fix: handle thinking/assistant messages at end of chat history (#11791)

* fix: handle thinking/assistant messages at end of chat history

extractToolSequence threw "no user/tool message found" when the last
message was thinking or assistant (common with reasoning models when
assistant content is empty after thinking and gets filtered out).

* fix: guard against non-string NO_PROXY env value in getEnvNoProxyPatterns

Add typeof check before calling .split() on the NO_PROXY environment
variable to prevent "envValue.split is not a function" errors when the
value is not a string.