Fix a pipeline freeze when using AWS Nova Sonic. The freeze occurs if the user starts speaking before we've finished sending the "trigger " audio (AWS Nova Sonic can only start speaking in response to a user utterance, so we have a simulated user utterance to "trigger" the bot speaking without the user having actually spoken first).

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to **Pipecat** will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Fix a pipeline freeze when using AWS Nova Sonic, which would occur if the
+  user started early, while the bot was still working through
+  `trigger_assistant_response()`.
+
 ## [0.0.75] - 2025-07-08
 
 ### Added