document contract late locking

doc/contracts.md

@@ -39,6 +39,8 @@ Each party chooses `--min_conf` when it first joins and cannot change it later.
 is used for the fee estimate, so any required inputs need enough confirmations at that point.
 A value of `0` allows unconfirmed non-coinbase outputs. Open contracts do not reserve funds,
 so a late-locked contract can fail if another transaction spends the available outputs first.
+Signing then returns `NotEnoughFunds`; revoke and recreate the contract, or use `--add-outputs`
+when creating it to reserve inputs.
 
 `contract new --ttl_blocks N` stops contract signing after `N` blocks. Finalized transactions
 can still be posted afterward.

libwallet/src/contract/actions/README.md

@@ -37,8 +37,6 @@ Separating side effects until the 'save_step' part would make these functions mu
 
 #### TODOs
 
- - Reserve funds across open late-locked contracts, or make the possible signing failure
-   clearer to callers.
  - Raise the replacement fee when `revoke` races a transaction already in the mempool.
  - Merge invoice-proof retrieval with the existing payment-proof API.
  - Add a Grin node API for kernel lookup by MMR index, then use the witness index instead