tests: fix test_htlc_no_force_close flake

l3 was watching its own (censored) commitment tx, so it can take a while before it notices l2's commitment is the one onchain and tries to fulfill the HTLC. If we released the censored txs before that, we only broadcast l3's own commitment txs, which conflict with l2's already-mined commitment and are rejected, leaving the mempool empty and making the final generate_block(wait_for_mempool=1) time out.

Wait for l3's fulfill attempt (a tx spending an output of l2's commitment) before releasing. Also release only those txs, deduped by txid and in capture order, so duplicate or RBF fulfill attempts are not broadcast as stale versions.

Changelog-None

Author: daywalker90

tests/test_closing.py

@@ -4377,11 +4377,30 @@ def censoring_sendrawtx(r):
 
     # Now, surprise!  l3 fulfills htlc (l2 loses out!)
     assert htlc_txs != []
+    # l3 was watching its own (censored) commitment tx, so it takes a while
+    # before it notices l2's commitment is the one onchain and tries to fulfill
+    # the HTLC by spending its HTLC output.  Wait for that attempt before we
+    # release the censored txs, otherwise we only broadcast l3's own commitment
+    # txs, which conflict with l2's (already mined) commitment and are rejected.
+    commit_txid = only_one(l2.rpc.listpeerchannels(l3.info['id'])['channels'])['scratch_txid']
+    wait_for(lambda: any(vin['txid'] == commit_txid
+                         for tx in htlc_txs
+                         for vin in bitcoind.rpc.decoderawtransaction(tx)['vin']))
+
+    # l3 can try the fulfill more than once (it rebroadcasts the same tx, or
+    # RBFs it if the feerate estimate changed), so keep only the txs spending
+    # l2's commitment, deduped by txid and in capture order (so a later RBF
+    # version replaces an earlier one).  l3's own commitment txs conflict with
+    # l2's mined commitment and can never be mined, so don't bother releasing
+    # them.
+    fulfill_txs = {}
     for tx in htlc_txs:
-        try:
-            bitcoind.rpc.sendrawtransaction(tx)
-        except bitcoin.rpc.VerifyError:
-            pass
+        d = bitcoind.rpc.decoderawtransaction(tx)
+        if any(vin['txid'] == commit_txid for vin in d['vin']):
+            fulfill_txs[d['txid']] = tx
+
+    for tx in fulfill_txs.values():
+        bitcoind.rpc.sendrawtransaction(tx)
 
     # l2 should note this, but not crash, at least.
     bitcoind.generate_block(1, wait_for_mempool=1)