SessionStart hooks fire on every user prompt instead of only at session
start. The root cause is clearSessionHookState(), called on every
session.idle event, which clears sessionFirstMessageProcessed. This
resets the isFirstMessage guard, making it always return true, so
SessionStart hooks execute on every prompt.
sessionFirstMessageProcessed is session-level state (tracks whether the
first message has been processed) and should only be cleared in
clearAllSessionHookState() on session deletion/disposal, not on idle.
sessionErrorState and sessionInterruptState remain cleared on idle since
they are per-response transient state.
brooksbUWO