v1.4.485

Changes

PR #2169 by ksylvan: fix(core): route user input to the user message in BuildSession

• Routed user input through user messages in BuildSession, ensuring every request ends with a user message for broader model compatibility.
• Tracked explicit input placeholders instead of automatically appending input to the prompt.
• Separated system instructions from user input so input is no longer duplicated.
• Preserved raw mode input, attachment text, and multipart content during message construction.
• Maintained pattern endpoint responses by appending input when necessary, with new regression tests for message routing and pattern substitution.