Week 40 · 2026

Highlights

3 PRs merged and 19 commits across two repos, with no releases. One issue was opened and is still open: #2891, that a ReqSn at the same version may drop or swap the pending incremental action. The merges are a fix for a node crash on fanout when a head holds tokens minted on layer 2, a fix to what the node reports as fanned out, and a code tidy. Both PRs opened this week merged within it.

Reactive. A head holding tokens minted on L2 crashed the node on Fanout (#2860, merged Friday, open since 8 September and first mentioned in W37). A fanout step spends the head output and re-creates it with the value of the distributed outputs taken off. A token minted inside the head was never in the head output on L1, so taking it off left a negative quantity, which tripped an assertion in cardano-ledger and killed the process. When choosing the outputs for a step, the node now leaves out any whose value the head output doesn't hold, so every other output can still be fanned out; outputs carrying L2-minted tokens stay behind, as they must (this is the limitation investigated in #2334). A step with nothing it can distribute is refused with FailedToConstructPartialFanoutTx, and if that was the first step the head reverts to closed. As a safety net, an assertion fired anywhere while building or posting a transaction is now caught and reported to clients as a new UnexpectedPostTxError instead of bringing the node down. Two end-to-end tests cover it: one mints on L2, closes, and checks the node reports the refusal and keeps running with the snapshot still held; the other mints on L1, deposits the tokens, and checks they come back on fanout. The profiled hydra-node build also now links with bfd on Linux, as gold couldn't reach its AArch64 branch stubs.

The fanout observation counted every output of the fanout transaction as fanned out, including the wallet's change output, so the TUI showed what looked like the full fee being sent back to the fuel key. It now takes only the number of outputs the redeemer says were distributed (#2892, opened and merged Friday). A follow-up commit on master fixed how the delegated demo from last week reads the head id.

A tidy across hydra-node and hydra-tx (#2890, merged Tuesday) replaced a number of comments with more self-descriptive code, a net 75 lines removed.

Ecosystem Support (M4). The Hydra Technical Workshop ran on Friday as Cardano Foundation Developer Office Hours #80, closing out M4.2 and with it the Ecosystem Support workstream.

KPI & Outcome Achievement (M6). Routine only: the W39 note published.