fix: handle CR in agent yes/no prompts

[arsis-dev]

Summary

ds4-agent now treats carriage return as a valid line terminator in its yes/no prompts.

This fixes an interactive exit path where a terminal could send \r after replying to:

Save current session? (y/n)

With the old fgets()-based parser, that response could remain visually stuck as y^M instead of being accepted cleanly.

Root cause

The prompt helper only parsed complete lines read by fgets(), which assumes newline-delimited input. Some terminal paths can deliver carriage return for Enter in this restored-terminal prompt path.

Change

agent_prompt_yes_no() now reads one byte at a time, records the first non-space answer, and accepts either \n or \r as the end of the response. EOF / Ctrl+D still declines the prompt.

Validation

Machine/backend: macOS on Apple M5 Max, Metal backend, default ds4_test model (ds4flash.gguf).

Commands run:

git diff --check -- ds4_agent.c
./ds4_test --server
make clean
make ds4-agent
make test

Results:

• git diff --check -- ds4_agent.c: passed.
• ./ds4_test --server: passed.
• make clean && make ds4-agent: passed.
• make test: passed (long-context, tool-call-quality, logprob-vectors, metal-kernels, and server all OK).