UPSTREAM PR #16971: webui: Add a "Continue" Action for Assistant Message

[DajanaV]

Mirrored from ggml-org/llama.cpp#16971

Close #16097

Add Continue and Save features for chat messages

What's new

Continue button for assistant messages

• Click the arrow button on any assistant response to keep generating from where it left off
• Useful for getting longer outputs or continuing after you've edited a response
• New content gets appended to the existing message

Save button when editing user messages

• Now you get three options when editing: Cancel, Save, and Send
• Save keeps your edit without regenerating the response (preserves the conversation below)
• Send saves and regenerates like before
• Useful when you just want to fix a typo without losing the assistant's response

Technical notes

• Added continueAssistantMessage() and editUserMessagePreserveResponses() methods to ChatStore
• Continue feature sends a synthetic "continue" prompt to the API (not saved to the database)
• Assistant message edits now preserve trailing whitespace for proper continuation
• Follows existing component architecture patterns

Demos

ggml-org/gpt-oss-20b-GGUF

demo1.mp4

unsloth/Qwen3-Coder-30B-A3B-Instruct-GGUF

demo2.mp4