Previously --log-file only captured LOG()/LOG_TEE() macro output; the
LLAMA_LOG_* engine lines, server_log() output, and common_log (SLT_*/SRV_*)
slot/checkpoint lines all went to stderr only.
Route all three sinks to --log-file:
- llama_log_tee_callback tees raw llama/ggml output to the file and stderr
- server_log() mirrors its stdout line to the file
- common_log_set_file_ptr() shares LOG_TARGET's FILE* with the common_log
worker, which natively tees to stderr and file (so the SLT_*/SRV_* macros
stay untouched and bare LOG_*/QUE_*/RES_* calls are captured too)
Gate every sink on log_target_changed() (set only by log_set_target_impl(),
the wrapper --log-file calls) plus a != stdout && != stderr guard mirroring
LOG_TEE_IMPL. LOG_TARGET is non-null by default (log_handler() lazily opens
llama.log), so a plain null check would capture every line into a surprise
llama.log with no flag, and on a non-writable cwd would double-print to
stderr. log_target_changed() is marked at the wrapper rather than inside
log_handler1_impl because --log-file is parsed before any LOG() call, making
the first invocation's filename comparison vacuously false.
common_log_set_file_ptr shares the already-opened FILE* rather than calling
common_log_set_file, whose own fopen("w") would open a second handle on the
same path and let the two writes corrupt each other.
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