestParams construction in ZeroConfCoinSelector

[HashEngineering]

Problem

ZeroConfCoinSelector.isTransactionSelectable() compares a pending transaction's params against RegTestParams.get() for every pending output it evaluates:

(confidence.numBroadcastPeers() > 1 || tx.getParams() == RegTestParams.get());

RegTestParams.get() lazily runs the RegTestParams constructor, which recomputes the regtest genesis X11 hash and checkState()s it against a hardcoded constant.

When that lazy construction is first triggered on a contended background thread — notably the wallet's CoinJoin IO coroutines, which do heavy concurrent X11 hashing — a transient bad X11 result makes the checkState throw IllegalStateException, crashing coin selection / balance calculation. This happens on mainnet/testnet wallets that never use regtest.

Observed crash (dash-wallet, CoinJoin balance update):

java.lang.IllegalStateException
  at com.google.common.base.Preconditions.checkState(Preconditions.java:486)
  at org.bitcoinj.params.RegTestParams.<init>(RegTestParams.java:46)
  at org.bitcoinj.params.RegTestParams.get(RegTestParams.java:138)
  at org.bitcoinj.wallet.ZeroConfCoinSelector.isTransactionSelectable(ZeroConfCoinSelector.java:48)
  at org.bitcoinj.wallet.ZeroConfCoinSelector.shouldSelect(ZeroConfCoinSelector.java:36)
  at org.bitcoinj.wallet.DefaultCoinSelector.select(DefaultCoinSelector.java:62)
  at org.bitcoinj.wallet.WalletEx.selectCoinsGroupedByAddresses(WalletEx.java:502)
  at org.bitcoinj.wallet.WalletEx.getAnonymizableBalance(WalletEx.java:672)

The hardcoded regtest genesis constant is correct — verified that RegTestParams.get() succeeds under a correct X11 — so the failures are transient corruption of the X11 computation, not a stale constant.

Fix

Compare against NetworkParameters.ID_REGTEST (a plain field lookup) instead of constructing RegTestParams. Behavior is unchanged: RegTestParams sets id = ID_REGTEST, so the regtest special-case still applies — it just no longer recomputes/asserts the genesis hash on a hot, concurrent path.

🤖 Generated with Claude Code

Summary by CodeRabbit

Bug Fixes

• Fixed handling of zero-confirmation transactions in regression test mode, ensuring transactions are correctly identified and eligible for coin selection.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 47d0fca5-a639-466f-a9c3-a861b359bdd3

📥 Commits

Reviewing files that changed from the base of the PR and between b9856fd and e11e26f.

📒 Files selected for processing (1)

• core/src/main/java/org/bitcoinj/wallet/ZeroConfCoinSelector.java

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📝 Walkthrough

Walkthrough

ZeroConfCoinSelector now detects regtest mode via network ID comparison instead of reference equality. The logic in isTransactionSelectable checks NetworkParameters.ID_REGTEST.equals(tx.getParams().getId()) to determine transaction eligibility, supported by updated imports.

Changes

Network ID comparison for regtest eligibility

Layer / File(s)	Summary
Network ID comparison for regtest eligibility core/src/main/java/org/bitcoinj/wallet/ZeroConfCoinSelector.java	isTransactionSelectable regtest mode check changed from tx.getParams() == RegTestParams.get() reference equality to NetworkParameters.ID_REGTEST.equals(tx.getParams().getId()) network ID comparison. Imports updated to add NetworkParameters and remove RegTestParams.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A regtest check hops from reference to ID,
No more equality games, just network harmony,
Imports rearranged with gentle care,
One file fixed, zero flaws laid bare! 🎯

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and specifically describes the main change: replacing RegTestParams construction with NetworkParameters.ID_REGTEST comparison in ZeroConfCoinSelector.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/zeroconf-avoid-regtestparams-construction

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