HRX llama-cli: unknown flag (-no-cnv) silently enters interactive mode and busy-loops >-prompts into output when stdin is not a TTY (fills disk) #561

Summary

On the HRX llama.cpp fork, llama-cli with an unknown flag (e.g. -no-cnv, which this fork does not define — it wants -st / --single-turn) silently drops into interactive conversation mode, and when stdin is not a TTY (piped, redirected, run under a job wrapper) it busy-loops printing > prompts to the output with no input ever arriving. In a redirected run this fills the output file unbounded — observed twice, once reaching 9.4 GB before it was caught and killed.

Repro

llama-cli -m <model.gguf> -ngl 99 -fa on -dev HRX0 -no-cnv -p "..." -n 32 </dev/null >out.txt 2>&1

-no-cnv is not a recognized flag on this fork; instead of erroring, the CLI enters interactive mode, and with stdin closed/redirected it loops emitting > into out.txt until killed or the hold expires.

Impact

• Unbounded output file growth (9.4 GB and 2×20 GB observed in HRX bring-up runs) → can drive a shared box below its disk floor.
• Silent: the run looks "started" but produces only prompt characters.

Proposed fix (any of)

1. Treat -no-cnv as an alias of -st / --single-turn (it was clearly intended as "no conversation").
2. Refuse unknown flags with a nonzero exit and usage, instead of ignoring them and falling through to interactive mode.
3. Add a stdin-is-not-a-TTY guard: in (accidental) interactive mode, if isatty(STDIN) is false, exit cleanly at EOF instead of looping on empty reads.

(1)+(3) together are the most robust. Filed on the engine tracker because fork issues are disabled.